[tcpm] Example of 1323 window retraction problemPer my comments at the microphone at TCPM...
Matt Mathis <mathis@psc.edu> Tue, 11 March 2008 18:13 UTC
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Date: Tue, 11 Mar 2008 14:11:06 -0400
From: Matt Mathis <mathis@psc.edu>
To: TCP Maintenance and Minor Extensions WG <tcpm@ietf.org>
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Subject: [tcpm] Example of 1323 window retraction problemPer my comments at the microphone at TCPM...
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Consider a established TCP connection with WSCALE=7 (128 byte receiver window quantization), that is running with a very small windows because the receiver is bottlenecked and both ends are doing small reads and writes. Consider the ACKs coming back: seg.ack seg.win computed snd.win reviver's actual window 1000 2 1256 1300 sender writes 40 bytes and receiver ACKs: 1040 2 1296 1300 sender writes 5 more bytes and the receiver has a problem. Two choices: 1045 2 1301 1300 - BEYOND BUFFER 1045 1 1173 1300 - RETRACTED WINDOW This problems is completely general and can in principle happen any time the sender does a write which is smaller than the window scale quanta. In most stacks it is at least partially obscured when the window size is larger than some small number of segments because the stacks prefer to announce windows that are integral numbers of segments (rounded up to the next window quanta). This plus silly window suppression tends to cause less frequent, larger window updates. If the window was rounded down to a segment size there is more opportunity to advance it ("beyond buffer" case above) rather than retracting it. Thanks, --MM-- ------------------------------------------- Matt Mathis http://staff.psc.edu/mathis Work:412.268.3319 Home/Cell:412.654.7529 ------------------------------------------- Evil is defined by mortals who think they know "The Truth" and use force to apply it to others. _______________________________________________ tcpm mailing list tcpm@ietf.org https://www.ietf.org/mailman/listinfo/tcpm