[lwip-devel] [bug #20506] HTTP server doesn't call tcp_output

[Kieran Mansley]

Follow-up Comment #31, bug #20506 (project lwip):

Yes, set initial cwnd to 2 mss.  

Hmm, interesting point about the SYNs getting lost - with the change you
suggest we'd set cwnd to 1 (really 1, not 1 mss) when the SYN is sent, 1 mss
when retransmitting the SYN and then up to 2 mss when the connection was
established.  I wonder if that's what it means?

An alternative would be to set it to 2 mss when sending the SYN, then back to
1 MSS if we retransmit (and don't change it in tcp_in.c line 515) but this
might have its own problems.  For example, the SYN and SYN-ACK aren't
supposed to inflate the congestion window as far as I remember, and this
scheme might lead to that.  I'm also not sure what effect the change from 1
(really 1 not 1 mss) to 2 mss when sending the SYN would be - i.e. it could
be 1 for a reason there!

Perhaps we could, in tcp_in.c line 515, look and see what the congestion
window is currently.  If we've had a retransmission I think it will already
be 1 MSS (as that's what the tcp timer sets it to on retransmission).  If
we've not had a retransmission I think it will still be 1.  We can use this
to decide whether to set it to 2 MSS.  Could you see if that would work?  I'm
suggesting this from memory rather than looking at the code.

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