Subject: Re: Strange TCP behavior over HSDPA

From: Kristian Evensen <[email-masked]>
Date: Tue, 29 Dec 2009 10:59:43 +0100

Den 29.12.2009 09:30, skrev Jarek Poplawski:
> The most obvious difference seems to be the SACK option used in [2],
> so maybe something on the route breaks it (without tunnels).
>
> Jarek P.
>    
Thank you for your reply. I have tried disabling SACK and then the 
performance when packet loss occured got even worse, and the rest of the 
time it was pretty similar.

After finally getting hold of someone I know at my ISP, I was told that 
they use TCP accelerators in their mobile network. Also, when looking at 
the packet captures from the server side I see that the sequene numbers 
are changed, so there is a machine doing something to the packets along 
the route. What I suspect is that this or these machines somehow breaks 
when a retransmission occurs. I am not quire sure what could cause it 
though, for example all dupAcks generated by the client are recieved by 
the server, but hopefully my ISP will be able to figure it out.

-Kristian