Network Working Group                                       G. Camarillo
Request for Comments: 3524                                     A. Monrad
Category: Standards Track                                       Ericsson
                                                             April 2003


        Mapping of Media Streams to Resource Reservation Flows

Status of this Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

  This document defines an extension to the Session Description
  Protocol (SDP) grouping framework.  It allows requesting a group of
  media streams to be mapped into a single resource reservation flow.
  The SDP syntax needed is defined, as well as a new "semantics"
  attribute called Single Reservation Flow (SRF).

Table of Contents

  1.  Introduction ........................................    2
      1.1  Terminology ....................................    2
  2.  SRF Semantics .......................................    2
  3.  Applicability Statement .............................    3
  4.  Examples ............................................    3
  5.  IANA Considerations .................................    4
  6.  Security Considerations .............................    4
  7.  Acknowledgements ....................................    4
  8.  Normative References ................................    5
  9.  Informative References ..............................    5
  10. Authors' Addresses ..................................    5
  11. Full Copyright Statement ............................    6









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RFC 3524  Mapping Media Streams to Resource Reservation Flows April 2003


1.  Introduction

  Resource reservation protocols assign network resources to particular
  flows of IP packets.  When a router receives an IP packet, it applies
  a filter in order to map the packet to the flow it belongs.  The
  router provides the IP packet with the Quality of Service (QoS)
  corresponding to its flow.  Routers typically use the source and the
  destination IP addresses and port numbers to filter packets.

  Multimedia sessions typically contain multiple media streams (e.g. an
  audio stream and a video stream).  In order to provide QoS for a
  multimedia session it is necessary to map all the media streams to
  resource reservation flows.  This mapping can be performed in
  different ways.  Two possible ways are to map all the media streams
  to a single resource reservation flow or to map every single media
  stream to a different resource reservation flow.  Some applications
  require that the former type of mapping is performed while other
  applications require the latter.  It is even possible that a mixture
  of both mappings is required for a particular media session.  For
  instance, a multimedia session with three media streams might require
  that two of them are mapped into a single reservation flow while the
  third media stream uses a second reservation flow.

  This document defines the SDP [1] syntax needed to express how media
  streams need to be mapped into reservation flows.  For this purpose,
  we use the SDP grouping framework [2] and define a new "semantics"
  attribute called Single Reservation Flow (SRF).

1.1 Terminology

  In this document, the key words "MUST", "MUST NOT", "REQUIRED",
  "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
  and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
  [3] and indicate requirement levels for compliant SIP
  implementations.

2.  SRF Semantics

  We define a new "semantics" attribute within the SDP grouping
  framework [2]: Single Reservation Flow (SRF).

  Media lines grouped using SRF semantics SHOULD be mapped into the
  same resource reservation flow.  Media lines that do not belong to a
  particular SRF group SHOULD NOT be mapped into the reservation flow
  used for that SRF group.






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RFC 3524  Mapping Media Streams to Resource Reservation Flows April 2003


  Note that an SRF group MAY consist of a single media line.  In that
  case, following the definition above, that media line will be mapped
  into one reservation flow.  That reservation flow will carry traffic
  from that media line, and from no other media lines.

3. Applicability Statement

  The way resource reservation works in some scenarios makes it
  unnecessary to use the mechanism described in this document.  Some
  resource reservation protocols allow the entity generating the SDP
  session description to allocate resources in both directions (i.e.,
  sendrecv) for the session.  In this case, the generator of the
  session description can chose any particular mapping of media flows
  and reservation flows.

  The mechanism described in this document is useful when the remote
  party needs to be involved in the resource reservation.

4.  Examples

  For this example, we have chosen to use SIP [4] to transport SDP
  sessions and RSVP [5] to establish reservation flows.  However, other
  protocols or mechanisms could be used instead without affecting the
  SDP syntax.

  A user agent receives a SIP INVITE with the SDP below:

     v=0
     o=Laura 289083124 289083124 IN IP4 one.example.com
     t=0 0
     c=IN IP4 192.0.0.1
     a=group:SRF 1 2
     m=audio 30000 RTP/AVP 0
     a=mid:1
     m=video 30002 RTP/AVP 31
     a=mid:2

  This user agent uses RSVP to perform resource reservation.  Since
  both media streams are part of an SRF group, the user agent will
  establish a single RSVP session.  An RSVP session is defined by the
  triple:  (DestAddress, ProtocolId[, DstPort]).  Table 1 shows the
  parameters used to establish the RSVP session.

  If the same user agent received an SDP session description with the
  same media streams but without the group line, it would be free to
  map the two media streams into two different RSVP sessions.





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     Session Number  DestAddress  ProtocolId  DstPort
     ________________________________________________
           1          192.0.0.1      UDP        any

     Table 1: Parameters needed to establish the RSVP session

5.  IANA Considerations

  IANA has registered the following new "semantics" attribute for the
  SDP grouping framework [2].  It has been registered in the SDP
  parameters registry (http://www.iana.org/assignments/sdp-parameters)
  under Semantics for the "group" SDP Attribute:

  Semantics                  Token      Reference
  -------------------        -----      ---------
  Single Reservation flow     SRF       [RFC3524]

6.  Security Considerations

  An attacker adding group lines using the SRF semantics to an SDP
  session description could force a user agent to establish a larger or
  a smaller number of resource reservation flows than needed.  This
  could consume extra resources in the end-point or degrade the quality
  of service for a particular session.  It is thus STRONGLY RECOMMENDED
  that integrity protection be applied to the SDP session descriptions.
  For session descriptions carried in SIP, S/MIME is the natural choice
  to provide such end-to-end integrity protection, as described in RFC
  3261 [4]. Other applications MAY use a different form of integrity
  protection.

7.  Acknowledgements

  Jonathan Rosenberg provided useful comments about the applicability
  of the mechanism described in this document.

















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8.  Normative References

  [1]  Handley, M. and V. Jacobson, "SDP: Session Description
       Protocol", RFC 2327, April 1998.

  [2]  Camarillo, G., Eriksson, G., Holler, J. and H. Schulzrinne,
       "Grouping of Media Lines in the Session Description Protocol
       (SDP)", December 2002.

  [3]  Bradner, S., "Key words for use in RFCs to indicate requirement
       levels", BCP 14, RFC 2119, March 1997.

9.  Informative References

  [4]  Rosenberg, J., Schulzrinne, H., Camarillo,  G., Johnston, A.,
       Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
       Session Initiation Protocol", RFC 3261, June 2002.

  [5]  Braden, R., Zhang, L., Berson, S., Herzog, S. and S. Jamin,
       "Resource ReSerVation protocol (RSVP) -- Version 1 Functional
       Specification", RFC 2205, September 1997.

10.  Authors' Addresses

  Gonzalo Camarillo
  Ericsson
  Advanced Signalling Research Lab.
  FIN-02420 Jorvas
  Finland

  EMail:  [email protected]


  Atle Monrad
  Ericsson
  N-4898 Grimstad
  Norway

  EMail:  [email protected]












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11.  Full Copyright Statement

  Copyright (C) The Internet Society (2003).  All Rights Reserved.

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published
  and distributed, in whole or in part, without restriction of any
  kind, provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be
  followed, or as required to translate it into languages other than
  English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.



















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