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

Junho Choi <notifications@github.com> Mon, 18 November 2019 04:45 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

I believe the basic intention of RFC3465 (section 2.3) is limiting cwnd *increase* during slow start per ACK,  (e.g. one ACK acknowledges 4 MSS --> only increase cwnd by 2 MSS, not 4 MSS), not resetting cwnd. If cwnd is reset to 2xMSS, it is basically same to idle timeout scenario.

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