[HECnet] ANF10 network --> DN200 (RJE, Decnet) --> should be Ddcmp --> Re:4 --> Cryptic

[Johnny Billquist]

Well, I meant this in the context of a DUP11, but sure, it's also true 
with DMC.

But basically, in RSX, DECnet is just a component of something called 
the communications executive, or CEX. CEX provides its own environment 
in which multiple processes run, and provide services.

CEX then provides an interface to its drivers from RSX, which means that 
any RSX program can make use of the services and protocols that CEX 
have, without have DECnet in the picture.

So for example, CEX provides communication lines, which are packet 
based. If that is over asynch lines it utlizes DDCMP over async serial. 
Any application in RSX can make use of this. If you instead have a synch 
line, like a DUP11, or DMC, that is another interface inside CEX. From 
the outside it makes no difference if it is a DUP or a DMC. Bottom side 
is synch serial, using DDCMP. With DMC this is all done in the hardware. 
With a DUP11, CEX is doing the DDCMP layer in software.

For the user program this is all invisible. You just communicate over 
the DUP11, and it will be doing DDCMP.

If you actually want to use the DUP11 *whithout* DDCMP, then you'd go 
for the DUP11 device driver instead of accessing it through CEX.

And talking to a device using CEX in RSX means you talk to the "direct 
line access" interface, or DLX. That is just one interface, independent 
of what underlying hardware you are going to access. In the DLX, you 
start by opening the link, and for that you use the name, which is the 
same as the line name you see for DECnet. But you are in fact then just 
talking at the line level, using whatever protocol layer is used for 
that line. DDCMP, for example.

Anything using DDCMP is always in packets. Don't matter how the hardware 
looks.

DLX is also used to access ethernet, by the way. And that is how I 
coexist with DECnet in RSX, since ethernet can allow multiple channels 
on the same hardware.

I hope this makes sense. Else I can try to explain it more.

   Johnny

On 2021-11-19 17:22, Paul Koning wrote:
> I assume it means that RSX (and RSTS too) lets you use a DMC directly from an application as an I/O device you can open.  If so, you get a packet service that lets you transmit whatever packets you want, which will be sent encapsulated in DDCMP protocol.  In the RSX case I'd assume that includes support for maintenance mode (in RSTS that isn't supported).
> 
> 	paul
> 
>> On Nov 19, 2021, at 11:14 AM, R. Voorhorst <R.Voorhorst at swabhawat.com> wrote:
>>
>> Please can you explain your second sentence somewhat? I read:  "... the Ddcmp layer ... it does present it as a device ...". I do not perceive the connotation.
>>
>>
>> Reindert
>>
>> -----Original Message-----
>> From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On Behalf Of Johnny Billquist
>> Sent: Friday, 19 November, 2021 14:46
>> To: hecnet at Update.UU.SE
>> Subject: Re: [HECnet] ANF10 network --> DN200 (RJE, Decnet) --> should be Ddcmp --> Re:4
>>
>> RSX definitely can use a DUP11 standalone through DECnet. In which case it's software side DDCMP.
>>
>> Heck, you can also use the DDCMP layer yourself, without involving DECnet. It does present it as a device to the system on which you can send/receive packets.
>>
>>    Johnny
> 

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol