[e2e] A simple scenario. (Basically the reason for the sliding window thread ; -))

Joe Touch touch at ISI.EDU
Thu Jan 11 10:13:13 PST 2007

Agarwal, Anil wrote:
> Joe Touch wrote -
>>> Well, it´s just how I understand the semantics of a "CLOSE ACK". When a
>>> receiver issues a CLOSE ACK, we know that all data has reached the
>>> receiving socket.
>> We should know that. But when we have intermidiates spoofing ACKs, all
>> we know is that the two endpoints agree that they have closed. The data
>> itself is not known.
>> Case in point - if the intermediary ACKs data and continues to buffer
>> it, and the window wraps, and then the intermediary goes down, the
>> endpoints think the data reached the buffer correctly but it really
> did not.
> Are you describing a scenario where a TCP-Splitter buffers up 2^32 bytes
> of sender
> data without delivering any to the receive end-point, then goes down, and
> the end-points continue the connection using the wrapped
> sequence number, which in this case match up just right, so that the
> intervening
> 2^32 bytes disappear down a black hole, without the sender or receive
> being any wiser?

Yes. The system can wrap without things matching up _exactly_, depending
on how big the CWND is, though, so this isn't as absurdly specific as it
appears at first glance.


Joe Touch
Sr. Network Engineer, USAF TSAT Space Segment

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