[HECnet] DECnet session control specification

[Paul Koning]

I'm not having much luck looking for newer ones.   It may be possible to
reverse engineer the differences from the implementation source code, if
available.   I looked a bit at DECnet/E but it's not easily to parse...

Keep in mind the DECnet version handling and reserved field rules.

When mixed versions communicate, both sides report their version and the
higher version system is then responsible for speaking in a way that the
older system will understand.

"Reserved" means "send zero, ignore on receipt".   It most definitely
does NOT mean "check on receive that this is zero", that's a silly
mistake all too often make in protocol design.   This too is for mixed
version handling.   If a new flag can safely be ignored by an older
system, then the newer system can simply send that flag in what used to
be a reserved field, and the right thing happens.

Finally, proxy was originally a VMS specific enhancement and was adopted
in some other implementations (I know DECnet/E picked it up, at least in
a semi-compatible form).   I'm not sure that it was ever specified in an
architecture spec.

	paul

-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On
Behalf Of gerry77 at mail.com
Sent: Tuesday, January 05, 2010 8:46 PM
To: hecnet at Update.UU.SE
Subject: [HECnet] DECnet session control specification

Hello everyone!

During the last week or so I've spent many hours studying some DECnet
traffic because I was willing to better understand its inner working.

Well, I've discovered that the session control specification commonly
available on the Internet (V1.0) is not the latest, and it seems that
another newer version is not readily available.

While other DECnet protocols such as DRP and NSP appear to be current
(and
in facts their description matches actual data captured from the
Ethernet),
the SCP is obviously different both in formal definition and in
practice.

For example, the specification states that for V1.0 the version field
should
be 000 binary, but VMS sets it to 001 and a bit field that should be
reserved for future use and always set to zero has actually a meaning
(at
least one bit seems to be used to signal proxy access requests).

So the question is: does anyone here has a copy of a newer session
control
specification or at least knows which are the the differences between
V1.0
and the following (V1.1?) version?

Thank you very much,
G.