North American Network Operators Group

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Re: TCP congestion

  • From: Warren Kumari
  • Date: Fri Jul 13 14:33:53 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 - [email protected] Impulse Internet Service - Your local telephone and internet company - 805 884-6323 - WB6RDV

-- She'd even given herself a middle initial - X - which stood for "someone who has a cool and exciting middle name".

-- (Terry Pratchett, Maskerade)