4 May
2018
4 May
'18
11:03 p.m.
On May 4, 2018, at 2:46 AM, Johnny Billquist <bqt
at softjar.se> wrote:
On 2018-05-04 05:55, Robert Armstrong wrote:
That's not exactly right. There are a number of different objects at several layers.
The routing layer has two: "circuit" and "adjacency". Circuit is the
communication service provided by the datalink layer. Adjacency is the information the
routing layer has about a given neighbor. If the circuit is point to point, there is
exactly one adjacency per circuit. If broadcast, there can be many (and they can be
mixed: some endnode adjacencies, some routing adjacencies).
The data link layer also has two objects: "line" and "circuit". Line
corresponds to a physical wire. Circuit is the communication service provided to the
layers above. I don't remember how X.25 links are modeled in the DECnet data link
layer, never worked on that stuff. Broadcast links like Ethernet have one circuit per
line. Point to point links like the DMC-11 also have one circuit per line. Multipoint
links such as a DMP-11 at the master end have as many circuits as there are configured
drops; each circuit describes the connectivity to a particular multidrop slave station.
So from the routing layer point of view, there is NO difference between DMC and DMP -- in
each case, routing sees point to point circuits. The multiplexing for a multipoint link,
if used, is in the data link layer, not in routing. On the other hand, with Ethernet the
multiplexing (for the different neighbors) is in the routing layer, NOT the data link
layer.
It would certainly be plausible to model Multinet as a multidrop link, like a DMP-11. If
you do that, you'd still see multiple circuit objects in routing, each with its own
name and state and all that. Then you can make the TCP (or UDP) port number be a line
attribute in the datalink layer. That all fits.
I should look at the X.25 model more closely; it might be a better fit still.
Meanwhile, on an unrelated topic, are there any Multinet implementations that support
IPv6? My home IP connection supposedly is IPv6 capable, though I've never succeeded
in getting that to work.
paul
I guess a more direct question for the DECnet
experts out there would be, "can any DECnet circuit cope with multiple adjacent nodes
on the same circuit?" I always thought Ethernet circuits were special in that
regard, but maybe not. If any single circuit can have multiple adjacencies, then you
could make a Multinet driver that accepted multiple connections.
There are a little bit more to it, but first of all, ethernet is special. The protocol
DECnet uses over ethernet is a bit different than the protocol used over point-to-point
links.
But in addition, you also have multipoint circuits, which is a variant of point-to-point
circuits, but which have several endpoints/adjacent nodes. So ethernet is not the only one
able to do that.