Re: [Tsvwg] overlapping TCP segments during reassembly

On Monday, August 25, 2003, at 08:56 PM, Murali Bashyam wrote:

> Hi
>
> Is there any guidelines outlined by any TCP RFC's  for determining what
> data in the sequence space to keep and what to drop during TCP out of
> order packet reassembly when there are overlaps? The BSD code tries to
> trim the incoming segment when there is an overlap with a previous
> segment in sequence space, and trims the already queued segments when
> there is an overlap with succeeding segments in sequence space. I was
> curious abt the motivation behind this strategy.
>
> Murali
>

Certain things are implied:

1) overlaps indicate retransmissions.

2) multiple valid segments must all have the same value
    for any given byte in the TCP stream, i.e. the
    retransmit can only correct transmission errors
    it cannot "fix" the data.

3) you can only deliver a given byte to the TCP consumer once.

So, if you have a buffered but undelivered sequence, should
you replace it with new content? Well, since you know the
values are the same, why not optimize the copy by simply
not performing it?

Caitlin Bestler - cait@asomi.com - http://asomi.com/

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