IAB Concerns Regarding Congestion Control for Voice Traffic in the Internet
RFC 3714
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RFC - Informational
(March 2004; No errata)
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Last updated |
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2013-03-02
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IAB
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plain text
pdf
html
bibtex
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IAB state
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(None)
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Consensus Boilerplate |
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Unknown
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RFC Editor Note |
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Network Working Group S. Floyd, Ed.
Request for Comments: 3714 J. Kempf, Ed.
Category: Informational March 2004
IAB Concerns Regarding Congestion Control for
Voice Traffic in the Internet
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document discusses IAB concerns about effective end-to-end
congestion control for best-effort voice traffic in the Internet.
These concerns have to do with fairness, user quality, and with the
dangers of congestion collapse. The concerns are particularly
relevant in light of the absence of a widespread Quality of Service
(QoS) deployment in the Internet, and the likelihood that this
situation will not change much in the near term. This document is
not making any recommendations about deployment paths for Voice over
Internet Protocol (VoIP) in terms of QoS support, and is not claiming
that best-effort service can be relied upon to give acceptable
performance for VoIP. We are merely observing that voice traffic is
occasionally deployed as best-effort traffic over some links in the
Internet, that we expect this occasional deployment to continue, and
that we have concerns about the lack of effective end-to-end
congestion control for this best-effort voice traffic.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. An Example of the Potential for Trouble. . . . . . . . . . . . 4
3. Why are Persistent, High Drop Rates a Problem? . . . . . . . . 6
3.1. Congestion Collapse. . . . . . . . . . . . . . . . . . . 6
3.2. User Quality . . . . . . . . . . . . . . . . . . . . . . 7
3.3. The Amorphous Problem of Fairness. . . . . . . . . . . . 8
4. Current efforts in the IETF. . . . . . . . . . . . . . . . . . 10
4.1. RTP. . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. TFRC . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.3. DCCP . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Floyd & Kempf Informational [Page 1]
RFC 3714 IAB Concerns Regarding Congestion Control March 2004
4.4. Adaptive Rate Audio Codecs . . . . . . . . . . . . . . . 12
4.5. Differentiated Services and Related Topics . . . . . . . 13
5. Assessing Minimum Acceptable Sending Rates . . . . . . . . . . 13
5.1. Drop Rates at 4.75 kbps Minimum Sending Rate . . . . . . 17
5.2. Drop Rates at 64 kbps Minimum Sending Rate . . . . . . . 18
5.3. Open Issues. . . . . . . . . . . . . . . . . . . . . . . 18
5.4. A Simple Heuristic . . . . . . . . . . . . . . . . . . . 19
6. Constraints on VoIP Systems . . . . . . . . . . . . . . . . . . 20
7. Conclusions and Recommendations. . . . . . . . . . . . . . . . 20
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.1. Normative References . . . . . . . . . . . . . . . . . . 21
9.2. Informative References . . . . . . . . . . . . . . . . . 22
10. Appendix - Sending Rates with Packet Drops . . . . . . . . . . 26
11. Security Considerations. . . . . . . . . . . . . . . . . . . . 29
12. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 29
13. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30
14. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 31
1. Introduction
While many in the telephony community assume that commercial VoIP
service in the Internet awaits effective end-to-end QoS, in reality
voice service over best-effort broadband Internet connections is an
available service now with growing demand. While some ISPs deploy
QoS on their backbones, and some corporate intranets offer end-to-end
QoS internally, end-to-end QoS is not generally available to
customers in the current Internet. Given the current commercial
interest in VoIP on best-effort media connections, it seems prudent
to examine the potential effect of real time flows on congestion. In
this document, we perform such an analysis. Note, however, that this
document is not making any recommendations about deployment paths for
VoIP in terms of QoS support, and is not claiming that best-effort
service can be relied upon to give acceptable performance for VoIP.
This document is also not discussing signalling connections for VoIP.
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