Interworking SIP and Intelligent Network (IN) Applications
RFC 3976

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Network Working Group                                      V. K. Gurbani
Request for Comments: 3976                     Lucent Technologies, Inc.
Category: Informational                                       F. Haerens
                                                            Alcatel Bell
                                                              V. Rastogi
                                                      Wipro Technologies
                                                            January 2005

       Interworking SIP and Intelligent Network (IN) Applications

Status 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 (2005).

IESG Note

   This RFC is not a candidate for any level of Internet Standard.  The
   IETF disclaims any knowledge of the fitness of this RFC for any
   purpose, and in particular notes that the decision to publish is not
   based on IETF review for such things as security, congestion control,
   or inappropriate interaction with deployed protocols.  The RFC Editor
   has chosen to publish this document at its discretion.  Readers of
   this document should exercise caution in evaluating its value for
   implementation and deployment.  See RFC 3932 for more information.

Abstract

   Public Switched Telephone Network (PSTN) services such as 800-number
   routing (freephone), time-and-day routing, credit-card calling, and
   virtual private network (mapping a private network number into a
   public number) are realized by the Intelligent Network (IN).  This
   document addresses means to support existing IN services from Session
   Initiation Protocol (SIP) endpoints for an IP-host-to-phone call.
   The call request is originated on a SIP endpoint, but the services to
   the call are provided by the data and procedures resident in the
   PSTN/IN.  To provide IN services in a transparent manner to SIP
   endpoints, this document describes the mechanism for interworking SIP
   and Intelligent Network Application Part (INAP).

Gurbani, et al.              Informational                      [Page 1]
RFC 3976                 Interworking SIP & IN              January 2005

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Access to IN-Services from a SIP Entity. . . . . . . . . . . .  4
   3.  Additional SIN Considerations  . . . . . . . . . . . . . . . .  7
       3.1.  The Concept of State in SIP. . . . . . . . . . . . . . .  7
       3.2.  Relationship between SCP and a SIN-Enabled SIP entity. .  7
       3.3.  SIP REGISTER and IN services . . . . . . . . . . . . . .  8
       3.4.  Support of Announcements and Mid-Call Signaling. . . . .  8
   4.  The SIN Architecture . . . . . . . . . . . . . . . . . . . . .  8
       4.1.  Definitions. . . . . . . . . . . . . . . . . . . . . . .  8
       4.2.  IN Service Control Based on the SIN Approach . . . . . .  9
   5.  Mapping of the SIP State Machine to the IN State Model . . . . 10
       5.1.  Mapping SIP Protocol State Machine to O_BCSM . . . . . . 11
       5.2.  Mapping SIP Protocol State Machine to T_BCSM . . . . . . 16
   6.  Example Call Flows . . . . . . . . . . . . . . . . . . . . . . 20
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
       8.1.  Normative References . . . . . . . . . . . . . . . . . . 21
       8.2.  Informative References . . . . . . . . . . . . . . . . . 22
       Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . 23
       Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 24
       Author's Addresses . . . . . . . . . . . . . . . . . . . . . . 24
       Full Copyright Statement . . . . . . . . . . . . . . . . . . . 25

1.  Introduction

   PSTN services such as 800-number routing (freephone), time-and-day
   routing, credit-card calling, and virtual private network (mapping a
   private network number into a public number) are realized by the
   Intelligent Network.  IN is an architectural concept for the real-
   time execution of network services and customer applications [1].  IN
   is, by design, de-coupled from the call processing component of the
   PSTN.  In this document, we describe the means to leverage this
   decoupling to provide IN services from SIP-based entities.

   First, we will explain the basics of IN.  Figure 1 shows a simplified
   IN architecture, in which telephone switches called Service Switching
   Points (SSPs) are connected via a packet network called Signaling
   System No. 7 (SS7) to Service Control Points (SCPs), which are
   general purpose computers.  At certain points in a call, a switch can
   interrupt a call and request instructions from an SCP on how to
   proceed with the call.  The points at which a call can be interrupted