Network Working Group M. Handley
Request for Comments: 3448 S. Floyd
Category: Standards Track ICIR
J. Padhye
Microsoft
J. Widmer
University of Mannheim
January 2003
TCP Friendly Rate Control (TFRC):
Protocol Specification
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 (2003). All Rights Reserved.
Abstract
This document specifies TCP-Friendly Rate Control (TFRC). TFRC is a
congestion control mechanism for unicast flows operating in a best-
effort Internet environment. It is reasonably fair when competing
for bandwidth with TCP flows, but has a much lower variation of
throughput over time compared with TCP, making it more suitable for
applications such as telephony or streaming media where a relatively
smooth sending rate is of importance.
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Mechanism. . . . . . . . . . . . . . . . . . . 3
3.1. TCP Throughput Equation. . . . . . . . . . . . . . 4
3.2. Packet Contents. . . . . . . . . . . . . . . . . . 6
3.2.1. Data Packets. . . . . . . . . . . . . . . . 6
3.2.2. Feedback Packets. . . . . . . . . . . . . . 7
4. Data Sender Protocol. . . . . . . . . . . . . . . . . . 7
4.1. Measuring the Packet Size. . . . . . . . . . . . . 8
4.2. Sender Initialization. . . . . . . . . . . . . . . 8
Handley, et. al. Standards Track [Page 1]
RFC 3448 TFRC: Protocol Specification January 2003
4.3. Sender behavior when a feedback packet is
received. . . . . . . . . . . . . .. . . . . . . . 8
4.4. Expiration of nofeedback timer . . . . . . . . . . 9
4.5. Preventing Oscillations. . . . . . . . . . . . . . 10
4.6. Scheduling of Packet Transmissions . . . . . . . . 11
5. Calculation of the Loss Event Rate (p). . . . . . . . . 12
5.1. Detection of Lost or Marked Packets. . . . . . . . 12
5.2. Translation from Loss History to Loss Events . . . 13
5.3. Inter-loss Event Interval. . . . . . . . . . . . . 14
5.4. Average Loss Interval. . . . . . . . . . . . . . . 14
5.5. History Discounting. . . . . . . . . . . . . . . . 15
6. Data Receiver Protocol. . . . . . . . . . . . . . . . . 17
6.1. Receiver behavior when a data packet is
received . . . . . . . . . . . . . . . . . . . . . 18
6.2. Expiration of feedback timer . . . . . . . . . . . 18
6.3. Receiver initialization. . . . . . . . . . . . . . 19
6.3.1. Initializing the Loss History after the
First Loss Event . . . . . . . . . . . . . 19
7. Sender-based Variants . . . . . . . . . . . . . . . . . 20
8. Implementation Issues . . . . . . . . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . 21
10. IANA Considerations . . . . . . . . . . . . . . . . . . 22
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . 22
12. Non-Normative References. . . . . . . . . . . . . . . . 22
13. Authors' Addresses. . . . . . . . . . . . . . . . . . . 23
14. Full Copyright Statement. . . . . . . . . . . . . . . . 24
1. Introduction
This document specifies TCP-Friendly Rate Control (TFRC). TFRC is a
congestion control mechanism designed for unicast flows operating in
an Internet environment and competing with TCP traffic [2]. Instead
of specifying a complete protocol, this document simply specifies a
congestion control mechanism that could be used in a transport
protocol such as RTP [7], in an application incorporating end-to-end
congestion control at the application level, or in the context of
endpoint congestion management [1]. This document does not discuss
packet formats or reliability. Implementation-related issues are
discussed only briefly, in Section 8.
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