A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)
RFC 3890
Network Working Group M. Westerlund
Request for Comments: 3890 Ericsson
Category: Standards Track September 2004
A Transport Independent Bandwidth Modifier
for the Session Description Protocol (SDP)
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 (2004).
Abstract
This document defines a Session Description Protocol (SDP) Transport
Independent Application Specific Maximum (TIAS) bandwidth modifier
that does not include transport overhead; instead an additional
packet rate attribute is defined. The transport independent bit-rate
value together with the maximum packet rate can then be used to
calculate the real bit-rate over the transport actually used.
The existing SDP bandwidth modifiers and their values include the
bandwidth needed for the transport and IP layers. When using SDP
with protocols like the Session Announcement Protocol (SAP), the
Session Initiation Protocol (SIP), and the Real-Time Streaming
Protocol (RTSP), and when the involved hosts has different transport
overhead, for example due to different IP versions, the
interpretation of what lower layer bandwidths are included is not
clear.
Westerlund Standards Track [Page 1]
RFC 3890 Bandwidth Modifier for SDP September 2004
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. The Bandwidth Attribute. . . . . . . . . . . . . . . . . 3
1.1.1. Conference Total . . . . . . . . . . . . . . . . 3
1.1.2. Application Specific Maximum . . . . . . . . . . 3
1.1.3. RTCP Report Bandwidth. . . . . . . . . . . . . . 4
1.2. IPv6 and IPv4. . . . . . . . . . . . . . . . . . . . . . 4
1.3. Further Mechanisms that Change the Bandwidth
Utilization. . . . . . . . . . . . . . . . . . . . . . . 5
1.3.1. IPsec. . . . . . . . . . . . . . . . . . . . . . 5
1.3.2. Header Compression . . . . . . . . . . . . . . . 5
2. Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Terminology. . . . . . . . . . . . . . . . . . . . . . . 6
3. The Bandwidth Signaling Problems . . . . . . . . . . . . . . . 6
3.1. What IP Version is Used. . . . . . . . . . . . . . . . . 6
3.2. Taking Other Mechanisms into Account . . . . . . . . . . 7
3.3. Converting Bandwidth Values. . . . . . . . . . . . . . . 8
3.4. RTCP Problems. . . . . . . . . . . . . . . . . . . . . . 8
3.5. Future Development . . . . . . . . . . . . . . . . . . . 9
3.6. Problem Conclusion . . . . . . . . . . . . . . . . . . . 9
4. Problem Scope. . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 11
6.2. The TIAS Bandwidth Modifier. . . . . . . . . . . . . . . 11
6.2.1. Usage. . . . . . . . . . . . . . . . . . . . . . 11
6.2.2. Definition . . . . . . . . . . . . . . . . . . . 12
6.2.3. Usage Rules. . . . . . . . . . . . . . . . . . . 13
6.3. Packet Rate Parameter. . . . . . . . . . . . . . . . . . 13
6.4. Converting to Transport-Dependent Values . . . . . . . . 14
6.5. Deriving RTCP bandwidth. . . . . . . . . . . . . . . . . 15
6.5.1. Motivation for this Solution. . . . . . . . . . . 15
6.6. ABNF Definitions . . . . . . . . . . . . . . . . . . . . 16
6.7. Example. . . . . . . . . . . . . . . . . . . . . . . . . 16
7. Protocol Interaction . . . . . . . . . . . . . . . . . . . . . 17
7.1. RTSP . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.2. SIP. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.3. SAP. . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations. . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 18
10. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 19
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