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Network Working Group                                L. Slutsman, EditorRequest for Comments: 3136                                     AT&T LabsCategory: Informational                                      I. Faynberg                                                                   H. Lu                                                             M. Weissman                                                     Lucent Technologies                                                               June 2001The SPIRITS ArchitectureStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2001).  All Rights Reserved.Abstract   This document describes the architecture for supporting SPIRITS   services, which are those originating in the PSTN (Public Switched   Telephone Network)and necessitating the interactions between the PSTN   and the Internet.  (Internet Call Waiting, Internet Caller-ID   Delivery, and Internet Call Forwarding are examples of SPIRIT   services.)  Specifically, it defines the components constituting the   architecture and the interfaces between the components.1. Introduction   This document describes the architecture for supporting SPIRITS   services, which are those originating in the PSTN (Public Switched   Telephone Network) and necessitating the interactions between the   PSTN and the Internet.  (Internet Call Waiting, Internet Caller-ID   Delivery, and Internet Call Forwarding are examples of SPIRIT   services.)  Specifically, it defines the components constituting the   architecture and the interfaces between the components.   The rest of the document is organized as follows:   +Section 2 describes example SPIRITS services from the end-user      point of view;   +Section 3 describes the SPIRITS architecture;Slutsman, et al.             Informational                      [Page 1]

RFC 3136                The SPIRITS Architecture               June 2001   +Section 4 contains security considerations;   +Section 5 contains acknowledgments;   +Section 6 contains references; and   +  Appendix contains the figure.2. Brief Description of Example SPIRITS Services   To illustrate the motivation for the overall SPIRIT architecture,   this section provides a brief description of the example SPIRITS   services:   +  Internet Call Waiting (ICW),   +  Internet Caller-ID Delivery, and   +  Internet Call Forwarding.   These services are considered from the end-user point of view under   the assumptions below:   +  Service subscription (or cancellation) is a separate process and      may be done over the telephone, via postal mail, or over the Web.   +  The subscriber's IP host (e.g., a PC) is loaded with the necessary      software [including a Personal Identification Number (PIN) and the      IP addresses of the SPIRITS servers] for realizing the SPIRITS      services.  The software may be sent by postal mail or downloaded      from the Web.   +  The subscriber activates a SPIRITS service by an act of service      session registration, which can take place anytime after he (or      she) is connected to the Internet.  The subscriber may specify the      life span of the session.  As soon as the session ends, the      SPIRITS service is deactivated.  Naturally, the subscriber should      also be able to deactivate a SPIRITS service anytime during the      service session.   For certain services (such as ICW or Caller-ID Delivery) the   assumption is that the service subscriber has a single telephone line   and a PC, which is connected to the Internet via this telephone.   (Only under this assumption these services make sense.)   Nevertheless, in other services (such as Web-based Call Center, in   which a call center assistant could re-direct or reject a call   presented in a pop-up window) this assumption may be unnecessary or   even inapplicable.Slutsman, et al.             Informational                      [Page 2]

RFC 3136                The SPIRITS Architecture               June 20012.1 Internet Call Waiting (ICW)   The Internet call waiting service enables a subscriber engaged in an   Internet dial-up session to      o  be notified of an incoming call to the very same telephone line         that is being used for the Internet connection;      o  specify the desirable treatment of the call; and      o  have the call handled as specified.   The details of the ICW service lie in the ways that a waiting call   can be treated [1].  Typical ways for handling a call include:   +  Accept the incoming call over the PSTN by terminating the Internet      connection.  (As switching cannot be done immediately, the caller      may hear an opening announcement followed by the "ringing" tone.)   +  Forward the incoming call to another telephone number.  The      subscriber will remain connected to the Internet, while the caller      will hear an announcement indicating the call is being forwarded      and eventually be connected to the new destination number.   +  Accept the incoming call by voice over IP.  The subscriber will      answer the incoming call via the already established Internet      connection.  (The proposed SPIRITS architecture, however, does not      reflect this feature.)   +  Redirect the incoming call to voice mail.  The subscriber will      remain connected to the Internet, while the caller will hear an      announcement inviting him (or her) to leave a message.   +  Play a pre-recorded message to the calling party and disconnect      the call.  The subscriber will remain connected to the Internet.   +  Reject the incoming call.  The subscriber will remain connected to      the Internet, while the caller will hear an announcement rejecting      the call.   The subscriber may specify the call treatment on the fly when   notified of an incoming call.  Alternatively, the subscriber may   specify a priori a general treatment for all calls (e.g., re-directed   to voice mail) or call treatments tailored to the origination   numbers.  As a result, when a call comes in, the subscriber won't be   presented the call but can examine afterwards the treatment and   outcome of the call from the log that is kept for all the callsSlutsman, et al.             Informational                      [Page 3]

RFC 3136                The SPIRITS Architecture               June 2001   processed during the ICW service.  Typical information recorded in   the log includes the incoming call date and time, calling party   number, calling party name, and call disposition.2.2 Internet Caller-ID Delivery   This service allows the subscriber to see the caller's number or name   or both while being connected to the Internet.  If the subscriber has   only one telephone line and is using the very line for the Internet   connection, the service is a subset of the ICW service and follows   the relevant description inSection 2.1.  Otherwise, the subscriber's   IP host serves as an auxiliary device of the telephone to which the   call is first sent.2.3 Internet Call Forwarding   The Internet call forwarding service allows a service subscriber to   forward an incoming call to another telephone number while being   connected to the Internet.  If the subscriber has only one telephone   line and is using the very line for the Internet connection, the   service is a subset of the ICW service and follows the relevant   description inSection 2.1.  Otherwise, the subscriber's IP host   serves as an auxiliary device of the telephone to which the call is   first sent.3. SPIRITS Architecture   Figure 1 of the Appendix depicts the SPIRITS architecture, which   includes the following entities:   1. Service Control Function (SCF) [2], which executes service logic,      interacts with the entities in the IP domain (e.g., the SPIRITS      Gateway and PINT Server) through the SPIRITS Client, and instructs      the switches on how to complete a call.  Physically, the SCF may      be located in either stand-alone general-purpose computers called      Service Control Points (SCPs) or specialized pieces of equipment      called Service Nodes (SNs) [2].   2. Service Switching Function (SSF) [2], which normally resides in a      switch and is responsible for the recognition of Intelligent      Network (IN) triggers and interactions with the SCF.   3. SPIRITS Client, which is responsible for receiving PSTN requests      from the SCF as well as sending responses back.  It may be co-      located with the SCF.  If not, it communicates with the SCF over      the D interface.Slutsman, et al.             Informational                      [Page 4]

RFC 3136                The SPIRITS Architecture               June 2001   4. PINT Server, which receives PINT requests from the PINT Client and      relays them to the PSTN for execution over the E interface.   5. SPIRITS Gateway, which is co-located with the PINT Server or PINT      Gateway (or both when they are co-located as assumed here for      simplicity) and serves as an intermediary between the SPIRITS      Server and SPRITS Client via the B and C interfaces, respectively.   6. PINT Client, which resides in the subscriber's IP host and is      responsible for initiating PINT requests, which are sent to the      PINT server over the A interface.   7. SPIRITS Server, which terminates PSTN requests and is responsible      for all interactions (e.g., incoming call notification and      relaying the call treatment) between the subscriber and the      SPIRITS Gateway.   The rest of the Section describes the interfaces between the entities   in detail.3.1 Interface A   This interface is used for sending PINT requests to PINT Server.  Its   principal use is for service session registration and as a result   activation of a SPIRITS service (seeSection 2).  In addition, this   interface may be used for service subscription.3.2 Interface B   This interface serves two main purposes: 1) to notify the subscriber   of incoming calls together with the calling number and name, if   available; and 2) to send to the SPRITS Gateway the subscriber's   choice of call disposition specified on the fly.3.3 Interface C   This interface is used for communications between the SPIRITS Client   and SPIRITS Gateway.  The SPIRITS Gateway may in turn communicate   with the SPIRITS Server, or may act as a virtual server, terminating   the requests without sending them down to the SPIRITS Server.3.4 Interface D   This interface is for communications between the SPIRITS Client and   the SCF.  Specifically, from the SCF to the SPIRITS Client, the   parameters associated with the applicable IN triggers are sent.  From   the SPIRITS Client to SCF, the subscriber's call disposition is sent.Slutsman, et al.             Informational                      [Page 5]

RFC 3136                The SPIRITS Architecture               June 2001   The SCF "transforms" the user's disposition into appropriate actions,   such as playing an announcement to the caller, and resuming the   suspended call processing in the SSP.3.5 Interface E   This interface is for sending PINT requests to the SCF for execution.4. Security Considerations   As Figure 1 demonstrates, there are two distinct communications   interfaces, B and C.  The B interface is, in general, across the   public Internet and is thus most vulnerable to security attacks   resulting in theft or denial of service.  The C interface, on the   other hand is likely to be implemented across a service provider's   intranet, where the security measures should be applied at the   discretion of the service provider.  Even then, because at least one   IP host (the PINT gateway) is connected to the Internet, special   measures (e.g., installation of firewalls, although this particular   measure alone may be insufficient) need to be taken to protect the   interface C and the rest of the network from security attacks.   The assumption that the PINT Client and SPIRITS server are co-   located, dictates that the security considerations for the A and B   interfaces are exactly the same.  Detailed security requirements and   solutions for interface A (and, consequently, B) can be found inRFC2848 [3].  In addition, security requirements are listed in the   companion SPIRITS Protocol Requirements RFC.5. Acknowledgments   We would like to thank Alec Brusilovsky, Jorgen Bjorkner, Scott   Bradner, Jim Buller, Lawrence Conroy, Jorge Gato, Dave Hewins, Naoto   Makinae, and Dave Shrader for their comments and input.Slutsman, et al.             Informational                      [Page 6]

RFC 3136                The SPIRITS Architecture               June 20016. References   [1] Lu, H., Editor, Faynberg, I., Voelker, J., Weissman, M., Zhang,       W., Rhim, S., Hwang, J., Ago, S., Moeenuddin, S., Hadvani, S.,       Nyckelgard, S., Yoakum, J. and L. Robart, "Pre-SPIRITS       Implementations of PSTN-Initiated Services",RFC 2995, November       2000.   [2] Faynberg, I., L. Gabuzda, M. Kaplan, and N.Shah, "The Intelligent       Network Standards: Their Application to Services", McGraw-Hill,       1997.   [3] Petrack, S. and L. Conroy, "The PINT Service Protocol: Extensions       to SIP and SDP for IP Access to Telephone Call Services",RFC2848, June 2000.Slutsman, et al.             Informational                      [Page 7]

RFC 3136                The SPIRITS Architecture               June 2001Appendix                                       ......................       +----------------+              .                    .       | +------------+ |              .   +------------+   .       | |            | |       A      .   |            |   .       | | PINT Client|********************|PINT Server/|********       | |            | |              .      Gateway   |       *       | +------------+ |              .   +------------+   .   *       |                |              .                    .   *       |  Subscriber's  |              .                    .   *       |                |              .                    .   *       |  IP Host       |              .                    .   *       |                |              .   +------------+   .   *       | +------------+ |              .   | SPIRITS    |   .   *       | | SPIRITS    | |       B      .   | Gateway    |   .   *       | | Server     |********************|            |   .   * E       | |            | |              .   +------------+   .   *       | +------------+ |              .          *         .   *       +----------------+              .          *         .   *                                       ...........*..........   *            //-------\\                           *             *         ///           \\\                        *             *        |   Subscriber's  |                       *  C          *        |   Telephone     |                       *             *         \\\           ///                        *             *           \\ -------//                           *             *                *                                 *             *                *                                 *             *      ++++++++++++++++++++++++++  PSTN   ++++++++++++++++++++++++++                *                                 *             *                *                                 *             *                *                          +------------------+ *                * Line                     | SPIRITS Client   | *                *                          |                  | *       +--------------------+          +---+----- D  ---------+-*+       |                    | INAP/SS7 |                         |       |Service Switching   ************Service Control Function |       |    Function        |          |                         |       |                    |          +-------------------------+       |                    |       |                    |       +--------------------+                     Figure 1:  SPIRITS ArchitectureSlutsman, et al.             Informational                      [Page 8]

RFC 3136                The SPIRITS Architecture               June 2001Authors' Addresses   Igor Faynberg   Lucent Technologies   Room 4D-601A   101 Crawfords Corner Road   Holmdel, NJ 07733-3030 US   Phone: +1 732 949 0137   EMail: faynberg@lucent.com   Hui-Lan Lu   Lucent Technologies Room 4C-607A   101 Crawfords Corner Road   Holmdel, NJ 07733-3030 US   Phone: +1 732 949 0321   EMail: huilanlu@lucent.com   Mark Weissman   Lucent Technologies   Room NE406B   200 Lucent Lane   Cary, NC 27511   Phone: +1 919 463 3258   EMail: maw1@lucent.com   Lev Slutsman   AT&T Labs   Room D5-3D26   200 Laurel Avenue   Middletown, NJ 07748   Phone: 732-420-3756   EMail: lslutsman@att.comSlutsman, et al.             Informational                      [Page 9]

RFC 3136                The SPIRITS Architecture               June 2001Full Copyright Statement   Copyright (C) The Internet Society (2001).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Slutsman, et al.             Informational                     [Page 10]