Best Current Practices for Third Party Call Control (3pcc) in the Session Initiation Protocol (SIP)
RFC 3725

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Network Working Group                                       J. Rosenberg
Request for Comments: 3725                                   dynamicsoft
BCP: 85                                                      J. Peterson
Category: Best Current Practice                                  Neustar
                                                          H. Schulzrinne
                                                     Columbia University
                                                            G. Camarillo
                                                                Ericsson
                                                              April 2004

       Best Current Practices for Third Party Call Control (3pcc)
                in the Session Initiation Protocol (SIP)

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   Third party call control refers to the ability of one entity to
   create a call in which communication is actually between other
   parties.  Third party call control is possible using the mechanisms
   specified within the Session Initiation Protocol (SIP).  However,
   there are several possible approaches, each with different benefits
   and drawbacks.  This document discusses best current practices for
   the usage of SIP for third party call control.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  3pcc Call Establishment  . . . . . . . . . . . . . . . . . .   3
       4.1.  Flow I . . . . . . . . . . . . . . . . . . . . . . . .   4
       4.2.  Flow II. . . . . . . . . . . . . . . . . . . . . . . .   5
       4.3.  Flow III . . . . . . . . . . . . . . . . . . . . . . .   7
       4.4.  Flow IV. . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Recommendations  . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Error Handling . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Continued Processing . . . . . . . . . . . . . . . . . . . .  11
   8.  3pcc and Early Media . . . . . . . . . . . . . . . . . . . .  13

Rosenberg, et al.        Best Current Practice                  [Page 1]
RFC 3725                        SIP 3pcc                      April 2004

   9.  Third Party Call Control and SDP Preconditions . . . . . . .  16
       9.1.  Controller Initiates . . . . . . . . . . . . . . . . .  16
       9.2.  Party A Initiates. . . . . . . . . . . . . . . . . . .  18
   10. Example Call Flows . . . . . . . . . . . . . . . . . . . . .  21
       10.1. Click-to-Dial. . . . . . . . . . . . . . . . . . . . .  21
       10.2. Mid-Call Announcement Capability . . . . . . . . . . .  23
   11. Implementation Recommendations . . . . . . . . . . . . . . .  25
   12. Security Considerations. . . . . . . . . . . . . . . . . . .  26
       12.1. Authorization and Authentication . . . . . . . . . . .  26
       12.2. End-to-End Encryption and Integrity. . . . . . . . . .  27
   13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  28
   14. References . . . . . . . . . . . . . . . . . . . . . . . . .  28
       14.1. Normative References . . . . . . . . . . . . . . . . .  28
       14.2. Informative References . . . . . . . . . . . . . . . .  29
   15. Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  30
   16. Full Copyright Statement . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   In the traditional telephony context, third party call control allows
   one entity (which we call the controller) to set up and manage a
   communications relationship between two or more other parties.  Third
   party call control (referred to as 3pcc) is often used for operator
   services (where an operator creates a call that connects two
   participants together) and conferencing.

   Similarly, many SIP services are possible through third party call
   control.  These include the traditional ones on the PSTN, but also
   new ones such as click-to-dial.  Click-to-dial allows a user to click
   on a web page when they wish to speak to a customer service
   representative.  The web server then creates a call between the user
   and a customer service representative.  The call can be between two
   phones, a phone and an IP host, or two IP hosts.

   Third party call control is possible using only the mechanisms
   specified within RFC 3261 [1].  Indeed, many different call flows are
   possible, each of which will work with SIP compliant user agents.
   However, there are benefits and drawbacks to each of these flows.
   The usage of third party call control also becomes more complex when
   aspects of the call utilize SIP extensions or optional features of