Competitive Mode Enhancement for Delay-Based Congestion Control Algorithms
draft-zhao-iccrg-competitive-mode-01

iccrg                                                            G. Zhao
Internet-Draft                                                   G. Chen
Intended status: Informational                              China Mobile
Expires: 19 February 2027                                 18 August 2026

    Competitive Mode Enhancement for Delay-Based Congestion Control
                               Algorithms
                  draft-zhao-iccrg-competitive-mode-01

Abstract

   This document proposes introducing a "Competitive Mode" into delay-
   based congestion control algorithms to improve their competitiveness
   and fairness during coexistence scenarios.

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   This Internet-Draft will expire on 19 February 2027.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Introducing Competitive Mode into Delay-Based Congestion
           Control Algorithms  . . . . . . . . . . . . . . . . . . .   2
     2.1.  Method for Determining Competitive Mode . . . . . . . . .   2
     2.2.  Congestion Window Compensation in Competition Mode  . . .   3
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Copa with Competitive Mode  . . . . . . . . . . . . . . .   3
     3.2.  Vegas with Competitive Mode . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Congestion control algorithms can be categorized into loss-based and
   delay-based algorithms based on their congestion detection
   mechanisms.  Loss-based congestion control algorithms typically fill
   the link buffer until packet loss occurs, then reduce the sending
   rate.  In contrast, delay-based congestion control algorithms
   proactively reduce the sending rate when queuing delay increases.
   Representative delay-based congestion control algorithms (e.g.,
   Vegas[Vegas], FAST[FAST], Copa[Copa]) measure RTT or queuing delay,
   calculate the expected throughput based on delay variations,
   determine congestion, and adjust the congestion window size.

   While delay-based algorithms generally exhibit lower packet loss
   rates and smaller queuing delays than loss-based algorithms, they
   fail to fairly share link bandwidth with loss-based algorithms (e.g.,
   Cubic) when both types of traffic coexist.

2.  Introducing Competitive Mode into Delay-Based Congestion Control
    Algorithms

2.1.  Method for Determining Competitive Mode

   Determine whether the current flow is in a coexistence/competition
   phase with Cubic traffic based on the magnitude of queuing delay
   variation.  The COPA provides a method to determine whether it is in
   competitive mode.

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   Specifically, upon receiving an ACK, the algorithm calculates the RTT
   for each flow and maintains a historical minimum RTT value(min_rtt).
   Based on RTT samples, it records the maximum(max_delay) and
   minimum(min_delay) RTT values over a 4-RTT window.  Competitive Mode
   is triggered based on the following inequality.

   min_delay < min_rtt + 0.1(max_delay - min_rtt) Formula 1

   Here, max_delay and min_delay represent the maximum and minimum RTT
   values within the last 4 RTT intervals, and min_rtt is the historical
   minimum RTT.  The difference between min_delay and min_rtt represents
   the minimum queuing delay at the bottleneck link during this period,
   while the difference between max_delay and min_rtt represents the
   maximum queuing delay.  If the inequality is not satisfied, it
   indicates that the bottleneck link's queue has not emptied during
   this period, suggesting likely competition from Cubic-like flows.
   Consequently, the algorithm enters Competitive Mode.  If the
   inequality holds, the algorithm operates in Default Mode.

2.2.  Congestion Window Compensation in Competition Mode

   When the algorithm determines it is in Competition Mode, it
   introduces an additional congestion window gain factor to moderately
   increase the congestion window size.  Cubic persistently fills the
   switch buffer, and a larger window size leads to more severe delay
   inflation.  Accordingly, the congestion window can be adjusted based
   on delay variations to match Cubic's window size.  Since the delay
   gradient effectively characterizes the rise and fall of delay, the
   congestion control algorithm computes this gradient every round trip
   time(RTT) and adjusts the window size accordingly.

   TBD.

3.  Examples

3.1.  Copa with Competitive Mode

   TBD.

3.2.  Vegas with Competitive Mode

   TBD.

4.  IANA Considerations

   TBD.

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5.  Security Considerations

   TBD.

6.  Contributors

   The following people have substantially contributed to this document:

           Zhiqiang Li
           lizhiqiangyjy@chinamobile.com

           Hongwei Yang
           yanghongwei@chinamoblie.com

7.  Acknowledgements

   TBD.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [Vegas]    Brakmo, L., O'Malley, S., and L. Peterson, "TCP Vegas: New
              Techniques for Congestion Detection and Avoidance", ACM
              SIGCOMM Computer Communication Review 24.4(1994) , August
              1994.

   [FAST]     Wei, D., Jin, C., and S. Low, "FAST TCP : motivation,
              architecture, algorithms, performance", IEEE/ACM
              Transactions on Networking 14(2006) , December 2006.

   [Copa]     Arun, V. and H. Hari, "Practical delay-based congestion
              control for the internet", the Applied Networking Research
              Workshop 2018. , April 2018.

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   [I-D.ietf-ccwg-bbr]
              Cardwell, N., Swett, I., and J. Beshay, "BBR Congestion
              Control", Work in Progress, Internet-Draft, draft-ietf-
              ccwg-bbr-06, 6 July 2026,
              <https://datatracker.ietf.org/doc/html/draft-ietf-ccwg-
              bbr-06>.

Authors' Addresses

   Guangyu Zhao
   China Mobile
   No.32 XuanWuMen West Street
   Beijing
   100053
   China
   Email: zhaoguangyu@chinamobile.com

   Guowei Chen
   China Mobile
   No.2 Qianfu Road, Xishan District
   Kunming
   650228
   China
   Email: chenguowei@yn.chinamobile.com

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