[lwip-users] Window size for large data reception

[Mykola Kyrylenko]

Hi,

We are developing with LwIP 1.3.2 using callback routines (no RTOS or
threads or sockets or ...).
Using a ST Micro STR912, with Micrel KSZ8893MQL PHY.

I have implemented a HTTP server, and am now trying to implement POST
processing for file upload.

With fairly "standard" settings, the POST file upload resulted in a lot
of retransmissions.
What appeared to be occurring, was that the browser was sending multiple
(2) packets before waiting for an ACK.  This makes sense, because
TCP_WND = 4 * TCP_MSS.  But the TCP stack (or my handling of the stack)
could not cope, resulting in the large number of retransmission
requests.

I made TCP_WND = TCP_MSS = 512, and all seems to work well.

In 'opt.h', there was a warning which has me concerned:
/**
 * TCP_WND: The size of a TCP window.  This must be at least 
 * (2 * TCP_MSS) for things to work well
 */
Will this be an issue?
What issues (besides performance)?

Is it possible to have TCP_WND = TCP_MSS for packet reception, but have
the recommended TCP_WND = 4 * TCP_MSS for packet transmission?
If so, pointers on where to look would be good.

Regards,
Mykola Kyrylenko