Re: Excessive TCP retransmits over lossless, high latency link

Jamie Lokier
2001-09-03T17:59:30Z

kuznet@ms2.inr.ac.ru wrote:
> > Yes, definitely. Btw, I saw a ping round trip time of 162s just now.
>
> I do not understand, do you share this link with someone or
> ping over tcp connection?

I was doing ping with the TCP connection going. When there is no TCP
connection, ping time is 1-1.5 seconds.

> > I saw very few retransmits in a single message download. SACK appears
> > occasionally. I don't really understand the local reaction to SACK, or
> > why a SACK option appears in one ACK sent locally and not the following
> > ACK, even though the SACK mentions data that does not arrive between the
> > two locally sent ACKs.
>
> But I do not see _any_ sacks in your tcpdumps.

Sorry, you are right. I did see an sack, but not in this trace.

> > The throughput difference was obvious: POP3 negotiation + 30k message +
> > headers took:
> >
> > 5 min 31 sec downloading unknown OS -> Linux 2.4.7
> > 2 min 15 sec downloading Linux 2.4.2 -> Linux 2.4.7
>
> It is dominated by rtt, one rtt per segment. It is very strange
> that cwnd does not want to open. Maybe, it is worth to tcpdump at proxy.

Do you mean that you want to see the Linux -> Linux connection, with
tcpdumps at both ends?

-- Jamie