nanog mailing list archives
Re: TCP congestion
From: Warren Kumari <warren () kumari net>
Date: Fri, 13 Jul 2007 14:23:45 -0400
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 100kTypical 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/ Your local telephone and internet company - 805 884-6323 - WB6RDV
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Current thread:
- TCP congestion Philip Lavine (Jul 12)
- RE: TCP congestion Brian Knoll (TTNET) (Jul 12)
- Re: TCP congestion Fred Baker (Jul 12)
- Re: TCP congestion Jared Mauch (Jul 12)
- Re: TCP congestion Valdis . Kletnieks (Jul 12)
- RE: TCP congestion michael.dillon (Jul 12)
- Re: TCP congestion Joe Loiacono (Jul 12)
- Re: TCP congestion Jay Hennigan (Jul 12)
- Re: TCP congestion Warren Kumari (Jul 13)
- <Possible follow-ups>
- Re: TCP congestion Philip Lavine (Jul 12)
- Re: TCP congestion Stephen Wilcox (Jul 12)
- Re: TCP congestion Philip Lavine (Jul 12)
- RE: TCP congestion Brian Knoll (TTNET) (Jul 12)
- Re: TCP congestion Iljitsch van Beijnum (Jul 12)
- Re: TCP congestion Stephen Wilcox (Jul 12)
- Re: TCP congestion Kevin Loch (Jul 12)
- Re: TCP congestion Joel Jaeggli (Jul 12)
- Re: TCP congestion Leigh Porter (Jul 12)
- RE: TCP congestion Brian Knoll (TTNET) (Jul 12)