[Info-vax] What would you miss if DECnet got the chop? Was: "bad select 38" (OpenSSL on VMS)

[Johnny Billquist]

On 2016-10-05 17:19, Michael Moroney wrote:
> Johnny Billquist <bqt at softjar.se> writes:
>
>> From DECnet point of view, it is just a simple line. Called something
>> like TCP-0-0. And you work with it just like any other line in DECnet.
>> It's a point-to-point line, over which DECnet establish a circuit to the
>> remote machine. No different than if you were to just have a simple
>> RS-232 cable between two machines, using DDCMP, and then have DECnet
>> communicate over that.
>
>> Really, this is identical.
>
> Oh, that is interesting. So the Multinet DECnet over IP is just a
> virtual point-to-point serial line, not a fake Ethernet like I was
> thinking it might be.  Real point-to-point links were common in the
> early days of DECnet before ethernet pretty much took over for
> short distance links.

Correct.

>> Multinet then have a tool to define the TCP/IP connection between the
>> two points, which is totally outside the knowledge of DECnet.
>
> So for a more complicated network, you'd need several of these virtual
> point-to-point links so everyone could talk to everyone else.

Well, depends on what you want. DECnet can forward as well as route 
traffic. You do not need a full mesh of connectivity. As long as there 
is just one path (no matter how convoluted) between two points, DECnet 
will work.
Additional paths are just for redundancy, and possibly increased 
throughput by path splitting.

> I don't know offhand if DECnet V has support for point-to-point links
> at all but if it does, Multinet's virtual p-p links should work with
> it as well. But with OSI over IP, there is no need other than to talk
> to a Phase IV node.

Right. I don't know either, and it also then becomes a question if a ptp 
link would be compatible between phase IV and phase V. But mixing phase 
IV and phase V is chancy at best.

>> And in the Multinet tool, you define the remote host and port. Multinet
>> will then establish that connection, using TCP or UDP. And once it is
>> up, then from the DECnet point of view, you have a link which transports
>> bytes between the two nodes, using that line.
>
> That makes sense.  A TCP link from A to B with a driver for a virtual
> serial line on each end that puts the stuff over the TCP link.
> (Or UDP. I don't know the advantage of one over the other for something
> like that)

Right.
And actually, the Multinet people should not really have done UDP, as it 
breaks a basic DECnet assumption.
DECnet assumes that any ptp link is error free, and delivers all data in 
order. This is ensured by DDCMP for an actual serial port link, for 
example. UDP violates this assumption, and DECnet does not always deal 
that well with it, so I would recommend people to use TCP. However, the 
overhead of TCP is a bit higher, so it becomes a bit of a tradeoff, as 
usual.

>> DECnet can route things just as normal. One more line does not change
>> anything fundamentally. It's just a line.
>
>
>
> As to the argument over the Multinet Phase IV p-p connections and the
> Phase V OSI over IP stuff, there is no reason why both can't coexist,
> as long as they use different TCP/UDP ports. To IP it's just more
> TCP/UDP packets.

Right!

> As to VSI, for Phase IV it's just a matter of not breaking anything
> in the Multinet code.  For Phase V it may depend on working on the
> Multinet PWIP driver, or maybe it will just work.

Exactly.

So I don't understand why Dirk is having so many issues with it all. The 
existing code for Phase IV in no way interferes with Phase V. If Phase V 
will work at all, or not, is unknown to me. And that is something VSI 
will have to deal with, Phase IV functionality or not.

And I would never expect interconnects over IP between Phase IV and 
Phase V to be relevant, or possible. And I don't think anyone would care 
about that use case.

	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