Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!cs.utexas.edu!usc!apple!well!gors From: gors@well.UUCP (Gordon Stewart) Newsgroups: comp.protocols.tcp-ip Subject: Re: Info on implementation details... Message-ID: <13201@well.UUCP> Date: 18 Aug 89 15:58:00 GMT References: <21853@louie.udel.EDU> <718@east.East.Sun.COM> Reply-To: gors@well.UUCP (Gordon Stewart) Distribution: usa Organization: Whole Earth 'Lectronic Link, Sausalito, CA Lines: 36 In article <718@east.East.Sun.COM> geoff@East.Sun.COM (Geoff Arnold @ Sun BOS - R.H. coast near the top) writes: > >What seven levels? Not even ISO has seven levels. You need to read >Mike Padlipsky's "Elements of Networking Style" to get rid of Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Application Layer Presentation Layer I count seven. But then, I'm off caffeine this week, so maybe I miscounted! :-) In answer to the original query, and your flippant reply, it is true that most implementations provide a programmatic interface, which means Transport level at best, with some Session material (connection-oriented sockets). There is considerable effort to implement all seven (SEVEN, count 'em) layers of ISO OSI on top of TCP/IP, despite the fact that they are not isomorphic in the first few layers. DOD and others have a big investment in TCP/IP, but there is a billion dollar push for OSI. The physical and data-link layers are usually hardware/device - driver level; The Network and Transport level services are provided by daemon processes in most unix systems - session level services involve library function calls that give access to lower levels. -- {apple, pacbell, hplabs, ucbvax}!well!gors gors@well.sf.ca.us (Doolan) | (Meyer) | (Sierchio) | (Stewart)