Re: [quicwg/base-drafts] Limit CWND increase in slow start (#3232)

Vidhi Goel <notifications@github.com> Wed, 13 November 2019 22:49 UTC

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Subject: Re: [quicwg/base-drafts] Limit CWND increase in slow start (#3232)
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goelvidhi commented on this pull request.



> @@ -1368,7 +1377,15 @@ acked_packet from sent_packets.
        return
      if (congestion_window < ssthresh):
        // Slow start.
-       congestion_window += acked_packet.size
+       if (pacing):
+         congestion_window += acked_packet.size
+       else:
+         // If pacing is not used, limit the increase to
+         // 2*max_datagram_size per ACK as described in
+         // {{?RFC3465}}
+         if (cwnd_increase < 2 * max_datagram_size):
+           cwnd_increase += bytes_acked
+           congestion_window += bytes_acked

There is a problem with my suggested code that the cwnd could end up being less than 2*MSS.

This is my updated proposal:
```
if (pacing):
         congestion_window += acked_packet.size
       else:
         // If pacing is not used, limit the increase to
         // 2*max_datagram_size per ACK as described in
         // {{?RFC3465}}
         if (cwnd_increase  < 2 * max_datagram_size):
           cwnd_increase = min(cwnd_increase + acked_packet.size,
                                            2 * max_datagram_size)
           congestion_window = cwnd_increase
```

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