Re: [lwip-users] Window size for large data reception

[Kieran Mansley]

On Tue, 2010-02-02 at 15:07 -0800, Myk wrote:
> Thanks for the reply.
> 
> In theory, the receiver should have a large window, and the LwIP server
> can control transmissions, but the problem I had was the large amount
> of retransmission requests for a file upload (large data transmission to
> server).
> 
> Setting TCP_WND = TCP_MSS fixed the problem, since the browser only
> sent 1 packet and then waited for an ACK, rather than sending 2 packets
> at one time before getting an ACK, and the TCP stack not coping.

Which TCP wasn't coping?  If the stack can't manage receiving 2 packets
at a time, there is something odd going on.  This is most likely a bug
somewhere.  

> Why does the receiver need a large window?  The browser seem to behave well
> with the window size.

With a small window like that TCP is reduced to a ping-pong style of
transfer, with one packet in flight at any one time.  On a link with any
kind of noticeable round trip time, and a transfer that is longer than a
single frame, this will give really bad performance.

Kieran