[lwip-devel] [bug #51154] ABC (Appropriate Byte Counting) fails to work with TCP_WND set to maximum.

[Joel Cunningham]

Follow-up Comment #8, bug #51154 (project lwip):

Simon,

TCP_WND controls our receiving window, not the remote's receive window (which
is what the sending is limited by).  Maybe we could stop at pcb->snd_wnd_max,
though I'm not sure 100% sure about the relationship between snd_wnd_max and
ssthresh and if its ok to stop growing cwnd when snd_wnd_max < ssthresh.

Having cwnd grow larger than snd_wnd_max is what LwIP has historically done
and is safe because we do:


wnd = LWIP_MIN(pcb->snd_wnd, pcb->cwnd);


in tcp_output() to gate sending.  Setting cwnd to the maximum value in the
rollover case really just lets the sender use that last bit of window for
cases when snd_wnd_max == maximum value of tcpwnd_size_t, which is likely in
the non-scaling case where the remote's window is 65535 or close to!



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