Re: [lwip-users] Compensating for longer latency connections

[Kieran Mansley]

On Tue, Mar 02, 2010 at 09:57:12AM -0800, JM wrote:
> I'm using lwIP 1.3.0 for a streaming music player.? I've noticed that I 
> generally have issues when playing higher bitrate streams from servers 
> overseas.? For example, I can play a 192Kbit stream from a domestic host with 
> no problems.? But, when I try playing another 192Kbit stream from across the 
> pond, the audio buffer level is ok for maybe 5-10 seconds, then the buffer 
> level starts dropping, and soon after, it no longer keeps up.? 
> 
> This occurs in every instance I've tried so I believe it's a 
> latency/distance issue.? Also, I can successfully play all these 
> streams on my computer.? I haven't tried Wiresharking it yet, but I 
> suspect this may not tell me much being sort of an "obvious" problem 
> to those who are well versed on this sort of thing.? Plus, my 
> computer's
>  ethernet hardware doesn't help much by hiding bad packets from me.? 
>  What are the likely culprits as far as lwIP configuration?? I have 
>  increased the number of pbufs some, but maybe it's not enough, or 
>  maybe I'm not addressing the correct parameters.

If you get sufficient throughput from the local network, but not when 
the connection involves a higher round trip time, that suggests that 
your TCP window is too small.  To get the bandwidth you need, measure 
the round trip time, multiply by the bandwidth required, round up to 
a sensible number and set TCP_WND to that.

Kieran