Re: [lwip-users] transfer stucks when snd_wnd is less than TCP_MSS

[Kieran Mansley]

On Fri, 2007-03-09 at 11:17 +0200, Vlad wrote:
> lwip connected to internet throught router:
> 
> lwip(192.168.0.2) <--- 1 GB ethernet ---> router(192.168.0.1/x.x.x.x real ip) 
> <--- 128k adsl connection ----> internet <----> remoute linux server (to 
> which lwip connects)
> 
> router is masquerading linux 2.6 server.
> 
> router returns quickly ack-s on most of my outgoing packets, returning less 
> window size on each ack. lwip transfers 365kbytes traffic out and then hangs 
> because of small window.
> 
> i see with tcpdump that router transfers out only 86kbytes and then stops 
> transfering.
> 
> if i connect lwip to internet directly, all works fine.

Very strange - the router should not be acking packets as you suggest it
is.  Packets should only be acked by the remote linux server to which
lwIP connects.  It sounds like you have a problem with your router,
particularly as lwIP works fine when you remove the router.  

> is "slow start" will be a solution for me ? 

slow start is an internal TCP mechanism that the stack should invoke
when appropriate.  It's not something you should need to worry about in
your application.

Again, it sounds like lwIP is not at fault here and is doing the right
thing, so I'm not sure what help I can be.

Kieran