TCP congestion

Fri Jul 13 02:42:38 UTC 2007

Philip Lavine wrote:
> Can someone explain how a TCP conversation could degenerate into congestion av
oidance on a long fat pipe if there is no packet/segment loss or out of order se
gments?
>
> 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 afte
r 15-20 seconds. Prior to the drop off (based on packet capture) there is usuall
y a DUP ACK/SACK coming from the receiver followed by the Retransmits and conges
tion avoidence. What is strange is there is nothing prior to the drop off that w
ould 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 S
P1? Mainly are there issues regarding the handling of SACK, DUP ACK's and Fast R
etransmits.
>
> Of course we all know that this is not a application issue since developers ma
ke flawless socket code, but if it is network issue how is caused?

Duplex mismatch on an intermediate ethernet segment?

--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV