Internet Engineering Task Force SIP WG
Internet Draft G. Camarillo
Ericsson
A. Monrad
Ericsson
draft-ietf-mmusic-reservation-flows-00.txt
October 14, 2002
Expires: April 2003
Mapping of Media Streams to Resource Reservation Flows
STATUS OF THIS MEMO
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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.
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Table of Contents
1 Introduction ........................................ 3
1.1 Terminology ......................................... 3
2 SRF Semantics ....................................... 3
3 Examples ............................................ 4
4 IANA Considerations ................................. 4
5 Security Considerations ............................. 5
6 Authors' Addresses .................................. 5
7 Normative References ................................ 5
8 Informative References .............................. 5
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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
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from that media line, and from no other media lines.
3 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 IANA Considerations
IANA needs to register the following new "semantics" attribute for
the SDP grouping framework [2]:
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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 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 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 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 Informative References
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[4] J. Rosenberg, H. Schulzrinne, et al. , "SIP: Session initiation
protocol," Internet Draft, Internet Engineering Task Force, Feb.
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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