[lwip-users] Re: [lwip] MSS and config generally

[Dirk Koopman]

On Thu, 2002-06-06 at 16:32, Kieran Mansley wrote:
> On 6 Jun 2002, Dirk Koopman wrote:
> > On Thu, 2002-06-06 at 15:50, Kieran Mansley wrote:
> > > Alter TCP_MSS (in lwipopts.h) to your requirements?
> >
> > Tried that. Made no obvious difference.
> 
> Hmm.  What is the MTU of your physical network?

1500 (actually it tries to negotiate 2000). The problem appears to be
that lwip negotiates an MSS of 128 in the syn packet (or at least: I
think it is). Having said that, I am talking over GPRS to a publically
accessible server on the internet.

> 
> > >
> > > Also, make sure that the config options related to this are set to
> > > sensible amounts.  Your poor performance could be due to insufficiently
> > > sized TCP_SND_BUF, TCP_SND_QUEUELEN or TCP_WND
> > >
> >
> > Given say a 1024 byte MSS, what would say the other parameters should
> > look like?
> 
> I would say, around 8k for the TCP_WND and TCP_SND_BUF should be
> sufficient, and at least 2*(TCP_SND_BUF/TCP_MSS) for TCP_SND_QUEUELEN.
> 
> Out of interest, can you quantify how poor your poor performance is?

About one packet every 15-30 seconds (it is quite variable). Using linux
IP directly via the same route it just works with normal packet sizes
and at the sort of speeds I would expect (ie in bursts - up to
~30Kb/sec).

Dirk

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