North American Network Operators Group

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Re: TCP congestion

  • From: Leigh Porter
  • Date: Thu Jul 12 19:29:45 2007



Come on folks, don't be afraid. We all know the beast is to blame for
this, just don't say the name three times...

Shub Internet


Philip Lavine wrote:
I just don't understand how if there is 1 segment that gets lost how this coul
d translate to such a catastrophic long period of slow-start. How can I minimize
the impact of  the inevitable segment loss/out of order over a WAN. Is QoS the
only option?

----- Original Message ---- From: Stephen Wilcox <[email protected]> To: Philip Lavine <[email protected]> Cc: nanog <[email protected]> Sent: Thursday, July 12, 2007 1:09:24 PM Subject: Re: TCP congestion

Well, if its out of order its the same as if its lost or delayed, it needs to
see that missing segment before the window is full

As mentioned you need to get dumps from both ends, you will almost definitely
find that you have packet loss which tripped tcp's slow start mechanism.

Steve


On Thu, Jul 12, 2007 at 12:02:49PM -0700, Philip Lavine wrote:


Even if the segment was received out of order what would cause congestion avo
idance to starve the connection of legitimate traffic for 15 to 20 seconds? That
is the core of the problem.

----- Original Message ---- From: Fred Baker <[email protected]> To: Brian Knoll <[email protected]> Cc: Philip Lavine <[email protected]>; nanog <[email protected]> Sent: Thursday, July 12, 2007 11:56:06 AM Subject: Re: TCP congestion


On Jul 12, 2007, at 11:42 AM, Brian Knoll ((TTNET)) wrote:



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.

or received it out of order.

Yes, a tcpdump trace is the first step.






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