The Session Description Protocol (SDP) Alternate Connectivity (ALTC) Attribute
RFC 6947

Independent Submission                                      M. Boucadair
Request for Comments: 6947                                France Telecom
Category: Informational                                        H. Kaplan
ISSN: 2070-1721                                              Acme Packet
                                                               R. Gilman
                                                             Independent
                                                         S. Veikkolainen
                                                                   Nokia
                                                                May 2013

                 The Session Description Protocol (SDP)
                Alternate Connectivity (ALTC) Attribute

Abstract

   This document proposes a mechanism that allows the same SDP offer to
   carry multiple IP addresses of different address families (e.g., IPv4
   and IPv6).  The proposed attribute, the "altc" attribute, solves the
   backward-compatibility problem that plagued Alternative Network
   Address Types (ANAT) due to their syntax.

   The proposed solution is applicable to scenarios where connectivity
   checks are not required.  If connectivity checks are required,
   Interactive Connectivity Establishment (ICE), as specified in RFC
   5245, provides such a solution.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see 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/rfc6947.

Boucadair, et al.             Informational                     [Page 1]
RFC 6947          SDP Alternate Connectivity Attribute          May 2013

Copyright Notice

   Copyright (c) 2013 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overall Context . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Purpose . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.4.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Overview of the ALTC Mechanism  . . . . . . . . . . . . . . .   6
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Rationale for the Chosen Syntax . . . . . . . . . . . . .   7
   4.  Alternate Connectivity Attribute  . . . . . . . . . . . . . .   8
     4.1.  ALTC Syntax . . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Usage and Interaction . . . . . . . . . . . . . . . . . .   9
       4.2.1.  Usage . . . . . . . . . . . . . . . . . . . . . . . .   9
       4.2.2.  Usage of ALTC in an SDP Answer  . . . . . . . . . . .  11
       4.2.3.  Interaction with ICE  . . . . . . . . . . . . . . . .  11
       4.2.4.  Interaction with SDP-Cap-Neg  . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  ALTC Use Cases . . . . . . . . . . . . . . . . . . .  15
     A.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .  15
     A.2.  Multicast Use Case  . . . . . . . . . . . . . . . . . . .  16
     A.3.  Introducing IPv6 into SIP-Based Architectures . . . . . .  17
       A.3.1.  Avoiding Crossing CGN Devices . . . . . . . . . . . .  17
       A.3.2.  Basic Scenario for IPv6 SIP Service Delivery  . . . .  17
       A.3.3.  Avoiding IPv4/IPv6 Interworking . . . . . . . . . . .  18
       A.3.4.  DBE Bypass Procedure  . . . . . . . . . . . . . . . .  20