Session Description Protocol (SDP) Extension for Setting Audio and Video Media Streams over Circuit-Switched Bearers in the Public Switched Telephone Network (PSTN)
RFC 7195

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Internet Engineering Task Force (IETF)                  M. Garcia-Martin
Request for Comments: 7195                                      Ericsson
Category: Standards Track                                S. Veikkolainen
ISSN: 2070-1721                                                    Nokia
                                                                May 2014

            Session Description Protocol (SDP) Extension for
 Setting Audio and Video Media Streams over Circuit-Switched Bearers in
              the Public Switched Telephone Network (PSTN)

Abstract

   This memo describes use cases, requirements, and protocol extensions
   for using the Session Description Protocol (SDP) offer/answer model
   for establishing audio and video media streams over circuit-switched
   bearers in the Public Switched Telephone Network (PSTN).

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7195.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's 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.

Garcia-Martin & Veikkolainen Standards Track                    [Page 1]
RFC 7195          PSTN Circuit-Switched Bearers in SDP          May 2014

Table of Contents

   1. Introduction ....................................................3
   2. Conventions Used in This Document ...............................4
   3. Requirements ....................................................5
   4. Overview of Operation ...........................................5
      4.1. Example Call Flow ..........................................6
   5. Protocol Description ............................................7
      5.1. Level of Compliance ........................................7
      5.2. Extensions to SDP ..........................................7
           5.2.1. Connection Data .....................................7
           5.2.2. Media Descriptions ..................................9
           5.2.3. Correlating the PSTN Circuit-Switched
                  Bearer with SDP ....................................10
                  5.2.3.1. The "cs-correlation" Attribute ............11
                  5.2.3.2. Caller ID Correlation Mechanism ...........12
                  5.2.3.3. User-User Information Element
                           Correlation Mechanism .....................13
                  5.2.3.4. DTMF Correlation Mechanism ................14
                  5.2.3.5. External Correlation Mechanism ............15
                  5.2.3.6. Extensions to Correlation Mechanisms ......16
      5.3. Negotiating the Correlation Mechanisms ....................17
           5.3.1. Determining the Direction of the
                  Circuit-Switched Bearer Setup ......................17
           5.3.2. Populating the "cs-correlation" Attribute ..........18
           5.3.3. Considerations for Correlations ....................18
      5.4. Considerations for Usage of Existing SDP ..................19
           5.4.1. Originator of the Session ..........................19
           5.4.2. Contact Information ................................20
      5.5. Considerations for Usage of Third Party Call
           Control (3PCC) ............................................20
      5.6. Offer/Answer Mode Extensions ..............................20
           5.6.1. Generating the Initial Offer .......................21
           5.6.2. Generating the Answer ..............................23
           5.6.3. Offerer Processing the Answer ......................26
           5.6.4. Modifying the Session ..............................27
      5.7. Formal Syntax .............................................28
   6. Examples .......................................................30
      6.1. Single PSTN Audio Stream ..................................30
      6.2. Advanced SDP Example: Circuit-Switched Audio and
           Video Streams .............................................32