Path: utzoo!attcan!uunet!cs.utexas.edu!csd4.csd.uwm.edu!mailrus!husc6!genrad!decvax!jfcl.dec.com!frg
From: frg@jfcl.dec.com (Fred R. Goldstein)
Newsgroups: comp.protocols.iso
Subject: Re:  ISDN and OSI relationship
Message-ID: <503@jfcl.dec.com>
Date: 3 Aug 89 15:01:42 GMT
References: <8906172235.AA25320@ucbvax.Berkeley.EDU>
Reply-To: frg@jfcl.nac.dec.com.UUCP (Fred R. Goldstein)
Organization: Digital Equipment Corporation
Lines: 28

In article <8906172235.AA25320@ucbvax.Berkeley.EDU> dcrocker@AHWAHNEE.STANFORD.EDU (Dave Crocker) writes:
>Let me try to parade my ignorance and see if anyone wants to join,
>waiving flags are playing appropriate marching music:
>
>As I perceive ISDN, it is a conduit for raw bits, roughly on the "level"
>with X.25.  (Lots of differences in mechanism, etc, but its actual
>utility to a person/resource is at that level.)

Actually, ISDN Packet Mode (X.31) is pretty much identical with X.25
if you use one of the options (circuit-mode call to an X.25 switch);
if you use the other option (packet-mde call), the data transfer phase
is still pretty much the same thing.  ISDN didn't reinvent the wheel.

>Hence, it fits into OSI Layer 2 and the sub-network sub-layer of Layer
>3.  To plug it into the rest of the OSI stack, you build an appropriate
>Subnetwork Dependent Convergence Module, also in Layer 3, and then the
>rest of the stack doesn't know there is anything special to deal with.
>
>Yes?

Yes!  Indeed your description is remarkably accurate, especially since
most ISDN weenies don't know what the subnetwork role (not "sub-layer",
for some odd reason ISO doesn't like that term) even is.  But ISDN
packet mode is precisely a connection-oriented subnetwork that is 
capable of delivering the OSI Network Service, per ISO 8648.

ISDN Circuit Mode is just a Layer 1 bit-delivery service.
     fred (member, ANSI T1S1)