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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.


 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

Camarillo & Monrad Standards Track [Page 1] 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",
 and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
 [3] and indicate requirement levels for compliant SIP

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.

Camarillo & Monrad Standards Track [Page 2] 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:
    o=Laura 289083124 289083124 IN IP4
    t=0 0
    c=IN IP4
    a=group:SRF 1 2
    m=audio 30000 RTP/AVP 0
    m=video 30002 RTP/AVP 31
 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.

Camarillo & Monrad Standards Track [Page 3] RFC 3524 Mapping Media Streams to Resource Reservation Flows April 2003

    Session Number  DestAddress  ProtocolId  DstPort
          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 (
 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

7. Acknowledgements

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

Camarillo & Monrad Standards Track [Page 4] RFC 3524 Mapping Media Streams to Resource Reservation Flows April 2003

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
 Advanced Signalling Research Lab.
 FIN-02420 Jorvas
 Atle Monrad
 N-4898 Grimstad

Camarillo & Monrad Standards Track [Page 5] RFC 3524 Mapping Media Streams to Resource Reservation Flows April 2003

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
 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


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

Camarillo & Monrad Standards Track [Page 6]

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