Network Working Group                                            A. LiorInternet-Draft                                               IndependentIntended status: Informational                                 P. YeganiExpires: August 29, 2013                                         Juniper                                                            K. Chowdhury                                               Radio Mobile Access, Inc.                                                           H. Tschofenig                                                  Nokia Siemens Networks                                                           A. Pashalidis                                                                     KUL                                                       February 25, 2013    Prepaid Extensions to Remote Authentication Dial-In User Service                                (RADIUS)              draft-lior-radius-prepaid-extensions-22.txtAbstract   This document specifies an extension to the Remote Authentication   Dial-In User Service (RADIUS) protocol that enables service providers   to charge for prepaid services.  The supported charging models   supported are volume-based, duration-based, and based on one-time   events.Status of this Memo   This Internet-Draft is submitted in full conformance with the   provisions of BCP 78 and BCP 79.   Internet-Drafts are working documents of the Internet Engineering   Task Force (IETF).  Note that other groups may also distribute   working documents as Internet-Drafts.  The list of current Internet-   Drafts is at http://datatracker.ietf.org/drafts/current/.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   time.  It is inappropriate to use Internet-Drafts as reference   material or to cite them other than as "work in progress."   This Internet-Draft will expire on August 29, 2013.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject to BCP 78 and the IETF Trust's LegalLior, et al.             Expires August 29, 2013                [Page 1]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5     1.2.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  7       1.2.1.  Architectural Model  . . . . . . . . . . . . . . . . .  7       1.2.2.  Motivation . . . . . . . . . . . . . . . . . . . . . .  9     1.3.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . . 11     1.4.  Example Use Case . . . . . . . . . . . . . . . . . . . . . 11   2.  Supported Features . . . . . . . . . . . . . . . . . . . . . . 14     2.1.  Services and Quotas  . . . . . . . . . . . . . . . . . . . 14     2.2.  Resource Pools . . . . . . . . . . . . . . . . . . . . . . 14     2.3.  Rating Groups  . . . . . . . . . . . . . . . . . . . . . . 16     2.4.  Tariff Switching . . . . . . . . . . . . . . . . . . . . . 17     2.5.  Support for Roaming  . . . . . . . . . . . . . . . . . . . 18     2.6.  Dynamic Termination  . . . . . . . . . . . . . . . . . . . 19     2.7.  One Time Event . . . . . . . . . . . . . . . . . . . . . . 19       2.7.1.  One-Time Charging  . . . . . . . . . . . . . . . . . . 19       2.7.2.  Resource Consumption Query . . . . . . . . . . . . . . 20       2.7.3.  Service Price Enquiry  . . . . . . . . . . . . . . . . 20       2.7.4.  Balance Check  . . . . . . . . . . . . . . . . . . . . 21       2.7.5.  Refund . . . . . . . . . . . . . . . . . . . . . . . . 21   3.  Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 22     3.1.  Capability Discovery . . . . . . . . . . . . . . . . . . . 22     3.2.  Authentication and Authorization Operation . . . . . . . . 22     3.3.  Session Start Operation  . . . . . . . . . . . . . . . . . 24     3.4.  Mid-Session Operation  . . . . . . . . . . . . . . . . . . 24     3.5.  Dynamic Operations . . . . . . . . . . . . . . . . . . . . 26       3.5.1.  Unsolicited Session Termination Operation  . . . . . . 26       3.5.2.  Unsolicited Change of Authorization Operation  . . . . 26     3.6.  Termination Operation  . . . . . . . . . . . . . . . . . . 27     3.7.  Mobile IP Operations . . . . . . . . . . . . . . . . . . . 27     3.8.  Operation Considerations for Multiple Services . . . . . . 28       3.8.1.  Initial Quota Request  . . . . . . . . . . . . . . . . 28       3.8.2.  Quota Update . . . . . . . . . . . . . . . . . . . . . 29       3.8.3.  Termination  . . . . . . . . . . . . . . . . . . . . . 29       3.8.4.  Dynamic Operations . . . . . . . . . . . . . . . . . . 29       3.8.5.  Support for Resource Pools . . . . . . . . . . . . . . 30Lior, et al.             Expires August 29, 2013                [Page 2]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       3.8.6.  One-time Charging  . . . . . . . . . . . . . . . . . . 30       3.8.7.  Error Handling . . . . . . . . . . . . . . . . . . . . 30       3.8.8.  Accounting Considerations  . . . . . . . . . . . . . . 31   4.  Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . 32     4.1.  PrePaid Accounting Capability (PPAC) Attribute . . . . . . 32     4.2.  Session Termination Capability Attribute . . . . . . . . . 34     4.3.  Prepaid Accounting Operation (PPAQ) Attribute  . . . . . . 36     4.4.  Fields . . . . . . . . . . . . . . . . . . . . . . . . . . 52     4.5.  Prepaid Tariff Switching (PTS) Attribute . . . . . . . . . 53   5.  Diameter RADIUS Interoperability . . . . . . . . . . . . . . . 59   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 60   7.  Table of Attributes  . . . . . . . . . . . . . . . . . . . . . 61   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 62   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 66   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 67     10.1. Normative References . . . . . . . . . . . . . . . . . . . 67     10.2. Informative References . . . . . . . . . . . . . . . . . . 67   Appendix A.  Example flows . . . . . . . . . . . . . . . . . . . . 69     A.1.  A simple flow  . . . . . . . . . . . . . . . . . . . . . . 69     A.2.  A flow with prepaid tariff switching . . . . . . . . . . . 72     A.3.  Resource pools and Rating Groups . . . . . . . . . . . . . 75     A.4.  One-time charging  . . . . . . . . . . . . . . . . . . . . 80     A.5.  Price enquiry  . . . . . . . . . . . . . . . . . . . . . . 81     A.6.  Balance check  . . . . . . . . . . . . . . . . . . . . . . 82   Appendix B.  Translation between RADIUS Prepaid and Diameter                Credit Control  . . . . . . . . . . . . . . . . . . . 84   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 93Lior, et al.             Expires August 29, 2013                [Page 3]Internet-Draft        Prepaid Extentions for RADIUS        February 20131.  Introduction   This document specifies an extension to the RADIUS protocol that   enables service providers to perform accounting and charging in an   "online" fashion.  In particular, they enable the service provider to      (a) ensure that subscriber's remaining funds suffice before the      service is delivered, and      (b) interrupt service provision when the funds are exhausted.   These capabilities are typically used in scenarios where the   subscriber maintains a prepaid account with the service provider;   hence, this extension is called the "prepaid" extension for RADIUS.   The functionality described in this document is often referred as   "online charging" in comparison to "offline charging" support   provided by RFC 2866 [RFC2866].   Note that this document does not follow the RADIUS design guidelines   outlined in RFC 6158 [RFC6158] since it predates the publication of   RFC 6158.  This document documents existing implementations.   The extensions were designed with the following goals in mind:   o  Make use of existing infrastructure as much as possible (including      enabling the interworking of RADIUS-based and Diameter-based      infrastructures), and thereby limit the amount of necessary      capital expenditures,   o  provide the ability to rate service requests in an "online"      fashion,   o  provide the ability to charge the user's account prior to service      provision,   o  protect against revenue loss, i.e., to prevent an end user from      obtaining service when the available funds do not suffice,   o  protect against fraud, and   o  be deployable for a number of services independent of the access      network technology.   The architecture between the entities that execute the RADIUS   protocols, with the extensions defined in this document, assumes that   the rating of chargeable events does not occur in the element that   provides the service.  Instead, the rating may be performed at a   dedicated server, termed the "prepaid-enabled AAA server" or simplyLior, et al.             Expires August 29, 2013                [Page 4]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   "prepaid server" (PPS).  Alternatively, the actual rating may occur   in an entity related to this prepaid server.   Furthermore, this document assumes that a "quota server" is available   which, through co-ordination with the rating entity and an account   balance manager, is able to provide a quota indication for a   particular user when requested.  This quota server may or may not   coexist in the prepaid server.1.1.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in RFC 2119 [RFC2119].   Prepaid Client (PPC):      The entity which triggers the RADIUS message exchange, including      the prepaid extensions defined in this document.  The PPC provides      the service to the users, and executes the RADIUS client which,      for the purposes of this document, is termed the "PrePaid Client"      (PPC).  When the prepaid service is used the PPC collects service      event information and reports it while the services is provided to      the user.  This event information is sent to the PPS using the      extensions defined in this document.   Prepaid Server (PPS):      The entity that interacts with the PPC using the RADIUS prepaid      extensions defined in this document.   Rating Entity:      This entity converts the credit that is allocated by the PPS into      a "quota".  This quota is then returned to the requesting PPC via      the PPS.  The rating entity may also determine that during service      provision a tariff switch will occur.  In this case the rating      entity will include details of when exactly tariff switch will      occur.   Quota:      A quota denotes the amount of granted units to be consumed without      performing another credit control interaction.Lior, et al.             Expires August 29, 2013                [Page 5]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Home Network:      The network which contains the user profile and the user's prepaid      account.   Authorize-Only Access Request:      A RADIUS message of type "Access Request" (code field = 1) that      contains a "Service-Type" AVP (type = 6) with value "Authorize-      Only".   Offline Charging:      Offline charging is a process where charging information for      resource usage is collected concurrently with that resource usage.      The charging information is then passed through a chain of logical      charging functions.  At the end of this process, Charging Data      Record (CDR) files are generated, which are then transferred to      the operator's billing domain for the purpose of subscriber      billing and/or inter-operator accounting (or additional functions,      e.g., statistics, at the operator's discretion).  The billing      domain typically comprises post-processing systems, such as the      operator's billing system or billing mediation device.  In      conclusion, offline charging is a mechanism where charging      information does not affect, in real-time, the service rendered.      [TS32240]   Online Charging:      Online charging is a process where charging information for      resource usage is collected concurrently with that resource usage      in the same fashion as in offline charging.  However,      authorization for the network resource usage must be obtained      prior to the actual resource usage to occur.  This authorization      is granted by the PPS upon request from the PPC.  When receiving a      resource usage request, the PPS assembles the relevant charging      information and generates a charging event in real-time.  The PPS      then returns an appropriate resource usage authorization.  The      resource usage authorization may be limited in its scope (e.g.,      volume of data or duration), therefore the authorization may have      to be renewed from time to time as long as the resource usage      persists.  Note that the charging information utilized in online      charging is not necessarily identical to the charging information      employed in offline charging.  In conclusion, online charging is a      mechanism where charging information can affect, in real-time, theLior, et al.             Expires August 29, 2013                [Page 6]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      service rendered and therefore a direct interaction of the      charging mechanism with the control of resource usage is required.      [TS32240]1.2.  Overview   This section provides an overview of the prepaid charging models and   architectures, which are supported by the extensions described in   this document.   A number of models of how to charge customers for services in a   prepaid manner are supported:   o  Volume-based charging (e.g., 2 Cents/KiloByte).   o  Duration-based charging (e.g., 3 Cents/minute).   o  Resource-based charging (e.g., 3 videos for 10 Euros)   o  Event-based charging (e.g., 7 Cents/ring tone) .   This draft assumes that the user maintains a prepaid account with his   home network.  This account may be used to fund multiple services,   some of which may use the extensions defined in this document, and   some may use other mechanisms.  The interworking of these mechanisms   is outside the scope of this document.  Similarly, the means by which   the subscriber obtains funds is also outside the scope of this   document.1.2.1.  Architectural Model   This section describes the architectural model of the protocol   extensions described in this document.  Figure 1 describes the   involved entities.   The end user establishes a connection with one of possibly multiple   PPCs during service access.  The selected PPC communicates with a   HAAA server (directly or indirectly via a broker network).   The interface between the HAAA and the PPS is implemented using the   RADIUS protocol together with the extensions described in this   document.  However, in cases where the PPS does not implement the   RADIUS protocol, the implementation would have to map the   requirements defined in this document to a functionally equivalent   protocol.   The requesting PPC meters the consumption of the service according to   the instructions provided by the PPS.  After service completion, orLior, et al.             Expires August 29, 2013                [Page 7]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   on reception of a subsequent request for service, the PPS deducts the   corresponding amount of credit from the user account.  When a user   terminates an on-going service, the PPC informs the PPS with a   suitable indication about the unused portion of the allocated quota.   The PPS then refunds the user account accordingly.  Note that   multiple PPSs may be deployed for reasons of redundancy and load   sharing.  The system may also employ multiple rating servers.                       Service                    Access Device   Accounting   +----------+      +---------+    Protocol  +------------+   |  End     |<---->|+-------+|<------------>| Accounting |   |  User    |   +->||  PCC  ||              |   Server   |   |          |   |  ||       ||<----+        |            |   +----------+   |  |+-------+|     |        +------------+                  |  +---------+     |   +----------+   |                  |   |  End     |<--+                  |   |  User    |                      |        +----------+   +----------+                      +------->|          |                                     Prepapid | PPS      |                                     Protocol |          |                                              +----------+                   Figure 1: Basic Prepaid Architecture   The PPS and the accounting server in this architecture MAY be   combined.  The PPC must have the ability to meter the consumption of   a prepaid data session.  This metering is typically based on time   (i.e., seconds) or volume (i.e., octets).   The device running the PPC may also have "Dynamic Session   Capabilities", such as the ability to terminate a data session or to   change the filters associated with a specific data session by   processing "Disconnect" messages and "Change of Authorization"   messages as per RFC 3576 [RFC3576].   This document assumes that the PPS is used as the AAA server.  There   are three types of AAA server, as follows.   The AAA server in the home network (HAAA) is responsible for   authentication of the subscriber.  In addition, the HAAA communicates   with the PPS using the RADIUS protocol in order to authorize   subscribers.   This document assumes that the PPS communicates with the HAAA for the   purposes of authentication and authorisation.  The PPS, in turn,Lior, et al.             Expires August 29, 2013                [Page 8]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   interfaces to entities which   o  keep the subscriber's account balance (balance manager),   o  rate access service requests in real-time (rating engine), and   o  manage quota for a particular prepaid service (quota server).   The balance manager, the rating engine and the quota server belong to   the service provider's backend infrastructure and are outside the   scope of this specification.  In particular, as far as this   specification is concerned, they are assumed to exist in the PPS.   Accounting messages are not needed to deliver a prepaid service.   However, accounting messages can be used to keep the PPS up-to-date   as to what is happening with the prepaid data session.1.2.2.  Motivation   Why not use existing RADIUS attributes to construct a protocol for   prepaid scenarios?  This could lead to a solution where no code has   to be modified at existing devices.   It is indeed possible to construct a solution for prepaid scenarios   using existing RADIUS attributes.  The RADIUS server would send an   Access-Accept message containing a Session-Timeout(27) and include a   Termination-Action(29) in the RADIUS-request.  Upon receiving the   Access-Accept message, the NAS would meter the duration of the   session and upon termination of the session the NAS would generate an   Access-Request message again.  The RADIUS server would then re-   authenticate the session and reply with an Access-Accept message   indicating the amount of additional time in a Session-Timeout(27).   Alternatively, it could respond with an Access-Reject message if   there were no more resources in the user account.   Moreover, if the user terminates the session prematurely, the NAS   could indicate this in the accounting stream so that unused funds can   be returned into the prepaid user account.   Unfortunately, the above "solution" has a number of drawbacks,   including the following.   o  It only supports time-based charging.  The solution presented in      this document supports multiple charging metrics.   o  Using accounting messages to recoup unused time may be problematic      because RADIUS accounting messages are not delivered in real-time.      A RADIUS server may store-and-forward accounting messages inLior, et al.             Expires August 29, 2013                [Page 9]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      batches.  Thus, relying on accounting messages for the purposes of      prepaid may cause revenue leakage.  The solution presented in this      document does not rely on Accounting packets at all.  It uses      Access-Request messages, which are required to flow through any      network in real-time.   o  Session-Timeout(27) is not a mandatory attribute.  If a prepaid      subscriber is served by a NAS that does not adhere to Session-      Timeout then that subscriber may use the service for an      undetermined period of time.   o  Termination-Action(29) presents its own issues.  Firstly, the      behaviour of Termination-Action(29) is not mandatory.  Secondly,      according to RFC 2865 [RFC2865], Termination-Action fires when the      provision of the service has completed.  However, service should      not be terminated when negotiating additional quota, because this      should happen in a manner transparent to the subscriber.  Due to      the fact that Termination-Action occurs when the service is      completed, it is unclear whether or not user experience would be      affected if this attribute would be used in a prepaid scenario.      The RADIUS server might even allocate a new IP address to the      subscriber device after a Termination-Action.  Also, the RADIUS      server has no way of telling why a given Access-Request message      was generated.  The RADIUS server might have to wait for the      corresponding accounting packet to determine the reason.  Finally,      re-authenticating the subscriber may take too long.  The solution      presented in this document allows quota replenishing to occur      without affecting user experience.  No re-authentication is      required and quotas can be negotiated before the available credit      actually runs out.   o  Due to the fact that the standard RADIUS attributes are not      mandatory, the correct prepaid operation is really an act of faith      on the part of the RADIUS server.  If Session-Timeout(27) and/or      Termination-Action(29) are not supported, the prepaid subscriber      might be able to obtain the service for free.  The solution      described in this document requires that a PPC informs the RADIUS      server, regardless of whether or not the latter supports the      prepaid extensions.  The RADIUS server can then determine whether      or not service should be granted.  For example, if a prepaid      subscriber is connected to a NAS that does not support prepaid,      the RADIUS server can either instruct the NAS to tunnel the      traffic to another entity in the home network (e.g., an Home      Agent) that supports prepaid, or cause it to provide only a      restricted service.   The solution presented in this document requires the support of two   mandatory and one optional attribute.  Furthermore, it does notLior, et al.             Expires August 29, 2013               [Page 10]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   require a great amount of additional code at a NAS (or similar   device) that already supports time or volume-based metering.  The   solution requires that RADIUS entities advertise their prepaid   capabilities in an Access-Request and that they generate an Access-   Request packet with Service-Type="Authorize-Only" in order to obtain   more quota when or before the current quota is used up.  It also   requires the NAS to send an Access-Request with Service-   Type="Authorize-Only" when the session terminates in order to refund   the subscriber account.1.3.  Assumptions   This document makes the following assumptions.   o  The values carried in the Service Identifiers are pre-configured      between the PPC and the PPS.   o  The decision about the service rating happens at the PPS.   o  The decision whether credit control requests for two services are      placed in a resource pool are made by the PPS.   o  The decision which services belong to the same rating group are      pre-configured at the PPC.  Once a rating group is authorized it      is not necessary to re-authorize an additional service that      belongs to the same rating group at the PPS again.   o  A price enquiry is done purely for the purpose of providing AoC      for the end user, not for processing at the PPC nor to trigger any      specific actions.1.4.  Example Use Case   This section describes the sequence of events in an example RADIUS   prepaid transaction.   1.  When an end host attaches to a network (for example, using IEEE       802.1X), as usual, the PPC that is servicing the subscriber uses       the AAA infrastructure in order to authenticate and authorize the       subscriber with respect to the requested service.  In order to do       this, it sends a RADIUS Access-Request to the AAA server.  This       Access-Request contains the subscriber's credentials and may       contain the prepaid capabilities of the PPC.   2.  The authentication procedure proceeds.  This may involve several       message exchanges, as it is the case with the Extensible       Authentication Protocol (EAP) [RFC2284].  Once the subscriber has       been successfully authenticated, the home AAA server determinesLior, et al.             Expires August 29, 2013               [Page 11]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       that the subscriber is a prepaid subscriber and requests       authorisation from the PPS.  This request MUST include the       prepaid capabilities of the serving PPC.   3.  The PPS, possibly with the help of the backend infrastructure,       validates that the subscriber has a prepaid account and that the       account is active.  It further validates that the PPC has the       appropriate prepaid capabilities.  If all is in order, the PPS       authorises the subscriber to use the network.  Otherwise it       rejects the request.  The decision is sent to the AAA system in       the form of a response message.  In the case of success, this       message contains attributes that indicate the allocation of a       portion of the subscriber credit.  This portion is called the       "initial quota" and is expressed in units of time or volume.  The       response may also include a threshold value.  Note that only a       portion of the user's funds is allocated because the user may be       engaged in other services that may draw on the same account.  For       example, the user may be engaged in a data session and a voice       session.  Although these two services would draw from the same       account, they form separate parts of the overall system.  If the       entire quota was allocated to the data session then the user       would have no more funds for a voice session.   4.  The AAA system incorporates the attributes received from the PPS       into an Access-Accept message that it sends to the PPC.  Note       that the AAA system is responsible for authorizing the service       whereas the prepaid system is responsible for prepaid       authorization.   5.  Upon receiving the Access-Response, the PPC starts the prepaid       data session and meters the session based on time or volume, as       indicated in the message.   6.  Once the consumption approaches the allocated limit (as expressed       by the threshold), the PPC will request additional quota.  Re-       authorization for additional quota flows through the AAA system       to the PPS.  The PPS revalidates the subscriber account and       subtracts the previously allocated quota from the current       balance.  If there is remaining balance, it reauthorizes the       request with an additional quota allotment.  Otherwise, the PPS       rejects the request.  Note that the replenishment of the quota is       a re-authorization procedure and does not require the subscriber       to authenticate himself again.   7.  Upon receiving a re-allotment of the quota, the PPC continues to       provide the requested service until the new threshold is reached.       If the request for additional quota cannot be fulfilled then the       PPC lets the subscriber use the remaining quota and terminatesLior, et al.             Expires August 29, 2013               [Page 12]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       the session.  Alternatively, instead of terminating the session,       the PPC may restrict service access in such a way that the       subscriber can only reach a particular web server.  This web       server maybe used to allow the subscriber to replenish his       account.  This restriction can also be used to allow new       subscribers to set up prepaid accounts in the first place.   8.  Should the subscriber terminate the session before the quota is       exhausted, the remaining balance allotted to the session is       refunded into his account.   Note that the subscriber may have disconnected while the PPC is   waiting for the initial quota.  The entire allocated quota will have   to be credited back to the subscribers account in this case.  Also   note that the PPS maintains session state for the subscriber.  This   state includes how much account balance was allocated during the last   quota enquiry and how much is left in the account.  Therefore, it is   required that all messages about the session reach the same (and   correct) PPS.   For a simple message flow, along the lines of this use case, please   see Appendix A.Lior, et al.             Expires August 29, 2013               [Page 13]Internet-Draft        Prepaid Extentions for RADIUS        February 20132.  Supported Features   This section describes the features that are supported by the   extensions specified in this document.2.1.  Services and Quotas   Examples of services that the user may be using are browsing the web,   participating in a VoIP conversation, watching streaming video and   downloading a ring tone.  Some operators may want to distinguish   between these services and to charge them at different rates and   meters them differently.  Therefore, the prepaid solution needs to be   able to distinguish services, and allocate quota to the services   using different unit types (time, volume) and allow for those quotas   to be consumed at different rates.   +---------+            +---------+            +-------+   |         | 1        N |         | 1        1 |       |   | Session |<---------->| Service |<---------->| Quota |   |         |            |         |            |       |   +---------+            +---------+            +-------+            Figure 2: Multiple services within a single session   As shown in Figure 2, a session may be associated with multiple   services.  Each service is identified by a service identifier   (Service-ID).  The format of the Service-ID is not in the scope of   this document.  It may, for example, be expressed as a 5-tuple {i.e.,   source IP address, destination IP address, source port, destination   port, and protocol type}.  Each service is associated with a quota   whereby a quota might be applicable to multiple services.  An example   message flow that involves multiple services within a single session   is given in the Appendix A.2.2.  Resource Pools   When working with multiple services a new problem arises because one   service may consume its quota faster than another service.  When the   user balance is close to exhaustion, a situation could arise where   one service is unable to obtain quota while another service has   plenty of quota remaining.  Unless the quotas can be rebalanced, the   SAD would then have to terminate the former service.  Moreover, it is   likely that each service generates a certain amount of RADIUS prepaid   traffic.  In an environment with many users and charged services,   this amount of traffic may become a considerable overhead that could   lead to inefficiency.Lior, et al.             Expires August 29, 2013               [Page 14]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   One method to circumvent the above situation is to use a so-called   "resource pool".  Resource pools enable the allocation of resources   to multiple services of a session by allocating resources to a pool   and have services draw their quota from the pool at a rate   appropriate to that service.  When the quota that has been allocated   to the pool is close to exhaustion, the entire pool (rather than   individual services) is replenished.              +-----------+              | Service-A |-----+         +--------+              +-----------+     |    Ma   |        |                                +-------->|        |                                          |  Pool  |                                +-------->|   (1)  |              +-----------+     |    Mb   |        |              | Service-B |-----+         +--------+              +-----------+                      Figure 3: Resource pool example   As shown in Figure 3, Service-A and Service-B are bound to Pool(1).   Ma and Mb are the pool multipliers (that are associated with   Service-A and Service-B respectively) that determine the rate at   which Service-A and Service-B draw from the pool.   The pool is initialized by taking the quota allocated to service n   and multiplying it by Mn.  Therefore, the amount of resources   allocated to a pool is given by Poolr = Ma*Qa + Mb*Qb + . . ., where   Qn denotes the amount of quota that is allocated to service n.   Further, the pool is considered to be empty if           Poolr <= Ca*Ma + Cb*Mb + . . .,                                 Figure 4   where Ca and Cb are resources consumed by Service-A and Service-B   respectively.   Note that the resources assigned to the pool are not associated with   a metric.  That is, Service-A can be rated at $1 per MB and Service-B   can rated at $0.10 per minute.  In this case, if $5 worth of   resources are allocated for service-A to the pool and if Ma = 10,   then 50 units would be placed into the pool.  If a further $5 are   allocated for service-B to the pool, then M=1 and 50 units are   deposited into the pool.  The pool would then have a total sum of 100   units to be shared between the two services.  The PPC would thenLior, et al.             Expires August 29, 2013               [Page 15]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   mater the services such that each Mbyte used by Service-A will draw   10 units from the pool and each minute used by Service-B will draw 1   unit from the pool.2.3.  Rating Groups   A Rating Group gathers a set of services, identified by a service   identifier, and subject to the same cost and rating type (e.g., $0.1/   minute).   The rating of a service can be quite complex.  While some operators   follow linear pricing models, others may wish to apply more complex   functions.  For example, a service provider may wish to rate a   service such that the first N MBytes are free, then the next M Mbytes   are rated at $1 per MB and volume above (N+M) MB be rated at $0.50   per MB.  Such a function could be implemented by repeated message   exchanges in the prepaid system.   To avert the need to exchange many messages while still supporting   such complex rating functions, the concept of the Rating Group was   introduced.   As shown in Figure 5, a Rating Group is associated with one or more   services and defines the rate that the services associated with the   Rating Group consume an allocated amount of quota.                           +--------------+       +--------------+   +-----------+ N     1   |              | M  1  | Resource Pool|   | Service-A +---------->| Rating Group |------>|      or      |   +-----------+           |              |       |    Quota     |                           +--------------+       +--------------+                          Figure 5: Rating Group   During the usage of a service that is associated with a Rating Group,   the PPC sends the ID of the Rating Group to the PPS.  The PPS   authorises the Rating Group by allocating a quota to it and assign it   to a Resource Pool.  When an additional service that belongs to an   already authorised Rating Group is instantiated, the PPC does not   need to re-authorize this service.  This effectively means that the   PPC meters the service such that it draws from the already allocated   quota.  Therefore, no RADIUS messages need to be exchanged in this   case.  This limits the amount of traffic between the PPC and the PPS.   An example of a flow that uses Rating Groups is given in Appendix A.3Lior, et al.             Expires August 29, 2013               [Page 16]Internet-Draft        Prepaid Extentions for RADIUS        February 20132.4.  Tariff Switching   Tariff is the set of parameters defining the utilization charges for   the use of a particular service.   This mechanism is useful if, for example, as shown in Figure 6,   traffic before 18:00 is rated at rate r1 and traffic after 18:00 is   rated at rate r2.  The mechanism requires the PPC to report usage   before and after the switch occured.                           18:00            ------------------+-----------------                   r1         |      r2            ------------------+-----------------                 ^                        ^                 |<----TSI--->            |                 |                        |           Access-Accept            Access-Request           (quota allocated)        (quota consumed)                   Figure 6: Example of Tariff Switching   The PPC indicates support for tariff switching by setting the   appropriate bit in the PPAC.  If the PPS needs to signal a tariff   switch time it will send a PTS attribute that indicates the point in   time when the switch will occur.  This indication represents the   number of seconds from current time (TariffSwitchInterval TSI).   At some point after the tariff switch the PPC sends another Access-   Request, as a result of either the user having logged off or the   volume threshold being reached.  The PPC reports how much volume was   used in total (in a PPAQ attribute) and how much volume was used   after the tariff switch (in a PTS VUATS subtype attribute).   In situations with multiple tariff switches, the PPS has to specify   the length of the tariff switch period using the   TimeIntervalAfterTariffSwitchUpdate (TITSU) field in the PTS   attribute, as shown in Figure 7.Lior, et al.             Expires August 29, 2013               [Page 17]Internet-Draft        Prepaid Extentions for RADIUS        February 2013                            18:00                 23:30            ------------------+---------------------+--------------                   r1         |      r2             |     r3            ------------------+---------------------+--------------                 ^                        ^         ^                 |<----TSI---><-----------|-------->|TITSU                 |                        |           Access-Accept            Access-Request                    Figure 7: Multiple Tariff Switches   When a TITSU is specified in the PTS, the PPC MUST generate an   Access-Request within the time after TSI and before TITSU expires.   Note that, typically, the PPC will be triggered by the Volume   Threshold.  However, it is possible that, during period r2, resources   are not entirely consumed and, thus, the threshold is not reached.   The TITSU attribute ensures that, even in this case, the PPC will   generate the new Access-Request in good time.   For time based services, the quota is continuously consumed at the   regular rate of 60 seconds per minute.  At the time when credit   resources are allocated, the server already knows how many units will   be consumed before the tariff time change and how many units will be   consumed afterward.  Similarly, the server can determine the units   consumed at the before rate and the units consumed at the rate   afterward in the event that the end user closes the session before   the consumption of the allotted quota.  There is no need for   additional traffic between the PPC and the PPS in the case of tariff   time changes for continuous time based service.  Therefore, the   tariff change mechanism is not used for such services.  For time-   based services in which the quota is not continuously consumed at a   regular rate, the tariff change mechanism described for volume and   event units may be used.2.5.  Support for Roaming   In certain networks it is essential for prepaid data services to be   available to roaming subscribers.  Support for both static and   dynamic roaming models is needed.  In a static roaming scenario the   subscriber connects to a foreign network which has a roaming   agreement either directly with the home network, or through a broker   network.  When the subscriber logs into another foreign network, a   new login procedure has to be executed.   In a dynamic roaming scenario the subscriber may move between   networks while maintaining his connection.  In such a scenario the   data session is seamlessly handed off between the networks.Lior, et al.             Expires August 29, 2013               [Page 18]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   In both roaming scenarios, the subscriber always authenticates   himself to the home network.  Authorization for the prepaid session   and quota replenishing occurs at the home network and more   specifically at the PPS where state is being maintained.   Roaming is challenging because a subscriber who established a prepaid   data session may move to another PPC that does not support the   prepaid extensions.2.6.  Dynamic Termination   When fraud or an error is detected, either only the affected session,   or all sessions of the affected subscriber should be immediately   terminated.  Under certain conditions, the system may wish to   terminate the session in order to make sure that the user is not   charged for services it does not use.   Certain handoff procedures used in dynamic roaming scenarios require   that the system terminates the subscribers prepaid data session at a   PPC.  This is the case, for example, when time-based prepaid is used   and the mobile subscriber performs a dormant handoff.2.7.  One Time Event2.7.1.  One-Time Charging   One-time charging is a mode of operation where the RADIUS prepaid   extensions are used for charging of a service that is provided   instansteneously.  An example of such an event is the purchase of a   ring tone.  Subscription based services can also be modeled as a one-   time event.  In this case the one-time service event is the purchase   of a subscription.   For a given user, one-time charging may occur in parallel with other   charging models.  For example, the subscriber may be connected to the   Internet, which is metered (based on time or volume), while he also   purchases a ring tone (a one-time-based event).   Note that it is up to the service providers to decide whether or not   the user will be charged for the download of, for example, the video   and also be charged for the data volume required to download the   video.  The facilities provided by this document gives the service   provider the capability to achieve their service charging business   goals.   The PPC signals one-time charging to the PPS with an indication that   identifies the service and the units that should be debited from the   user account.Lior, et al.             Expires August 29, 2013               [Page 19]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   A PPC may decide to perform one-time charging and the PPC may need to   authenticate the user before sending the relevant message to the   user's home AAA server (and to the PPS).   Note that one-time charging can also be used to credit the prepaid   account.  For example, the PPC can return resources to the subscriber   by issuing a one-time charging request that includes the amount of   resources to be credited into the account.2.7.2.  Resource Consumption Query   It should be possible for the PPS to query the PPC for the current   resource consumption and to adjust the users account balance.  For   example, a request to the PPS is made (e.g., a one-time charging   event), the account is depleted and resources have been allocated to   the PPC.  The PPS should have the ability to query the PPC and, if it   has the spare resources, to reassign the quotas to the PPC and to the   pending request.  Note that the PPS does not know resource usage   until the PPC request for more resources.  This can be a long time.   In the absence of this capability the PPS can minimize the effect of   this phenomenon by allocating small quotas, a practice that results   in more message exchanges.2.7.3.  Service Price Enquiry   The PPC may need to know the price of the service event.  Services   offered by application service providers whose prices are not known   in the PPC might exist.  The end user might also want to get an   estimation of the price of a service event before requesting it.   A PPC issues a PPAQ to the PPS including the Requested-Action SubType   with the value set to "Price Enquiry" (2).  The request includes   enough information to identify the service, namely a Service-   Identifier or a Rating-Group-Identifer.   The PPS calculates the cost of the requested service event, but it   does not perform any account balance check or credit reservation from   the account.   The estimated cost of the requested service event is returned to the   PPS with a PPAQ in the Cost-Information SubType.  The PPC may   transfer the information to the end user as an advice of charge.   More information regarding the price enquiry functionality is   provided in Section 4.3.15 and in Section 4.3.17.Lior, et al.             Expires August 29, 2013               [Page 20]Internet-Draft        Prepaid Extentions for RADIUS        February 20132.7.4.  Balance Check   The PPC may only have to verify that the end user's account balance   covers the cost of a certain service without reserving any units from   the account at the time of the inquiry.  This method does not   guarantee that credit would be left when the PPC requests the   debiting of the account with a separate request.   A PPC issues a PPAQ to the PPS including the Requested-Action SubType   with the value set to "Balance Check" (1).  The request includes   enough information to identify the service, namely a Service-   Identifier or a Rating-Group-Identifer.   The PPS makes the balance check, but it does not make any credit-   reservation from the account.   The result of balance check, namely "Success" (1) or "Failure" (2),   is returned to the PPC in the Check-Balance-Result SubType conveyed   in the PPAQ attribute from the PPS to the PPC.   More information regarding the balance check functionality is   provided in Section 4.3.15 and in Section 4.3.16.2.7.5.  Refund   Some services may refund service units to the end user's account; for   example, gaming services.   To initiate refunding the PPC includes the PPAQ attribute in an   Access-Request packet and the amount (as a negative value) to be   refunded is specified using the Resource Quota and Resource Quota   overflow subtypes.  This functionality is similar to one-time   charging with the difference that refunding uses negative values   Information about the service need to be provided by the PPC to allow   service identification, namely the Service-ID field of the PPAQ   identifies the prepaid service.   Note that a monetary amount itself to be refunded is not provided but   rather abstract units.  Based on prior out-of-band agreements between   the PPC and the PPS these abstract units are translated into a   monetary amount.   More information regarding the refund functionality is provided in   Section 3.8.6.Lior, et al.             Expires August 29, 2013               [Page 21]Internet-Draft        Prepaid Extentions for RADIUS        February 20133.  Operations   This section contains the normative text for the prepaid extension.3.1.  Capability Discovery   The PPC initiates the authentication and authorization procedure by   sending a RADIUS Access-Request to the HAAA.  Since the PPC MUST   include a PPAC attribute in the RADIUS Access-Request.  The PPAC   attribute indicates to the PPS which prepaid capabilities are   possessed by the PPC.  These are required in order to complete the   prepaid authorization procedure.Moreover, if the PPC supports the   Disconnect-Message or the Change-of-Authorization capabilities, then   it SHOULD include the Session Termination attribute.   In certain deployments, there may be other ways to terminate a data   session, or change authorization of an active session.  For example,   some PPCs provide a session termination service via Telnet or SNMP.   In these cases, the AAA server MAY add the Dynamic-Capabilities   message to the Access-Request.  Upon receiving the Change-of-   Authorization message, the AAA server would then be responsible for   terminating the session using the means that are supported by the   device.   If the authentication procedure involves multiple message exchanges   (as it is the case with EAP), the PPC MUST include the PPAC attribute   in at least the last Access-Request of the authentication procedure.3.2.  Authentication and Authorization Operation   Once the Access-Request arrives at the HAAA, the HAAA authenticates   the subscriber.  If this fails, the HAAA sends an Access-Reject   message to the client.  If authentication succeeds, the HAAA   determines whether or not the subscriber is a prepaid subscriber.  If   the subscriber is not a prepaid subscriber, then the HAAA responds as   usual with an Access-Accept or an Access-Reject message.  If the   subscriber is a prepaid subscriber then the HAAA MAY forward the   Access-Request to the PPS for further authorization.   The Access-Request contains the PPAC attribute and the Dynamic-   Capabilities attribute if one was included.  The User-Name(1)   attribute MAY be set to a value that identifies the subscriber.  This   attribute is used by the PPS to locate his account.  For added   security, the HAAA MAY also set the User-Password(2) attribute to the   password used between the HAAA and the PPS.   The PPS locates the subscriber account and authorizes him.  During   this procedure, the PPS takes into consideration the PPCsLior, et al.             Expires August 29, 2013               [Page 22]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   capabilities.  Upon successful authorization, the PPS generates an   Access-Accept containing an PPAC attribute and an PPAQ attribute.   The PPAC attribute returned to the client indicates the type of   prepaid service to be provided for the session.  The PPAQ attribute   includes the following information.   o  The QID, which is set by the PPS to a unique value, is used to      correlate quota requests.   o  Volume and/or Time quota, which is set to a value representing a      portion of the subscriber's credit.   o  Time or Volume Threshold that indicates when the PPC should      request additional quota.  This information is optional.   o  The IP address of the serving PPS and one or more alternative      PPSs.  This is used by the HAAA to route subsequent quota      replenishing messages to the appropriate PPS(s).   o  A State attribute, as defined in RFC 2865 [RFC2865].  This is      necessary in order to satisfy the requirements of Section 5.44 of      RFC 2865 [RFC2865], which mandates that an Access-Request with      Service-Type="Authorize-Only" must contain a State attribute.      Since the PPC sends subsequent quota replenishment requests in the      form of such "Authorize-Only" requests, a State attribute MUST be      present in all Access-Accept messages that also carry a PPAQ      attribute.   Note: The Idle-Timeout(28) attribute can be used to trigger the   premature termination of a prepaid service, for example as a result   of inactivity.   Depending on site policies, after failed authorization, the PPS may   generate an Access-Reject in order to terminate the session   immediately.  Alternatively, the PPS may generate an Access-Accept   blocking some or all of the traffic and/or redirect some or all of   the traffic to a location to a fixed server.  (This feature could be   used, for example, to prompt the user to replenish their account.)   Blocking of traffic is achieved by either Filter-ID(11) or NAS-   Filter-Rule (see [RFC4849]).  A description of the redirect   functionality is outside the scope of this document.  The time period   before the session is blocked/redirected is specified by the Session-   Timeout(27) attribute.   Upon receiving an Access-Accept from the PPS, the HAAA appends the   usual service attributes and forward the packet to the PPC.  The HAAA   SHOULD NOT overwrite any attributes already set by the PPS.  If the   HAAA receives an Access-Reject message, it will simply forward theLior, et al.             Expires August 29, 2013               [Page 23]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   packet to its client.  Depending on site policies, if the HAAA does   not receive an Access-Accept or an Access-Reject message from the PPS   it MAY do nothing or send an Access-Reject or an Access- Accept   message back to the PPC.3.3.  Session Start Operation   The start of the session is indicated by the arrival of an   Accounting-Request(Start) packet.  The Accounting-Request (Start) MAY   be routed to the PPS such that it can confirm the initial quota   allocation.   Note that the role of the PPS is not to record accounting messages   and therefore it SHOULD NOT respond with an Accounting Response   packet.  If the PPS does not receive the Accounting-Request(start)   message it will only know that the session has started upon the first   reception of a quota replenishment operation.   If the PPS does not receive indication directly (via Accounting-   Request(start)) or indirectly, it SHOULD, after some configurable   time, deduce that the session has not started.  If the PPC supports   termination capabilities, the PPS SHOULD send a Disconnect Message to   the PPC as a measure to ensure that the session is indeed dead.3.4.  Mid-Session Operation   During the lifetime of a prepaid data session the PPC may request the   replenishment of the quotas using an Authorize-Only Access-Request   message.  Once either the allocated quota has been exhausted or the   threshold has been reached, the PPC MUST send an Access-Request with   Service-Type(6) set to a value of "Authorize-Only" and the PPAQ   attribute.   The PPC MUST also include NAS identifiers, and Session Identifier   attributes in the Authorize-Only Access-Request.  The Session   Identifier should be the same as the one used during the initial   Access-Request.  For example, if the User-Name(1) attribute was used   in the Access-Request it has to be included in the Authorize-Only   Access-Request as well, especially if the User-Name(1) attribute is   used to route the Access-Request to the Home AAA server.   The Authorize-Only Access-Request MUST NOT include a User Password   and MUST NOT include a CHAP Password.  In order to enable the   receiver to authenticate the message, the PPC MUST include a Message-   Authenticator(80).  In order to satisfy the requirements of Section   5.44 of RFC 2865 [RFC2865], the PPC MUST also include the State   attribute.  It is anticipated that the inclusion of the State   attribute will enable the PPS to map the Authorize-Only AccessLior, et al.             Expires August 29, 2013               [Page 24]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Request to the authentication context that was established when the   PPC authenticated itself at the beginning of the session.  The PPC   computes the value for the Message-Authenticator and the State   attributes according to RFC 2869 [RFC2869] and RFC 2865 [RFC2865]   respectively.   When the HAAA receives an Authorize-Only Access-Request that contains   a PPAQ, it validates the message using the Message-Authenticator(80),   according to RFC 2869.  If the HAAA receives an Authorize-Only   Access-Request that contains a PPAQ and either no or an invalid   Message-Authenticator(80) it SHALL silently discard the message.  An   Authorize Only Access-Request message that does not contain a PPAQ is   either erroneous or belongs to another application (for example, a   Change of Authorization message [RFC3576]).  In this case the   Authorize-Only Access-Request is either silently discarded or handled   by another application.   Once the Authorize-Only Access-Request message is validated, the HAAA   SHALL forward the Authorize-Only Access-Request to the appropriate   PPS.  The HAAA MUST forward the Authorize-Only Access-Request to the   PPS specified in the PPAQ.  The HAAA MUST add a Message-   Authenticator(80) to the message, according to RFC 2869.  As with the   Access-Request message, the HAAA MAY modify the User-Name(1)   attribute such that it identifies the user to the PPS.   When the PPS receives the Authorize-Only Access-Request containing a   PPAQ attribute, it MUST validate the Message-Authenticator(80) as   described in RFC 2869.  If validation fails, the PPS MUST silently   discard the message.  If it receives an Authorize-Only Access-Request   message that does not contain a PPAQ, it MUST silently discard the   message.   The PPS locates the prepaid session state and uses the QID contained   within the PPAQ to detect replays.  The PPS takes the most recently   allocated quota and subtracts it from the user balance.  If   sufficient balance remains, the PPS authorizes the PPS and allocates   additional quota.  The PPS may also calculate a new threshold value.   Upon successful re-authorization, the PPS generates an Access-Accept   containing the PPAQ attribute.   Depending on site policies, upon unsuccessful authorization, the PPS   generates an Access-Reject or an Access-Accept with Filter-Id(11) or   Ascend-Data-Filter attribute (if supported) and the Session-   Timeout(27) attribute such that the subscriber can get access to a   restricted set of locations for a short period of time.  This feature   could be used to enable users to replenish their accounts, create new   accounts, or to access free content.Lior, et al.             Expires August 29, 2013               [Page 25]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Upon receiving an Access-Accept from the PPS, the HAAA forwards the   message to its client.  If the HAAA receives an Access-Reject   message, it forwards the message.  Depending on site policies, if the   HAAA does not receive an Access-Accept or an Access-Reject message   from the PPS it MAY do nothing or it MAY send an Access-Reject   message back to its client.   Upon receiving an Access-Accept, the PPC updates its quotas and   threshold parameters with the values contained in the PPAQ attribute.   Note that the PPS MAY update the PrePaidServer attribute(s) and these   may have to be saved as well.  If the Access-Accept message contains   a Filter-Id(11), an Ascend-Data-Filter attribute, or Session   Timeout(27), the PPC SHALL restrict the subscriber session   accordingly.3.5.  Dynamic Operations   The PPS may take advantage of the dynamic capabilities that are   supported by the PPC as advertised in the Session Termination and the   PPAC attribute during the initial Access-Request.  There are two   types of actions that the PPS may perform.  Firstly, it may request   the session to be terminated.  Secondly, it may request the   attributes associated with the session to be modified.  More   specifically, it may modify a previously sent PPAQ.   Both of these actions require that the session be uniquely identified   at the PPC as described in [RFC3576].3.5.1.  Unsolicited Session Termination Operation   At anytime during a session the PPS may send a Disconnect Message in   order to terminate a session, see in [RFC3576].  Upon successful   termination of a session the PPC MUST return any unused quota to the   PPS by issuing an Authorize-Only Access-Request containing the PPAQ   which contains any unused quota and the Update-Reason set to "Remote   Forced Disconnection".3.5.2.  Unsolicited Change of Authorization Operation   At any time during the session the PPC may receive a Change of   Authorization (CoA) message.  A PPS may send a new quota to either   add or to remove quota that is allocated to the service.  If the   Change of Authorization contains a PPAQ then that PPAQ overrides a   previously received PPAQ.  The PPS MUST NOT change the units used in   the PPAQ.   If the newly received PPAQ reduces the amount of allocated quota   beyond what is already used then the PPC accepts the new PPAQ and actLior, et al.             Expires August 29, 2013               [Page 26]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   as it normally would when the quota is used up.  For example, if the   threshold is reached then is request a quota update.3.6.  Termination Operation   The termination phase is initiated when (i) the subscriber logs off,   (ii) the subscriber balance is exhausted, or (iii) when the PPC   receives a Disconnect Message.   In case the user logged off, or the PPC receives a Disconnect   Message, the PPC sends an Authorize-Only Access-Request message with   a PPAQ and Update-Reason attribute set to either "Client Service   Termination" or "Remote Forced Disconnect".  This message indicates   the amount of consumed quota.   In case the currently allocated quota is exhausted, if the PPAQ   contained the Termination-Action subytype, the PPC follows the   specified action.3.7.  Mobile IP Operations   In roaming scenarios with Mobile-IP, the prepaid data session should   be maintained transparently if the HA is acting as the access device   hosting the PPC.  As the subscriber device associates with a new   access service device (AP or PDSN that supports PPC capability), this   service access device sends a RADIUS Access-Request and the   subscriber is re-authenticated and reauthorized.  The service access   device SHALL include the PPAC attribute in the RADIUS Access-Request.   In this manner, the procedure follows the Authentication and   Authorization procedure described earlier.   If the HA was acting as the service access device before handoff,   then the prepaid session does not undergo any change after the   handoff because the Mobile IP session is anchored at the HA and the   user's Home IP address does not change.   In the case of a wireless access point or PDSN acting as the service   access device, it is likely that the user's (care-of) IP address will   change.  The prepaid session will be affected by this.  In this   scenario the service access device shall send an Access-Request   message which is routed to the home network and SHALL reach the PPS   that is serving this session.  The PPS correlates the new   authorization request with the existing active session and assigns a   quota to the new request.  Any outstanding quota at the old service   access device SHALL be returned to the PPS if the Mobile-IP nodes (HA   and FA) support registration revocation (Mobile IPv4 only).   Specifically, the quota SHOULD be returned when the service access   device sends the Authorize-Only Access-Request with PPAQ Update-Lior, et al.             Expires August 29, 2013               [Page 27]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Reason set to either "Remote Forced Disconnect" or "Client Service   Termination".  In order to trigger the sending of this last   Authorize-Only Access- Request, the PPS may issue a Disconnect   Message [3576] to the service access device.   Even if the subscriber moves to a service access device that does not   have prepaid capabilities can the prepaid data service continue.   This can be done by requesting the Home Agent (assuming it has such   capabilities) to take over the responsibilities of the service access   device (i.e. metering).  This scenario will be discussed in detail in   a later version of this document.3.8.  Operation Considerations for Multiple Services   This section describes the support for multiple prepaid services on a   single PPC.  Message flows illustrating the various interactions are   presented in Appendix A.   A PPC that supports prepaid operations for multi-services SHOULD set   the "Multi-Services Supported" bit in the PPAC.  When working with   multi-services, we need to differentiate between the services.  A   Service-Id attribute is used in the PPAQ in order to uniquely   differentiate between the services.  The exact definition of the   Service-Id attribute is outside the scope of this document.   A PPAQ that contains a Service-Id is associated with that service.  A   PPAQ that contains a Rating-Group-Id is associated with that Rating-   Group.  A PPAQ MUST NOT contain both a Rating-Group-Id and a   Service-Id.  A PPAQ that contains neither a Rating-Group-Id nor a   Service-Id then the default service is used, i.e., the "Access   Service".3.8.1.  Initial Quota Request   When operations with multiple services is desired then the PPC   requests the initial quota by sending a PPAQ containing the   Service-Id in an Authorize-Only Access-Request packet for that   service.  Similarly, if the PPC supports rating groups then it may   request a quota for the rating group by sending a PPAQ containing the   Rating-Group-Id.  In both cases the Update-Reason is set to "Initial-   Request".  The Authorize-Only Access-Request message MAY contain more   than one PPAQ.   Upon receiving an Authorize-Only Access-Accept message containing one   or more PPAQs, the PPS allocates resources to each PPAQ.  Each PPAQ   is assigned a unique QID that MUST appear in subsequent PPAQ updates   for that service or rating group.  Additionally, the PPAQ MUST   contain the Service-ID or Rating-Group-Id, unless the PPAQ is theLior, et al.             Expires August 29, 2013               [Page 28]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   generic "Access Service".3.8.2.  Quota Update   Once the services start to utilize their allotted quota they will   eventually need to replenish their quotas (either the threshold is   reached or no more quota remains).  In order to replenish the quota,   the PPC sends an Authorize-Only Access-Request message containing one   or more PPAQs.  Each PPAQ MUST contain the appropriate QID,   Service-ID or Rating-Group-Id (or neither the Service-ID or Rating-   Group-Id if the quota replenishment is for the "Access Service").   The Update-Reason filed indicates either "Threshold reached"(3), or   "Quota reached"(4).   Upon receiving an Authorize-Only Access-Request packet with one or   more PPAQs the PPS responds with a new PPAQ for that service.  The   PPAQ contains a new QID, the Service-Id or the Rating-Group-Id, and a   new QID.  If the PPS does not grant additional quota for the service   it MUST include the Termination-Action subfield in the PPAQ that will   instruct the PPC to take appropriate actions.3.8.3.  Termination   When the allotted quota for a service is exhausted, the PPC shall act   in accordance with the flags set in the Termination-Action subtype.   If the Termination-Action subtype is absent then the service MUST be   terminated.  If the service is to be terminated, then the PPC shall   send a PPAQ with the appropriate QID, the Service-Id, the used quota,   and the Update-Reason set to "Client Service Termination".   If the "Access Service" has terminated, then all other services must   be terminated as well.  In this case the PPC MUST report on all   issued quotas for the various services.  The Update-Reason field   should be set to "Access Service Terminated".3.8.4.  Dynamic Operations   Dynamic operations for multi-services are similar to dynamic   operations described for single service operations.  The PPS MAY send   a COA message containing a PPAQ for an existing service instance.   The PPC matches the PPAQ with the service using the Service-ID or the   Rating-Group-Id attribute.  The new quota could differ from the   previously allocated value.   A disconnect message terminates the "Access Service".  As such the   PPC MUST report all unused quotas by sending an Authorize-Only Access   Request message containing a PPAQ for each active service.  The   Update-Reason MAY indicate that the reason for the update.Lior, et al.             Expires August 29, 2013               [Page 29]Internet-Draft        Prepaid Extentions for RADIUS        February 20133.8.5.  Support for Resource Pools   If the PPC supports pools as indicated by setting the "Pools   supported" bit in the PPAC then the PPS may associate a quota with a   Pool by including the Pool-Id and the Pool-Multiplier in the PPAQ.   When Resource Pools are used, the PPAQ MUST NOT use the threshold   field.3.8.6.  One-time Charging   To initiate one-time charging the PPC includes the PPAQ attribute in   an Access-Request packet.  The Service-ID field of the PPAQ   identifies the prepaid service.  The amount to be charged is   specified using the Resource Quota and Resource Quota overflow   subtypes.  If the value specified is negative then the resources are   credited to the user account.  This functionality corresponds to   refunding.   The QID subtype MUST be set to a unique value and is used by the PPS   to detect duplicates.  The Update Reason field MUST be set to One-   Time Charging.  Upon receiving a One-Time charge PPAQ, the RADIUS   server authenticates the user and, if successful, passes the PPAQ to   the PPS.  The PPS locates the account and debits or credits it   accordingly.  The PPS MUST respond to the PPS with an Access-Accept   message if successful, or an Access-Reject message otherwise.   In case of a successful operation the HAAA forwards the message to   the PPC with an Access Accept message.  Since this is a one-time   charge the PPC MUST NOT allow the session to continue.  Therefore,   the RADIUS server SHOULD include in the Access-Accept a Session-   Timeout set to 0.  Upon receiving an Access-Accept response the PPC   SHOULD generate an Accounting Stop message.   A PPAQ used for One-Time charging MAY appear in an Authorize-Only   Access Request.  This is the case when the session already exists.   The PPS responds with an Access-Accept to indicate that the user   account has been debited or an Access-Reject otherwise.3.8.7.  Error Handling   If the PPS receives a PPAQ with an invalid QID it MUST ignore that   PPAQ.   If the PPS receives a PPAQ containing a Service-Id, or a Rating-   Group-Id that it does not recognize, then it MUST ignore that PPAQ.   If the PPC receives a PPAQ containing a Service-Id, or a Rating-   Group-Id that it does not recognize, then it MUST ignore that PPAQ.Lior, et al.             Expires August 29, 2013               [Page 30]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   If the PPC receives a PPAQ that contains a Pool-Id without a Pool-   Multiplier or a Pool-Multiplier without a Pool-Id it MUST ignore that   PPAQ.3.8.8.  Accounting Considerations   Although typically generated, accounting messages are not required to   deliver a prepaid data service.  When generated, accounting messages   are used for auditing purposes and for billing.  Accounting messages   associated with prepaid data sessions should include the PPAQ   attribute.Lior, et al.             Expires August 29, 2013               [Page 31]Internet-Draft        Prepaid Extentions for RADIUS        February 20134.  Attributes   This section specifies the attributes that implement the RADIUS   extensions for prepaid.4.1.  PrePaid Accounting Capability (PPAC) Attribute   The PrepaidAccountingCapability (PPAC) attribute is sent in the   Access-Request message by a PPC to describe its prepaid capabilities.     0                   1                   2                   3     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |     Type      |  Length       |            Vendor-Id    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         Vendor-Id (cont)           | Vendor type   | Vendor length |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |  Continuation | VALUE ...    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-      The fields have the following meaning and encoding:      Type:        26 for Vendor-Specific      Length:        6 + 3 + length of SubTypes      Vendor-Id:        The Vendor-Id value for WiMAX is 24757.      Vendor type:        35 for PPAC      Vendor length:        3 + length of VALUE      Continuation:        The Continuation Field is defined as follows:        0Lior, et al.             Expires August 29, 2013               [Page 32]Internet-Draft        Prepaid Extentions for RADIUS        February 2013        0 1 2 3 4 5 6 7        +-+-+-+-+-+-+-+-+        |C|r|r|r|r|r|r|r|        +-+-+-+-+-+-+-+-+        The C-bit of the continuation field indicates        if a attribute is being fragmented. When the        C-bit is set to one '1' this indicates that        the attribute is being fragmented that is        the next VSA of the same type is to be appended        to this attribute. When the C-bit is set to zero        '0' this indicates that the next attribute is        not a fragment of this attribute.        An attribute that is not being fragmented will        have the C-bit set to '0'. An attribute that is        being fragmented will have its C-bit set to '1'        for all fragments until the last fragment, which        will have its C-bit set to '0' indicating it's        the last fragment of the attribute. The r-bits        are reserved for future use. They SHALL be set        to zero by the sender and SHALL be ignored by        the receiver.        The value of the C-bit MUST be 0.       VALUE :        The content of the AvailableInClient (AiC) SubType fields        are encoded using the data type String.                         Figure 8: PPAC Attribute   The AvailableInClient (AiC) SubType is encoding as follows:Lior, et al.             Expires August 29, 2013               [Page 33]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       | LENGTH        | AvailableInClient (AiC)      ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  AvailableInClient (AiC)      |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value (1)      LENGTH  : 2 + 4      AvailableInClient (AiC): The bitmap is encoded as:      Value          | Description      ------------  -+-------------------------------------       0x00000001    | Volume metering supported       0x00000010    | Duration metering supported       0x00000100    | Resource metering supported       0x00001000    | Pools supported       0x00010000    | Rating groups supported       0x00100000    | Multi-Services supported       0x01000000    | Tariff Switch supported       0x10000000    | Reserved                 Figure 9: AvailableInClient (AiC) SubType4.2.  Session Termination Capability Attribute   The Session Termination Capability attribute is included in the   RADIUS Access-Request message towards the RADIUS server to indicate   whether or not the NAS supports Dynamic Authorization.     0                   1                   2                   3     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |     Type      |  Length       |            Vendor-Id    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         Vendor-Id (cont)           | Vendor type   | Vendor length |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |  Continuation | String ...    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-      The fields have the following meaning and encoding:Lior, et al.             Expires August 29, 2013               [Page 34]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      Type:        26 for Vendor-Specific      Length:        6 + 3 + 4      Vendor-Id:        The Vendor-Id value for WiMAX is 24757.      Vendor type:        36 for Session Termination Capability      Vendor length:        3 + 4      Continuation:        The Continuation Field is defined as follows:        0        0 1 2 3 4 5 6 7        +-+-+-+-+-+-+-+-+        |C|r|r|r|r|r|r|r|        +-+-+-+-+-+-+-+-+        The C-bit of the continuation field indicates        if a attribute is being fragmented. When the        C-bit is set to one '1' this indicates that        the attribute is being fragmented that is        the next VSA of the same type is to be appended        to this attribute. When the C-bit is set to zero        '0' this indicates that the next attribute is        not a fragment of this attribute.        An attribute that is not being fragmented will        have the C-bit set to '0'. An attribute that is        being fragmented will have its C-bit set to '1'        for all fragments until the last fragment, which        will have its C-bit set to '0' indicating it's        the last fragment of the attribute. The r-bits        are reserved for future use. They SHALL be set        to zero by the sender and SHALL be ignored by        the receiver.Lior, et al.             Expires August 29, 2013               [Page 35]Internet-Draft        Prepaid Extentions for RADIUS        February 2013        The value of the C-bit MUST be 0.      String:        This field is encoded as a bitmap.      Value          | Description      ---------------+-------------------------------------       0x00000000    | Reserved       0x00000001    | Dynamic Authorization Extensions                     | (RFC 3576) is supported.       ...           | All further values are reserved.            Figure 10: Session Termination Capability Attribute4.3.  Prepaid Accounting Operation (PPAQ) Attribute   One or more PPAQ attributes are sent in an Access Request, Authorize-   Only Access-Request and Access-Accept message.  In an Access Request   message, the PPAQ attribute is used to facilitate one-time charging   transactions.  In Authorize-Only Access-Request messages it is used   for one-time charging, report usage and to request further quota.  It   is also used in order to request prepaid quota for a new service   instance.  In an Access-Accept message it is used in order to   allocate the (initial and subsequent) quotas.   When multiple services are supported, a PPAQ is associated with a   specific service as indicated by the presence of a Service-Id, a   Rating-Group-Id, or the "Access Service" (as indicated by the absence   of both, the Service-Id and the Rating-Group-Id).   Note: Either Volume-Quota, Time-Quota, or Resource-Quota SubTypes   MUST appear in the PPAQ attribute, except for the price enquiry   message exchange where these subtypes MUST be absent.  A single PPAQ   attribute MUST NOT contain more than one Service-Id, MUST NOT contain   more than one Rating-Group-Id, and MUST NOT contain both a Service-Id   and a Rating-Group-Id.  A PPAQ that does not contain a Service-ID or   a Rating-Group-Id refers to the "Access Service".  A PPAQ MUST NOT   contain more than one Pool-Id.  A PPAQ that contains a Pool-Id MUST   also contain a Pool-Multiplier SubType.   The PPAQ attribute, as shown in Figure 11, has a variable length   (greater than 8, encoded into one octet), and consists of a variable   number of subtypes.  Unused subtypes are omitted from the message.   The following table summarizes the presence of various SubTypes in   the PPAQ attribute carried in the Access-Request and Access-AcceptLior, et al.             Expires August 29, 2013               [Page 36]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   messages.   Request             Accept        #  SubType Name   0-1(g)              0-1(m,n)      1  Quota Identifier   0-1(a,g)            0-1(a,k,n)    2  VolumeQuota    0                  0-1(a,m,n)    3  VolumeThreshold   0-1(b,g)            0-1(b,k,n)    4  DurationQuota    0                  0-1(b,m,n)    5  DurationThreshold   0-1(c,g)            0-1(c,k,n)    6  ResourceQuota    0                  0-1(c,m,n)    7  ResourceThreshold   0-1(d,g)              0           8  Update-Reason   0-n(e,g)            0-n(e,m,n)    9  PrepaidServer   0-1(g,h,j)          0-1(m,n)     10 Service-ID   0-1(g,h,j)          0-1(m,n)     11 Rating-Group-ID    0                  0-1(m,n)     12 Termination-Action    0                  0-1(m,n)     13 Pool-ID    0                  0-1(f,m,n)   14 Pool-Multiplier   0-1(g)                0          15 Requested-Action    0                  0-1(k,m,n)   16 Check-Balance-Result    0                  0-1(n)       17 Cost-Information   None of the above-listed SubTypes appears in the Access-Reject nor in   the Access-Challenge.   Notes:      (a) SHALL be present if volume based charging is used.  SHALL NOT      be present otherwise.  Volume- Threshold is optional.      (b) SHALL be present if duration-based charging is used.  SHALL      NOT be present otherwise.  Duration- Threshold is optional.      (c) SHALL be present if resource-based charging is used.  SHALL      NOT be present otherwise.  Resource- Threshold is optional.      (d) SHALL be present in an Authorize-Only Access-Request.      (e) MAY be present in an Access-Accept.  If present in Access      Accept it SHALL be present in Access- Request (except for the      first Access-Request).      (f) Pool-Multiplier SHALL be present when Pool-ID is present      otherwise Pool-Multiplier SHALL NOT be present in the PPAQ.      (g) If Requested-Action is present then Service-ID SHALL also be      present and all other attributes SHALL NOT be present.Lior, et al.             Expires August 29, 2013               [Page 37]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      (h) PPAQ SHALL NOT contain both a Service-ID and a      Rating-Group-ID.      (j) A PPAQ that does not contain a Service-ID or a Rating-Group-Id      refers to the "Access Service"(ISF).      (k) If Balance-Check-Result is present and set to 0 then either      Volume-Quota, Duration-Quota or Resource- Quota SHALL be present.      (m) If Balance-Check-Result is present then Service-ID SHALL also      be present and other attributes (tagged with m) SHALL NOT be      present.      (n) The PPAQ in which a Cost-Information occurs SHALL NOT include      a Quota-Identifier, because no quota is actually reserved by the      PPS.  The Service-ID SHALL be present with the Cost-Information      for that Service-ID may not be present if the Cost-Information      cannot be provided.  All other attribute SHALL not appear.   In the following subsections the various subtypes of the PPAQ   attribute are specified.    0                   1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |  Length       |            Vendor-Id   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+        Vendor-Id (cont)           | Vendor type   | Vendor length |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Continuation | VALUE ...   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-     The fields have the following meaning and encoding:     Type:       26 for Vendor-Specific     Length:       6 + 3 + length of SubTypes     Vendor-Id:       The Vendor-Id value for WiMAX is 24757.     Vendor type:Lior, et al.             Expires August 29, 2013               [Page 38]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       37 for PPAQ     Vendor length:       3 + length of SubTypes     Continuation:       The Continuation Field is defined as follows:       0       0 1 2 3 4 5 6 7       +-+-+-+-+-+-+-+-+       |C|r|r|r|r|r|r|r|       +-+-+-+-+-+-+-+-+       The C-bit of the continuation field indicates       if a attribute is being fragmented. When the       C-bit is set to one '1' this indicates that       the attribute is being fragmented that is       the next VSA of the same type is to be appended       to this attribute. When the C-bit is set to zero       '0' this indicates that the next attribute is       not a fragment of this attribute.       An attribute that is not being fragmented will       have the C-bit set to '0'. An attribute that is       being fragmented will have its C-bit set to '1'       for all fragments until the last fragment, which       will have its C-bit set to '0' indicating it's       the last fragment of the attribute. The r-bits       are reserved for future use. They SHALL be set       to zero by the sender and SHALL be ignored by       the receiver.       The value of the C-bit MAY be 0 or 1.     VALUE:       Data type String       Each SubType is then encoded in the following style:      0                   1                   2                   3      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     | SubType       | LENGTH        | VALUE                        ...     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     The fields have the following meaning and encoding:Lior, et al.             Expires August 29, 2013               [Page 39]Internet-Draft        Prepaid Extentions for RADIUS        February 2013     SubType :        Contains an 8 bit unsigned integer.     LENGTH  :        Contains an 8 bit unsigned integer.        The value of the LENGTH field is calculated as the length of the        VALUE field plus two octets (one octet for the length of the        SubType field and another octet for the length of the LENGTH        field).                 Figure 11: PPAQ Attribute Encoding Style4.3.1.  Quota Identifier (QID) SubType   The Quota Identifier (QID) is generated by the PPS and subsequently   returned in a PPAQ->QID subtype from the PPC to the PPS.  This field   has the semantic of a transaction identifier and therefore changes   with every transaction initiated by the PPS to the PPC.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  VALUE                        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(1)      LENGTH  : 2 + length of VALUE field.      VALUE : Data type String                      Quota Identifier (QID) SubType4.3.2.  VolumeQuota SubType   TVolumeQuota SubType is only present when volume-based charging is   used.  In a RADIUS Access-Accept message (PPS to PPC direction), it   indicates the volume (in octets) allocated for the session by the   PPS.  In a RADIUS Authorize-Only Access-Request message (PPC to PPS   direction), it indicates the totally used volume (in octets) for both   inbound and outbound traffic.  The Exponent Field, if present, MUSTLior, et al.             Expires August 29, 2013               [Page 40]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   NOT encode a negative number or zero.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(2)      LENGTH  : 2 + (8 or 12)      VALUE : Data type String      The content of the VALUE field either contains the      Value-Digits Field (8 octets long) or the Value-Digits Field      plus the Exponent Field (12 octets long).                            VolumeQuota SubType4.3.3.  VolumeThreshold SubType   The value of the type field of the VolumeThreshold SubType is TBD and   its length is 10 or 14 octets.  This SubType is optionally present if   the VolumeQuota is present in a RADIUS Access-Accept message (PPS to   PPC direction).  It is generated by the PPS and indicates the volume   (in octets) that has to be consumed before a new quota is requested.   This threshold MUST NOT be larger than the VolumeQuota.  The Exponent   Field, if present, MUST NOT encode a negative number or zero.Lior, et al.             Expires August 29, 2013               [Page 41]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(3)      LENGTH  : 2 + (8 or 12)      VALUE : Data type String      The content of the VALUE field either contains the      Value-Digits Field (8 octets long) or the Value-Digits      SubType plus the Exponent Field 12 octets long).                          VolumeThreshold SubType4.3.4.  DurationQuota SubType   The optional DurationQuota SubType is only present if duration-based   charging is used.  In a RADIUS Access-Accept message (PPS to PPC   direction), it indicates the duration (in seconds) allocated for the   session by the PPS.  In a RADIUS Access-Request message (PPC to PPS   direction), it indicates the total duration (in seconds) since the   start of the accounting session related to the QID subtype of the   PPAQ attribute in which it occurs.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  VALUE                        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(4)      LENGTH  : 2 + 4      VALUE : Data type string.      The content of this field contains a 32-bit unsigned integerLior, et al.             Expires August 29, 2013               [Page 42]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      (with the values 0 to +4,294,967,295).                           DurationQuota SubType4.3.5.  DurationThreshold SubType   The DurationThreshold SubType is optionally present if the   DurationQuota is present in a RADIUS Access-Accept message (PPS to   PPC direction).  It represents the duration (in seconds) after which   new quota should be requested.  This threshold MUST NOT be larger   than the DurationQuota SubType.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  VALUE                        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(5)      LENGTH  : 2 + 4      VALUE : Data type string.      The content of this field contains a 32-bit unsigned integer      (with the values 0 to +4,294,967,295).                         DurationThreshold SubType4.3.6.  ResourceQuota SubType   The optional ResourceQuota SubType is only present if resource-based   or one-time charging is used.  In the RADIUS Access-Accept message   (PPS to PPC direction) it indicates the resources allocated for the   session by the PPS.  In RADIUS Authorize-Only Access-Request message   (PPC to PPS direction), it indicates the resources used in total,   including both incoming and outgoing chargeable traffic.  In one-time   charging scenarios, the subtype represents the number of units to   charge the user.  The attribute consists of a Value-Digits Field and   optionally an Exponent Field (as indicated by the length field).Lior, et al.             Expires August 29, 2013               [Page 43]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(6)      LENGTH  : 2 + (8 or 12)      VALUE : Data type String      The content of the VALUE field either contains the      Value-Digits Field (8 octets long) or the Value-Digits Field      plus the Exponent Field (12 octets long).                           ResourceQuota SubType4.3.7.  ResourceThreshold SubType   The semantic of the ResourceThreshold SubType follow those of the   VolumeThreshold and DurationThreshold SubType.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(7)      LENGTH  : 2 + (8 or 12)      VALUE : Data type String      The content of the VALUE field either contains the      Value-Digits Field (8 octets long) or the Value-Digits Field      plus the Exponent Field (12 octets long).                         ResourceThreshold SubTypeLior, et al.             Expires August 29, 2013               [Page 44]Internet-Draft        Prepaid Extentions for RADIUS        February 20134.3.8.  Update-Reason SubType   The Update-Reason SubType is present in a RADIUS Access-Request   message (PPC to PPS direction) and indicates the reason for   initiating the quota update operation.  Update reasons (6), (7), (8)   and (9) indicate that the associated resources are released at the   PPC side, and that therefore the PPS MUST NOT allocate a new quota in   the RADIUS Access-Accept message.      0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType         | LENGTH        |      VALUE                  |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(8)      LENGTH  : 2 + 1      VALUE : Data type string      This field contains a byte      (with the values 0 to 255).                           Update-Reason SubType   The following values for the Update-Reason SubType are defined:    Value        | Description    -------------+--------------------------------------      0          | Reserved      1          | Pre-initialization      2          | Initial Request      3          | Threshold Reached      4          | Quota Reached      5          | TITSU Approaching      6          | Remote Forced Disconnect      7          | Client Service Termination      8          | "Access Service" Terminated      9          | Service not established     10          | One-Time Charging     11...255    | **Available for IANA registration**                Figure 12: Values for Update-Reason SubTypeLior, et al.             Expires August 29, 2013               [Page 45]Internet-Draft        Prepaid Extentions for RADIUS        February 20134.3.9.  PrepaidServer SubType   The optional PrepaidServer SubType indicates the address of the   serving PPS.  If present, the Home RADIUS server uses this address to   route the message to the serving PPS.  Multiple instances of this   subtype MAY be present in a single PPAQ attribute.   If present in the PrepaidServer SubType of an incoming RADIUS Access-   Accept message, the PPC returns this SubType back without modifying   it in the subsequent RADIUS Access-Request message.  If multiple   values are present, the PPC MUST NOT change their order.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | Address                      ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(9)      LENGTH  : 2 + (4 or 16)      Address : Data type String      For IPv4, the Address field is 4 octets based on the encoding of      the NAS-IP-Address defined in RFC 2138. For IPv6, the Address      field is 16 octets long.                           PrepaidServer SubType4.3.10.  Service-ID SubType   The Service-ID SubType is handled as an opaque string that uniquely   describes the service instance for which prepaid metering should be   applied.   A Service-Id could be an IP 5-tuple (source address, source port,   destination address, destination port, protocol).  If a Service-ID   SubType is present in the PPAQ, the entire PPAQ attribute refers to   that service.  If a PPAQ attribute does not contain a Service-Id or   Rating-Group-ID, then the PPAQ attribute refers to the "Access   Service".Lior, et al.             Expires August 29, 2013               [Page 46]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | Service                      ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(10)      LENGTH  : 2 + length (Service)      Service : Data type String                            Service-ID SubType4.3.11.  Rating-Group-ID SubType   The Rating-Group-ID SubType indicates that this PPAQ attribute is   associated with resources allocated to a Rating Group with the   corresponding ID.  This SubType is encoded as a string.  A single   PPAQ MUST NOT contain more than one Rating-Group-ID.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  VALUE                        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(11)      LENGTH  : 2 + 4      VALUE : Data type string with a length of 4 octets                          Rating-Group-ID SubType4.3.12.  Termination-Action SubType   The value of the type field of the Termination-Action SubType is TBD.   The length of this SubType is 3 octets.  This SubType contains an   enumeration of the action to take when the PPS does not grant   additional quota.  Valid actions are as follows.Lior, et al.             Expires August 29, 2013               [Page 47]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       0                   1                   2       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | Action        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(12)      LENGTH  : 2 + 1      Action : Data type string.      The content is a byte (with the values 0 to +255).                        Termination-Action SubType   The following values for the Termination-Action SubType are defined:    Value        | Description    -------------+------------------------------------      0          | Reserved      1          | Terminate      2          | Request More Quota      3          | Redirect/Filter      4..255     | **Available for IANA registration**           Figure 13: Values for the Termination-Action SubType4.3.13.  Pool-ID SubType   The Pool-ID SubType identifies the resource pool.  It is encoded as a   string.Lior, et al.             Expires August 29, 2013               [Page 48]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | Poolid                        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(13)      LENGTH  : 2 + 4      Poolid : Data type string with length of 4 octets.                              Pool-ID SubType4.3.14.  Pool-Multiplier SubType   The Pool-Multiplier SubType determines the weight of resources when   they are inserted into the pool that is identified by the   accompanying Pool-ID SubType, and the rate at which resources are   taken out of the pool by the relevant Service or Rating-Group.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(14)      LENGTH  : 2 + (8 or 12)      VALUE : Data type String      The content of the VALUE field either contains the      Value-Digits Field (8 octets long) or the Value-Digits Field      plus the Exponent Field (12 octets long).                          Pool-Multiplier SubTypeLior, et al.             Expires August 29, 2013               [Page 49]Internet-Draft        Prepaid Extentions for RADIUS        February 20134.3.15.  Requested-Action SubType   The Requested-Action SubType is only be present in messages sent from   the PPC to the PPS.  It indicates that the PPC desires the PPS to   perform the indicated action and to return the result.  The PPAQ in   which a Requested-Action SubType occurs MUST NOT contain a QID, and   MUST contain a Service-Identifier or a Rating-Group-Identifer that   allows the PPS to uniquely identify the service for which the   indicated action is requested.       0                   1                   2       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | Action        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(15)      LENGTH  : 2 + 1      Action : Data type string.      The content is a byte (with the values 0 to +255).      The values are listed below.                         Requested-Action SubType   The following values for the Action field of the Requested-Action   SubType are defined:    Value        | Description    -------------+-------------------------------------      0          | Reserved      1          | Balance Check      2          | Price Enquiry      3..255     | **Available for IANA registration**            Figure 14: Values for the Requested-Action SubType4.3.16.  Check-Balance-Result SubType   The Check-Balance-Result SubType can only be present in messages sent   from the PPS to the PPC.  It indicates the balance check decision of   the PPS about a previously received Balance Check Request (asLior, et al.             Expires August 29, 2013               [Page 50]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   indicated in a Requested-Action SubType).  The PPAQ attribute in   which a Check-Balance-Result occurs MUST NOT include a QID beause no   quota is reserved by the PPS.       0                   1                   2       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | Decision      |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(16)      LENGTH  : 2 + 1      Decision : Data type string.      The content is a byte (with the values 0 to +255).      The values are listed below.                       Check-Balance-Result SubType   The following values for the Decision field of the Check-Balance-   Result SubType are defined:    Value        | Description    -------------+-------------------------------------------      0          | Success; Sufficient funds available                 | in the user's prepaid account      1          | Failure; Insufficient funds available      2..255     | **Available for IANA registration**          Figure 15: Values for the Check-Balance-Result SubType4.3.17.  Cost-Information SubType   The Cost-Information SubType is used in order to return the cost   information of a service, which the PPC can transfer transparently to   the end user.  This SubType is sent from the PPS to the PPC as a   response to a "Price Enquiry", as indicated by the Requested-Action   SubType.Lior, et al.             Expires August 29, 2013               [Page 51]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(17)      LENGTH  : 2 + 12 + 4 + length of the Cost-Unit Field      VALUE : Data type String      The content of the VALUE field contains (in this order) the      Value-Digits Field, Exponent Field, Currency-Code Field      and the Cost-Unit Field.                         Cost-Information SubType   For example, the cost of 7.75 Malawi kwacha per hour would be encoded   as follows.  Value-Digits = 775, Exponent = -2, Currency Code = 454,   and Cost-Unit = "hour".   The PPAQ that carries a Cost-Information MUST NOT include a QID.   The Currency-Code Field is of type Unsigned32 and used inside the   Check-Balance-Result SubType and contains a currency code that   specifies in which currency the values of AVPs containing monetary   units were given.  It is specified by using the numeric values   defined in the ISO 3166-1 standard.   The Cost-Unit Field is used inside the Check-Balance-Result SubType   and contains a human readable UTF8 encoded string that can be   displayed to the end user.  It specifies the applicable unit to the   Cost-Information when the service cost is a cost per unit (e.g., cost   of the service is $1 per minute).  The Cost-Unit can, for example, be   minutes, hours, days, kilobytes, megabytes, etc.4.4.  Fields4.4.1.  Value-Digits Field   The Value-Digits Field is an Unsigned64 value (with a length of 8   octets) that contains the significant digits of the number.  If   decimal values are needed to present the number, the scaling MUST be   indicated with a related Exponent Field, see Section 4.4.2.Lior, et al.             Expires August 29, 2013               [Page 52]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   For example, the decimal number 0.05 is encoded by a Value-Digits   Field set to 5, and a scaling that is indicated with the Exponent   Field set to -2.   The encoding of this SubType is not done in an TLV format but rather   the encoded value is added to existing subtypes.4.4.2.  Exponent Field   The Exponent field is a Integer32 value that contains the exponent   value that is to be applied to the accompanying Value-Digit Field.4.5.  Prepaid Tariff Switching (PTS) Attribute   This specification defines the PTS attribute, which allows to switch   from one rate to another during service provision.  Support for   tariff switching is optional to implement and to use for the PPC and   the PPS.  PPCs use the flag "Tariff Switching supported" in the   AvailableInClient field of the PPAC attribute in order to indicate   support for tariff switching.  PPSs employ the PTS attribute in order   to announce their support for tariff switching.   If a RADIUS message contains a PTS attribute, it MUST also contain at   least one PPAQ attribute.  If a RADIUS Access-Request message   contains a PTS attribute or the "Tariff Switching supported" flag in   the AvailableInClient field of the PPAC attribute, it MUST also   contain an Event-Timestamp RADIUS attribute (see [RFC2869]).   Every PTS attribute MUST include a QID SubType, as specified in   Section 4.3.1.  In a RADIUS Access-Request message sent from the PPC   to the PPS, the QID SubType MUST contain the value of the Quota   Identifier SubType that was previously received from the PPS and MUST   be the same as the value carried in the QID SubType of one of the   PPAQ attributes included the same RADIUS message.   If multiple services are supported and if the PPAQ is associated with   a service as indicated by the Service-ID SubType, then the PTS refers   to the tariff switch for that service.  If the PPAQ does not have a   Service-ID, then the PTS refers to tariff switch for the "Access   Service".   A PPAQ attribute that is transported along with a PTS attribute and   has the same value as the QID SubType contained in the PTS attribute   in its own QID SubType is referred to as the "accompanying PPAQ   attribute".  If a PPS receives an Access-Request message from a PPC,   it associates a unique value for the QID SubType to this request.   The following table summarizes the presence of various SubTypes inLior, et al.             Expires August 29, 2013               [Page 53]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   the PTS attribute carried in the Access-Request and Access-Accept   messages. Request           Accept        #  SubType Name  1                  1           1  Quota Identifier  1                  0           2  VolumeUsedAfterTariffSwitch  0                 0-1          3  TarrifSwitchInterval  0                 0-1(a)       4  TimeIntervalAfterTarriffSwitchUpdate   None of the above-listed SubTypes appears in the Access-Reject nor in   the Access-Challenge.   Notes:      (a) The PPS SHALL include this AVP if there is another tariff      switch period after the period that ends as indicated by the TSI      attribute.     0                   1                   2                   3     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |     Type      |  Length       |            Vendor-Id    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         Vendor-Id (cont)           | Vendor type   | Vendor length |    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |  Continuation | VALUE ...    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-      The fields have the following meaning and encoding:      Type:        26 for Vendor-Specific      Length:        6 + 3 + length of SubTypes      Vendor-Id:        The Vendor-Id value for WiMAX is 24757.      Vendor type:        38 for PTSLior, et al.             Expires August 29, 2013               [Page 54]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      Vendor length:        3 + length of SubTypes      Continuation:        The Continuation Field is defined as follows:        0        0 1 2 3 4 5 6 7        +-+-+-+-+-+-+-+-+        |C|r|r|r|r|r|r|r|        +-+-+-+-+-+-+-+-+        The C-bit of the continuation field indicates        if a attribute is being fragmented. When the        C-bit is set to one '1' this indicates that        the attribute is being fragmented that is        the next VSA of the same type is to be appended        to this attribute. When the C-bit is set to zero        '0' this indicates that the next attribute is        not a fragment of this attribute.        An attribute that is not being fragmented will        have the C-bit set to '0'. An attribute that is        being fragmented will have its C-bit set to '1'        for all fragments until the last fragment, which        will have its C-bit set to '0' indicating it's        the last fragment of the attribute. The r-bits        are reserved for future use. They SHALL be set        to zero by the sender and SHALL be ignored by        the receiver.        The value of the C-bit MAY be 0 or 1.      VALUE : Variable length content of data type String containing              one or multiple SubTypes.      Each SubType is then encoding in the following style:       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       | LENGTH        | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType:Lior, et al.             Expires August 29, 2013               [Page 55]Internet-Draft        Prepaid Extentions for RADIUS        February 2013         Contains an 8 bit unsigned integer.      LENGTH:         Contains an 8 bit unsigned integer.      VALUE:         Contains the content of the SubType.                         Figure 16: PTS Attribute4.5.1.  VolumeUsedAfterTariffSwitch SubType   The optional VolumeUsedAfterTariffSwitch (VUATS) SubType is used in   the RADIUS Access-Request messages (PPC to PPS direction).  It   indicates the volume (in octets) used during a session after the last   tariff switch for the service specified via the QID SubType and the   accompanying PPAQ attribute.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(23)      LENGTH  : variable (8 or 14)      VALUE : Data type String      The content of the VALUE field either contains the      Value-Digits Field or the Value-Digits Field plus the      Exponent Field. The length field indicates whether one or      both subtypes are included.                    VolumeUsedAfterTariffSwitch SubType4.5.2.  TariffSwitchInterval SubType   The TariffSwitchInterval (TSI) SubType MUST be present in each PTS   attribute that is part of a RADIUS Access-Accept message (PPS to PPC   direction).  It indicates the interval (in seconds) between the valueLior, et al.             Expires August 29, 2013               [Page 56]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   of Event-Timestamp RADIUS attribute (see [RFC2869]) of the   corresponding RADIUS Access-Request message and the next tariff   switch condition.       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  VALUE                        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(24)      LENGTH  : 6      VALUE : Data type string      This field contains a 16-bit unsigned integer      (with the values 0 to +65,535).                       TariffSwitchInterval SubType4.5.3.  TimeIntervalafterTariffSwitchUpdate SubType   The PPS MUST include TimeIntervalafterTariffSwitchUpdate (TITSU)   SubType if there is another tariff switch period after the period   that ends as indicated by the TSI SubType.  The value of the TITSU   SubType contains the number of seconds of the tariff period that   begins immediately after the period that ends as indicated by the TSI   attribute.  If the TITSU SubType is not present, the PPC assumes that   the tariff period, which ends as indicated by the TSI SubType, lasts   until further notice.  If TITSU is specified, the PPC MUST send a   quota update before the point in time specified by the TITSU SubType   (see Figure 7).Lior, et al.             Expires August 29, 2013               [Page 57]Internet-Draft        Prepaid Extentions for RADIUS        February 2013       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | SubType       |    LENGTH     | VALUE                        ...      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |  VALUE                        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      The fields have the following meaning and encoding:      SubType : Value(25)      LENGTH  : 6      VALUE : Data type string      This field contains a 16-bit unsigned integer      (with the values 0 to +65,535).                TimeIntervalafterTariffSwitchUpdate SubTypeLior, et al.             Expires August 29, 2013               [Page 58]Internet-Draft        Prepaid Extentions for RADIUS        February 20135.  Diameter RADIUS Interoperability   The RADIUS Prepaid extension described in this document may need to   interoperate with the Diameter Credit Control Application.  Two   interoperability scenarios exist, as follows.  Either the AAA server   is Diameter based and the AAA client is RADIUS based, or the AAA   client is Diameter based and the AAA server is RADIUS based.   The Diameter Credit Control Application [RFC4006] describes how to   implement a prepaid accounting system using a Diameter based   infrastructure.   A possible procedure for accomplishing the translation of the   functionality defined in Diameter Credit Control and in the RADIUS   Prepaid specification is described in Appendix B.Lior, et al.             Expires August 29, 2013               [Page 59]Internet-Draft        Prepaid Extentions for RADIUS        February 20136.  Security Considerations   This specification describes the use of RADIUS for purposes of real-   time accounting.  Threats and security issues for this application   are described in [RFC3579] and [RFC3580]; security issues encountered   in roaming are described in [RFC2607].   This document specifies new attributes that can be included in   existing RADIUS packets, which are protected as described in   [RFC3579] and [RFC3576].  See those documents for a more detailed   description.   The security mechanisms supported in RADIUS are focused on preventing   an attacker from spoofing packets or modifying packets in transit.   They do not prevent an authorized RADIUS/Diameter server or proxy   from modifying, inserting, or removing attributes with malicious   intent.  When the attributes defined in this document are modified or   removed by a RADIUS proxy they may lead to incorrect accounting   records being delivered to users or wrong resource consumption being   collected.   The described mechanism add the mechanism of capability negotiation,   so that a RADIUS server can automatically discover whether a NAS   supports the real-time accounting features described in this document   (and even more detailed capabilities can be learned by the RADIUS   server).  These mechanisms are being added to ensure that neither the   NAS nor the RADIUS server make incorrect assumptions about the   capabilities of the other party; potentially leading to incorrect   accounting and improper access to the network or other services.Lior, et al.             Expires August 29, 2013               [Page 60]Internet-Draft        Prepaid Extentions for RADIUS        February 20137.  Table of Attributes   The following table provides a guide which attributes may be found in   which RADIUS messages, and in what quantity.   Request Accept Reject Challenge Accounting  #  Attribute                                   Request   0-1     0      0      0         0          35  PPAC   0-1     0      0      0         0          36  Session Termination                                                  Capability   0+      0+     0      0         0+         37  PPAQ   0+      0+     0      0         0+         38  PTSLior, et al.             Expires August 29, 2013               [Page 61]Internet-Draft        Prepaid Extentions for RADIUS        February 20138.  IANA Considerations   This document contains a number of instructions to IANA.8.1.  RADIUS Attributes   This document does not require IANA to register the following four   RADIUS attributes as the code registered by the Wimax Forum is re-   used.  The Wimax Forum SMI Network Management Private Enterprise Code   is 24757.    Attribute Name                        |  Attribute Type Value    --------------------------------------+-----------------------------    Prepaid-Accounting-Capability (PPAC)  |  35    Session Termination Capability        |  36    Prepaid-Accounting-Operation (PPAQ)   |  37    Prepaid Tariff Switching (PTS)        |  388.2.  New Registry: PPAC SubTypes   Section 4.1 defines the SubTypes used within the PPAC attribute.   IANA is asked to create a registry for these SubTypes.  Each registry   entry consists of a 8 bit number together with a description of the   PPAC SubType.  This document creates the following PPAC SubTypes for   this registry:    Value    |  SubType Name    ---------+-----------------------------      0      |  Reserved      1      |  AvailableInClient      2..255 |  **Available for IANA registration**   The semantic of the above-listed SubType is described in Section 4.1.   Following the policies outline in [RFC3575] the available SubTypes   (i.e., value 0 and values 2-255) with a description of their semantic   will be assigned after the expert review process.  Updates can be   provided based on expert approval only.  Based on expert approval it   is possible to mark entries as "deprecated".  A designated expert   will be appointed by the IESG.   Each registration must include a number for the SubType and the   semantic of the SubType.Lior, et al.             Expires August 29, 2013               [Page 62]Internet-Draft        Prepaid Extentions for RADIUS        February 20138.3.  New Registry: PPAQ SubTypes   Section 4.3 defines the SubTypes used within the PPAQ attribute.   IANA is asked to create a registry for these SubTypes.  Each registry   entry consists of a 8 bit number together with a description of the   PPAQ SubType.  This document creates the following PPAQ SubTypes for   this registry:    Value    |  SubType Name    ---------+-----------------------------      0      |  Reserved      1      |  Quota Identifier      2      |  VolumeQuota      3      |  VolumeThreshold      4      |  DurationQuota      5      |  DurationThreshold      6      |  ResourceQuota      7      |  ResourceThreshold      8      |  Update-Reason      9      |  PrepaidServer     10      |  Service-ID     11      |  Rating-Group-ID     12      |  Termination-Action     13      |  Pool-ID     14      |  Pool-Multiplier     15      |  Requested-Action     16      |  Check-Balance-Result     17..255 |  **Available for IANA registration**   The semantic of the above-listed SubTypes is described in   Section 4.3.   Following the policies outline in [RFC3575] the available SubTypes   (i.e., value 0 and values 22-255) with a description of their   semantic will be assigned after the expert review process.  Updates   can be provided based on expert approval only.  Based on expert   approval it is possible to mark entries as "deprecated".  A   designated expert will be appointed by the IESG.   Each registration must include a number for the SubType and the   semantic of the SubType.8.4.  New Registry: PTS SubTypes   Section 4.5 defines the SubTypes used within the PTS attribute.  IANA   is asked to create a registry for these SubTypes.  Each registry   entry consists of a 8 bit number together with a description of theLior, et al.             Expires August 29, 2013               [Page 63]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   PTS SubType.  This document creates the following PTS SubTypes for   this registry:    Value    |  SubType Name    ---------+-----------------------------      0      |  Reserved      1      |  Quota Identifier      2      |  VolumeUsedAfterTariffSwitch      3      |  TariffSwitchInterval      4      |  TimeIntervalafterTariffSwitchUpdate      5..255 |  **Available for IANA registration**   The semantic of the above-listed SubTypes is described in   Section 4.5.   Following the policies outline in [RFC3575] the available SubTypes   (i.e., value 0 and values 5-255) with a description of their semantic   will be assigned after the expert review process.  Updates can be   provided based on expert approval only.  Based on expert approval it   is possible to mark entries as "deprecated".  A designated expert   will be appointed by the IESG.   Each registration must include a number for the SubType and the   semantic of the SubType.8.5.  New Registry: Update-Reason   Section 4.3.8 defines the Update-Reason SubType.  IANA is asked to   create a registry for the values contained in the Update-Reason   SubType, as shown in Figure 12.  Each registry entry consists of a 16   bit number together with a description of the update reason.   Following the policies outline in [RFC3575] the available values   together with a description of their semantic will be assigned after   the expert review process.  Updates can be provided based on expert   approval only.  Based on expert approval it is possible to mark   entries as "deprecated".  A designated expert will be appointed by   the IESG.8.6.  New Registry: Termination-Action   Section 4.3.12 defines the Termination-Action SubType.  IANA is asked   to create a registry for the values contained in the Termination-   Action SubType, as shown in Figure 13.  Each registry entry consists   of a 8 bit number together with a description of the termination   action.Lior, et al.             Expires August 29, 2013               [Page 64]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Following the policies outline in [RFC3575] the available values   together with a description of their semantic will be assigned after   the expert review process.  Updates can be provided based on expert   approval only.  Based on expert approval it is possible to mark   entries as "deprecated".  A designated expert will be appointed by   the IESG.8.7.  New Registry: Requested-Action   Section 4.3.15 defines the Requested-Action SubType.  IANA is asked   to create a registry for the values contained in the Requested-Action   SubType, as shown in Figure 14.  Each registry entry consists of a 8   bit number together with a description of the requested reason.   Following the policies outline in [RFC3575] the available values   together with a description of their semantic will be assigned after   the expert review process.  Updates can be provided based on expert   approval only.  Based on expert approval it is possible to mark   entries as "deprecated".  A designated expert will be appointed by   the IESG.8.8.  New Registry: Check-Balance-Result   Section 4.3.16 defines the Check-Balance-Result SubType.  IANA is   asked to create a registry for the values contained in the Check-   Balance-Result SubType, as shown in Figure 15.  Each registry entry   consists of a 8 bit number together with a description of the   requested reason.   Following the policies outline in [RFC3575] the available values   together with a description of their semantic will be assigned after   the expert review process.  Updates can be provided based on expert   approval only.  Based on expert approval it is possible to mark   entries as "deprecated".  A designated expert will be appointed by   the IESG.Lior, et al.             Expires August 29, 2013               [Page 65]Internet-Draft        Prepaid Extentions for RADIUS        February 20139.  Acknowledgements   The authors would like to thank Bernard Aboba, Christian Guenther,   Dirk Kroeselberg and John Loughney for their feedback throughout the   development of this document.  Additionally, the authors would like   to thank the members of the Wimax Forum and the members of 3GPP2 for   their help with this specification.Lior, et al.             Expires August 29, 2013               [Page 66]Internet-Draft        Prepaid Extentions for RADIUS        February 201310.  References10.1.  Normative References   [RFC2119]  Bradner, S., "RFC 2119: Key words for use in RFCs to              Indicate Requirement Levels", March 1997.   [RFC2865]  Rigney, C., Rubens, A., Simpson, W., and S. Willens, "RFC              2865: Remote Authentication Dial In User Server (RADIUS)",              June 2000.   [RFC3576]  Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.              Adoba, "RFC 3576: Dynamic Authorization Extensions to              Remote Authentication Dial-In User Service (RADIUS)",              February 2003.10.2.  Informative References   [RFC2284]  Blunk, L. and J. Vollbrecht, "PPP Extensible              Authentication Protocol (EAP)", RFC 2284, March 1998.   [RFC2607]  Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy              Implementation in Roaming", RFC 2607, June 1999.   [RFC2866]  Rigney, C., "RFC 2866: RADIUS Accounting", June 2000.   [RFC2869]  Rigney, C., Willats, W., and P. Calhoun, "RFC 2869: RADIUS              Extensions", June 2000.   [RFC3575]  Aboba, B., "IANA Considerations for RADIUS (Remote              Authentication Dial In User Service)", RFC 3575,              July 2003.   [RFC3579]  Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication              Dial In User Service) Support For Extensible              Authentication Protocol (EAP)", RFC 3579, September 2003.   [RFC3580]  Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,              "IEEE 802.1X Remote Authentication Dial In User Service              (RADIUS) Usage Guidelines", RFC 3580, September 2003.   [RFC3748]  Adoba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.              Levkowetz, "RFC 3748: Extensible Authentication Protocol",              June 2004.   [RFC4006]  Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.              Loughney, "RFC 4006: Diameter Credit Control Application",              August 2005.Lior, et al.             Expires August 29, 2013               [Page 67]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   [RFC4849]  Congdon, P., Sanchez, M., and B. Aboba, "RADIUS Filter              Rule Attribute", RFC 4849, April 2007.   [RFC6158]  DeKok, A. and G. Weber, "RADIUS Design Guidelines",              BCP 158, RFC 6158, March 2011.Lior, et al.             Expires August 29, 2013               [Page 68]Internet-Draft        Prepaid Extentions for RADIUS        February 2013Appendix A.  Example flows   Note: This section is informative.   This section presents certain example flows that involve the RADIUS   prepaid extensions.  By no means is the intent of this section to   specify or recommend business logic, rating strategies, and   application-level behaviour.  The intent of this section is purely to   illustrate some fictive scenarios and the RADIUS prepaid message   flows that could be associated with these scenarios.  The contents of   this section should be regarded as a collection of informative   examples that aim to provide guidance to implementors.A.1.  A simple flow      End user          PPC                  PPS      user logs on      ------(1)--------->                            Access Request                            {RADIUS BASE AVPS,                             PPAC=00...00011}                            -------(2)-------->                                               [allocates                                               5MB quota]                                Access Accept                               {RADIUS BASE AVPS,                               PPAQ={QID=5, VQ = 5MB,                               VTH = 4.5 MB}}                               <-------(3)--------      service provision/metering      -------(4)--------->      4.5 MB consumed                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={QID=5, VQ=4.5MB,                          REASON=THRESHOLD REACHED}}                          -------(5)--------->                                       [allocates another 7MB                                      to the access service]Lior, et al.             Expires August 29, 2013               [Page 69]Internet-Draft        Prepaid Extentions for RADIUS        February 2013                              Access Accept                              {RADIUS BASE AVPS,                              PPAQ={QID=8, VQ=12MB,                              VTH = 11.5 MB}}                          <----------(6)--------------        user logs off      ------(7)-------                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={QID=8, VQ=7 MB,                          REASON=ACCESS SERV TERMINATED}}                          -------(8)--------->                                        [reimburses                                        user account]                              AA Accept                             {RADIUS BASE AVPS}                            <-------(9)--------                 Figure 17: A simple example message flow   The user logs on (1).  The PPC sends a RADIUS Access Request message   to the PPS (2), and includes the prepaid-specific PPAC AVP.  This AVP   indicates that both duration-based and volume-based metering is   supported.  However, it also indicated that multiple services, rating   groups and resource pools are not supported.  Note that, since this   is not an "Authorize-Only" message, no PPAQ attribute with Update   Reason="initial request" is included (see Section 3.7.1).  The PPS   then authenticates the user and authorizes the access service, as is   usual in RADIUS.  Note that the PPAC AVP is appended by the PPC in at   least the last message that is sent to the home AAA server during   this possibly multiple-round exchange.   If authentication and authorization is successful (in this example   this is assumed), then the PPS identifies the user's prepaid account   from the included base RADIUS AVPs, and determines the capabilities   of the PPC from the PPAC attribute.  Assuming that sufficient funds   are available in the user's prepaid account, the PPS reserves some of   these and rates the service.  In this example, the PPS reserves, say,   2 Euros and determines that the access service is rated at 0.4 Euro   per MB.  This results in 5 MB of quota being granted.  The PPS also   determines that the PPC should ask for this quota to be replenished   once 4.5 MB have been consumed.  Thus, it creates an Access Accept   message with a Volume-Threshold indication of 4.5MB.  It further   associates the QID=5 to this reservation.  This identifier can be   used to later uniquely identify the prepaid session, user, account,   etc.  The resulting Access Accept message is sent to the PPC (3).Lior, et al.             Expires August 29, 2013               [Page 70]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Upon reception of message (4), the PPC provides the access service to   the user and meters it accordingly.  At some point in time, the   threshold is reached, i.e., 4.5MB of "access service" have been   consumed by the user.  At that point, the PPC generates an Authorize-   Only Access Request that contains the usual RADIUS attributes and a   PPAQ attributes that reports the amount of consumed quota, and the   request for replenishment, i.e., the Update-Reason= THRESHOLD REACHED   (5).  Note that the QID in this message is the same as the one   previously received from the PPS.   Upon reception of message (5), the PPS identifies the user and his   account from the QID.  In also determines that a prepaid session is   ongoing, and that enough credit remains in the prepaid account in   order for the access service to continue being provided.  Since 4.5   MB have been consumed, the PPS subtracts 1.8 Euros from the user's   prepaid account.  The PPS decides to reserve another 2.8 euros from   the user's account.  (This results in 3 euros being reserved in total   at this point in time.)  As the access service is rated at 0.4 euros   per MB, the PPS determines that another 7 MB of quota should be   granted.  This results in a total cumulative quota allocation of 12   MB for the access service.  The PPS further calculates the new   threshold value of 11.5 MB.  Since this is a new quota reservation,   the PPS also allocates a new QID to it, in this example QID=8.  The   resulting RADIUS message is sent to the PPC (6).   Upon reception of message (6), the PPC updates its records and   continues provisioning access to the user.  At some point the user   logs off (7).  The PPC must then report how many resources were   consumed, so that the PPC can subtract the appropriate monetary   amount from the user's prepaid account.  To this end the PPC   constructs an Authorize-Only Access Request message with a PPAQ   attributes for the access service.  In this example, 7 MB were   consumed by the access service in total.  The PPC reports 7 MB its   final message (8).  The PPS correlates the report, using the QID, to   the previous session state.  It determines, from the previous   records, that the access service had consumed another 4.5 MB before   (as indicated in message (6)).  This means that, of the 7 MB, only   3.5 MB have not yet been subtracted from the user's account.  Thus,   the PPS subtracts another 1.4 euros from the user's account and,   since the session is to be terminated (REASON=ACCESS SERVICE   TERMINATED), releases any reserved monetary amount.   The PPS responds with an Access Response as required by the RADIUS   base specification (9).Lior, et al.             Expires August 29, 2013               [Page 71]Internet-Draft        Prepaid Extentions for RADIUS        February 2013A.2.  A flow with prepaid tariff switching   End user          PPC                  PPS      user logs on      ------(1)--------->                            Access Request                            {RADIUS BASE AVPS,                             PPAC=00...00111}                            -------(2)-------->                                        [allocates                                        20MB quota]                                   Access Accept                                {RADIUS BASE AVPS,                           PPAQ={QID=5, VQ = 20MB,                              VTH = 18 MB}, PTS={                            QID=5, PTS{TSI=300sec,                                   TITSU=6000sec}}                              <-------(3)-------      service provision/metering      -------(4)--------->      5900 seconds      passed                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={QID=5, VQ=14MB,                          REASON=TITSU APPROACH.},                          TSI={QID=5, VUATS=11MB}}                          -------(5)--------->                                  [allocates another 10MB                                  to the access service]                          Access Accept                          {RADIUS BASE AVPS,                          PPAQ={QID=8, VQ=30MB,                          VTH = 28 MB},PTS={                          QUD=8, PTS=95 sec}}                     <----------(6)--------------        user logs offLior, et al.             Expires August 29, 2013               [Page 72]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      ------(7)-------                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={QID=8, VQ=17 MB,                          REASON=ACCESS SERV TERMINATED},                          PTS={QID=8, VUATS=2.5 MB}                          -------(8)--------->                                          [reimburses                                          user account]                                AA Accept                               {RADIUS BASE AVPS}                              <-------(9)--------            Figure 18: Example message flow with Tariff Switch   The user logs on (1).  The PPC sends a RADIUS Access Request message   to the home AAA server (2), and includes the prepaid-specific PPAC   AVP.  This AVP indicates that both duration-based and volume-based   metering is supported, as well as tariff switching.  The home AAA   server then may authenticate and user and authorize the access   service, as is usual in RADIUS.  Note that the PPAC AVP is appended   by the PPC in at least the last message that is sent to the PPS   during this possibly multiple-round exchange.   If authentication and authorization is successful (in this example   this is assumed), the PPS identifies the user's prepaid account from   the included base RADIUS AVPs, and determines the capabilities of the   PPC from the PPAC attribute.  In this example, it is assumed that a   tariff switch is about to occur in 300 seconds from the current time.   Suppose that the access service is currently rated at 0.5 euros per   MB and in the next tariff period it is rated at 0.6 euros per MB.   Suppose further that a third tariff period is about to start in 6000   seconds from current time and that that access service is rated at   0.8 euros per MB in that period.  The PPS then decides to reserve 12   euros from the user's account.  Since it is conceivable that the user   may consume all allocated quota in the (more expensive) "0.6-euro"   period, the PPS reserves 20 MB of quota, and determines a threshold   value of 18 MB.  It constructs a Radius Access Accept message with a   PPAQ attribute that reflects these choices, and carries a Quota   Identifier QID=5.  It further adds a PTS AVP in the message which is   linked to the PPAQ via the common QID value.  The PTS AVP contains a   TSI attribute indicating that a tariff switch will occur in 300   seconds.  It also includes a TITSU attribute with the value of 6000   seconds.  This is included in order to make sure that the PPC willLior, et al.             Expires August 29, 2013               [Page 73]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   report the consumed quota before the "2-euro" tariff period will   start.  The message is sent to the PPC (3).   Upon reception of message (3), the PPC provides the access service to   the user and meters it accordingly (4).  It also keeps track of time.   That is, it remembers how many octets are consumed before and how   many after the tariff switch that will take place in 300 seconds.   In this example it is assumed that the user consumes the allocated   quota rather slowly.  In particular, nearly 6000 seconds (the value   indicated by TITSU SubType) pass without the threshold of 18 MB being   reached.  The PPC notices this and must therefore report usage and   request the quota to be replenished despite the fact that the   threshold has not been reached.  In this example, it decides to do so   100 seconds before the 6000 seconds are reached.  To this end, it   constructs an Authorization Access Request message including a PPAQ   that indicates that 14 MB have been consumed up to now.  It also   includes a PTS attribute in order to indicate, using the VUATS   SubType, that 11 MB of these were consumed after the tariff switch.   The message is sent to the the PPS (5).   The PPS can link the message to previous session state via the QID.   It now rates the consumed volume as follows.  The 11 MB that were   consumed after the tariff switch correspond to 11 * 0.6 = 6.6 euros   and the remaining 14-11=3 MB to 3 * 0.5 = 1.5 euros.  Thus, the PPS   subtracts the amount of 6.6+1.5=8.1 euros from the user's account,   which leads to a remainder of 12 - 8.1 = 3.9 euros being reserved.   The PPS now determines that message (5) was sent in order to   replenish the quota for this prepaid session.  This can be deduced   from the UPDATE REASON field, which indicates that the PPC sent this   message because the time indicated by the TITSU SubType is   approacing.  The PPS now determines that enough credit remains in the   user's prepaid account in order for the access service to continue   being provided and decides to reserve another 8.9 euros from the   user's account.  Since it is conceivable that the user will consume   the 6 unused MB of quota from the previous allocation, as well as the   entire quota that is to be allocated now, entirely in the "0.8-euro"   period, the quota that should now be granted in addition to the   previous 20 MB should be 10 MB.  This is because 0.9 of the 8.9 euros   are being reserved in order to "cover the worst case scenario".  The   fact that 0.9 euros are reserved for this purpose is due to the fact   that the unused 6 MB from the previous allocation correspond to 4.8   euros (with 0.8 euros per MB).  This is 4.8 - 3.9 = 0.9 euros more   than the amount of funds that are still "reserved" from the previous   allocation.  (After this reservation, the total amount of reserved   money is 8.9 + 3.9 = 12.8 euros, which corresponds to 16 (10+6) MB   being consumed in the "0.8-euro" period.)Lior, et al.             Expires August 29, 2013               [Page 74]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Since quotas are encoded in a cumulative way in RADIUS, the PPS   includes a VolumeQuota of 30 MB into the Access Accept message (6).   The PPS further calculates the new threshold value of 28 MB.  Since   this is a new quota reservation, the PPS also allocates a new QID to   it, in this example QID=8.  The resulting RADIUS message is sent to   the PPC (6).   Upon reception of message (6), the PPC updates its records and   continues providing access to the user.  At some point the user logs   off (7).  The PPC must then report how many resources were consumed,   so that the PPC can subtract the appropriate monetary amount from the   user's prepaid account.  To this end the PPC constructs an Authorize-   Only Access Request message with a PPAQ attributes for the access   service.  In this example, 17 MB were consumed by the access service   in total.  The PPC reports 17 MB its final message (8).  The PPS   correlates the report, using the QID, to the previous session state.   It determines, from the previous records, that the access service had   consumed 14 MB before (as indicated in message (5)).  This means   that, of the 17 MB, only the monetary equivalent for 3 MB have not   yet been subtracted from the user's account.  The PPS calculates how   much should be deducted from the user's account as follows.  Since   the VUATS SubType indicates that 2.5MB were consumed after the tariff   switch, only 0.5 MB were consumed before that.  Thus, the monetary   equivalent is 0.5 * 0.6 + 2.5 * 0.8 = 3.6 euros.  That is, the PPS   subtracts 3.6 euros from the user's prepaid account.  Since the   session has by now be terminated by the PPC (REASON=ACCESS SERVICE   TERMINATED), the PPS now releases any reserved monetary amount, in   this example 12.8 - 3.6 = 9.2 euros.   The PPS responds with an Access Response as required by the RADIUS   base specification (9).   Remark: In this example, two tariff switches take place.  In other   scenarios, of course, only one tariff switch may occur.  In such   scenarios the TITSU SubType is not used.A.3.  Resource pools and Rating Groups      End user          PPC                  PPS      user logs on      ------(1)--------->                            Access Request                            {RADIUS BASE AVPS,                             PPAC=00...00101111}                            -------(2)-------->Lior, et al.             Expires August 29, 2013               [Page 75]Internet-Draft        Prepaid Extentions for RADIUS        February 2013                                          [allocates                                          5MB quota]                            Access Accept                           {RADIUS BASE AVPS,                           PPAQ={QID=5, VQ = 5MB,                           poolID=1,mult=1}}                          <-------(3)--------      service provision/metering      -------(4)--------->      user requests service A      -------(5)--------->                          Access Request                          {RADIUS BASE AVPS,PPAQ={                          SID="A", RGROUP=1}}                           -------(6)-------->                           [allocates 50 min                                       quota]                          Access Accept                         {RADIUS BASE AVPS,                         PPAQ={QID=7, DQ=3000sec                         poolID=1,RGROUP=1, SID="A"                         mult=1747.63}}                         <---------(7)---------------      user requests service B      -------(8)-------->      Pool 1 close to exhaustion                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={QID=5, VQ=4MB,                          REASON=QUOTA REACHED,                          PoolID=1, mult=1}                          PPAQ={QID=7, DQ=3300sec                          REASON=QUOTA REACHED,                          PoolID=1, mult=1747.63,                          SID="A",RGROUP=1}}                          -------(9)--------->                                       [allocates another                                       3 MB to access serviceLior, et al.             Expires August 29, 2013               [Page 76]Internet-Draft        Prepaid Extentions for RADIUS        February 2013                                       and 30 minutes to                                       service "A"]                          Access Accept                         {RADIUS BASE AVPS,                         PPAQ={QID=8, VQ=8MB,                         PoolID=1, mult=1, RGROUP=1},                         PPAQ={QID=9, DQ=4800sec                         PoolID=1, mult=1747.63,                         SID="A"}}     \                    <----------(10)--------------        user logs off      ------(11)-------                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={QID=8, VQ=6.5MB,                          REASON=ACCESS SERV TERMINATED,                          PoolID=1, mult=1}                          PPAQ={QID=9, DQ=5400sec                          REASON=ACCESS SERV TERMINATED,                          PoolID=1, mult=1747.63,                          SID="A",RGROUP=1}}                          -------(12)--------->                                            [reimburses                                            user account]                          AA Accept                         {RADIUS BASE AVPS                         <------(13)--------   Figure 19: Example message flow with resource pools and rating groups   The user logs on (1).  The PPC sends a RADIUS Access Request message   to the PPS (2), and includes the prepaid-specific PPAC AVP,   indicating that multiple services, rating groups and resource pools   are supported.  Note that, since this is not an "Authorize- Only"   message, no PPAQ attribute with Update Reason="initial request" is   included (see Section 3.7.1).  The PPS then may authenticate the user   and authorize the access service, as is usual in RADIUS.  Note that   the PPAC AVP is appended by the PPC in at least the last message that   is sent to the PPS during this possibly multiple-round exchange.   If authentication and authorization is successful (in this example   this is assumed), the PPS identifies the user's prepaid account from   the included base RADIUS AVPs, and determines the capabilities of the   PPC from the PPAC attribute.  Assuming that sufficient funds areLior, et al.             Expires August 29, 2013               [Page 77]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   available in the user's prepaid account, the PPS reserves some of   these and rates the service.  In this example, the PPS reserves 5   Euros and determines that the access service is rated at 1 Euro per   MB.  In anticipation that the user requests more chargeable services   throughout this prepaid session, and since this is supported by the   PPC, the PPS further associates a resource pool with this   reservation, in this example PoolID=1.  The PPC also specifies the   multiplier = 1 for the access service.  Note that, since 5MB =   5242880 octets, 1 unit in the resource pool corresponds to 5 /   5242880 euros, which is about 0.000095367431640625 Eurocents.   (However, the PPC does not need to know that.)  Moreover, the PPS   associates the QID=5 to this reservation.  This identifier can be   used to later uniquely identify the prepaid session, user, account,   etc.  The resulting Access Accept message is sent to PPC (3).   Upon reception of message (3), the PPC provides the access service to   the user and meters it accordingly (4).  That is, for every octet   consumed, the PPC subtracts 1 unit (since the multiplier is 1) from   the resouce pool with PoolID=1.   At some point in time, the user requests another chargeable service,   namely service A (5).  The PPC generates an Authorize-Only Access   Request that contains the usual RADIUS attributes and the Service-ID   identifying service A (6).  The PPC has determined that service A is   rated in an identical way as at least one more service.  Thus,   service A has been configured to belong to a rating group, in this   example the group with Rating-Group-ID=1.  This identifier is   included is message (6).   Upon reception of message (6), the PPS identifies the user and his   account from the base RADIUS attributes, the fact that a prepaid   session is ongoing, and determines that enough credit remains in the   prepaid account in order for service A to be provided.  The PPS also   determines that service A is rated at 0.10 euros per minute.  The PPS   decides to reserve another 5 euros from the users account; this   corresponds to 50 minutes or, as encoded in the DurationQuota   SubType, 3000 seconds.  As service A draws from the same prepaid   account as the access service, the PPS associates this reservation   with the same resource pool as the previous reservation (QID=5),   namely the pool with PoolID=1.  Note that, in order for the abstract   units in the pool to be consistent, the multiplier has to be 1747.63.   This is because each second corresponds to about 0.10 / 60 = 0.00167   euros, which is about 1747.63 times the value of an abstract resource   pool unit, as this was determined by the first allocation of quota to   the pool (i.e., 0.000095367431640625 Eurocents).  Since this is a new   quota reservation, the PPS also allocates a new QID to it, in this   example QID=7.  The resulting RADIUS message is sent to the PPC (7).Lior, et al.             Expires August 29, 2013               [Page 78]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Upon reception of message (7), the PPC adjusts the units in resource   pool 1.  That is, it first determines how much quota had been   allocated to service A in the past, and subtracts this from the quota   reservation found in the message.  Since this is the first quota   reservation for service A, there is nothing to subtract.  Thus, it   adds 3000 * 1747.63 = 5242890 units to the pool and remembers that   3000 seconds have been allocated to service A during this prepaid   session.  The PPC then provides service A to the user, and meters it   against resource pool 1.  That is, for every second it subtracts   1747.63 units from the pool.   At some point in time, the user requests service B (8).  The PPC   determines that service B is rated exactly in the same way as service   A, i.e., that they belong to the same rating group, namely the one   with Rating-Group-ID=1.  Since this rating group has been effectively   authorised by the allocation of quota with QID=7, the PPC provides   service B to the user immediately.  It is rated in the same way as   service A, i.e., for every second provided, 1747.63 units are   subtracted from credit pool 1.   At some point in time, resource pool 1 is close to exhaustion.  (For   example, the PPC may determine that the pool is "close to exhaustion"   when has less than 10% its initial amount of units.)  At that point,   the PPC needs to ask for replenishment for the pool.  Suppose that,   at that point in time, 4MB of "access service", 45 minutes of   "service A", and 10 minutes of "service B" were provided to the user.   Note that this corresponds to (4*1048576) + (55*60*1747.63) = 4194304   + 5767179 = 9961483 abstract service units from the pool.  The PPC   constructs an Authorize-Only Access Request message that reports the   usage for the "access service" and "service A".  This message   contains two PPAQ attributeS, is sent to the PPS (9).  Note that is   the message it appears that "service A" has consumed more than it was   allocated (i.e., 55 minutes although only 50 minutes were initially   allocated to it).  This is not a a problem since the PPS knows that   "service A" was drawing from the same pool as the "access service"   and that the "access service" did only consume 4 out of the 5 MB it   was allocated.   Upon reception of message (9), the PPS subtracts 4 euros from the   user's account for the "access service" and another 5.5 euros for   "service A".  (This includes the charge incurred by "service B" up to   that point in time, although the PPS is not aware of "service B"   being provisioned to the user.)  The PPS then determines that   sufficient funds remain in the prepaid account in order for both   services to be continued.  The PPS decides to reserve another 3MB for   the access service and 30 minutes for "service A".  This corresponds   to 3+3=6 euros.  Since in RADIUS prepaid the quotas are encoded in a   cumulative manner, the PPAQ attribute that grants the quota for theLior, et al.             Expires August 29, 2013               [Page 79]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   "access service" contains a Volume-Quota SubType of 8MB (8388608   octets), which is the 5MB that were initially allocated, plus the 3MB   allocated now.  The resource pool identifier is, as previously,   PoolID=1 and the multiplier is 1.  Similarly, the PPAQ that grants   quota for "service A" contains 4800 seconds (the initial 3000 plus   1800 that correspond to the 30 additional minutes).  Again, the   PoolID=1 and multiplier=1747.63.  The resulting Access Response   message is sent to the PPC (10).   When the PPC received message (10) it checks how much quota has been   allocated previously to the "access service".  It finds that the   answer is 5MB (5242880 octets); thus, out of the 8MB (8388608 octets)   that are indicated by the PPAQ with QID=8, only 3MB (3145728 octets)   have not yet been added to resource pool 1.  The PPC thus adds   3145728 abstract units to resource pool 1 (since the multiplier is   1).  The PPC then acts similarly on the other PPAQ attribute that   exists in message (11).  That is, the PPC determines that 3000   seconds of quota for "service A" had already been added to the pool.   Thus only 1800 out of the 4800 should be additionally added to the   pool.  Since the applicable multiplier here is 1747.63, the PPC adds   further 3145734 abstract units to the pool 1.   The PPC then continues to provide the access service, "service A" and   "service B" to the user, and meters them against the pool, as   previously.   At some point the user logs off (11).  The PPC must then report how   many resources were consumed, so that the PPC can subtract the   appropriate monetary amount from the user's prepaid account.  To this   end the PPC constructs an Authorize-Only Access Request message with   two PPAQ attributes; one for the access service and one for "service   A".  Suppose that, in total, 6.5MB were consumed by the access   service, 70 minutes were consumed by "service A" and 20 minutes by   "service B".  The PPC reports 6.5MB (6815744 octets) and 90 minutes   (5400 seconds) in its final message (12).  The PPS determines, from   the previous records, that the access service consumed another 2.5MB   (since 4MB out of the 6.5MB were already reported in message (9), and   that "service A" consumed further 600 seconds.  This corresponds to   2.5 + (600/60)*0.1 = 2.5+ 1=3.5 euros.  Thus, the PPS only subtracts   2.5 out of the 6 previously reserved euros from the user's prepaid   account and responds with an Access Response as required by the   RADIUS base specification (13).A.4.  One-time chargingLior, et al.             Expires August 29, 2013               [Page 80]Internet-Draft        Prepaid Extentions for RADIUS        February 2013     End user          PPC                  PPS      user requests ring tone      ------(1)--------->                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={QID=321, SID=X, RQ=650,                          REASON=10 (ONE-TIME CHARGING}}                          -------(2)--------->                                   [rates 650 abstract units                                   deducts from user's account]                                Access Accept                                {RADIUS BASE AVPS}                      <----------(3)--------------        ring tone is delivered      <------(4)-------          Figure 20: Example message flow with one-time charging   The user requests a chargeable ring tone (1).  The PPC sends a RADIUS   Access Request message to the PPS (2), and includes a PPAQ attribute   with Update Reason="one-time charging" is included (see   Section 3.8.6).  The Service ID indicates to the PPS that the   charging event is connected to a ring tone, so that the PPS can rate   the event accordingly.  The PPAQ also contains a unique Quota   Identifier.   The PPS then may authenticate the user as is usual in RADIUS.  If   authentication is successful (in this example this is assumed), the   home AAA server forwards the PPC converts the 650 reported abstract   units into monetary value, according to the service type, and debit   the user's account accordingly.  This happens, of course, only if   sufficient funds are available in the user's prepaid account.  The   PPC then responds with an an Access Accept message (3).  The PPS adds   a "session timeout = 0 AVP" (see Section 3.8.6).A.5.  Price enquiryLior, et al.             Expires August 29, 2013               [Page 81]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      End user          PPC                  PPS      user requests AoC      ------(1)--------->                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={SID=X, VQ=10MB,                          REQ_ACT=2(PRICE ENQUIRY}}                          -------(2)--------->                              [rates 10MB for requested                                                service]                           Access Accept                          {RADIUS BASE AVPS,                          PPAQ={SID=X, VQ=10MB,                   COST INFORMATION= 0.6 euros                          per MB}}                        <----------(3)--------------        AoC is delivered      <------(4)-------   Figure 21: Example message flow with price enquiry (advice of charge)   Please refer to Section 2.7.3 for an explanation of this message   flow.A.6.  Balance checkLior, et al.             Expires August 29, 2013               [Page 82]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   End User               PPC                  PPS                          Access Request                          {RADIUS BASE AVPS,                          PPAQ={SID=X, VQ=10MB,                          REQ_ACT=BALANCE CHECK}}                          -------(2)--------->                                       [rates requested                                       Service and checks                                       remaining funds]                          Access Accept                         {RADIUS BASE AVPS,                         PPAQ={SID=X, VQ=10MB,                   BALANCE_CHECK_RESULT}}                    <----------(3)--------------            Figure 22: Example message flow with balance check   Please refer to Section 2.7.4 for an explanation of this message   flow.Lior, et al.             Expires August 29, 2013               [Page 83]Internet-Draft        Prepaid Extentions for RADIUS        February 2013Appendix B.  Translation between RADIUS Prepaid and Diameter Credit             Control   Note: This section is informative.   In scenarios where the service metering device uses the "RADIUS   prepaid" (RPP) protocol for accounting and prepaid charging while the   AAA infrastructure uses the "Diameter Credit Control" (DCC) protocol,   a translation agent that enables the interoperation of both systems,   is desirable.  This also applies vice versa, i.e., in scenarios where   the AAA infrastructure uses RADIUS and the service metering device   uses Diameter.   The idea of such a translation agent would be to convert incoming RPP   (resp. DCC) messages into outgoing DCC (resp. RPP) messages.  It   would be, in principle, desirable for the translation agent to be   stateless.  That is, the agent should not be required to internally   maintain information about each ongoing RADIUS or Diameter session.   However, under the current specification of RPP and DCC, this appears   to be impossible due to a number of reasons.  These include the   following.   1.  The transport mechanism for DCC is TCP, which requires per-       session state to be maintained at both endpoints of the       communication.  Note, however, that, in principle, each DCC       message could be sent over a dedicated TCP connection which is       torn down as soon as the message is sent.  This, however, is       likely to be unacceptable in terms of efficiency.   2.  While RPP messages encode the cumulative amount of consumed/       requested resources, DCC messages carry the difference from the       previous message.  This means that the translation agent has to       maintain the current amount of consumed/requested resources in       order to be able to calculate the correct amount to be put into       an outgoing message.   The translator maps each incoming RPP (resp. DCC) message into an   outgoing DCC (resp. RPP) message, and possibly establishes or updates   local state that is associated with the session.  The translated   (i.e., outgoing) message is a function of the incoming message as   well as existing state that is associated with the current session.   Translation occurs on an attribute-by-attribute basis.  Certain   attributes are translated without consideration of local per-session   state.  Other attributes, namely those that are bound to a particular   session, require such consideration.  The translation agent has to   identify the session (and possibly subsession) an incoming message   belongs to in order to consult the appropriate local per-sessionLior, et al.             Expires August 29, 2013               [Page 84]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   state.   Note that certain DCC attributes cannot be translated due to their   semantics not being present in RPP, and vice versa.  This results in   the messages, in which these attributes occur, not being delivered to   their intended destination.  In such cases it is desirable to inform   the originator about the failure and terminate the session.   In each scenario (i.e., RPP client / DCC AAA infrastructure and DCC   client / RPP AAA infrastructure), the translator operates in two   directions, namely RPP to DCC and vice versa.  In the following   sections, the notation c->s means that the attribute in question may   occur only in the direction from the client to the server.  The   notation s->c denotes the converse and the notation c<->s denotes   that the attribute may occur in messages that are directed in either   direction.B.1.  Session Identification   The translation agent has to keep per-session state in order to   perform its task.  A session may be identified based on the RPP   identifier or the DCC session identifier.  That is, the translation   agent should always maintain a pair of (RPP, DCC) session identifiers   and maintain the per-session state in association with that pair.   This per-session state must be addressable by either of these two   identifiers.  Moreover, an RPP session identifier must uniquely   correspond to a DCC identifier.  (If this holds, the converse also   holds.)  Each subsession identifier within an RPP session must also   uniquely correspond to a subsession identifier within its   corresponding DCC session.  (If this holds the converse also holds.)B.2.  Translation between RADIUS Prepaid and Diameter Credit Control   This section describes the translator in the "RPP client / DCC AAA   infrastructure" case.  In other words, in this section it is assumed   that the client "talks" RPP and the AAA inftrastructure "talks" DCC.   The translator is assumed to sit somewhere in the middle and to   mediate between client and server.   For each RPP AVP (i.e., AVPs that are specified in the present   document), the transformation into a semantically equivalent DCC AVP   (if such an AVP exists), along with what per-session state the   translator has to create or consult, is described.  For clarity of   exposition, each RPP AVP is addressed in a separate subsection.   Since in this scenario, the PPC is typically the initiator a session,   the focus is on the RPP AVPs.Lior, et al.             Expires August 29, 2013               [Page 85]Internet-Draft        Prepaid Extentions for RADIUS        February 2013B.2.1.  PPAC (c<->s)   A DCC client is assumed to always support Volume metering, Duration   metering, Resource metering, Pools, Rating groups, and Tariff   Switching.  Thus, if a PPAQ that indicates any of the above is sent   client->server, the translator does the following: It lets message go   through but remembers what exactly the client supports.  If the   server later requests (servier -> client direction) an unsupported   metering to be performed, send failure to server and cause the   session to be terminated at the client.   If a PPAC indicates support for multiple services (0x00000020), the   translator maps this onto a DCC Multiple-Services- Indicator AVP.B.2.2.  Service Termination Attribute (c->s)   The Diameter base protocol assumes that the client always supports   dynamic session termination.  If this AVP is present, the translator   does not need to do anything, i.e., there exists no DCC AVP that this   AVP can be mapped to.  If this AVP is absent, the message in which it   appears should either be discarded and originator should be informed   of a failure, or the message can be passed on (without this AVP being   mapped onto a DCC AVP).  However, in the latter case, the translator   has to remember that the client does not support dynamic termination.   Thus, the translatior has to initiate the normal session termination   procedure with the client when (if) dynamic termination is later   initiated by the server.B.2.3.  Quota Identifier Attribute (c<->s)   When quota is allocated for the first time by the DCC server, the   translator has to create a QID AVP, as required by this   specification.  The translator later uses a QID AVP that is sent in   the client-to-server direction in order to identify the corresponding   DCC session.  The QID has to be saved in the translator's per session   state.B.2.4.  Volume Quota Attribute (c<->s)   If this AVP occurs in a message that is sent in the server-to-client   direction, it is translated into a Granted-Service-Unit AVP with an   embedded CC-Total-Octets AVP.   If this AVP occurs in a message that is sent in the client-to-server   direction, then it is translated into a Used-Service-Unit AVP with an   embedded CC-Total-Octets AVP.  Note that only the difference between   current cumulative quota for the (sub)session and the quota in   incoming messages is indicated in the translated DCC message.  LocalLior, et al.             Expires August 29, 2013               [Page 86]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   state is updated with cumulative consumed resources.   Conversely, if the server grants quota using the DCC Granted-Service-   Unit AVP with an embedded CC-Total-Octets AVP, then the translation   agent must translate this into a Volume Quota Attribute.  Again,   local state must be consulted so that the cumulative amount of octets   is indicated in the Volume Quota attribute.B.2.5.  Duration Quota Attribute (c<->s)   If this AVP occurs in a message that is sent in the server-to-client   direction, it is translated into a Granted-Service-Unit AVP with an   embedded CC-Time AVP.   If this AVP occurs in a message that is sent in the client-to-server   direction, then it is translated into a Used-Service-Unit AVP with an   embedded CC-Time AVP.  Note that only the difference between current   cumulative quota for the (sub)session and the quota in incoming   messages is indicated in the translated DCC message.  Local state is   updated with cumulative consumed resources (i.e., time).   Conversely, if the server grants quota using the DCC Granted-Service-   Unit AVP with an embedded CC-Time AVP, then the translation agent   must translate this into a Duration Quota attribute.  Again, local   state must be consulted so that the cumulative amount of seconds is   indicated in the Duaration Quota attribute.B.2.6.  Resource Quota Attribute (c<->s)   If this AVP occurs in a message that is sent in the server-to-client   direction, it is translated into a Granted-Service-Unit AVP with an   embedded CC-Service-Specific-Units AVP.   If this AVP occurs in a message that is sent in the client-to-server   direction, then it is translated into a Used-Service-Unit AVP with an   embedded CC-Service-Specific-Units AVP.  Note that only the   difference between current cumulative quota for the (sub)session and   the quota in incoming messages is indicated in the translated DCC   message.  Local state is updated with cumulative consumed resources   (i.e., resources).   Conversely, if the server grants quota using the DCC Granted-Service-   Unit AVP with an embedded CC-Service-Specific-Units AVP, then the   translation agent must translate this into a Resource Quota   attribute.  Again, local state must be consulted so that the   cumulative amount of resource units is indicated in the Resource   Quota attribute.Lior, et al.             Expires August 29, 2013               [Page 87]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   Note that the "resource" type is application dependent.  This means   that a DCC application unit corresponds to n RPP application units,   where n may be any real number.  If n is not 1, then the RPP/DCC   translator must be aware of that and translate resource units   accordingly.B.2.7.  Value Digits Attribute (c<->s)   The encoding of this AVP is similar in RPP and DCC, and the value it   holds may have to be evaluated in conjunction with an acommpanying   "Exponent" AVP.  It should be kept in mind that, in RPP the   cumulative amount of granted/consumed quota is typically encoded into   an AVP of this type, while in DCC only the difference from a previous   message.B.2.8.  Exponent Attribute (c<->s)   The encoding of this AVP is similar in RPP and DCC, and the value it   holds may have to be evaluated in conjunction with an acommpanying   "Value Digits" AVP.  It should be kept in mind that, in RPP the   cumulative amount of granted/consumed quota is typically encoded into   a related "Value Digits" and "Exponent" AVP pair, while in DCC only   the difference from a previous message is encoded into such a pair.B.2.9.  Volume/Duration/Resource Threshold Attributes (s->c)   In DCC the concept of "threshold" does not exist.  Instead, the DCC   client is assumed to ask for the replenishment of quota in good time.   In RPP, on the other hand, the server may optionally include a   threshold AVP, as an indication to the PPC about when to ask for   quota replenishment.   Thus, in this scenario, there is no need for the translator to ever   include a threshold attribute into the messages that it sends to the   PPC.  If, however, there is a need for a threshold attribute to be   present in order to avoid a possible service provisionB.2.10.  Update Reason Attribute (c->s)   The DCC AVP that is semantically closer to the Update Reason AVP than   any other AVP is the CC-Request-Type AVP.  This AVP indicates whether   the message is which it appears is intended to indicate an "initial",   an "intermediate" or a "final interrogation".  Morever, in case of   the session being terminated at the client, it indicates the reason   for this termination.   The following list lists the possible values of an "Update Reason"   attribute, along with corresponding values for the CC-Request-TypeLior, et al.             Expires August 29, 2013               [Page 88]Internet-Draft        Prepaid Extentions for RADIUS        February 2013   AVP.   o  Pre-initialization: No action/value defined.   o  Initial Request: Typically an "intial interrogation" is triggered      as a result of the reception of the message that contains this      Update Reason AVP.  Hence, CC-Request-Type AVP indicates      "INITIAL_REQUEST".   o  Threshold Reached: The reception of the message containing this      Update Reason AVP typically triggers an "intermediate      interrogation".  Hence, CC-Request-Type AVP indicates      "UPDATE_REQUEST".   o  Quota Reached: The reception of the message containing this Update      Reason AVP typically triggers an "intermediate interrogation".      Hence, CC-Request-Type AVP indicates "UPDATE_REQUEST".   o  TITSU Approaching: The reception of the message containing this      Update Reason AVP typically triggers an "intermediate      interrogation".  Hence, CC-Request-Type AVP indicates      "UPDATE_REQUEST".   o  Remote Forced Disconnect: Reception of such an Update Reason      indicates that the client has terminated the session.  The      corresponding value for the CC-Request-Type AVP is      "TERMINATION_REQUEST".   o  Client Service Termination: Reception of such an Update Reason      indicates that the client has terminated the session.  The      corresponding value for the CC-Request-Type AVP is      "TERMINATION_REQUEST".   o  "Access Service" Terminated: Reception of such an Update Reason      indicates that the client has terminated the session.  The      corresponding value for the CC-Request-Type AVP is      "TERMINATION_REQUEST".   o  Service not established: Reception of such an Update Reason      indicates that the client has terminated the session.  The      corresponding value for the CC-Request-Type AVP is      "TERMINATION_REQUEST".   o  One-Time Charging: Such an Update Reason indicates that a one-time      charging event is initiated by the client.  The corresponding      value for the CC-Request-Type AVP is "EVENT_REQUEST".  Note that a      "Requested-Action: AVP MUST also be included in the outgoing DCC      message.  Typically, this would be of the type "DIRECT_DEBITING",Lior, et al.             Expires August 29, 2013               [Page 89]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      or "REFUND_ACCOUNT", depending on other AVPs present in the      message.B.2.11.  PrepaidServer Attribute (s<->c)   The PPC typically never sets the value of a PrepaidServer attribute.   Instead, it repeats those values that it receives from the AAA   infrastructure, in this scenario from the translator.  This attribute   is therefore not used in a translation scenario.  Nevertheless, the   translator must make sure that messages about the same RPP session   are forwarded to the same DCC server, throughout the whole session.   This may be easy to guarantee since the transport of Diameter is TCP.B.2.12.  Service-ID Attribute (s<->c)   The DCC equivalent of a RPP "Service-ID" AVP is the combination of   Service-Context-Id and Service-Identifier AVPs.  The translator must   keep a static equivalence table of the RPP Service-ID and the   corresponding DCC combination in order to correctly translate an RPP   service identifier into DCC and back.B.2.13.  Rating-Group-ID Attribute (s<->c)   The DCC equivalent of a RPP "Rating-Group-ID" AVP is also called a   "Rating-Group-ID".  Depending on the configuration, this AVP may   contain the same value on both the RPP and the DCC side of the   communication.  If, however, static rating groups are configured   between the RCC client and the translator, and different rating   groups between the DCC server and the translator, then the translator   has to maintain a static translation table for the rating group   identifier.  In any case, the translation of a rating group AVP, is   not a function of the translator's local per-session state.B.2.14.  Termination-Action Attribute (s->c)   The DCC equivalent of the "Termination-Action" AVP is called the   "Final-Unit-Action" AVP.  In this scenario (RPP client and DCC AAA   infrastructure), a DCC "Final-Unit-Action" AVP is translated into a   "Termination-Action" AVP.  The following list contains the possible   "Final-Unit-Action" values along with their "Termination-Action"   equivalent.   o  TERMINATE (DCC): This value has a direct equivalent in RPP, also      called "Terminate".   o  REDIRECT (DCC): If this value appears in a "Final-Unit-Action"      AVP, then a "Redirect-Server-Address" AVP must also appear in the      same DCC message.  The translator translates these two AVPs into aLior, et al.             Expires August 29, 2013               [Page 90]Internet-Draft        Prepaid Extentions for RADIUS        February 2013      "Termination-Action" with value "Redirect/Filter" and an      eqiovalent NAS-Filter-Rule attribute (specified in http://      www.ietf.org/internet-drafts/draft-ietf-radext-ieee802-00.txt).   o  RESTRICT_ACCESS (DCC): If this value appears in a "Final-Unit-      Action" AVP, then a "Restriction-Filter-Rule" AVP must also appear      in the same DCC message.  The translator translates these two AVPs      into a "Termination-Action" with value "Redirect/Filter" and an      eqiovalent Filter-ID attribute (specified in http://www.ietf.org/      internet-drafts/draft-ietf-radext-ieee802-00.txt).   o  In the absence of a "Final-Unit-Action" AVP, the DCC server      assumes that the DCC client will ask for replenishment of quota at      some suitable time.  In RPP, this is explicitly conveyed via a      "Termination-Action" AVP with the value "Request More Quota".      Thus, in the absence of a "Final-Unit-Action" AVP, the translator      in this scenario appends such an AVP into the outgoing RPP      message.B.2.15.  Pool-ID Attribute (s<->c)   The DCC equivalent of a RPP "Pool-ID" AVP is also called a "Pool-ID".   Typically, no translation needs to be done to the "Pool-ID"   attribute.B.2.16.  Multiplier Attribute (s<->c)   The multiplier attribute, which is a pair of "Value-Digits" and   "Exponent" AVPs, typically needs no translation, since the value it   carries (inside a "Value-Digits" and an "Exponent" AVP) represents   the rating of the service or rating group to which it refers, with   respect to abstract units.  As such, the same multiplier value would   typically applyt be conveyed from a DCC server to an PPC, and vice   versa.B.2.17.  Requested-Action Attribute (c->s)   The "Requested Action" AVP can be directly translated into its DCC   equivalent, which carries the same name.   1.  Balance Check (PCC): CHECK_BALANCE (DCC)   2.  Price Enquiry (PCC): PRICE_ENQUIRY (DCC)Lior, et al.             Expires August 29, 2013               [Page 91]Internet-Draft        Prepaid Extentions for RADIUS        February 2013B.2.18.  Check-Balance-Result Attribute (s->c)   This attribute carries only a binary value.  Hence, its translation   is straightforward.B.2.19.  Cost-Information Attribute (s->c)   This attribute consists of a Value-Digits AVP, an Exponent AVP, a   Currency Code AVP, and a Cost-Unit AVP.  All these AVPs do likewise   exist in DCC, and carry identical semantics in the context of the   "Cost-Information" AVP.  Thus, the translation of this attribute is   straightforward.B.2.20.  VolumeUsedAfterTariffSwitch attribute (c->s)   This attribute carries the amount of octets that were consumed after   a tariff change.  It always appears in a message with an accompanying   PPAQ attribute in which the total amount of octets (i.e., those that   were consumed both before and after the tariff switch) is reported.   Thus, the translation agent can compute the amount of octets that   were consumed before the tariff change.   In DCC, the two amounts, i.e., the octets that were consumed before a   tariff change and those that were consumed afterwards, are reported   in separate Used-Service-Unit AVPs.  The two Used-Service-Unit AVPs   have an embedded CC-Total-Octets AVP that indicates the appropriate   amount of octets.  Furthermore, the Used-Service-Unit AVP that   carries the amount that was consumed before the tariff switch also   carries an embedded Tariff-Change-Usage AVP with the value   UNIT_BEFORE_TARIFF_CHANGE (0).  Similarly, the Used-Service-Unit AVP   that carries the amount that was consumed after the tariff switch   also carries an embedded Tariff-Change-Usage AVP with the value   UNIT_AFTER_TARIFF_CHANGE (1).Lior, et al.             Expires August 29, 2013               [Page 92]Internet-Draft        Prepaid Extentions for RADIUS        February 2013Authors' Addresses   Avi Lior   Independent   Email: avi.ietf@lior.org   Parviz Yegani   Juniper   Email: pyegani@juniper.net   Kuntal Chowdhury   Radio Mobile Access, Inc.   Email: kc@radiomobiles.com   Hannes Tschofenig   Nokia Siemens Networks   Linnoitustie 6   Espoo  02600   Finland   Phone: +358 (50) 4871445   Email: Hannes.Tschofenig@gmx.net   URI:   http://www.tschofenig.priv.at   Andreas Pashalidis   K.U.Leuven, ESAT/SCD/COSIC   Kasteelpark Arenberg 10, bus 2446   Leuven-Heverlee  B-3001   Belgium   Email: andreas.pashalidis@esat.kuleuven.beLior, et al.             Expires August 29, 2013               [Page 93]