🚀 go-pugleaf

Hi,
I was in Marshall Rose's (very well done) class at InterOp, and that
is essentially what I know about OSI (plus some OSI sessions and random
stuff picked up from this newsgroup).  Please bear this in mind if this
turns out to be a wildly stupid question.

I think I understand (at least some of) the controversy between
connectionless and connection-oriented Network layers, but I don't
understand why OSI has to have 5 Transport standards.  TP4 could certainly
run over X.25 as well as over connectionless couldn't it?

So, why not just run TP4 everywhere and leave the controversy in the 
Network layer?  

If you have two ES's connected with X.25, what cost would TP4 add if
you used it in place of TP0?  Wouldn't header prediction algorithms work
100% of the time in that case?  So, the extra cost would be the
checksumming and some timer maintanence.  But, Van Jacobson originally,
and now a whole host of other folks have shown that this processing is
NOT a bottleneck if your transport is properly implemented (and they've
also shown how to implement it).

It can't be this simple, I must be missing some important TECHNICAL
argument.  (I'm not interested in Political reasons at the moment.)
	Thanks very much,
			Cliff Frost <cliff@cmsa.berkeley.edu>