Re: TCP congestion

[Warren Kumari <warren () kumari net>]

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 () impulse net
> Impulse Internet Service  -  http://www.impulse.net/
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