Re: TCP congestion

[Jay Hennigan <jay () west net>]

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?

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Jay Hennigan - CCIE #7880 - Network Engineering - jay () impulse net
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