RFC 3649 (rfc3649) - Page 2 of 34

HighSpeed TCP for Large Congestion Windows

RFC 3649                     HighSpeed TCP                 December 2003


Table of Contents

   1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2. The Problem Description.. . . . . . . . . . . . . . . . . . . .  3
   3. Design Guidelines.. . . . . . . . . . . . . . . . . . . . . . .  4
   4. Non-Goals.. . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5. Modifying the TCP Response Function.. . . . . . . . . . . . . .  6
   6. Fairness Implications of the HighSpeed Response
      Function. . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   7. Translating the HighSpeed Response Function into
      Congestion Control Parameters . . . . . . . . . . . . . . . . . 12
   8. An alternate, linear response functions.. . . . . . . . . . . . 13
   9. Tradeoffs for Choosing Congestion Control Parameters. . . . . . 16
      9.1. The Number of Round-Trip Times between Loss Events . . . . 17
      9.2. The Number of Packet Drops per Loss Event, with Drop-Tail. 17
   10. Related Issues . . . . . . . . . . . . . . . . . . . . . . . . 18
      10.1. Slow-Start. . . . . . . . . . . . . . . . . . . . . . . . 18
      10.2. Limiting burstiness on short time scales. . . . . . . . . 19
      10.3. Other limitations on window size. . . . . . . . . . . . . 19
      10.4. Implementation issues.. . . . . . . . . . . . . . . . . . 19
   11. Deployment issues. . . . . . . . . . . . . . . . . . . . . . . 20
      11.1. Deployment issues of HighSpeed TCP. . . . . . . . . . . . 20
      11.2. Deployment issues of Scalable TCP . . . . . . . . . . . . 22
   12. Related Work in HighSpeed TCP. . . . . . . . . . . . . . . . . 23
   13. Relationship to other Work.. . . . . . . . . . . . . . . . . . 25
   14. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . 25
   15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
   16. Normative References . . . . . . . . . . . . . . . . . . . . . 26
   17. Informative References . . . . . . . . . . . . . . . . . . . . 26
   18. Security Considerations. . . . . . . . . . . . . . . . . . . . 28
   19. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 28
   A.  TCP's Loss Event Rate in Steady-State. . . . . . . . . . . . . 29
   B.  A table for a(w) and b(w). . . . . . . . . . . . . . . . . . . 30
   C.  Exploring the time to converge to fairness . . . . . . . . . . 32
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 33
       Full Copyright Statement . . . . . . . . . . . . . . . . . . . 34

1.  Introduction

   This document proposes HighSpeed TCP, a modification to TCP's
   congestion control mechanism for use with TCP connections with large
   congestion windows.  In a steady-state environment, with a packet
   loss rate p, the current Standard TCP's average congestion window is
   roughly 1.2/sqrt(p) segments.  This places a serious constraint on
   the congestion windows that can be achieved by TCP in realistic
   environments.  For example, for a Standard TCP connection with 1500-
   byte packets and a 100 ms round-trip time, achieving a steady-state
   throughput of 10 Gbps would require an average congestion window of



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