[e2e] TCP fragmentation and reassembly

[Joe Touch]

David Borman wrote:
> 
> On Dec 8, 2005, at 1:11 PM, Joe Touch wrote:
> ...
> 
>> (i.e., it doesn't require 'equal to') I'm suggesting that an
>> _additional_ requirement is that TCP be able to support the reassembled
>> payload. There's nothing in 1122 that precludes that, and 793 implies it.
> 
> That already exists.  It's called the receive window.  Or are you
> suggesting that there are TCPs that can't handle packets that fit within
> their receive window?

I guess it's handled on the send side - the side would have an MSS
that's larger than the receive window, but never end up using it. It
seems odd to advertise the ability to receive a packet at TCP that it
not actually able to ever receive, however.

> ...
>>> Provided you know for sure which is the incoming interface.  You can
>>> always know what interface you are using to send packets, but in many
>>> multi-homed situations you can't guarantee on which interface the
>>> traffic will arrive.
>>
>> You know which ones were used; it might be sufficient to use the lower
>> bound of the incoming interfaces that were actually used as a limit
>> (lower bound of all interfaces if you haven't received anything).
> 
> Not necessarily.  For an outbound connection, you have to put the MSS in
> the initial SYN, so you haven't received any packets yet for that
> connection.  For an inbound connection, yes, you can look at what
> interface the SYN arrived on and use that in determining the MSS value
> to put in the SYN/ACK.
>         -David

Right.

Joe

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