Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!UM.CC.UMICH.EDU!Dave_Katz
From: Dave_Katz@UM.CC.UMICH.EDU
Newsgroups: comp.protocols.tcp-ip
Subject: How is TCP/IP carried on T1's?
Message-ID: <5427798@um.cc.umich.edu>
Date: 4 Jan 90 04:19:10 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 17

>Someone I know claims that most TCP/IP packets transmitted on T1 lines are
>imbedded in X.25 protocol packets.  Is this true, or what is actually
>used?   Or it TCP/IP alone with maybe an alternate checksum (CRC) sufficient?
 
It depends on which manufacturer makes the routers.  A number of proprietary
schemes are in use today;  I know of at least one vendor that uses pieces
of X.25.
 
Running IP directly over the data link is insufficient if you ever intend
to run multiple protocol families over the same link, since you need a
method of demultiplexing the different protocols.  For example, some
routers use a proprietary header containing the ethertype of the protocol.
 
The Point-to-Point protocol addresses these issues and is available
as an Internet Draft;  vendors will be quick to implement it once it
becomes an Internet standard, after which routers from different vendors
will actually interwork on point-to-point links.