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)