Re: [quicwg/base-drafts] Byte counting at Congestion avoidance (#3917)

[ianswett <[e-mail]>]

@ianswett commented on this pull request.

A suggestion in order to maintain byte quantization instead of packet quantization, which minimizes changes from the existing draft.

> +      bytes_acked += acked_packet.sent_bytes
+      if (bytes_acked >= congestion_window):
+        bytes_acked -= congestion_window
+        congestion_window += max_datagram_size

This part contains the larger change.  Previously, congestion_window was adjusted in 1 byte increments.  Now it's adjusted in max_datagram_size increments.  In practice, it likely doesn't matter that much, but I am concerned about perpetuating packet-size quantization in congestion control, since my impression is that it's an artifact of the Linux kernel, not an intentional design choice.

I believe BSD-based OS's use bytes instead of packets, and bytes always seemed more correct to me.

However, this isn't that difficult to fix.  How about:
  cwnd_in_packets = congestion_window / max_datagram_size
  congestion_window += bytes_acked / cwnd_in_packets
  bytes_acked = bytes_acked % cwnd_in_packets

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