[tor-commits] [torspec] 03/04: Prop 324: Describe how to reset RTT if cc_cwnd_min is hit.

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commit d339bb9fab10c32c10fce0e06421bbadaffe2777
Author: Mike Perry <mikeperry-git at torproject.org>
AuthorDate: Wed Aug 10 22:28:33 2022 +0000

    Prop 324: Describe how to reset RTT if cc_cwnd_min is hit.
---
 proposals/324-rtt-congestion-control.txt | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/proposals/324-rtt-congestion-control.txt b/proposals/324-rtt-congestion-control.txt
index 0e8c349..c9997ef 100644
--- a/proposals/324-rtt-congestion-control.txt
+++ b/proposals/324-rtt-congestion-control.txt
@@ -389,6 +389,13 @@ Simplifying:
 
    BDP = cwnd * RTT_min / RTT_current_ewma
 
+The RTT_min for this calculation comes from the minimum RTT_current_ewma
+seen in the lifetime of this circuit. If the congestion window falls to
+`cc_cwnd_min`, implementations MAY choose to reset RTT_min for use in this
+calculation to either the RTT_current_ewma, or a percentile-weighted average
+between RTT_min and RTT_current_ewma, specified by `cc_rtt_reset_pct`. This
+helps with escaping starvation conditions.
+
 The net effect of this estimation is to correct for any overshoot of
 the cwnd over the actual BDP. It will obviously underestimate BDP if cwnd
 is below BDP.
@@ -1304,6 +1311,16 @@ These are sorted in order of importance to tune, most important first.
     - Shadow Tuning Results:
            Setting this to 2 helped reduce overshoot during Slow Start.
 
+  cc_rtt_reset_pct:
+    - Description: Describes a percentile average between RTT_min and
+                   RTT_current_ewma, for use to reset RTT_min, when the
+                   congestion window hits cwnd_min.
+    - Range: [0, 100]
+    - Default: 100
+    - Shadow Tuning Results:
+           cwnd_min is not hit in Shadow simulations, but it can be hit
+           on the live network while under DoS conditions, and with cheaters.
+
   cc_cwnd_inc:
     - Description: How much to increment the congestion window by during
                    steady state, every cwnd.

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