[tcpm] draft-moncaster-tcpm-rcv-cheat-02 probabilistic test

John Heffner <jheffner@psc.edu> Wed, 14 November 2007 16:57 UTC

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Date: Wed, 14 Nov 2007 11:57:04 -0500
From: John Heffner <jheffner@psc.edu>
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Subject: [tcpm] draft-moncaster-tcpm-rcv-cheat-02 probabilistic test
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Toby,

I'm not sure I completely understand some of the claims in Section 
6.2.2, particularly: "That is to say, a receiver can either honestly 
report the missing packets or it can suffer a reduced throughput by 
delaying segments and increasing the RTT," and "Equally, a receiver that 
delays transmission of the duplicate acknowledgements until it is sure 
it is being tested will leave an obvious pattern of acknowledgements 
that the sender can identify."

If I were designing a receiver to try to defeat this test, I would delay 
response by six segments, or a short timeout, whichever is less.  If I 
observe reordered segments, I would send the ACK/SACK that the sender 
would expect.  Additionally, I would ACK any lost segments, and any 
received segments as normal, only delayed by the time to receive the 
following six segments.

You seem to have thought about this strategy, but I'm not sure I see how 
the claims in section 6.2.2 apply.  I don't think this strategy will 
increase the RTT so much that it will cause significant performance 
reduction.  And I'm not sure how delaying the ACKs will leave an obvious 
pattern that the sender can identify.  Am I missing something?

   -John


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