One document matched: draft-begen-avt-rtcp-port-for-ssm-00.txt

AVT                                                             A. Begen
Internet-Draft                                                     Cisco
Updates:  5760 (if approved)                              March 22, 2010
Intended status:  Standards Track
Expires:  September 23, 2010


RTP Control Protocol (RTCP) Port for Source-Specific Multicast Sessions
                  draft-begen-avt-rtcp-port-for-ssm-00

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.  This imposes unnecessary restrictions on RTCP port
   selection in the SSM session.  To remove this restriction, this
   document introduces a new SDP attribute.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 23, 2010.

Copyright Notice



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   Copyright (c) 2010 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
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   described in the BSD License.


Table of Contents

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























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1.  Introduction

   The Session Description Protocol (SDP) [RFC4566] has an attribute
   that allows RTP applications 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.
   However, Section 10.2 of [RFC5760] does not specify how this
   derivation works.  Furthermore, this approach imposes unnecessary
   restrictions on RTCP port selection.

   In this specification, we introduce a new SDP attribute to remove
   this restriction.  The new attribute allows the distribution source
   to use its desired port in the SSM RTCP session.

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

   Editor's note:  Should we mandate the use of the new attribute or
   shall we keep it optional?


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 'ssm-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 'ssm-rtcp'.  By using this attribute, the
   distribution source MAY use a desired port for the SSM RTCP session.

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


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

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

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

   The 'ssm-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=ssm-
   rtcp:42000" line.  A feedback target with an address of 192.0.2.1 and
   port of 43000 is specified by the 'rtcp' attribute.

           v=0
           o=ali 1122334455 1122334466 IN IP4 ssm.example.com
           s='ssm-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=ssm-rtcp:42000
           a=rtcp:43000 IN IP4 192.0.2.1
           a=mid:1

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








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4.  Security Considerations

   The 'ssm-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

5.1.  Registration of SDP Attributes

   This document registers a new attribute name in SDP.


        SDP Attribute ("att-field"):
        Attribute name:     ssm-rtcp
        Long form:          Port in the SSM 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 for suggesting the name for the 'ssm-rtcp'
   attribute.  Some parts of this specification are based on [RFC3605]
   and [RFC5760].  So, thanks to those who contributed to those
   specifications, too.



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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.

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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