Internet Engineering Task Force                                   SIP WG
Internet Draft                                              G. Camarillo
                                                                Ericsson
                                                               A. Monrad
                                                                Ericsson
draft-ietf-mmusic-reservation-flows-00.txt
draft-ietf-mmusic-reservation-flows-01.txt
October 14, 29, 2002
Expires: April 2003

         Mapping of Media Streams to Resource Reservation Flows

STATUS OF THIS MEMO

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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Abstract

   This document defines an extension to the SDP grouping framework. It
   allows requesting that a group of media streams is mapped into a
   single resource reservation flow.

                           Table of Contents

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

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 and 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 SRF (Single Reservation Flow).

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 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]: SRF (Single Reservation Flow).

   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.

   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 the use of 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 a 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.

             Session Number  DestAddress  ProtocolId  DstPort
             ________________________________________________
                   1          192.0.0.1      UDP        any

   Table 1: Parameters needed 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.

4

             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 needs to register the following new "semantics" attribute for
   the SDP grouping framework [2]:

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

   It should be registered in the SDP parameters registry
   (http://www.iana.org/assignments/sdp-parameters) under Semantics for
   the "group" SDP Attribute.

5

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 RECOMMENDED that some
   kind of integrity protection is applied to SDP session descriptions.

6

7 Acknowledgements

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

8 Authors' Addresses

   Gonzalo Camarillo
   Ericsson
   Advanced Signalling Research Lab.
   FIN-02420 Jorvas
   Finland
   electronic mail:  Gonzalo.Camarillo@ericsson.com

   Atle Monrad
   Ericsson
   N-4898 Grimstad
   Norway
   electronic mail:  atle.monrad@ericsson.com

7

9 Normative References

   [1] M. Handley and V. Jacobson, "SDP: session description protocol,"
   RFC 2327, Internet Engineering Task Force, Apr. 1998.

   [2] G. Camarillo, J. Holler, G. Eriksson, and H. Schulzrinne,
   "Grouping of m lines in SDP," Internet Draft, Internet Engineering
   Task Force, Feb. 2002.  Work in progress.

   [3] S. Bradner, "Key words for use in RFCs to indicate requirement
   levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.

8

10 Informative References

   [4] J. Rosenberg, H. Schulzrinne,  et al.  , G. Camarillo, A. Johnston, J.
   Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: Session session
   initiation protocol," Internet Draft, RFC 3261, Internet Engineering Task Force, Feb. June
   2002.  Work in progress.

   [5] R. Braden, L. Zhang, S. Berson, S. Herzog, and S. Jamin, "Resource ReSerVation protocol (RSVP) -- version 1 functional
   specification," RFC 2205, Internet Engineering Task Force, Sept.
   1997.

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