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Versions: 00 01 draft-ietf-avt-rtcp-port-for-ssm

AVT                                                             A. Begen
Internet-Draft                                                     Cisco
Updates:  5760 (if approved)                               April 3, 2010
Intended status:  Standards Track
Expires:  October 5, 2010


        RTP Control Protocol (RTCP) Port for Multicast Sessions
                  draft-begen-avt-rtcp-port-for-ssm-01

Abstract

   The Session Description Protocol (SDP) has an attribute that allows
   RTP applications to specify an address and a port associated with the
   RTP Control Protocol (RTCP) traffic.  In RTP-based source-specific
   multicast (SSM) sessions, the same attribute is used to designate the
   address and the RTCP port of the Feedback Target in the SDP
   description.  However, the RTCP port associated with the SSM session
   itself cannot be specified by the same attribute to avoid ambiguity,
   and thus, is required to be derived from the "m=" line of the media
   description.  Similarly, in any-source multicast (ASM) sessions,
   there is no explicit way to specify the destination RTCP port.
   Deriving the RTCP port from the "m=" line imposes an unnecessary
   restriction.  This document removes this restriction by introducing a
   new SDP attribute.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 5, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . . . 3
   3.  The 'multicast-rtcp' Attribute  . . . . . . . . . . . . . . . . 3
     3.1.  SDP Example . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
     5.1.  Registration of SDP Attributes  . . . . . . . . . . . . . . 6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7


























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1.  Introduction

   The Session Description Protocol (SDP) [RFC4566] has an attribute
   that allows RTP applications [RFC3550] to specify an address and a
   port associated with the RTP Control Protocol (RTCP) traffic
   [RFC3605].  This attribute is called 'rtcp'.

   Now consider a network where one or more media senders send RTP
   packets to a distribution source, which then multicasts these RTP
   packets to multicast receivers using a source-specific multicast
   (SSM) arrangement [RFC5760].  The distribution source also multicasts
   the forward RTCP traffic (i.e., RTCP Sender Reports and Receiver
   Reports or their summaries) to the receivers in the same SSM session.

   In RTP-based SSM sessions, the 'rtcp' attribute is used to designate
   the address and the RTCP port of the Feedback Target in the SDP
   description [RFC5760].  However, the RTCP port associated with the
   SSM session itself cannot be specified by the same attribute since it
   could potentially cause ambiguity.  Thus, the multicast RTCP port is
   required to be derived from the "m=" line of the media description
   (See Section 10.2 of [RFC5760]) by following the +1 rule.  However,
   [RFC3550] lifted the requirement for the +1 rule since it imposed an
   unnecessary restriction on RTCP port selection.

   In this specification, we introduce a new SDP attribute to remove
   this restriction.  The new attribute allows the multicast sender to
   use its desired port in the RTCP session.  Similar to SSM sessions,
   in any-source multicast (ASM) sessions, there is no explicit way to
   specify the destination RTCP port, either, and the new SDP attribute
   is equally applicable in ASM sessions as well.

   If approved, this document intends to update [RFC5760].


2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


3.  The 'multicast-rtcp' Attribute

   In RTP-based SSM sessions, the distribution source may use different
   multicast RTP and RTCP ports to send the RTP and RTCP packets,
   respectively.  Alternatively, the distribution source may use RTP/
   RTCP port muxing [I-D.ietf-avt-rtp-and-rtcp-mux], in which case the
   RTP and RTCP packets are sent to the same destination port in the SSM



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   session.  For the former case, this document defines a new SDP
   attribute, called 'multicast-rtcp'.  By using this attribute, the
   distribution source MAY use a desired port for the SSM RTCP session.

   The formal description of the 'multicast-rtcp' attribute is defined
   by the following ABNF [RFC5234] syntax:


               rtcp-attribute = "a=multicast-rtcp:" port CRLF

         Figure 1: ABNF syntax for the 'multicast-rtcp' attribute

   Here, the 'port' token is defined as specified in Section 9 of
   [RFC4566].

   The 'multicast-rtcp' attribute MAY be used as a media-level
   attribute; it MUST NOT be used as a session-level attribute.

3.1.  SDP Example

   In the SDP description shown in Figure 2, a source stream is
   multicast from a distribution source (with a source IP address of
   198.51.100.1) to the multicast destination address of 233.252.0.2 and
   port 41000.  The forward RTCP traffic is multicast in the same
   multicast group but to port 42000 as specified by the "a=multicast-
   rtcp:42000" line.  A feedback target with an address of 192.0.2.1 and
   port of 43000 is specified by the 'rtcp' attribute.
























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           v=0
           o=ali 1122334455 1122334466 IN IP4 ssm.example.com
           s='multicast-rtcp' Example
           t=0 0
           a=rtcp-unicast:rsi
           m=video 41000 RTP/AVPF 98
           i=Multicast Stream
           c=IN IP4 233.252.0.2/255
           a=source-filter:incl IN IP4 233.252.0.2 198.51.100.1
           a=rtpmap:98 MP2T/90000
           a=multicast-rtcp:42000
           a=rtcp:43000 IN IP4 192.0.2.1
           a=mid:1

       Figure 2: Example SDP showing the use of the 'multicast-rtcp'
                                 attribute


4.  Security Considerations

   The 'multicast-rtcp' attribute is not believed to introduce any
   significant security risk to multimedia applications.  A malevolent
   third party could use this attribute to redirect the RTCP traffic,
   but this requires intercepting and rewriting the packets carrying the
   SDP description; and if an interceptor can do that, many more attacks
   are possible, including a wholesale change of the addresses and port
   numbers at which the media will be sent.  Therefore, as usual
   adequate security measures are RECOMMENDED to ensure the integrity
   and authenticity of the SDP descriptions so that transport addresses
   of the media senders, distribution sources, feedback targets as well
   as other session-specific information can be authenticated.


5.  IANA Considerations

   The following contact information shall be used for all registrations
   in this document:

   Ali Begen
   abegen@cisco.com

   170 West Tasman Drive
   San Jose, CA 95134 USA








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5.1.  Registration of SDP Attributes

   This document registers a new attribute name in SDP.


        SDP Attribute ("att-field"):
        Attribute name:     multicast-rtcp
        Long form:          Port in the multicast RTCP session
        Type of name:       att-field
        Type of attribute:  Media level
        Subject to charset: No
        Purpose:            See this document
        Reference:          This document
        Values:             See this document


6.  Acknowledgments

   Thanks to Colin Perkins amd Magnus Westerlund for suggesting the name
   for the 'multicast-rtcp' attribute.  Some parts of this specification
   are based on [RFC3605] and [RFC5760].  So, thanks to those who
   contributed to those specifications, too.


7.  References

7.1.  Normative References

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC3605]  Huitema, C., "Real Time Control Protocol (RTCP) attribute
              in Session Description Protocol (SDP)", RFC 3605,
              October 2003.

   [RFC5760]  Ott, J., Chesterfield, J., and E. Schooler, "RTP Control
              Protocol (RTCP) Extensions for Single-Source Multicast
              Sessions with Unicast Feedback", RFC 5760, February 2010.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.



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7.2.  Informative References

   [I-D.ietf-avt-rtp-and-rtcp-mux]
              Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
              Control Packets on a Single Port",
              draft-ietf-avt-rtp-and-rtcp-mux-07 (work in progress),
              August 2007.


Author's Address

   Ali Begen
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email:  abegen@cisco.com

































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