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Network Working Group                                       G. CamarilloRequest for Comments: 3524                                     A. MonradCategory: Standards Track                                       Ericsson                                                              April 2003Mapping of Media Streams to Resource Reservation FlowsStatus 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 Contents1.  Introduction ........................................21.1  Terminology ....................................22.  SRF Semantics .......................................23.  Applicability Statement .............................34.  Examples ............................................35.  IANA Considerations .................................46.  Security Considerations .............................47.  Acknowledgements ....................................48.  Normative References ................................59.  Informative References ..............................510. Authors' Addresses ..................................511. Full Copyright Statement ............................6Camarillo & Monrad          Standards Track                     [Page 1]

RFC 3524  Mapping Media Streams to Resource Reservation Flows April 20031.  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 inBCP 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.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:      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.Camarillo & Monrad          Standards Track                     [Page 3]

RFC 3524  Mapping Media Streams to Resource Reservation Flows April 2003      Session Number  DestAddress  ProtocolId  DstPort      ________________________________________________            1          192.0.0.1      UDP        any      Table 1: Parameters needed to establish the RSVP session5.  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 inRFC3261 [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.Camarillo & Monrad          Standards Track                     [Page 4]

RFC 3524  Mapping Media Streams to Resource Reservation Flows April 20038.  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:  Gonzalo.Camarillo@ericsson.com   Atle Monrad   Ericsson   N-4898 Grimstad   Norway   EMail:  atle.monrad@ericsson.comCamarillo & Monrad          Standards Track                     [Page 5]

RFC 3524  Mapping Media Streams to Resource Reservation Flows April 200311.  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.Camarillo & Monrad          Standards Track                     [Page 6]