TCP congestion

Fri Jul 13 18:23:45 UTC 2007

So, when you say "pickup again after 15-20 seconds" do you mean that
it takes 15-20 seconds to ramp back up to the original speed or that
the line is basically idle for 15-20 seconds before any packets start
flowing again? If the latter, I'd suggest that you take a look at the
apps some more..

Actually, you might want to try and duplicate the issue with
identical machines sitting next to each other and a piece of cable
between them...

On Jul 12, 2007, at 10:42 PM, Jay Hennigan wrote:

>
> Philip Lavine wrote:
>> Can someone explain how a TCP conversation could degenerate into
>> congestion avoidance on a long fat pipe if there is no packet/
>> segment loss or out of order segments? Here is the situation:
>> WAN = 9 Mbps ATM connection between NY and LA (70 ms delay)
>> LAN = Gig Ethernet
>> Receiver: LA server = Win2k3
>> Sender: NY server = Linux 2.4
>> Data transmission typical = bursty but never more that 50% of CIR
>> Segment sizes =  64k to 1460k but mostly less than 100k
>> Typical Problem Scenario: Data transmission is humming along
>> consistently at 2 Mbps, all of a sudden transmission rates drop to
>> nothing then pickup again after 15-20 seconds. Prior to the drop
>> off (based on packet capture) there is usually a DUP ACK/SACK
>> coming from the receiver followed by the Retransmits and
>> congestion avoidence. What is strange is there is nothing prior to
>> the drop off that would be an impetus for congestion (no high BW
>> utilization or packet loss).
>> Also is there any known TCP issues between linux 2.4 kernel and
>> windows 2003 SP1? Mainly are there issues regarding the handling
>> of SACK, DUP ACK's and Fast Retransmits. Of course we all know
>> that this is not a application issue since developers make
>> flawless socket code, but if it is network issue how is caused?
>
> Duplex mismatch on an intermediate ethernet segment?

Oooh, I like that one....

>
> --
> Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
> Impulse Internet Service  -  http://www.impulse.net/
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