Re: Odd sequence....

From: Rogier Wolff (
Date: Mon Jun 05 2000 - 03:37:42 EST

Andi Kleen wrote:
> But it has. See packet 1.
> >
> > After 20 seconds of patience (*), at 16:58:40 I type another "return"
> > to try and get things moving again. At that moment bwww, sends a
> > packet indicating that we've missed 864-1696. Rosie then doesn't react
> > and acks whatever it HAS recieved, to try to tempt bwww to perform a
> > fast(!)-retransmit.
> I see nothing wrong.

Agreed. Indeed I didn't look good enough at packet 1.

Sorry for the waste-of-bandwidth.

Fact remains that with 20% packetloss, (I have a cable that seems to
generate that kind of packetloss), many, many TCP/ip sessions
hang. Even if they generate only about 2 or 4k of datatransfer. I
thought I had cought a "baddie" here, but you set me right on that.

I'll see if I can catch the reason why things seem to hang that

> 12 16:58:20.329548 14dyn184.61101 > bwww.ssh: . 856:856(0) ack 924
> 13 16:58:40.477658 14dyn184.61101 > bwww.ssh: P 856:876(20) ack 924
> 14 16:58:40.744978 bwww.ssh > 14dyn184.61101: . 1696:1696(0) ack 876

Some packet got lost.

> 15 16:59:19.536500 14dyn184.61101 > bwww.ssh: P 876:896(20) ack 924

14dyn acks immediately, but piggy backs some data in the ack.

Isn't it kind of odd, that in the 20 seconds between :20 and :40 the
original packet and something like 3 retransmits were lost? Would
TCP/IP allow bwww to reset the retransmit timer one notch down if it
receives the ack 924 ?

(TCP/IP algorithms are based on the "fact" that packetloss is caused
by overloaded routers. In my case that often isn't the case. I now
found a cable that I could use that generates 20% packetloss, but my
cable-company seems to find 5-10% packetloss in their network
acceptable, and it isn't related to congestion or anything.
Retransmitting every 3 seconds (no exponential backoff) would be the
best strategy to get "things done" under these circumstances).


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