[HECnet] Hecnet and DDCMP

[Paul_Koning at Dell.com]

Sorry about being unclear.

Among the advantages of DDCMP is that it works on any link that can transmit 8 bit byte values, that's all it cares about.   Bisync has the same property, but HDLC does not (it has much stricter requirements).   That's why DDCMP works on both sync and async links essentially without any change (and for that matter works, at least in principle, on an 8 bit parallel link such as a classic PC printer port, though I don't know that it has actually been used on parallel links in the real world).   The same goes for Bisync (if you can speak of that protocol "working" at all, bletch); I remember having the distinct lack of pressure debugging an application that used bisync across DL11-E async links.

	paul

-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On Behalf Of Johnny Billquist
Sent: Thursday, January 05, 2012 1:37 AM
To: hecnet at Update.UU.SE
Subject: Re: [HECnet] Hecnet and DDCMP

Excellent. Then it do not require anything more than a link that can 
transport a stream of bytes.
You made it sound (to me), as if DDCMP expected the underlying link to 
provide more structure, which is what I wanted to check.

	Johnny

On 2012-01-05 02.23, Paul_Koning at Dell.com wrote:
Yes, DDCMP does its own block delimiting on both sync and async lines, basically the same way for both.   It recognizes the header by byte patterns plus good CRC, and the payload framing is controlled by the payload byte count that's mentioned in the header.

It's all in the spec.   Take a look, it's a very clear and very simple document.

	paul

-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On Behalf Of Johnny Billquist
Sent: Wednesday, January 04, 2012 6:46 PM
To: hecnet at Update.UU.SE
Subject: Re: [HECnet] Hecnet and DDCMP

On 2012-01-04 23.15, Paul_Koning at Dell.com wrote:
I assume there has to be a bit more to it, because DDCMP is a packet based protocol
(not a stream protocol as TCP is) and the higher layers rely on that.   So there
presumably is some form of framing in the emulated data stream to indicate where the
packet boundaries are.

Paul, how does this work when you have DDCMP over an asynch serial line?
There are no frames there. It is just a stream of bytes at the physical
layer, exactly the same as TCP for example. Yet, DDCMP talks over that
too... DDCMP must be implementing the blocking/deblocking on its own in
that case.

	Johnny


	paul

-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On Behalf Of Rob Jarratt
Sent: Wednesday, January 04, 2012 5:11 PM
To: hecnet at Update.UU.SE
Subject: RE: [HECnet] Hecnet and DDCMP

All I do in SIMH is to take the data bytes each end wants to send to the other end and send them over a socket, so I don't get involved with DDCMP itself. Both ends have to be SIMH for this to work. I don't do anything at the actual hardware level, although that would be nice. I think you can get synchronous serial cards for the PC but they are quite expensive.

Regards

Rob

-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE]
On Behalf Of Paul_Koning at Dell.com
Sent: 03 January 2012 21:18
To: hecnet at Update.UU.SE
Subject: RE: [HECnet] Hecnet and DDCMP

DMC-11 speaks DDCMP V3.1 (give or take some bugs in the "high speed"
version).   But that's sync only.   Depending on what you want to talk
to, a
DMC
(or its relatives DMR-11, DMP-11, or DMV-11) may not help; if the
other
end
speaks DDCMP over an async link (UART) then it won't work because the
character framing doesn't match.

That said, I wonder what it means to emulate a DMC-11.   You could have
it speak DDCMP over a UART, or something else entirely.   If the former
it
would
talk to another DDCMP node; if the latter it would not but it would
still
work
for tying one emulated DMC-11 to another.

If you want DDCMP, one approach is to get a copy of the spec, and
implement
what it says.   That works; it is how I implemented DDCMP support for
RSTS
V10
(based on an earlier version based on V9.6).   The protocol is quite
simple
and
the spec is well enough written that, if you do what it says, the
result
WILL
interoperate with hardware such as the DMR-11.   The only tricky one is
the
DMC-11 because it has some undocumented bugs;   the main one I remember
is that the high speed version can't handle back to back packets.   I
wish
I could
contribute the code   I wrote but I can't, for various reasons one of
them
is that
it's a RSTS device driver and written in 100% assembly language.

It would not be hard to do a version for other platforms; I once
looked at
a
Linux terminal protocol handler (forgot what that is called) that
could
hook
into DECnet/Linux.   Didn't get far enough on that, though.

	paul

-----Original Message-----
From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE]
On Behalf Of Mark Abene
Sent: Sunday, January 01, 2012 6:06 PM
To: hecnet at update.uu.se
Subject: Re: [HECnet] Hecnet and DDCMP

Jarratt, did you make this publicly available on the SIMH list?   It
would
be great
to have a DMC11 device emulated, since I insist on running RSTS/E v8
(for historical reasons... it was the last real RSTS before "the pollution").
RSTS/E v8
doesn't have ethernet support, so the only way I could have DECnet is
via
a
(previously unemulated)
DMC11 interface.   Does yours work well?

-Mark

On Sun, Jan 1, 2012 at 3:23 AM, Jarratt RMA
<robert.jarratt at ntlworld.com>
wrote:
Working with a friend, I have written a SIMH emulation of the DMC11
device, so you can do this with SIMH. It tunnels the bytes sent
to/from the device over a socket. We have used the SIMH emulation to
connect my friend to HECnet over a (simulated) DMC11.

The bit I am not entirely sure about is to what extent this is using
DDCMP as I don't have a full understanding of DDCMP.

Regards

Rob
On 31 December 2011 18:46, The Presence<tpresence at hotmail.com>
wrote:

Hey guys,

Has anyone worked out a mechanism to connect a node to hecnet using
DDCMP?
    Perhaps some tunneling technology over IP, or virtualized serial?

Kevin