SV: RE: [HECnet] Hecnet and DDCMP

[Kevin Reynolds]

Johnny,

I entirely agree with you.   I do understand serial  signalling, however, I have zero experience with DDCMP.   I know it was one of the first pipelined protocols, had the ability to piggyback additional data with ACKs and such as well as error correction capabilities that were not very common at the time of the development completion.   I understand entirely that the speeds will be very slow, and I was expecting 1200bps and 2400bps, because that was the technology available at the time is deployed in the field.   Once I feel I have a good understanding of the protocol, I will likely move on to ethernet (although I have far more experience there), simply because I will step into the decnet plus arena.

Perhaps it seems more complex that I am making it, but I don't learn from reading as much as I do from using and troubleshooting.

Kevin


> Date: Tue, 3 Jan 2012 04:36:12 +0100
> From: bqt at softjar.se
> To: hecnet at Update.UU.SE
> Subject: Re: SV: RE: [HECnet] Hecnet and DDCMP
> 
> Kevin, what you are basically talking about here then is how do diagnose 
> and debug a broken serial connection. It's the same no matter if you are 
> running SLIP, PPP or DDCMP on that serial link. It's still just a cable 
> with GND, RX and TX, and possibly some modem control signals.
> 
> And it is no different if you instead are doing interactive traffic, 
> such as a normal terminal connected to a computer. It's still the same 
> serial connection.
> 
> If you want to understand how a serial port works, that is excellent. 
> But the first thing you need to understand is to differentiate between 
> the physical layer, and the communications protocol that runs on top of 
> that physical layer.
> 
> As for PPP or SLIP on VAX/VMS, no, that did not exist earlier than 
> DECnet over serial, as VAX/VMS had DECnet before it had TCP/IP, and SLIP 
> can only talk TCP/IP. PPP can in theory run any protocol, but it was 
> still not implemented on VAXen for DECnet.
> But my point was that if you want to tunnel DDCMP, it will be exactly 
> the same solution you'd do if you wanted to tunnel any protocol using a 
> serial interface. There are absolutely no difference from your tunnel 
> point of view whatever protocol is used on the link.
> It will only be a stream of bytes on a serial link anyway.
> 
> And yes, it will work just fine running DDCMP on top, and you can get 
> DECnet connectivity that way. However, it is not very fun, since the 
> actual speed of the serial interface will be 9600 bps no matter what, if 
> you have physical machines involved, since DECnet insists on setting the 
> speed of DDCMP interfaces to that, or slower.
> 
> Johnny
> 
> On 2012-01-03 04.02, Kevin Reynolds wrote:
> > Johnny,
> >
> > First and foremost, I want to learn how to configure and understand how
> > these devices connected historically so I can troubleshoot the
> > connectivity. This gives me the best feeling of true understanding.
> > Unfortunately, I don't have a slew of these systems (I have a single
> > Microvax II) that I can use to interconnect, so I am locked into
> > simulating at least one end of the connection. I was hoping to do this
> > with simh. Secondly, I was hoping to create error conditions and
> > determine whether I can diagnose the problem.
> >
> > As this is legacy hardware, protocols, and otherwise, I understand that
> > aside from understanding how some of our modern protocols and systems
> > emerged from knowledge of the old systems. I am I really hoping to start
> > a little further back to solidify my understanding of modern technology
> > without all of the additional layers of distraction included with modern
> > systems.
> >
> > Did the VAX/VMS platform have an option to include PPP or SLIP previous
> > to decnet +? I have a good knowledge of these protocols. I used slip
> > back in the day when I had to connect with a pr1mos system that wouldn't
> > allow pass-through connection to the internet. PPP, especially multilink
> > using PPP I have implemented multiple times (even recently...silly, but
> > I didn't choose). My ultimate goal is to pass decnet phase IV (not plus)
> > traffic over the connection.
> >
> > Thanks,
> > Kevin
> >
> > > Date: Mon, 2 Jan 2012 11:15:34 +0100
> > > From: bqt at softjar.se
> > > To: hecnet at Update.UU.SE
> > > Subject: Re: SV: RE: [HECnet] Hecnet and DDCMP
> > >
> > > The biggest issue I don't understand here is why.
> > > If you tunnel a serial port, you tunnel a serial port. DDCMP is totally
> > > invisible to you.
> > >
> > > You will not learn, or need to understand anything about DDCMP for this.
> > > A serial port sends bytes. You pass those bytes one. Everyone is happy.
> > >
> > > What kind of protocol is implemented, using those bytes, are very
> > > invisible and irrelevant to the tunnel, just as it is to a cable.
> > >
> > > You might as well tunnel SLIP, or PPP. It will work just the same.
> > > They are all just implementing a network layer on top of a serial
> > > connection.
> > >
> > > What are you really trying to accomplish?
> > >
> > > Johnny
> > >
> > > On 2012-01-01 01.57, The Presence wrote:
> > > > Bob,
> > > >
> > > > I really am wanting to use DDCMP for learning purposes. I want to build
> > > > a decnet phase IV network with DDCMP, however, I want to also have the
> > > > ability to pass traffic through to connect to additional nodes that are
> > > > net connected.
> > > >
> > > > Kevin
> > > >
> > > >
> > ------------------------------------------------------------------------
> > > > To: hecnet at Update.UU.SE
> > > > Date: Sat, 31 Dec 2011 16:41:02 -0800
> > > > Subject: Re: SV: RE: [HECnet] Hecnet and DDCMP
> > > > From: bob at jfcl.com
> > > >
> > > >
> > > > What is it that you actually want to connect? For the most part, a
> > > > Multinet link simulates the "user experience" of a DDCMP connection
> > > > tunneled over IP. Multinet is a point-to-point DECnet circuit which,
> > > > except for the device names, is functionally identical to any DDCMP
> > link.
> > > > The only reason I can see for using a real DDCMP serial connection
> > > > (either sync or async) would be to connect a machine that didn't
> > support
> > > > an Ethernet interface.
> > > > Bob
> > > >
> > >
>