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

Junho Choi <notifications@github.com> Thu, 14 November 2019 05:46 UTC

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

I think it will reset congestion_window to a small value (<=2 mss).

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