Re: [Linux-decnet-user] protocols

[Paul K. <pk...@eq...>]

Excerpt of message (sent 28 April 2002) by Brendan Minchin:

> Can you please tell me the layers of the DECnet protocol and compare
> them to the OSI seven layer model? Also can you tell me where to get
> info about each layer in the DECnet?

I meant to answer that first question too...

Decnet phase 4 predates the OSI model.  Phase 5 had a number of its
layer names changed so they wouldn't be as confusing to someone who
reads the OSI model.  Apart from that, the two have basically the same
layering:

Osi	Phase4		Phase5
7	apps		apps
6	-		-
5	(NSP)		Session Ctl
4	NSP		Transport
3	Transport	Routing
2	Data Link	Data Link
1	(data link)	Physical

So there's a pretty close match with two or three exceptions.  Phase 4
does not have a separate physical layer nor a separate transport
layer; you can see the functions of these two as part of the data link
and transport layers, respectively.  There is no layer 6 -- but then
again, I don't think there has ever been a layer 6 in recorded
history.  Finally, the names are different, which isn't all that bad
except for layer 3, which confusingly is called "transport" in Phase
4.  (Layer 4 is "NSP" which if you expand it also becomes confusing:
"Network services protocol".  So just keep it as "NSP"!)

	 paul