begin quoting Christian Seberino as of Fri, Nov 18, 2005 at 11:39:15AM -0800:
[snip]
> In short, every layer of network stack peel off *it's own* header as
> packet travels up to application layer IIRC.
It's its, not it's.
> I'm still not clear how come TCP stack doesn't need to care how big each
> TCP segment is. Sure it ultimately only cares about joining all
> segments in correct order but how can it do *that* without knowing where
> each segment begins and ends!?!?!
[snip]
> What about TCP and UDP's usage of a "pseudo IP header" when calculating
> their checksums? Those "pseudo IP headers" contain the sender and
> receiver's IP addresses!?
Ultimate addresses, yes. And the psuedo-header also provides a size.
> The TCP and UDP checksum fields
> therefore seems to lock-in TCP and UDP to use only IP!?!? (Very
> Microsoftish :)
According to RFC 793, page 51:
Any lower level protocol will have to provide the source address,
destination address, and protocol fields, and some way to
determine the "TCP length", both to provide the functional
equivlent service of IP and to be used in the TCP checksum.
The TCP protocol requires certain features of the protocol it runs over.
You're not locked into IP -- an even if you were "locked in", you can
route IP over other protocols, and many folks have done so.
-Stewart "We normally talk about TCP/IP as an indivisible tuple" Stremler
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