North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical RE: TCP congestion
In order to solve this, you need to see a trace from both sides of the WAN. Which side is your trace from? Can you see the original ACK on both ends? If the receiver is sending a DUP ACK, then the sender either never received the first ACK or it didn't receive it within the timeframe it expected. Brian -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Philip Lavine Sent: Thursday, July 12, 2007 1:07 PM To: nanog Subject: TCP congestion 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? Philip ________________________________________________________________________ ____________ Take the Internet to Go: Yahoo!Go puts the Internet in your pocket: mail, news, photos & more. http://mobile.yahoo.com/go?refer=1GNXIC
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