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Internet Engineering Task Force (IETF)                          S. OogheRequest for Comments: 5851                                Alcatel-LucentCategory: Informational                                         N. VoigtISSN: 2070-1721                                   Nokia Siemens Networks                                                              M. Platnic                                                             ECI Telecom                                                                 T. Haag                                                        Deutsche Telekom                                                               S. Wadhwa                                                        Juniper Networks                                                                May 2010Framework and Requirements for an Access Node Control Mechanismin Broadband Multi-Service NetworksAbstract   The purpose of this document is to define a framework for an Access   Node Control Mechanism between a Network Access Server (NAS) and an   Access Node (e.g., a Digital Subscriber Line Access Multiplexer   (DSLAM)) in a multi-service reference architecture in order to   perform operations related to service, quality of service, and   subscribers.  The Access Node Control Mechanism will ensure that the   transmission of the information does not need to go through distinct   element managers but rather uses a direct device-device   communication.  This allows for performing access-link-related   operations within those network elements, while avoiding impact on   the existing Operational Support Systems.   This document first identifies a number of use cases for which the   Access Node Control Mechanism may be appropriate.  It then presents   the requirements for the Access Node Control Protocol (ANCP) that   must be taken into account during protocol design.  Finally, it   describes requirements for the network elements that need to support   ANCP and the described use cases.  These requirements should be seen   as guidelines rather than as absolute requirements.RFC 2119   therefore does not apply to the nodal requirements.Ooghe, et al.                 Informational                     [Page 1]

RFC 5851                     ANCP Framework                     May 2010Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5851.Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   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.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Ooghe, et al.                 Informational                     [Page 2]

RFC 5851                     ANCP Framework                     May 2010Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .41.1.  Requirements Notation  . . . . . . . . . . . . . . . . . .51.2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .52.  General Architecture Aspects . . . . . . . . . . . . . . . . .72.1.  Concept of an Access Node Control Mechanism  . . . . . . .72.2.  Reference Architecture . . . . . . . . . . . . . . . . . .82.2.1.  Home Gateway . . . . . . . . . . . . . . . . . . . . .92.2.2.  Access Loop  . . . . . . . . . . . . . . . . . . . . .92.2.3.  Access Node  . . . . . . . . . . . . . . . . . . . . .92.2.4.  Access Node Uplink . . . . . . . . . . . . . . . . . .102.2.5.  Aggregation Network  . . . . . . . . . . . . . . . . .102.2.6.  Network Access Server  . . . . . . . . . . . . . . . .102.2.7.  Regional Network . . . . . . . . . . . . . . . . . . .102.3.  Prioritizing Access Node Control Traffic . . . . . . . . .112.4.  Interaction with Management Systems  . . . . . . . . . . .122.5.  Circuit Addressing Scheme  . . . . . . . . . . . . . . . .123.  Use Cases for Access Node Control Mechanism  . . . . . . . . .133.1.  Access Topology Discovery  . . . . . . . . . . . . . . . .133.2.  Access-Loop Configuration  . . . . . . . . . . . . . . . .153.3.  Remote Connectivity Test . . . . . . . . . . . . . . . . .163.4.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . .173.4.1.  Multicast Conditional Access . . . . . . . . . . . . .183.4.2.  Multicast Admission Control  . . . . . . . . . . . . .213.4.3.  Multicast Accounting and Reporting . . . . . . . . . .263.4.4.  Spontaneous Admission Response . . . . . . . . . . . .274.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .284.1.  ANCP Functional Requirements . . . . . . . . . . . . . . .284.2.  ANCP Multicast Requirements  . . . . . . . . . . . . . . .294.3.  Protocol Design Requirements . . . . . . . . . . . . . . .304.4.  Access Node Control Adjacency Requirements . . . . . . . .314.5.  ANCP Transport Requirements  . . . . . . . . . . . . . . .314.6.  Access Node Requirements . . . . . . . . . . . . . . . . .324.6.1.  General Architecture . . . . . . . . . . . . . . . . .324.6.2.  Control Channel Attributes . . . . . . . . . . . . . .334.6.3.  Capability Negotiation Failure . . . . . . . . . . . .334.6.4.  Adjacency Status Reporting . . . . . . . . . . . . . .334.6.5.  Identification . . . . . . . . . . . . . . . . . . . .344.6.6.  Multicast  . . . . . . . . . . . . . . . . . . . . . .344.6.7.  Message Handling . . . . . . . . . . . . . . . . . . .364.6.8.  Parameter Control  . . . . . . . . . . . . . . . . . .374.7.  Network Access Server Requirements . . . . . . . . . . . .374.7.1.  General Architecture . . . . . . . . . . . . . . . . .374.7.2.  Control Channel Attributes . . . . . . . . . . . . . .394.7.3.  Capability Negotiation Failure . . . . . . . . . . . .394.7.4.  Adjacency Status Reporting . . . . . . . . . . . . . .404.7.5.  Identification . . . . . . . . . . . . . . . . . . . .40Ooghe, et al.                 Informational                     [Page 3]

RFC 5851                     ANCP Framework                     May 20104.7.6.  Multicast  . . . . . . . . . . . . . . . . . . . . . .404.7.7.  Message Handling . . . . . . . . . . . . . . . . . . .424.7.8.  Wholesale Model  . . . . . . . . . . . . . . . . . . .425.  Management-Related Requirements  . . . . . . . . . . . . . . .436.  Security Considerations  . . . . . . . . . . . . . . . . . . .447.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .448.  References . . . . . . . . . . . . . . . . . . . . . . . . . .458.1.  Normative References . . . . . . . . . . . . . . . . . . .458.2.  Informative References . . . . . . . . . . . . . . . . . .451.  Introduction   Digital Subscriber Line (DSL) technology is widely deployed for   Broadband Access for Next Generation Networks.  Several documents   like Broadband Forum TR-058 [TR-058], Broadband Forum TR-059   [TR-059], and Broadband Forum TR-101 [TR-101] describe possible   architectures for these access networks.  The scope of these   specifications consists of the delivery of voice, video, and data   services.  The framework defined by this document is targeted at DSL-   based access (either by means of ATM/DSL or as Ethernet/DSL).  The   framework shall be open to other access technologies, such as Passive   Optical Networks using DSL technology at the Optical Network Unit   (ONU), or wireless technologies like IEEE 802.16.  Several use cases   such as Access Topology Discovery, Remote Connectivity Test, and   Multicast may be applied to these access technologies, but the   details of this are outside the scope of this document.   Traditional architectures require Permanent Virtual Circuit(s) per   subscriber.  Such a virtual circuit is configured on layer 2 and   terminated at the first layer 3 device (e.g., Broadband Remote Access   Server (BRAS)).  Beside the data plane, the models define the   architectures for element, network, and service management.   Interworking at the management plane is not always possible because   of the organizational boundaries between departments operating the   local loop, departments operating the ATM network, and departments   operating the IP network.  Besides, management networks are usually   not designed to transmit management data between the different   entities in real time.   When deploying value-added services across DSL access networks,   special attention regarding quality of service and service control is   required, which implies a tighter coordination between Network Nodes   (e.g., Access Nodes and Network Access Server (NAS)), without   burdening the Operational Support System (OSS) with unpractical   expectations.Ooghe, et al.                 Informational                     [Page 4]

RFC 5851                     ANCP Framework                     May 2010   Therefore, there is a need for an Access Node Control Mechanism   between a NAS and an Access Node (e.g., a Digital Subscriber Line   Access Multiplexer (DSLAM)) in a multi-service reference architecture   in order to perform operations related to service, quality of   service, and subscribers.  The Access Node Control Mechanism will   ensure that the transmission of the information does not need to go   through distinct element managers but rather using a direct device-   device communication.  This allows for performing access-link-related   operations within those network elements, while avoiding impact on   the existing OSSes.   This document provides a framework for such an Access Node Control   Mechanism and identifies a number of use cases for which this   mechanism can be justified.  Next, it presents a number of   requirements for the Access Node Control Protocol (ANCP) and the   network elements that need to support it.   The requirements spelled out in this document are based on the work   that is performed by the Broadband Forum [TR-147].1.1.  Requirements Notation   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 [RFC2119].1.2.  Definitions   o  Access Node (AN): network device, usually located at a service      provider central office or street cabinet, that terminates access-      loop connections from subscribers.  In case the access loop is a      Digital Subscriber Line (DSL), this is often referred to as a DSL      Access Multiplexer (DSLAM).   o  Network Access Server (NAS): network device that aggregates      multiplexed subscriber traffic from a number of Access Nodes.  The      NAS plays a central role in per-subscriber policy enforcement and      quality of service (QoS).  Often referred to as a Broadband      Network Gateway (BNG) or Broadband Remote Access Server (BRAS).  A      detailed definition of the NAS is given in [RFC2881].   o  "Net Data Rate": defined by ITU-T G.993.2 [G.993.2], section 3.39,      i.e., the portion of the total data rate that can be used to      transmit user information (e.g., ATM cells or Ethernet frames).      It excludes overhead that pertains to the physical transmission      mechanism (e.g., trellis coding in the case of DSL).  It includesOoghe, et al.                 Informational                     [Page 5]

RFC 5851                     ANCP Framework                     May 2010      TPS-TC (Transport Protocol Specific - Transmission Convergence)      encapsulation; this is zero for ATM encapsulation, and non-zero      for 64/65 encapsulation.   o  "Line Rate": defined by ITU-T G.993.2.  It contains the complete      overhead including Reed-Solomon and Trellis coding.   o  Access Node Control Mechanism: a method for multiple network      scenarios with an extensible communication scheme that conveys      status and control information between one or more ANs and one or      more NASes without using intermediate element managers.   o  Control Channel: a bidirectional IP communication interface      between the controller function (in the NAS) and the reporting/      enforcement function (in the AN).  It is assumed that this      interface is configured (rather than discovered) on the AN and the      NAS.   o  Access Node Control Adjacency: the relationship between an Access      Node and a NAS for the purpose of exchanging Access Node Control      Protocol messages.  The adjacency may either be up or down,      depending on the result of the Access Node Control Adjacency      protocol operation.   o  Multicast Flow: designates datagrams sent to a group from a set of      sources for which multicast reception is desired.  A distinction      can be made between Any Source Multicast (ASM) and Source-Specific      Multicast (SSM).   o  Join: signaling from the user equipment that it wishes to start      receiving a new multicast flow.  In ASM, it is referred to as a      "Join".  In SSM [RFC4607], it is referred to as a "subscribe".  In      IGMPv2, "joins" are indicated through an "IGMPv2 membership      report".  In IGMPv3 [RFC3376], "join" is indicated through      "membership report" using different Filter-Mode-Change (ASM) and      Source-List-Change Records.   o  Leave: signaling from the user equipment that it wishes to stop      receiving a multicast flow.  With IGMPv2, this is conveyed inside      the "Leave Group" message, while in IGMPv3, "leave" is indicated      through the "IGMPv3 membership report" message using different      Filter-Mode-Change (ASM) and Source-List-Change Records.Ooghe, et al.                 Informational                     [Page 6]

RFC 5851                     ANCP Framework                     May 20102.  General Architecture Aspects   This section introduces the basic concept of the Access Node Control   Mechanism and describes the reference architecture where it is being   applied.  Based on the reference architecture, the section then   describes how Access Node Control messages are to be prioritized over   other data traffic, and the interaction between ANCP and the network   management system.  Finally, the addressing schemes are described   that allow identifying an Access Port in Access Node Control   messages.2.1.  Concept of an Access Node Control Mechanism   The high-level communication framework for an Access Node Control   Mechanism is defined in Figure 1.  The Access Node Control Mechanism   defines a quasi-real-time, general-purpose method for multiple   network scenarios with an extensible communication scheme, addressing   the different use cases that are described throughout this document.                                                 +--------+                                                 | Policy |                                                 | Server |                                                 +--------+                                                      |                                                      |  +-----+  +-----+  +--------+                     +-----+  +----------+  | CPE |--| HGW |--|        |                     |     |  |          |  +-----+  +-----+  | Access |   +-------------+   |     |  | Regional |                    |  Node  |---| Aggregation |---| NAS |--| Network  |  +-----+  +-----+  |        |   |   Network   |   |     |  |          |  | CPE |--| HGW |--|        |   +-------------+   |     |  |          |  +-----+  +-----+  +--------+                     +-----+  +----------+                     Information Report / Admission Request                         ------------------------------>                      Admission Response / Control Request                         <------------------------------                               Control Response                         ------------------------------>                          Access Node Control Mechanism                         <----------------------------->                                 PPP, DHCP, IP    <---------><----------------------------------------->  CPE: Customer Premises Equipment  HGW: Home Gateway                   Figure 1: Access Network ArchitectureOoghe, et al.                 Informational                     [Page 7]

RFC 5851                     ANCP Framework                     May 2010   A number of functions can be identified:   o  A controller function: this function is used either to send out      requests for information to be used by the network element where      the controller function resides, or to trigger a certain behavior      in the network element where the reporting and/or enforcement      function resides.   o  A reporting function: this function is used to convey status      information to the controller function.  An example of this is the      transmission of the access-loop data rate from an Access Node to a      Network Access Server (NAS) tasked with shaping traffic to that      rate.   o  An enforcement function: this function is contacted by the      controller function to trigger a remote action on the Access Node.      An example is the initiation of a port-testing mechanism on an      Access Node.  Another example is enforcing whether a multicast      join is to be honored or denied.   The messages shown in Figure 1 show the conceptual message flow.  The   actual use of these flows, and the times or frequencies when these   messages are generated depends on the actual use cases, which are   described inSection 3.   The use cases in this document are described in an abstract way,   independent from any actual protocol mapping.  The actual protocol   specification is out of scope of this document, but there are certain   characteristics of the protocol that are required to simplify   specification, implementation, debugging and troubleshooting, and to   extend support for additional use cases.2.2.  Reference Architecture   The reference architecture used in this document can be based on ATM   or Ethernet access/aggregation.  Specifically:   o  In case of a legacy ATM aggregation network that is to be used for      the introduction of new QoS-enabled IP services, the architecture      builds on the reference architecture specified in the Broadband      Forum [TR-059];   o  In case of an Ethernet aggregation network that supports new QoS-      enabled IP services (including Ethernet multicast replication),      the architecture builds on the reference architecture specified in      the Broadband Forum [TR-101].Ooghe, et al.                 Informational                     [Page 8]

RFC 5851                     ANCP Framework                     May 2010   Given the industry's move towards Ethernet as the new access and   aggregation technology for triple-play services, the primary focus   throughout this document is on a TR-101 architecture.  However the   concepts are equally applicable to an ATM architecture based on TR-   059.2.2.1.  Home Gateway   The Home Gateway (HGW) connects the different Customer Premises   Equipment (CPE) to the Access Node and the access network.  In case   of DSL, the HGW is a DSL Network Termination (NT) that could either   operate as a layer 2 bridge or as a layer 3 router.  In the latter   case, such a device is also referred to as a Routing Gateway (RG).2.2.2.  Access Loop   The access loop ensures physical connectivity between the HGW at the   customer premises and the Access Node.  In case of DSL, the access-   loop physical layer could be, e.g., ADSL, ADSL2+, VDSL, VDSL2, or   SHDSL.  In order to increase bandwidth, it is also possible that   multiple DSL links are grouped together to form a single virtual   link; this process is called "DSL bonding".  The protocol   encapsulation on the access loop could be based on multi-protocol   encapsulation over ATM Adaption Layer 5 (AAL5) defined in [RFC2684].   This covers PPP over Ethernet (PPPoE, defined in [RFC2516]), bridged   IP (IP over Ethernet (IPoE), defined in [RFC894]) and routed IP (IP   over ATM (IPoA), defined in [RFC2225]).  Next to this, PPP over AAL5   (PPPoA) as defined in [RFC2364] can be used.  Future scenarios   include cases where the access loop supports direct Ethernet   encapsulation (e.g., when using VDSL or VDSL2).2.2.3.  Access Node   The Access Node (AN) may support one or more access-loop technologies   and allow them to interwork with a common aggregation network   technology.  Besides the access-loop termination, the AN can also   aggregate traffic from other Access Nodes using ATM or Ethernet.   The framework defined by this document is targeted at DSL-based   access (either by means of ATM/DSL or as Ethernet/DSL).  The   framework shall be open to non-DSL technologies, like Passive Optical   Networks (PONs) and IEEE 802.16 (WiMAX), but the details of this are   outside the scope of this document.   The reporting and/or enforcement function defined inSection 2.1   typically resides in an Access Node.Ooghe, et al.                 Informational                     [Page 9]

RFC 5851                     ANCP Framework                     May 20102.2.4.  Access Node Uplink   The fundamental requirements for the Access Node uplink are to   provide traffic aggregation, Class of Service (CoS) distinction, and   customer separation and traceability.  This can be achieved using an   ATM- or Ethernet-based technology.2.2.5.  Aggregation Network   The aggregation network provides traffic aggregation towards the NAS.   The aggregation technology can be based on ATM (in case of a TR-059   architecture) or Ethernet (in case of a TR-101 architecture).2.2.6.  Network Access Server   The Network Access Server (NAS) interfaces to the aggregation network   by means of standard ATM or Ethernet interfaces, and towards the   Regional Network by means of transport interfaces for Ethernet frames   (e.g., Gigabit Ethernet (GigE), Ethernet over Synchronous Optical   Network (SONET)).  The NAS functionality corresponds to the BNG   functionality described in Broadband Forum TR-101.  In addition to   this, the NAS supports the Access Node Control functionality defined   for the respective use cases throughout this document.   The controller function defined inSection 2.1 typically resides in a   NAS.2.2.7.  Regional Network   The Regional Network connects one or more NAS and associated Access   Networks to Network Service Providers (NSPs) and Application Service   Providers (ASPs).  The NSP authenticates access and provides and   manages the IP address to subscribers.  It is responsible for overall   service assurance and includes Internet Service Providers (ISPs).   The ASP provides application services to the application subscriber   (gaming, video, content on demand, IP telephony, etc.).   The Regional Network supports aggregation of traffic from multiple   Access Networks and hands off larger geographic locations to NSPs and   ASPs -- relieving a potential requirement for them to build   infrastructure to attach more directly to the various Access   Networks.Ooghe, et al.                 Informational                    [Page 10]

RFC 5851                     ANCP Framework                     May 20102.3.  Prioritizing Access Node Control Traffic   When sending Access Node Control messages across the aggregation   network, care is needed that messages won't get lost.  The   connectivity between the Access Node and the NAS may differ depending   on the actual layer 2 technology used (ATM or Ethernet).  This   section briefly outlines how network connectivity can be established.   In case of an ATM access/aggregation network, a typical practice is   to send the Access Node Control Protocol messages over a dedicated   Permanent Virtual Circuit (PVC) configured between the AN and the   NAS.  These ATM PVCs would then be given a high priority so that at   times of network congestion, loss of the ATM cells carrying the   Access Node Control Protocol is avoided or minimized.  It is   discouraged to route the Access Node Control Protocol messages within   the Virtual Path (VP) that also carries the customer connections, if   that VP is configured with a best-effort QoS class (e.g., Unspecified   Bitrate (UBR)).  The PVCs of multiple Access Node Control Adjacencies   can be aggregated into a VP that is given a high priority and runs   across the aggregation network.  This requires the presence of a VC   cross-connect in the aggregation node that terminates the VP.   In case of an Ethernet access/aggregation network, a typical practice   is to send the Access Node Control Protocol messages over a dedicated   Ethernet Virtual LAN (VLAN) using a separate VLAN identifier (VLAN   ID).  This can be achieved using a different VLAN ID for each Access   Node, or, in networks with many Access Nodes and a high degree of   aggregation, one Customer VLAN (C-VLAN) per Access Node and one   Service VLAN (S-VLAN) for the Access Node Control Adjacencies of all   Access Nodes.  The traffic should be given a high priority (e.g., by   using a high CoS value) so that the frame loss of Ethernet frames   carrying the Access Node Control Protocol messages is minimized in   the event of network congestion.   In both cases, the Control Channel between NAS and Access Node could   use the same physical network and routing resources as the subscriber   traffic.  This means that the connection is an inband connection   between the involved network elements.  Therefore, there is no need   for an additional physical interface to establish the Control   Channel.   Note that these methods for transporting Access Node Control Protocol   messages are typical examples; they do not rule out other methods   that achieve the same behavior.   The Access Node Control Adjacency interactions must be reliable.  In   addition to this, some of the use cases described inSection 3   require the interactions to be performed in a transactional fashion,Ooghe, et al.                 Informational                    [Page 11]

RFC 5851                     ANCP Framework                     May 2010   i.e., using a "request/response" mechanism.  This is required so that   the network elements always remain in a known state, irrespective of   whether or not the transaction is successful.2.4.  Interaction with Management Systems   When introducing an Access Node Control Mechanism, care is needed to   ensure that the existing management mechanisms remain operational as   before.   Specifically, when using the Access Node Control Mechanism for   performing a configuration action on a network element, one gets   confronted with the challenge of supporting multiple managers for the   same network element: both the Element Manager as well as the Access   Node Control Mechanism may now perform configuration actions on the   same network element.  Therefore, conflicts need to be avoided.   Using the Access Node Control Mechanism, the NAS retrieves and   controls a number of subscriber-related parameters.  The NAS may   decide to communicate this information to a central Policy or AAA   Server so that it can keep track of the parameters and apply policies   on them.  The Server can then enforce those policies on the NAS.  For   instance, in case a subscriber is connected to more than one NAS, the   policy server could be used to coordinate the bandwidth available on   a given Access Port for use amongst the different NAS devices.   Guidelines related to management will be addressed inSection 5.2.5.  Circuit Addressing Scheme   In order to associate subscriber parameters to a particular Access   Port, the NAS needs to be able to uniquely identify the Access Port   (or a specific circuit on an Access Port) using an addressing scheme.   In deployments using an ATM aggregation network, the ATM PVC on an   access loop connects the subscriber to a NAS.  Based on this   property, the NAS typically includes a NAS-Port-Id, NAS-Port, or   Calling-Station-Id attribute in RADIUS authentication and accounting   packets sent to the RADIUS server(s).  Such attribute includes the   identification of the ATM VC for this subscriber, which allows in   turn identifying the access loop.   In an Ethernet-based aggregation network, a new addressing scheme is   defined in [TR-101].  Two mechanisms can be used:Ooghe, et al.                 Informational                    [Page 12]

RFC 5851                     ANCP Framework                     May 2010   o  A first approach is to use a one-to-one VLAN assignment model for      all Access Ports (e.g., a DSL port) and circuits on an Access Port      (e.g., an ATM PVC on an ADSL port).  This enables directly      deriving the port and circuit identification from the VLAN tagging      information, i.e., S-VLAN ID or <S-VLAN ID, C-VLAN ID> pair.   o  A second approach is to use a many-to-one VLAN assignment model      and to encode the Access Port and circuit identification in the      "Agent Circuit ID" sub-option to be added to a DHCP or PPPoE      message.  The details of this approach are specified in [TR-101].   This document reuses the addressing scheme specified in TR-101.  It   should be noted however that the use of such a scheme does not imply   the actual existence of a PPPoE or DHCP session, nor the presence of   the specific interworking function in the Access Node.  In some   cases, no PPPoE or DHCP session may be present, while port and   circuit addressing would still be desirable.3.  Use Cases for Access Node Control Mechanism3.1.  Access Topology Discovery   [TR-059] and [TR-101] discuss various queuing/scheduling mechanisms   to avoid congestion in the access network while dealing with multiple   flows with distinct QoS requirements.  One technique that can be used   on a NAS is known as "Hierarchical Scheduling" (HS).  This option is   applicable in a single NAS scenario (in which case the NAS manages   all the bandwidth available on the access loop) or in a dual NAS   scenario (in which case the NAS manages some fraction of the access   loop's bandwidth).  The HS must, at a minimum, support 3 levels   modeling the NAS port, Access Node uplink, and access-loop sync rate.   The rationale for the support of HS is as follows:   o  Provide fairness of network resources within a class.   o  Allow for a better utilization of network resources.  Drop traffic      early at the NAS rather than letting it traverse the aggregation      network just to be dropped at the Access Node.   o  Enable more flexible CoS behaviors than only strict priority.   o  The HS system could be augmented to provide per-application      admission control.   o  Allow fully dynamic bandwidth partitioning between the various      applications (as opposed to static bandwidth partitioning).Ooghe, et al.                 Informational                    [Page 13]

RFC 5851                     ANCP Framework                     May 2010   o  Support "per-user weighted scheduling" to allow differentiated      Service Level Agreements (e.g., business services) within a given      traffic class.   Such mechanisms require that the NAS gains knowledge about the   topology of the access network, the various links being used, and   their respective rates.  Some of the information required is somewhat   dynamic in nature (e.g., DSL line rate -- thus also the net data   rate); hence, it cannot come from a provisioning and/or inventory   management OSS system.  Some of the information varies less   frequently (e.g., capacity of a DSLAM uplink), but nevertheless needs   to be kept strictly in sync between the actual capacity of the uplink   and the image the BRAS has of it.   OSS systems are typically not designed to enforce the consistency of   such data in a reliable and scalable manner across organizational   boundaries.  The Access Topology Discovery function is intended to   allow the NAS to perform these functions without having to rely on an   integration with an OSS system.   Communicating access-loop attributes is specifically important in   case the rate of the access loop changes overtime.  The DSL actual   data rate may be different every time the DSL NT is turned on.  In   this case, the Access Node sends an Information Report message to the   NAS after the DSL line has resynchronized.   Additionally, during the time the DSL NT is active, data rate changes   can occur due to environmental conditions (the DSL access loop can   get "out of sync" and can retrain to a lower value, or the DSL access   loop could use Seamless Rate Adaptation making the actual data rate   fluctuate while the line is active).  In this case, the Access Node   sends an additional Information Report to the NAS each time the   access-loop attributes change above a threshold value.   The hierarchy and the rates of the various links to enable the NAS   hierarchical scheduling and policing mechanisms are the following:   o  The identification and speed (data rate) of the DSL access loop      (i.e., the net data rate)   o  The identification and speed (data rate) of the Remote Terminal      (RT) / Access Node uplink (when relevant)   The NAS can adjust downstream shaping to the Access Loop's current   actual data rate, and more generally reconfigure the appropriate   nodes of its hierarchical scheduler (support of advanced capabilities   according to TR-101).Ooghe, et al.                 Informational                    [Page 14]

RFC 5851                     ANCP Framework                     May 2010   This use case may actually include more information than link   identification and corresponding data rates.  In case of DSL access   loops, the following access-loop characteristics can be sent to the   NAS (cf. ITU-T Recommendation G.997.1 [G.997.1]):   o  DSL Type (e.g., ADSL1, ADSL2, SDSL, ADSL2+, VDSL, VDSL2)   o  Framing mode (e.g., ATM, ITU-T Packet Transfer Mode (PTM), IEEE      802.3 Ethernet in the First Mile (EFM))   o  DSL port state (e.g., synchronized/showtime, low power, no power/      idle)   o  Actual net data rate (upstream/downstream)   o  Maximum achievable/attainable net data rate (upstream/downstream)   o  Minimum net data rate configured for the access loop (upstream/      downstream)   o  Maximum net data rate configured for the access loop (upstream/      downstream)   o  Minimum net data rate in low power state configured for the access      loop (upstream/downstream)   o  Maximum achievable interleaving delay (upstream/downstream)   o  Actual interleaving delay (upstream/downstream)   The NAS MUST be able to receive access-loop characteristics   information, and share such information with AAA/policy servers.3.2.  Access-Loop Configuration   access-loop rates are typically configured in a static way.  When a   subscriber wants to change its access-loop rate, the network operator   needs to reconfigure the Access Port configuration, possibly implying   a business-to-business transaction between an Internet Service   Provider (ISP) and an Access Provider.  From an Operating   Expenditures (OPEX) perspective this is a costly operation.   Using the Access Node Control Mechanism to change the access-loop   rate from the NAS avoids those cross-organization business-to-   business interactions and allows to centralize subscriber-related   service data in e.g., a policy server.  More generally, several   access-loop parameters (e.g., minimum data rate, interleaving delay)   could be changed by means of the Access Node Control Mechanism.Ooghe, et al.                 Informational                    [Page 15]

RFC 5851                     ANCP Framework                     May 2010   Triggered by the communication of the access-loop attributes   described inSection 3.1, the NAS could query a Policy or AAA Server   to retrieve access-loop configuration data.  The best way to change   access-loop parameters is by using profiles.  These profiles (e.g.,   DSL profiles for different services) are pre-configured by the   Element Manager managing the Access Nodes.  The NAS may then use the   Configure Request message to send a reference to the right profile to   the Access Node.  The NAS may also update the access-loop   configuration due to a subscriber service change (e.g., triggered by   the policy server).   The access-loop configuration mechanism may also be useful for   configuration of parameters that are not specific to the access-loop   technology.  Examples include the QoS profile to be used for an   access loop, or the per-subscriber multicast channel entitlement   information, used for IPTV applications where the Access Node is   performing IGMP snooping or IGMP proxy function.  The latter is also   discussed inSection 3.4.   It may be possible that a subscriber wants to change its access-loop   rate, and that the operator wants to enforce this updated access-loop   rate on the Access Node using ANCP, but that the Access Node Control   Adjacency is down.  In such a case, the NAS will not be able to   request the configuration change on the Access Node.  The NAS should   then report this failure to the external management system, which   could use application-specific signaling to notify the subscriber of   the fact that the change could not be performed at this time.3.3.  Remote Connectivity Test   Traditionally, ATM circuits are point-to-point connections between   the BRAS and the DSLAM or DSL NT.  In order to test the connectivity   on layer 2, appropriate Operations, Administration, and Maintenance   (OAM) functionality is used for operation and troubleshooting.  An   end-to-end OAM loopback is performed between the edge devices (NAS   and HGW) of the broadband access network.   When migrating to an Ethernet-based aggregation network (as defined   by TR-101), end-to-end ATM OAM functionality is no longer applicable.   Ideally in an Ethernet aggregation network, end-to-end Ethernet OAM   (as specified in IEEE 802.1ag and ITU-T Recommendation Y.1730/1731)   can provide access-loop connectivity testing and fault isolation.   However, most HGWs do not yet support these standard Ethernet OAM   procedures.  Also, various access technologies exist such as ATM/DSL,   Ethernet in the First Mile (EFM), etc.  Each of these access   technologies have their own link-based OAM mechanisms that have been   or are being standardized in different standard bodies.Ooghe, et al.                 Informational                    [Page 16]

RFC 5851                     ANCP Framework                     May 2010   In a mixed Ethernet and ATM access network (including the local   loop), it is desirable to keep the same ways to test and troubleshoot   connectivity as those used in an ATM-based architecture.  To reach   consistency with the ATM-based approach, an Access Node Control   Mechanism between NAS and Access Node can be used until end-to-end   Ethernet OAM mechanisms are more widely available.   Triggered by a local management interface, the NAS can use the Access   Node Control Mechanism to initiate an access-loop test between Access   Node and HGW.  In case of an ATM-based access loop, the Access Node   Control Mechanism can trigger the Access Node to generate ATM (F4/F5)   loopback cells on the access loop.  In case of Ethernet, the Access   Node can perform a port synchronization and administrative test for   the access loop.  The Access Node can send the result of the test to   the NAS via a Control Response message.  The NAS may then send the   result via a local management interface.  Thus, the connectivity   between the NAS and the HGW can be monitored by a single trigger   event.3.4.  Multicast   With the rise of supporting IPTV services in a resource efficient   way, multicast services are getting increasingly important.   In case of an ATM access/aggregation network, such as the reference   architecture specified in Broadband Forum [TR-059], multicast traffic   replication is performed in the NAS.  In this model, typically IGMP   is used to control the multicast replication process towards the   subscribers.  The NAS terminates and processes IGMP signaling   messages sent by the subscribers; towards the Regional Network, the   NAS typically uses a multicast routing protocol such as Protocol   Independent Multicast (PIM).  The ATM Access Nodes and aggregation   switches don't perform IGMP processing, nor do they perform multicast   traffic replication.  As a result, network resources are wasted   within the access/aggregation network.   To overcome this resource inefficiency, the Access Node, aggregation   node(s), and the NAS must all be involved in the multicast   replication process.  This prevents several copies of the same stream   from being sent within the access/aggregation network.  In case of an   Ethernet-based access/aggregation network, this may, for example, be   achieved by means of IGMP snooping or IGMP proxy in the Access Node   and aggregation node(s).   By introducing IGMP processing in the access/aggregation nodes, the   multicast replication process is now divided between the NAS, the   aggregation node(s), and Access Nodes.  In order to ensure backward   compatibility with the ATM-based model, the NAS, aggregation node,Ooghe, et al.                 Informational                    [Page 17]

RFC 5851                     ANCP Framework                     May 2010   and Access Node need to behave as a single logical device.  This   logical device must have exactly the same functionality as the NAS in   the ATM access/aggregation network.  The Access Node Control   Mechanism can be used to make sure that this logical/functional   equivalence is achieved by exchanging the necessary information   between the Access Node and the NAS.   Another option is for the subscriber to communicate the "join/leave"   information with the NAS.  This can for instance be done by   terminating all subscriber IGMP signaling on the NAS.  Another   example could be a subscriber using some form of application-level   signaling, which is redirected to the NAS.  In any case, this option   is transparent to the access and aggregation network.  In this   scenario, the NAS can use ANCP to create replication state in the AN   for efficient multicast replication.  The NAS sends a single copy of   the multicast stream towards the AN.  The NAS can perform conditional   access and multicast admission control on multicast joins, and create   replication state in the AN if the flow is admitted by the NAS.   The following subsections describe the different use cases related to   multicast.3.4.1.  Multicast Conditional Access   In a DSL broadband access scenario, service providers may want to   dynamically control, at the network level, access to some multicast   flows on a per-user basis.  This may be used in order to   differentiate among multiple Service Offers or to realize/reinforce   conditional access for sensitive content.  Note that, in some   environments, application-layer conditional access by means of   Digital Rights Management (DRM) may provide sufficient control, so   that Multicast Conditional Access may not be needed.   Where Multicast Conditional Access is required, it is possible, in   some cases, to provision the necessary conditional access information   into the AN so the AN can then perform the conditional access   decisions autonomously.  For these cases, the NAS can use ANCP to   provision the necessary information in the AN so that the AN can   decide locally to honor a join or to not honor a join.  This can be   done with the Control Request and Control Response messages.   Provisioning the conditional access information on the AN can be done   using a "white list", "grey list", and/or a "black list".  A white   list associated with an Access Port identifies the multicast flows   that are allowed to be replicated to that port.  A black list   associated with an Access Port identifies the multicast flows that   are not allowed to be replicated to that port.  A grey list   associated with an Access Port identifies the multicast flows forOoghe, et al.                 Informational                    [Page 18]

RFC 5851                     ANCP Framework                     May 2010   which the AN on receiving a join message, before starting traffic   replication queries the NAS for further authorization.  Each list   contains zero, one, or multiple entries, and each entry may specify a   single flow or contain ranges (i.e., mask on Group address and/or   mask on Source address).   Upon receiving a join message on an Access Port, the Access Node will   first check if the requested multicast flow is part of a white, grey,   or a black list associated with that Access Port.  If it is part of a   white list, the AN autonomously starts replicating multicast traffic.   If it is part of a black list, the AN autonomously discards the   message because the request is not authorized, and may thus inform   the NAS and log the request accordingly.  If it is part of a grey   list the AN uses ANCP to query the NAS, that in turn will respond to   the AN indicating whether the join is to be honored (and hence   replication performed by the AN) or denied (and hence replication not   performed by the AN).   If the requested multicast flow is part of multiple lists associated   with the Access Port, then the most specific match will be used.  If   the most specific match occurs in multiple lists, the black list   entry takes precedence over the grey list, which takes precedence   over the white list.   If the requested multicast flow is not part of any list, the message   should be discarded.  This default behavior can easily be changed by   means of a "catch-all" statement in either the white list or the grey   list.  For instance, adding (<S=*,G=*>) in the white list would make   the default behavior to accept join messages for a multicast flow   that has no other match on any list.  Similarly, if the default   behavior should be to send a request to the NAS, then adding   (<S=*,G=*>) in the grey list accomplishes that.   The white list, black list, and grey list can contain entries   allowing:   o  an exact match for a (*,G) ASM group (e.g., <G=g.h.i.l>);   o  an exact match for a (S,G) SSM channel (e.g.,      <S=s.t.u.v,G=g.h.i.l>);   o  a mask-based range match for a (*,G) ASM group (e.g., <G=g.h.i.l/      Mask>);   o  a mask-based range match for a (S,G) SSM channel (e.g.,      <S=s.t.u.v/Mask,G=g.h.i.l/Mask>);Ooghe, et al.                 Informational                    [Page 19]

RFC 5851                     ANCP Framework                     May 2010   The following are some example configurations:   o  Scenario 1: reject all messages      *  black list = {<S=*,G=*>}   o  Scenario 2: reject all messages, except Join (S=*,G=Gi) (1<=i<=n)      *  white list = { <S=*,G=G1> , <S=*,G=G2>, ... <S=*,G=Gn>}      *  black list = {<S=*,G=*>}   o  Scenario 3: AN performs autonomous decisions for some channels,      and asks the NAS for other channels      *  white list = { <S=*,G=G1> , <S=*,G=G2>, ... <S=*,G=Gn>}      *  grey list = { <S=s,G=Gm>} for m>n      *  black list = {<S=*,G=*>}      *  ==> Join (S=*,G=Gi) gets honored by AN (1<=i<=n)      *  ==> Join (S=s,G=Gm) triggers ANCP Admission Request to NAS      *  ==> everything else gets rejected by AN   The use of a white list and black list may be applicable, for   instance, to regular IPTV services (i.e., broadcast TV) offered by an   Access Provider to broadband (e.g., DSL) subscribers.  For this   application, the IPTV subscription is typically bound to a specific   DSL line, and the multicast flows that are part of the subscription   are well-known beforehand.  Furthermore, changes to the conditional   access information are infrequent, since they are bound to the   subscription.  Hence, the Access Node can be provisioned with the   conditional access information related to the IPTV service.   In some other cases, it may be desirable to have the conditional   access decision being taken by the NAS or a Policy Server.  This may   be the case when conditional access information changes frequently,   or when the multicast groups are not known to a client application in   advance.  The conditional access control could be tied to a more   complex policy/authorization mechanism, e.g., time-of-day access,   location-based access, or to invoke a remote authorization server.   For these cases, the AN can use ANCP to query the NAS that in turn   will respond to the AN indicating whether the join is to be denied or   honored (and hence replication performed by the AN).  This can be   done with the Admission Request and Admission Response messages.Ooghe, et al.                 Informational                    [Page 20]

RFC 5851                     ANCP Framework                     May 2010   Some examples of using NAS querying are the following:   o  Roaming users: a subscriber that logs in on different wireless      hotspots and would like to receive multicast content he is      entitled to receive;   o  Mobility or seamless handover (a related example): in both cases,      the burden of (re)configuring access nodes with white lists or      black lists may be too high;   o  "Over-the-top video partnerships": service providers may choose to      partner with Internet video providers to provide video content.      In this case, the multicast group mappings may not be known in      advance, or may be reused for different content in succession.   o  "Pay Per View": a subscriber chooses a specific IPTV channel which      is made available for a given amount of time.3.4.2.  Multicast Admission Control   The successful delivery of triple-play broadband services is quickly   becoming a big capacity planning challenge for most of the Service   Providers nowadays.  Solely increasing available bandwidth is not   always practical, cost-economical, and/or sufficient to satisfy end-   user experience given not only the strict requirements of unicast   delay sensitive applications like VoIP and video, but also the fast   growth of multicast interactive applications such as   videoconferencing, digital TV, digital audio, online movies, and   networked gaming.  These applications are typically characterized by   a delay-sensitive nature, an extremely loss-sensitive nature, and   intensive bandwidth requirements.  They are also typically "non-   elastic", which means that they operate at a fixed bandwidth that   cannot be dynamically adjusted to the currently available bandwidth.   Therefore, a Connection Admission Control (CAC) mechanism covering   admission of video traffic over the DSL broadband access is required,   in order to avoid oversubscribing the available bandwidth and   negatively impacting the end-user experience.   Considering specifically admission control over the access line,   before honoring a user request to join a new multicast flow, the   combination of AN and NAS must ensure admission control is performed   to validate that there is sufficient bandwidth remaining on the   access line to carry the new video stream (in addition to all other   multicast and unicast video streams sent over the access line).  The   solution needs to cope with multiple flows per access line and needsOoghe, et al.                 Informational                    [Page 21]

RFC 5851                     ANCP Framework                     May 2010   to allow access-line bandwidth to be dynamically shared across   multicast and unicast traffic (the unicast CAC is performed either by   the NAS or by some off-path policy server).   Thus, supporting CAC for the access line requires some form of   synchronization between the entity performing multicast CAC (e.g.,   the NAS or the AN), the entity performing unicast CAC (e.g., the   policy server), and the entity actually enforcing the multicast   replication (i.e., the AN).  This synchronization can be achieved in   a number of ways:   o  One approach is for the AN to query the NAS so that Admission      Control for the access line is performed by the NAS, or by the      policy server which interacts with the AN via NAS.  The AN can use      ANCP to query the NAS that in turn performs a multicast Admission      Control check for the new multicast flow and responds to the AN      indicating whether the join is to be denied or honored (and hence      replication performed by the AN).  The NAS may locally keep track      of the portion of the access-loop net data rate that is available      for (unicast or multicast) video flows and perform video bandwidth      accounting for the access loop.  Upon receiving an Admission      Request from the AN, the NAS can check available access-loop      bandwidth before admitting or denying the multicast flow.  In the      process, the NAS may communicate with the policy server.  For      unicast video services such as Video on Demand (VoD), the NAS may      also be queried (by a policy server or via on-path CAC signaling),      so that it can perform admission control for the unicast flow and      update the remaining available access-loop bandwidth.  The ANCP      requirements to support this approach are specified in this      document.   o  The above model could be enhanced with the notion of "Delegation      of Authorization".  In such a model, the NAS or the policy server      delegates authority to the Access Node to perform multicast      Admission Control on the access loop.  This is sometimes referred      to as "Bandwidth Delegation", referring to the portion of the      total access-loop bandwidth that can be used by the Access Node      for multicast Admission Control.  In this model, the NAS or the      policy server manages the total access-line bandwidth, performs      unicast admission control, and uses ANCP to authorize the Access      Node to perform multicast Admission Control within the bounds of      the "delegated bandwidth".  Upon receiving a request for a      multicast flow replication that matches an entry in the white or      grey list, the AN performs the necessary bandwidth admission      control check for the new multicast flow, before starting the      multicast flow replication.  At this point, there is typically noOoghe, et al.                 Informational                    [Page 22]

RFC 5851                     ANCP Framework                     May 2010      need for the Access Node to communicate with the NAS or the policy      server via the NAS.  The ANCP requirements to support this      approach are also specified in this document.   o  In case the subscriber communicates the "join/leave" information      with the NAS (e.g., by terminating all subscriber IGMP signaling      on the NAS or by using some form of application-level signaling),      the approach is very similar.  In this case, the NAS may locally      keep track of the portion of the access-loop bandwidth that is      available for video flows, perform CAC for unicast and multicast      flows, and perform video bandwidth management.  The NAS can set      the replication state on the AN using ANCP if the flow is      admitted.  For unicast video services, the NAS may be queried (by      a policy server or via on-path CAC signaling) to perform admission      control for the unicast flow, and update the remaining available      access-loop bandwidth.  The ANCP requirements to support this      approach are specified in this document.   o  In the last approach, the policy server queries the AN directly or      indirectly via the NAS, so that both unicast and multicast CAC for      the access line are performed by the AN.  In this case, a      subscriber request for a unicast flow (e.g., a Video on Demand      session) will trigger a resource request message towards a policy      server; the latter will then query the AN (possibly via the NAS),      that in turn will perform unicast CAC for the access line and      respond, indicating whether the unicast request is to be honored      or denied.  The above model could also be enhanced with the notion      of "Delegation of Authorization".  In such a model, the policy      server delegates authority to the Access Node to perform multicast      Admission Control on the access loop.  In the case when the policy      server queries the AN directly, the approach doesn't require the      use of ANCP.  It is therefore beyond the scope of this document.      In the case when the policy server queries the AN indirectly via      the NAS, the approach requires the use of ANCP and is therefore in      the scope of this document.3.4.2.1.  Delegation of Authority - Bandwidth Delegation   The NAS uses ANCP to indicate to the AN whether or not Admission   Control is required for a particular multicast flow on a given Access   Port.  In case Admission Control is required, the Access Node needs   to know whether or not it is authorized to perform Admission Control   itself and, if so, within which bounds it is authorized to do so   (i.e., how much bandwidth is "delegated" by the NAS or the policy   server).  Depending on the type of multicast flow, Admission Control   may or may not by done by the AN:Ooghe, et al.                 Informational                    [Page 23]

RFC 5851                     ANCP Framework                     May 2010   o  Multicast flows that require a Conditional Access operation to be      performed by the Access Node are put in the black or white list.      In addition, the Access Node performs Admission Control for those      flows in the white list for which it is authorized to do so.   o  Multicast flows that require a Conditional Access operation to be      performed by the NAS or the policy server, are put in the grey      list.  In addition, for those flows in the grey list for which the      Access Node should perform Admission Control, the NAS or the      policy server will delegate authority to the AN.   In some cases, the bandwidth that the NAS or the policy server   initially delegated to the AN may not be enough to satisfy a   multicast request for a new flow.  In this scenario, the AN can use   ANCP to query the NAS in order to request additional delegated   multicast bandwidth.  This is a form of extending the AN   authorization to perform Admission Control.  The NAS or the policy   server decides if the request for more bandwidth can be satisfied and   uses ANCP to send a response to the AN indicating the updated   delegated multicast bandwidth.  It is worth noting that in this case,   the time taken to complete the procedure is an increment to the   zapping delay.  In order to minimize the zapping delay for future   join requests, the AN can insert in the request message two values:   the minimum amount of additional multicast bandwidth requested and   the preferred additional amount.  The first value is the amount that   allows the present join request to be satisfied, the second value an   amount that anticipates further join requests.   In some cases, the NAS or the policy server may not have enough   unicast bandwidth to satisfy a new incoming video request: in these   scenarios, the NAS can use ANCP to query (or instruct) the AN in   order to decrease the amount of multicast bandwidth previously   delegated on a given Access Port.  This is a form of limiting/   withdrawing AN authorization to perform Admission Control.  The NAS   can use ANCP to send a response to AN indicating the updated   delegated multicast bandwidth.  Based on considerations similar to   those of the previous paragraph, it indicates the minimum amount of   multicast bandwidth that it needs released and a preferred amount,   which may be larger.   Note: in order to avoid impacting existing multicast traffic, the NAS   must not decrease the amount of delegated multicast bandwidth to a   value lower than the bandwidth that is currently in use.  This   requires the NAS to be aware of this information (e.g., by means of a   separate query action).Ooghe, et al.                 Informational                    [Page 24]

RFC 5851                     ANCP Framework                     May 2010   In addition, in some cases, upon receiving a leave for a specific   multicast flow, the AN may decide that it has an excess of delegated   but uncommitted bandwidth.  In such case, the AN can use ANCP to send   a message to the NAS to release all of part of the unused multicast   bandwidth that was previously delegated.  In this process, the Access   Node may decide to retain a minimum amount of bandwidth for multicast   services.3.4.2.2.  When Not to Perform Admission Control for a Subset of Flows   In general, the Access Node and NAS may not be aware of all possible   multicast groups that will be streamed in the access network.  For   instance, it is likely that there will be multicast streams offered   across the Internet.  For these unknown streams, performing bandwidth   Admission Control may be challenging.   To solve this, these requests could be accepted without performing   Admission Control.  This solution works, provided that the network   handles the streams as best effort, so that other streams (that are   subject to Admission Control) are not impacted at times of   congestion.   Disabling Admission Control for an unknown stream can be achieved by   adding a "catch-all statement" in the Access Node white list or grey   list.  In case the Access Node queries the NAS, the NAS on his turn   will have to accept the request.  That way, the unknown streams are   not blocked by default.   Next, in order to ensure that the streams are handled as best effort,   the flow must be marked as such when entering the service provider   network.  This way, whenever congestion occurs somewhere in the   access/aggregation network, this stream will be kicked out before the   access provider's own premium content.   The above concept is applicable beyond the notion of "Internet   streams" or other unknown streams; it can be applied to known   multicast streams as well.  In this case, the Access Node or NAS will   accept the stream even when bandwidth may not be sufficient to   support the stream.  This again requires that the stream be marked as   best-effort traffic before entering the access/aggregation network.3.4.2.3.  Multicast Admission Control and White Lists   As mentioned inSection 3.4.1, conditional access to popular IPTV   channels can be achieved by means of a white and black list   configured on the Access Node.  This method allows the Access Node to   autonomously decide whether or not access can be granted to a   multicast flow.Ooghe, et al.                 Informational                    [Page 25]

RFC 5851                     ANCP Framework                     May 2010   IPTV is an example of a service that will not be offered as best   effort, but requires some level of guaranteed quality of service.   This requires the use of Multicast Admission Control.  Hence, if the   Access Node wants to autonomously perform the admission process, it   must be aware of the bandwidth characteristics of multicast flows.   Otherwise, the Access Node would have to query the NAS for Multicast   Admission Control (per the grey list behavior); this would defeat the   purpose of using a white and black list.   Some network deployments may combine the use of white list, black   list, and grey list.  The implications of such a model to the overall   Multicast Admission Control model are not fully explored in this   document.3.4.3.  Multicast Accounting and Reporting   It may be desirable to perform time- and/or volume-based accounting   for certain multicast flows sent on particular Access Ports.  In case   the AN is performing the traffic replication process, it knows when   replication of a multicast flow to a particular Access Port or user   start and stops.  Multicast accounting can be addressed in two ways:   o  The AN keeps track of when replication for a given multicast flow      starts or ends on a specified Access Port, and generates time-      and/or volume-based accounting information per Access Port and per      multicast flow, before sending it to a central accounting system      for logging.  Given that the AN communicates with the accounting      system directly, the approach doesn't require the use of ANCP.  It      is therefore beyond the scope of this document;   o  The AN keeps track of when replication for a given multicast flow      starts or ends on a specified Access Port, and reports this      information to the NAS for further processing.  In this case, ANCP      can be used to send the information from the AN to the NAS.  This      will be discussed in the remainder of this document.   The Access Node can send multicast accounting information to the NAS   using the Information Report message.  A distinction can be made   between two cases:   o  Basic accounting information: the Access Node informs the NAS      whenever replication starts or ends for a given multicast flow on      a particular Access Port;   o  Detailed accounting information: the Access Node not only informs      the NAS when replication starts or ends, but also informs the NAS      about the multicast traffic volume replicated on the Access PortOoghe, et al.                 Informational                    [Page 26]

RFC 5851                     ANCP Framework                     May 2010      for that multicast flow.  This is done by adding a byte count in      the Information Report message that is sent to the NAS when      replication ends.   Upon receiving the Information Report messages, the NAS generates the   appropriate time- and/or volume-based accounting records per access   loop and per multicast flow to be sent to the accounting system.   The NAS should inform the Access Node about the type of accounting   needed for a given multicast flow on a particular Access Port:   o  No reporting messages need to be sent to the NAS.   o  Basic accounting is required.   o  Detailed accounting is required.   Note that in case of very fast channel changes, the amount of   Information Report messages to be sent to the NAS could become high.   The ANCP requirements to support this use case are specified below in   this document.   It may also be desirable for the NAS to have the capability to   asynchronously query the AN to obtain an instantaneous status report   related to multicast flows currently replicated by the AN.  Such a   reporting functionality could be useful for troubleshooting and   monitoring purposes.  The NAS can query the AN to know the following:   o  Which flows are currently being sent on a specific Access Port      (i.e., a report for one Access Port)   o  On which Access Ports a specified multicast flow is currently      being sent (i.e., a report for one multicast flow)   o  Which multicast flows are currently being sent on each of the      Access Ports (i.e., a global report for one Access Node)3.4.4.  Spontaneous Admission Response   The capability to dynamically stop the replication of a multicast   flow can be useful in different scenarios: for example in case of   prepaid service, when available credit expires, the Service Provider   may want to be able to stop multicast replication on a specified   Access Port for a particular user.  Another example of applicability   for this functionality is a scenario where a Service Provider would   like to show a "Content Preview": in this case, a multicast content   will be delivered just for a fixed amount of time.Ooghe, et al.                 Informational                    [Page 27]

RFC 5851                     ANCP Framework                     May 2010   In both cases, an external entity (for example, a policy server or an   external application entity) can instruct the NAS to interrupt the   multicast replication of a specified multicast flow to a specified   Access Port or user.  The NAS can then use ANCP to communicate this   decision to the Access Node.  This can be done with the Admission   Response message.   In some deployment scenarios, the NAS may be made aware of end-users'   requests to join/leave a multicast flow by other means than ANCP   Admission Requests sent by the AN.  One possible deployment scenario   where this model applies is the case where the Access Node doesn't   process the IGMP join/leave messages from the end-user (e.g., because   they are tunneled), but forwards them to the NAS.  In such   environments, the NAS can control multicast replication on the AN via   ANCP through the use of Spontaneous Admission Responses (i.e., sent   by the NAS without prior receipt of a corresponding Admission   Request).4.  Requirements4.1.  ANCP Functional Requirements   R-1  The ANCP MUST be easily extensible through the definition of new        message types or TLVs to support use cases beyond those        currently addressed in this document (this includes the use of        Access Nodes different from a DSLAM, e.g., a PON Access Node).   R-2  The ANCP MUST be flexible enough to accommodate the various        technologies that can be used in an access network and in the        Access Node; this includes both ATM and Ethernet.   R-3  The Access Node Control interactions MUST be reliable (using        either a reliable transport protocol (e.g., TCP) for the Access        Node Control Protocol messages, or by designing ANCP to be        reliable).   R-4  The ANCP MUST support "request/response" transaction-based        interactions for the NAS to communicate control decisions to the        Access Node, or for the NAS to request information from the        Access Node.  Transactions MUST be atomic, i.e., they are either        fully completed, or rolled back to the previous state.  This is        required so that the network elements always remain in a known        state, irrespective of whether or not the transaction is        successful.   In case the NAS wants to communicate a bulk of independent control   decisions to the Access Node, the transaction (and notion of   atomicity) applies to the individual control decisions.  This avoidsOoghe, et al.                 Informational                    [Page 28]

RFC 5851                     ANCP Framework                     May 2010   having to roll back all control decisions.  Similarly, if the NAS   wants to request a bulk of independent information elements from the   Access Node, the notion of transaction applies to the individual   information elements.   R-5  The ANCP MUST be scalable enough to allow a given NAS to control        at least 5000 Access Nodes.   R-6  The operation of the ANCP in the NAS and Access Nodes MUST be        controllable via a management station (e.g., via SNMP).  This        MUST allow a management station to retrieve statistics and        alarms related to the operation of the ANCP, as well as to allow        it to initiate OAM operations and retrieve corresponding        results.4.2.  ANCP Multicast Requirements   R-7   The ANCP MUST support providing multicast conditional access         information to Access Ports on an Access Node, using black,         grey, and white lists.   R-8   The ANCP MUST support binding a particular black, grey, and         white List to a given Access Port.   R-9   Upon receiving a join to a multicast flow that matches the grey         list, the ANCP MUST allow the AN to query the NAS to request an         admission decision for replicating that multicast flow to a         particular Access Port.   R-10  The ANCP MUST allow the NAS to send an admission decision to         the AN indicating whether or not a multicast flow may be         replicated to a particular Access Port.   R-11  The ANCP MUST allow the NAS to indicate to the AN whether or         not Admission Control is needed for some multicast flows on a         given Access Port, and (where needed) whether or not the Access         Node is authorized to perform Admission Control itself (i.e.,         whether or not AN Bandwidth Delegation applies).   R-12  In case of Admission Control without AN Bandwidth Delegation,         the ANCP MUST allow the NAS to reply to a query from the AN         indicating whether or not a multicast flow is allowed to be         replicated to a particular Access Port.   R-13  In case of Admission Control with AN Bandwidth Delegation, the         ANCP MUST allow the NAS to delegate a certain amount of         bandwidth to the AN for a given Access Port for multicast         services only.Ooghe, et al.                 Informational                    [Page 29]

RFC 5851                     ANCP Framework                     May 2010   R-14  In case of Admission Control with AN Bandwidth Delegation, the         ANCP MUST allow the AN to query the NAS to request additional         multicast bandwidth on a given Access Port.   R-15  In case of Admission Control with AN Bandwidth Delegation, the         ANCP MUST allow the NAS to query (or to instruct) the AN to         reduce the amount of bandwidth previously delegated on a given         Access Port.   R-16  In case of Admission Control with AN Bandwidth Delegation, the         ANCP MUST allow the AN to inform the NAS if it autonomously         releases redundant multicast bandwidth on a given Access Port.   R-17  The ANCP MUST allow the AN to send an Information Report         message to the NAS whenever replication of a multicast flow on         a particular Access Port starts or ends.   R-18  The ANCP MUST allow the AN to send an Information Report         message to the NAS indicating the multicast traffic volume that         has been replicated on that port.   R-19  The ANCP MUST allow the NAS to indicate to the AN whether or         not multicast accounting is needed for a multicast flow on a         particular Access Port.   R-20  In case multicast accounting is needed for a multicast flow on         a particular Access Port, the ANCP MUST allow the NAS to         indicate to the AN whether or not additional volume accounting         information is required.   R-21  The ANCP MUST allow the NAS to revoke a decision to replicate a         multicast flow to a particular Access Port, which had been         conveyed earlier to an AN.   R-22  The ANCP MUST support partial updates of the white, grey, and         black lists.   R-23  The ANCP MUST allow the NAS to query the AN to obtain         information on what multicast flows are currently being         replicated on a given Access Port, what Access Ports are         currently receiving a given multicast flow, or what multicast         flows are currently replicated on each Access Port.4.3.  Protocol Design Requirements   R-24  The ANCP SHOULD provide a "shutdown" sequence allowing the         protocol to inform the peer that the system is gracefully         shutting down.Ooghe, et al.                 Informational                    [Page 30]

RFC 5851                     ANCP Framework                     May 2010   R-25  The ANCP SHOULD include a "report" model for the Access Node to         spontaneously communicate to the NAS changes of states.   R-26  The ANCP SHOULD support a graceful restart mechanism to enable         it to be resilient to network failures between the AN and NAS.   R-27  The ANCP MUST provide a means for the AN and the NAS to inform         each peer about the supported use cases (either use cases         defined in this document or future use cases yet to be         defined), and to negotiate a common subset.4.4.  Access Node Control Adjacency Requirements   The notion of an Access Node Control Adjacency is defined inSection 1.2.   R-28  The ANCP MUST support an adjacency protocol in order to         automatically synchronize its operational state between its         peers, to agree on which version of the protocol to use, to         discover the identity of its peers, and to detect when they         change.   R-29  The ANCP MUST include a mechanism to automatically detect         adjacency loss.   R-30  A loss of the Access Node Control Adjacency MUST NOT affect         subscriber connectivity.   R-31  If the Access Node Control Adjacency is lost, it MUST leave the         network elements in a known state, irrespective of whether or         not the ongoing transaction was successful.   R-32  The ANCP MUST support a mechanism to synchronize access port         configuration and status information between ANCP peers as part         of establishing or recovering the Access Node Control         Adjacency.4.5.  ANCP Transport Requirements   R-33  The Access Node Control Mechanism MUST be defined in a way that         is independent of the underlying layer 2 transport technology.         Specifically, the Access Node Control Mechanism MUST support         transmission over an ATM as well as over an Ethernet         aggregation network.   R-34  The ANCP MUST use the IP protocol stack.Ooghe, et al.                 Informational                    [Page 31]

RFC 5851                     ANCP Framework                     May 2010   R-35  If the layer 2 transport technology is based on ATM, then the         ANCP peers must use the encapsulation according to [RFC2684]         (IPoA).   R-36  If the layer 2 transport technology is based on Ethernet, then         the ANCP peers must use the encapsulation according to [RFC894]         (IPoE).4.6.  Access Node Requirements   This section lists the requirements for an AN that supports the use   cases defined in this document.  Note that this document does not   intend to impose absolute requirements on network elements.   Therefore, the words "must" and "should" used in this section are not   capitalized.4.6.1.  General Architecture   The Access Node Control Mechanism is defined to operate between an   Access Node (AN) and a NAS.  In some cases, one AN can be connected   to more than one physical NAS device (e.g., in case different   wholesale service providers have different NAS devices).  In such a   model, the physical AN needs to be split in virtual ANs, each having   its own Access Node Control reporting and/or enforcement function.   R-37  An Access Node as physical device can be split in logical         partitions.  Each partition may have its independent NAS.         Therefore, the Access Node must support at least 2 partitions.         The Access Node should support 8 partitions.   R-38  One partition is grouped of several Access Ports.  Each Access         Port on an Access Node must be assigned uniquely to one         partition.   It is assumed that all circuits (i.e., ATM PVCs or Ethernet VLANs) on   top of the same physical Access Port are associated with the same   partition.  In other words, partitioning is performed at the level of   the physical Access Port only.   R-39  Each AN partition must have a separate Access Node Control         Adjacency to a NAS.   R-40  Each AN partition must be able to enforce access of the         controllers to their designated partitions.   R-41  The Access Node should be able to establish and maintain ANCP         Adjacencies to redundant controllers.Ooghe, et al.                 Informational                    [Page 32]

RFC 5851                     ANCP Framework                     May 20104.6.2.  Control Channel Attributes   The Control Channel is a bidirectional IP communication interface   between the controller function (in the NAS) and the reporting/   enforcement function (in the AN).  It is assumed that this interface   is configured (rather than discovered) on the AN and the NAS.   Depending on the network topology, the Access Node can be located in   a street cabinet or in a central office.  If an Access Node in a   street cabinet is connected to a NAS, all user traffic and Access   Node Control data can use the same physical link.   R-42  The Control Channel should use the same facilities as the ones         used for the data traffic.  Note that this is actually a         deployment consideration, which has no impact on the actual         protocol design.   R-43  The Access Node must process control transactions in real-time         (i.e., with a specific response latency).   R-44  The Access Node should mark Access Node Control Protocol         messages with a high priority (e.g., Variable Bit Rate - Real         Time (VBR-RT) for ATM cells, p-bit 6 or 7 for Ethernet packets)         in order to avoid or reduce the likelihood of dropping packets         in case of network congestion.   R-45  If ATM interfaces are used, then any Virtual Path Identifier         (VPI) and Virtual Circuit Identifier (VCI) value must be able         to be used for the purpose of supporting the Access Node         Control Channel.   R-46  If Ethernet interfaces are used then any C-VID and S-VID must         be able to be used for the purpose of supporting the Access         Node Control Channel.4.6.3.  Capability Negotiation Failure   R-47  In case the Access Node and NAS cannot agree on a common set of         capabilities, as part of the ANCP capability negotiation         procedure, the Access Node must report this to network         management.4.6.4.  Adjacency Status Reporting   R-48  The Access Node should support generating an alarm to a         management station upon loss or malfunctioning of the Access         Node Control Adjacency with the NAS.Ooghe, et al.                 Informational                    [Page 33]

RFC 5851                     ANCP Framework                     May 20104.6.5.  Identification   R-49  To identify the Access Node and Access Port within a control         domain, a unique identifier is required.  This identifier must         be in line with the addressing scheme principles specified inSection 3.9.3 of TR-101.   R-50  In a Broadband Forum TR-101 network architecture, an Access         Circuit Identifier (ACI) identifying an AN and Access Port is         added to DHCP and PPPoE messages.  The NAS must use the same         ACI format in ANCP messages in order to allow the NAS to         correlate this information with the information present in DHCP         and PPPoE messages.4.6.6.  Multicast   R-51  The AN must deny any join to a multicast flow matching the         black list for the relevant Access Port.   R-52  The AN must accept any join to a multicast flow matching the         white list and for which no Bandwidth Delegation is used.   R-53  Upon receiving a join to a multicast flow that matches the         white list and for which Bandwidth Delegation is used, the AN         must perform the necessary bandwidth admission control check         for the new flow before starting the multicast flow         replication.  This may involve a decision made locally, or         querying the NAS or external system such as a policy server, to         request additional delegated multicast bandwidth on a given         Access Port.   R-54  Upon receiving a join to a multicast flow which matches the         grey list and for which no Bandwidth Delegation is used, the AN         must support using ANCP to query the NAS to receive a response         indicating whether that join is to be honored or denied.  In         this case, the NAS will perform both the necessary conditional         access and the admission control checks for the new flow.   R-55  Upon receiving a join to a multicast flow that matches the grey         list and for which Bandwidth Delegation is used, the AN must         first perform the necessary bandwidth admission control check         for the new flow.  If successful, the AN must support using         ANCP to query the NAS to receive a response indicating whether         that join is to be honored or denied.   R-56  In case of Admission Control with AN Bandwidth Delegation, the         AN must support using ANCP to notify the NAS when the user         leaves the multicast flow.Ooghe, et al.                 Informational                    [Page 34]

RFC 5851                     ANCP Framework                     May 2010   R-57  In case of Admission Control with AN Bandwidth Delegation, the         AN must support using ANCP to query the NAS to request         additional delegated multicast bandwidth on a given Access         Port; the AN should be able to specify both the minimum and the         preferred amount of additional multicast bandwidth requested.   R-58  In case of Admission Control with AN Bandwidth Delegation, upon         receiving a Bandwidth Delegation Request from the NAS querying         the AN for the delegated multicast bandwidth on a given Access         Port, the AN must support using ANCP to send a Bandwidth         Delegation Response, indicating the currently delegated         multicast bandwidth.   R-59  In case of Admission Control with AN Bandwidth Delegation, it         may happen that the NAS wants to "revoke" all or part of the         delegated bandwidth.  Part of the previously delegated         bandwidth may however be in use by multicast services.         Therefore, upon receiving a Bandwidth Delegation Request from         the NAS instructing to decrease the delegated multicast         bandwidth on a given Access Port, the AN must support using         ANCP to send a Bandwidth Delegation Response, indicating the         delegated multicast bandwidth after the decrease (indicating         how much of the delegated bandwidth can be returned to the NAS         without impacting multicast services that are currently         running).   R-60  In case of Admission Control with AN Bandwidth Delegation, the         AN must support using ANCP to send a Bandwidth Release message         to the NAS in order to release unused delegated multicast         bandwidth on a given Access Port.   R-61  If the requested multicast flow is not part of any list         associated with the Access Port, the AN must discard the         message.   R-62  If the requested multicast flow is part of multiple lists         associated with the Access Port, the AN must use the most         specific match.   R-63  If the requested multicast flow has the same most specific         match in multiple lists, the AN must give precedence to the         black list, followed by the grey list, and then the white list.   R-64  The AN must support configuring a "catch-all" statement in the         black, white, or grey list in order to enforce a default         behavior for a join to a multicast flow which doesn't match any         other entry in a list for the relevant Access Port.Ooghe, et al.                 Informational                    [Page 35]

RFC 5851                     ANCP Framework                     May 2010   R-65  Upon querying the NAS, the AN must not propagate the join         message before the successful authorization from the NAS is         received.   R-66  Upon receiving a leave for a multicast flow that matches the         grey list, the AN should be able to autonomously stop         replication and advertise this event to the NAS.   R-67  The AN must support using ANCP to send an Information Report         message to the NAS whenever replication starts or ends.   R-68  The AN should support using ANCP to send an Information Report         message to the NAS indicating the multicast traffic volume that         has been replicated on that port.   R-69  Upon request by the NAS, the AN must support using ANCP to send         an Information Report message to the NAS, indicating what         multicast flows are currently being replicated on a given         Access Port.   R-70  Upon request by the NAS, the AN must support using ANCP to send         an Information Report message to the NAS, indicating what         Access Ports are currently receiving a given multicast flow.   R-71  Upon request by the NAS, the AN must support using ANCP to send         an Information Report message to the NAS, indicating what         multicast flows are currently being replicated on each Access         Port.   R-72  Upon receiving an Admission Response from the NAS, indicating         that replication of a multicast flow is to start or stop on a         given access port of the AN, the AN must enforce this decision.         This decision must be taken irrespective of whether or not a         corresponding Admission Request was issued by the AN earlier.4.6.7.  Message Handling   R-73  The Access Node must be designed to allow fast completion of         ANCP operations, in the order of magnitude of tens of         milliseconds.   R-74  The Access Node should avoid sending bursts of ANCP messages         related to notification of line attributes or line state, by         spreading message transmission over time.Ooghe, et al.                 Informational                    [Page 36]

RFC 5851                     ANCP Framework                     May 20104.6.8.  Parameter Control   Naturally, the Access Node Control Mechanism is not designed to   replace an Element Manager managing the Access Node.  There are   parameters in the Access Node, such as the DSL noise margin and DSL   Power Spectral Density (PSD), which are not allowed to be changed via   ANCP or any other control session, but only via the Element Manager.   This has to be ensured and protected by the Access Node.   When using ANCP for access-loop configuration, the EMS needs to   configure on the Access Node which parameters may or may not be   modified using the Access Node Control Mechanism.  Furthermore, for   those parameters that may be modified using ANCP, the EMS needs to   specify the default values to be used when an Access Node comes up   after recovery.   R-75  When access-loop configuration via ANCP is required, the EMS         must configure on the Access Node which parameter set(s) may be         changed/controlled using ANCP.   R-76  Upon receiving an Access Node Control Request message, the         Access Node must not apply changes to the parameter set(s) that         have not been enabled by the EMS.4.7.  Network Access Server Requirements   This section lists the requirements for a NAS that supports the use   cases defined in this document.  Note that this document does not   intend to impose absolute requirements on network elements.   Therefore, the words "must" and "should" used in this section are not   capitalized.4.7.1.  General Architecture   R-77  The NAS must establish ANCP Adjacencies only with authorized         ANCP peers.   R-78  The NAS must support the capability to simultaneously run ANCP         with multiple ANs in a network.   R-79  The NAS must be able to establish an Access Node Control         Adjacency to a particular partition on an AN and control the         access loops belonging to such a partition.   R-80  The NAS must support obtaining access-loop information (e.g.,         net data rate), from its peer Access Node partitions via the         Access Node Control Mechanism.Ooghe, et al.                 Informational                    [Page 37]

RFC 5851                     ANCP Framework                     May 2010   R-81  The NAS must support shaping traffic directed towards a         particular access loop to not exceed the net data rate learned         from the AN via the Access Node Control Mechanism.   R-82  The NAS should support reducing or disabling the shaping limit         used in the Hierarchical Scheduling process, according to per-         subscriber authorization data retrieved from a AAA or policy         server.   R-83  The NAS must support reporting of access-loop attributes         learned via the Access Node Control Mechanism to a Policy or         AAA Server using RADIUS Vendor-Specific Attributes (VSAs).   R-84  In a TR-059/TR-101 network architecture, the NAS shapes traffic         sent to a particular Access Port according to the bitrate         available on that port.  The NAS should take into account the         layer 1 and layer 2 encapsulation overhead on the Access Port,         retrieved from the AN via the Access Node Control Mechanism.   R-85  The NAS should support dynamically configuring and         reconfiguring discrete service parameters for access loops that         are controlled by the NAS.  The configurable service parameters         for access loops could be driven by local configuration on the         NAS or by a policy server.   R-86  The NAS should support triggering an AN via the Access Node         Control Mechanism to execute local OAM procedures on an access         loop that is controlled by the NAS.  If the NAS supports this         capability, then the following applies:         *  The NAS must identify the access loop on which OAM            procedures need to be executed by specifying an Access            Circuit Identifier (ACI) in the request message to the AN.         *  The NAS should support processing and reporting of the            remote OAM results learned via the Access Node Control            Mechanism.         *  As part of the parameters conveyed within the OAM message to            the AN, the NAS should send the list of test parameters            pertinent to the OAM procedure.  The AN will then execute            the OAM procedure on the specified access loop according to            the specified parameters.  In case no test parameters are            conveyed, the AN and NAS must use default and/or            appropriately computed values.Ooghe, et al.                 Informational                    [Page 38]

RFC 5851                     ANCP Framework                     May 2010         *  After issuing an OAM request, the NAS will consider the            request to have failed if no response is received after a            certain period of time.  The timeout value should be either            the one sent within the OAM message to the AN, or the            computed timeout value when no parameter was sent.         The exact set of test parameters mentioned above depends on the         particular OAM procedure executed on the access loop.  An         example of a set of test parameters is the number of loopbacks         to be performed on the access loop and the timeout value for         the overall test.  In this case, and assuming an ATM-based         access loop, the default value for the timeout parameter would         be equal to the number of F5 loopbacks to be performed,         multiplied by the F5 loopback timeout (i.e., 5 seconds per the         ITU-T I.610 standard).   R-87  The NAS must treat PPP or DHCP session state independently from         any Access Node Control Adjacency state.  The NAS must not         bring down the PPP or DHCP sessions just because the Access         Node Control Adjacency goes down.   R-88  The NAS should internally treat Access Node Control traffic in         a timely and scalable fashion.   R-89  The NAS should support protection of Access Node Control         communication to an Access Node in case of line card failure.4.7.2.  Control Channel Attributes   R-90  The NAS must mark Access Node Control Protocol messages as high         priority (e.g., appropriately set Diffserv Code Point (DSCP),         Ethernet priority bits, or ATM Cell Loss Priority (CLP) bit)         such that the aggregation network between the NAS and the AN         can prioritize the Access Node Control Protocol messages over         user traffic in case of congestion.4.7.3.  Capability Negotiation Failure   R-91  In case the NAS and Access Node cannot agree on a common set of         capabilities, as part of the ANCP capability negotiation         procedure, the NAS must report this to network management.   R-92  The NAS must only commence Access Node Control information         exchange and state synchronization with the AN when there is a         non-empty common set of capabilities with that AN.Ooghe, et al.                 Informational                    [Page 39]

RFC 5851                     ANCP Framework                     May 20104.7.4.  Adjacency Status Reporting   R-93  The NAS must support generating an alarm to a management         station upon loss or malfunctioning of the Access Node Control         Adjacency with the Access Node.4.7.5.  Identification   R-94  The NAS must support correlating Access Node Control Protocol         messages pertaining to a given access loop with subscriber         session(s) over that access loop.  This correlation must be         achieved by either:         *  Matching an Access Circuit Identifier (ACI) inserted by the            AN in Access Node Control Protocol messages with the            corresponding ACI value received in subscriber signaling            (e.g., PPPoE and DHCP) messages as inserted by the AN.  The            format of ACI is defined in [TR-101]; or         *  Matching an ACI inserted by the AN in Access Node Control            Protocol messages with an ACI value locally configured for a            static subscriber on the NAS.4.7.6.  Multicast   R-95   The NAS must support using ANCP to configure multicast          conditional access information to Access Ports on an Access          Node, using black lists, grey lists, and white lists.   R-96   The NAS must support using ANCP to indicate to the AN whether          or not Admission Control is needed for some multicast flows on          a given Access Port and where needed whether or not the Access          Node is authorized to perform Admission Control itself (i.e.,          whether or not AN Bandwidth Delegation applies).   R-97   Upon receiving a query from the AN for a request to replicate          a multicast flow to a particular Access Port, and no AN          Bandwidth Delegation is used for that flow, the NAS must be          able to perform the necessary checks (conditional access          and/or admission control) for the new flow.  The NAS must          support using ANCP to reply to the AN indicating whether the          request is to be honored or denied.  This may involve a          decision made locally or querying an external system such as a          policy server.Ooghe, et al.                 Informational                    [Page 40]

RFC 5851                     ANCP Framework                     May 2010   R-98   Upon receiving a query from the AN for a request to replicate          a multicast flow to a particular Access Port, and Admission          Control with AN Bandwidth Delegation is used for that flow,          the NAS must be able to perform the conditional access checks          (if needed), and must support using ANCP to delegate a certain          amount of bandwidth to the AN for a given Access Port.   R-99   In case of Admission Control with AN Bandwidth Delegation,          upon receiving a Bandwidth Delegation Request from the AN          requesting to increase the delegated multicast bandwidth on a          given Access Port, the NAS must support using ANCP to send a          Bandwidth Delegation Response indicating the new delegating          multicast bandwidth.   R-100  In case of Admission Control with AN Bandwidth Delegation, the          NAS must support using ANCP to send a request to the AN to          decrease the amount of multicast bandwidth previously          delegated on a given Access Port; the NAS should be able to          specify both the minimum and the preferred amount of decrement          of multicast bandwidth requested.   R-101  In case of Admission Control with AN Bandwidth Delegation,          upon receiving an ANCP Bandwidth Release message, the NAS must          be able to update accordingly its view of the multicast          bandwidth delegated to the AN.   R-102  The NAS must support using ANCP to configure the Access Node          with the "maximum number of multicast streams" allowed to be          received concurrently per Access Port.   R-103  The NAS must support using ANCP to incrementally add, remove,          and modify individual entries in white, black, and grey lists.   R-104  The NAS must support using ANCP to indicate to the AN whether          or not multicast accounting is needed for a multicast flow on          a particular Access Port.   R-105  In case multicast accounting is needed for a multicast flow on          a particular Access Port, the NAS should support using ANCP to          indicate to the AN whether or not additional volume accounting          information is required.   R-106  The NAS must support using ANCP to query the AN to obtain          information on what multicast flows are currently replicated          on a given Access Port.Ooghe, et al.                 Informational                    [Page 41]

RFC 5851                     ANCP Framework                     May 2010   R-107  The NAS must support using ANCP to query the AN to obtain          information on what Access Ports are currently receiving a          given multicast flow.   R-108  The NAS must support using ANCP to query the AN to obtain          information on what multicast flows are currently replicated          on each Access Port.   R-109  When Multicast replication occurs on the AN, the NAS must          support using ANCP to revoke the authorization to replicate a          multicast flow to a particular Access Port.   R-110  The NAS should support using ANCP to indicate to the AN that          replication of a multicast flow is to start or stop on a given          access port of the AN, without having received a corresponding          Admission Request from the AN earlier on.4.7.7.  Message Handling   R-111  The NAS must be designed to allow fast completion of ANCP          operations, in the order of magnitude of tens of milliseconds.   R-112  The NAS should protect its resources from misbehaving Access          Node Control peers by providing a mechanism to dampen          information related to an Access Node partition.4.7.8.  Wholesale Model   Broadband Forum TR-058 [TR-058], Broadband Forum TR-059 [TR-059], and   Broadband Forum TR-101 [TR-101] describe a DSL broadband access   architecture and how it enables wholesaling.  In such a model, the   broadband access provider has a wholesale agreement with one or more   service providers.  The access provider owns the broadband access   network and manages connectivity to the service providers.  This   allows service providers to provide broadband services to retail   customers without having to own the access network infrastructure   itself.   When applying the Access Node Control Mechanism to a wholesale   network architecture, a number of additional requirements apply.   R-113  In case of wholesale access, the network provider's NAS should          support reporting of access-loop attributes learned from the          AN via the Access Node Control Mechanism (or values derived          from such attributes), to a retail provider's network gateway          owning the corresponding subscriber(s).Ooghe, et al.                 Informational                    [Page 42]

RFC 5851                     ANCP Framework                     May 2010   R-114  In case of Layer 2 Tunneling Protocol (L2TP) wholesale, the          NAS must support a proxy architecture that gives different          providers conditional access to dedicated Access Node Control          resources on an Access Node.   R-115  The NAS when acting as an L2TP Access Concentrator (LAC) must          communicate generic access-line-related information to the          L2TP Network Server (LNS) in a timely fashion.   R-116  The NAS when acting as a LAC may asynchronously notify the LNS          of updates to generic access-line-related information.5.  Management-Related Requirements   This section lists the management-related requirements for the AN and   NAS.  Note that this document does not intend to impose absolute   requirements on network elements.  Therefore, the words "must" and   "should" used in this section are not capitalized.   R-117  It must be possible to configure the following parameters on          the Access Node and the NAS:          *  Parameters related to the Control Channel transport method:             these include the VPI/VCI and transport characteristics             (e.g., VBR-RT or Constant Bitrate (CBR)) for ATM networks,             or the C-VLAN ID, S-VLAN ID, and p-bit marking for Ethernet             networks;          *  Parameters related to the Control Channel itself: these             include the IP address of the IP interface on the Access             Node and the NAS.   R-118  When the operational status of the Control Channel is changed          (up>down, down>up) a linkdown/linkup trap should be sent          towards the EMS.  This requirement applies to both the AN and          the NAS.   R-119  The Access Node must provide the possibility using SNMP to          associate individual DSL lines with specific Access Node          Control Adjacencies.   R-120  The Access Node must notify the EMS of configuration changes          made by the NAS on the AN using ANCP, in a timely manner.   R-121  The Access Node must provide a mechanism that allows the          concurrent access on the same resource from several managers          (EMS via SNMP, NAS via ANCP).  Only one manager may perform a          change at a certain time.Ooghe, et al.                 Informational                    [Page 43]

RFC 5851                     ANCP Framework                     May 2010   R-122  The ANCP may provide a notification mechanism to inform the          NAS about configuration changes done by an EMS, in a timely          manner.  This applies only to changes of parameters that are          part of the use case "Access-Loop Configuration"          (Section 3.2).6.  Security Considerations   [RFC5713] lists the ANCP-related security threats that could be   encountered on the Access Node and the NAS.  It develops a threat   model and identifies requirements for ANCP security, aiming to decide   which security functions are required at the ANCP level.   With multicast handling as described in this document, ANCP protocol   activity between the AN and the NAS is triggered by join/leave   requests coming from the end-user equipment.  This could potentially   be used for denial-of-service attacks against the AN and/or the NAS.   This is not a new class of risk over already possible IGMP messages   sent from subscribers to the NAS when the AN uses no IGMP snooping,   and thus is transparent as long as processing of ANCP messages on the   NAS/AN is comparably efficient and protected against congestion.   To mitigate this risk, the AN MAY implement control-plane protection   mechanisms such as limiting the number of multicast flows a given   user can simultaneously join, or limiting the maximum rate of join/   leave from a given user.   We also observe that an operator can easily deploy some protection   against attacks using invalid multicast flows by taking advantage of   the mask-based match in the black list.  This way, joins for invalid   multicast flows can be denied at the AN level without any ANCP   protocol interactions and without NAS involvement.   R-123  The ANCP MUST comply with the security requirements spelled          out inRFC 5713.   R-124  The Access Node MUST NOT allow the sending of Access Node          Control Messages towards the customer premises.7.  Acknowledgements   The authors would like to thank everyone that has provided comments   or input to this document.  In particular, the authors acknowledge   the work done by the contributors to the activities related to the   Broadband Forum: Jerome Moisand, Wojciech Dec, Peter Arberg, and Ole   Helleberg Andersen.  The authors also acknowledge the inputs provided   by Roberta Maglione, Angelo Garofalo, Francois Le Faucheur, andOoghe, et al.                 Informational                    [Page 44]

RFC 5851                     ANCP Framework                     May 2010   Toerless Eckert regarding multicast.  Finally, the authors thank   Bharat Joshi, Stefaan De Cnodder, Kirubaharan Dorairaj, Markus   Freudenberger, Fortune Huang, and Lothar Reith for providing   comments.8.  References8.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2684]  Grossman, D. and J. Heinanen, "Multiprotocol Encapsulation              over ATM Adaptation Layer 5",RFC 2684, September 1999.   [RFC5713]  Moustafa, H., Tschofenig, H., and S. De Cnodder, "Security              Threats and Security Requirements for the Access Node              Control Protocol (ANCP)",RFC 5713, January 2010.   [RFC894]   Hornig, C., "A Standard for the Transmission of IP              Datagrams over Ethernet Networks", STD 41,RFC 894,              April 1984.   [TR-101]   Cohen, A. and E. Shrum, "Migration to Ethernet-Based DSL              Aggregation", Broadband Forum TR-101, May 2006.8.2.  Informative References   [G.993.2]  ITU-T, "Very high speed digital subscriber line              transceivers 2 (VDSL2)", ITU-T Rec. G.993.2, Feb 2006.   [G.997.1]  ITU-T, "Physical layer management for digital subscriber              line (DSL) transceivers", ITU-T Rec. G.997.1, Sep 2005.   [RFC2225]  Laubach, M. and J. Halpern, "Classical IP and ARP over              ATM",RFC 2225, April 1998.   [RFC2364]  Gross, G., Kaycee, M., Lin, A., Malis, A., and J.              Stephens, "PPP Over AAL5",RFC 2364, July 1998.   [RFC2516]  Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D.,              and R. Wheeler, "A Method for Transmitting PPP Over              Ethernet (PPPoE)",RFC 2516, February 1999.   [RFC2881]  Mitton, D. and M. Beadles, "Network Access Server              Requirements Next Generation (NASREQNG) NAS Model",RFC 2881, July 2000.Ooghe, et al.                 Informational                    [Page 45]

RFC 5851                     ANCP Framework                     May 2010   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.              Thyagarajan, "Internet Group Management Protocol, Version              3",RFC 3376, October 2002.   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for              IP",RFC 4607, August 2006.   [TR-058]   Elias, M. and S. Ooghe, "Multi-Service Architecture &              Framework Requirements", Broadband Forum TR-058,              September 2003.   [TR-059]   Anschutz, T., "DSL Evolution - Architecture Requirements              for the Support of QoS-Enabled IP Services", Broadband              Forum TR-059, September 2003.   [TR-147]   Voigt, N., Ooghe, S., and M. Platnic, "Layer 2 Control              Mechanism For Broadband Multi-Service Architectures",              Broadband Forum TR-147, November 2008.Authors' Addresses   Sven Ooghe   Alcatel-Lucent   Copernicuslaan 50   B-2018 Antwerpen   Belgium   Phone: +32 3 240 42 26   EMail: sven.ooghe@alcatel-lucent.com   Norbert Voigt   Nokia Siemens Networks   Siemensallee 1   17489 Greifswald   Germany   Phone: +49 3834 555 771   EMail: norbert.voigt@nsn.comOoghe, et al.                 Informational                    [Page 46]

RFC 5851                     ANCP Framework                     May 2010   Michel Platnic   ECI Telecom   30 Hasivim Street   49517 Petakh Tikva   Israel   Phone: + 972 54 33 81 567   EMail: mplatnic@gmail.com   Thomas Haag   Deutsche Telekom   Heinrich-Hertz-Strasse 3-7   64295 Darmstadt   Germany   Phone: +49 6151 628 2088   EMail: haagt@telekom.de   Sanjay Wadhwa   Juniper Networks   10 Technology Park Drive   Westford, MA 01886   US   Phone:   EMail: swadhwa@juniper.netOoghe, et al.                 Informational                    [Page 47]