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Faster Restart for TCP Friendly Rate Control (TFRC) ‏

This document discusses the Faster Restart mechanism for TCP Friendly Rate Control (TFRC) in DCCP, focusing on rate control after idle periods and data-limited periods. It outlines the impact on sender rates, feedback mechanisms, and interoperability issues with RFC 3448 and RFC3448bis. The document highlights the improvements in performance with the new CCID-3 protocol and addresses future simulation plans to evaluate the mechanism's impact and safety for internet use.

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Faster Restart for TCP Friendly Rate Control (TFRC) ‏

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  1. draft-ietf-dccp-tfrc-faster-restart-05.txt E. Kohler, S. Floyd, and A. Sathiaseelan March 2008, DCCP Working Group Faster Restart for TCP Friendly Rate Control (TFRC)‏

  2. Faster Restart for TFRC: • After an idle period of at least NFT (no feedback): • The allowed sending rate is not reduced below *twice* the initial sending rate; • Quadruple sending rate each RTT up to old rate (decayed over time);

  3. There have been no changes since last IETF! • There will be a report on new simulation results before the next IETF.

  4. Old slides:

  5. Changes from draft-ietf-dccp-tfrc-faster-restart-03.txt: • Removed Section 4.1 on receive rate, after it is made into an Errata for RFC 4342. Feedback from Gerrit Renker. • Additional reporting on simulations. • Added a section on Interoperability Issues. • Specified CCID 3 and 4 impact in the introduction. • Nits from Gorry Fairhurst and Arjuna. • Changed targeted decay time to configurable DelayTime. Feedback from Gerrit Renker.

  6. Performance after long idle periods: • RFC 3448: • Allowed sending rate is halved when NoFeedback Timer expires, down towards initial sending rate. • First feedback packet after idle period reports receive rate of one packet per RTT. • Allowed sending rate is at most twice receive rate. • RFC3448bis after a long idle period: • First feedback packet after idle period reports receive rate of one packet per RTT. • Receive rate is NOT based only on this feedback packet. • RFC3448bis with Faster Restart: • Allowed sending rate is halved when NFT expires, down towards *twice* initial sending rate. • Then each RTT quadruple allowed sending rate towards X_fast_max. (X_fast_max: interpolated highest receive rate since last loss)‏

  7. Performance in long data-limited periods: • RFC 3448: • Allowed sending rate is at most twice: receive rate. • RFC3448bis: • Allowed sending rate is at most twice: max (recent receive rate, receive rate before data-limited period). • RFC3448bis with Faster Restart: • Allowed sending rate is at most: max (value from RFC3448bis, X_fast_max). (X_fast_max: interpolated highest receive rate since last loss)‏

  8. Faster Restart Interoperability Issues with RFC 3448: • Faster Restart: • a sender-only change. • built upon RFC3448bis (not RFC 3448). • How does Faster Restart interact with a receiver using RFC 3448? • Performance is NOT higher than with a receiver using RFC3448bis. • No backwards interoperability issue.

  9. RFC 4342 Errata: • Section 6 says: • 2. A Receive Rate option, defined in Section 8.3, specifying the rate at which data was received since the last DCCP-Ack was sent. • It should say: • 2. A Receive Rate option, defined in Section 8.3, specifying the rate at which data was received over the last round-trip time. • Makes CCID-3 consistent with RFC 3448 and RFC3448bis.

  10. Faster Restart Interoperability Issuesin DCCP’s CCID 3: • Faster Restart builds on RFC3348bis, not RFC 3448. • New CCID-3: • CCID-3 with Faster Restart and RFC 4342 Errata. • Old CCID-3: • CCID-3 without Faster Restart and RFC 4342 Errata. • New CCID-3 improves performance after idle and data-limited periods. • Performance with a new CCID-3 sender and an old CCID-3 receiver is similar to performance with new CCID-3 for both end-nodes. • Partial-deployment is NOT an problem.

  11. Future simulations: • Can Faster Restart negatively impact others? • Simulation work to consider reverse traffic. • Simulations for wireless. • Experiments to assess incentive for padding. • Simulations will focus on packet drop rates during the Faster Restart period. • Assess if it is safe for use in Internet. • If not, what needs to be evaluated?

  12. End Date? • Some simulations already done. • More are planned for January 2008. • Expect to have answers for next IETF. • Also depends on maturity of RFC3448bis.

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