Re: [tcpm] New I-D posted : draft-moncaster-tcpm-rcv-cheat-00

On Tue, 2007-02-20 at 17:27 +0000, toby.moncaster@bt.com wrote:
> All, 
> 
> As you will shortly see we have just posted a new ID called "A  TCP Test
> To Allow Senders to Identify Receiver Cheating"
> draft-moncaster-tcpm-rcv-cheat-00. This draft was written as a result of
> (..)
> http://www.cs.ucl.ac.uk/staff/B.Briscoe/pubs.html#tcp-rcv-cheat.
> 
> After some background research we decided that an actual nonce would
> probably be impractical since it would require modifications to both

If you're referring to the ECN nonce, I think that it's not fair to
compare this with it (as you also do in the draft), as it additionally
tackles a different problem: concealing the reception of an ECN mark
is much easier to do / less problematic than optimistic acking /
concealing packet loss, and this is what the ECN nonce does but your
scheme doesn't.

On a side note, the following statement in the draft:

> The proposed solution depends, like the skipped segments solution, on
> the strict requirement that all TCP receivers have to send a
> duplicate acknowledgement as soon as they receive an out-of-order
> segment.

is at odds with RFC 2581, which says:

> Out-of-order data segments SHOULD be acknowledged immediately, in
> order to accelerate loss recovery. 

...although I wonder why this is only a SHOULD, and not a MUST,
and herewith suggest to change this in 2581bis, unless there's
a good reason not to do so.

Cheers,
Michael

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