Michael Padlipsky (PADLIPSKY@A.ISI.EDU)
16 Mar 1987 11:28:05 EST

It's "apples and eggplants" to compare TCP/IP header sizes
with X.25's, as a rudimentary knowledge of Layering should
show. Rather than be coy and make Marshall Rose or Mike
Corrigan do the explaining, I'll accept the risk that Steve
Silverman won't believe me and try to save time by pointing
out that X.25 is at the "bottom" of L3 whereas IP is
at the "top" of L3 and TCP is L4 (and subsumes some of the
functionality of L5). Or, as I'd prefer to express it, X.25
is L I, TCP/IP L II. So any inference that going X.25 saves
bits is fallacious (unless the argument is that we should
go with the CCITT Suite, which isn't OSI and hence isn't what
the argument is about).

Aside to Dennis Perry: if you want the ARPANET to carry ten
times as many packets as it does at the same (subnet) cost,
you could always make the maximum packet size be .1 of what
it is and come pretty close, especially if you ban character-
at-a-time Telnet. (This one might be artichokes and brussels
sprouts, actually, given all the possible differentiae--though
maybe not, since it's still in essence attempting to compare
the incommensurate.)

cheers, map

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