IAB Concerns Regarding Congestion Control for Voice Traffic in the Internet
RFC 3714
Document | Type |
RFC - Informational
(March 2004; No errata)
Was draft-iab-congestion (iab)
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Authors | Sally Floyd , James Kempf | ||
Last updated | 2013-03-02 | ||
Stream | IAB | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | IAB state | (None) | |
Consensus Boilerplate | Unknown | ||
RFC Editor Note | (None) |
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. However, voice traffic is in fact occasionally deployed as best effort traffic over some links in the Internet today, and we expectShow full document text