RFC 3448 (rfc3448) - Page 2 of 24

TCP Friendly Rate Control (TFRC): Protocol Specification

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.

   TFRC is designed to be reasonably fair when competing for bandwidth
   with TCP flows, where a flow is "reasonably fair" if its sending rate
   is generally within a factor of two of the sending rate of a TCP flow
   under the same conditions.  However, TFRC has a much lower variation
   of throughput over time compared with TCP, which makes it more
   suitable for applications such as telephony or streaming media where
   a relatively smooth sending rate is of importance.




Handley, et. al.            Standards Track