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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.




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