topic Re: Connecting Thinnet to 10Base5 in Operating System - OpenVMS

Connecting Thinnet to 10Base5

Duane Sadowski — Wed, 30 Jul 2008 02:09:50 GMT

Hi. I'm having a problem with a VAX 4000-300 that is connected to a 10Base5 network using the VAX's AUI connector. The AUI cable tends not to maintain adequate contact with the VAX's AUI connector. The VAX has two network connectors, an AUI connector and a BNC (Thinnet) connector, and one suggestion that I received was to use the BNC connector and a Thinnet cable instead of the AUI connector.

I'm writing to ask how one would connect a Thinnet cable to a 10Base5 network (to a DELNI or to a tap). I gather that one way to do this is to use a DEMPR repeater or a DESPR repeater to convert from Thinnet to AUI. Is that indeed an appropriate way to convert from Thinnet to AUI? Is there a better way?

Re: Connecting Thinnet to 10Base5

Hoff — Wed, 30 Jul 2008 03:23:04 GMT

The AUI connection was a more common path for this, as it was a powered connection; the DESTA or such was "just another transceiver", as far as the host Ethernet NIC was concerned.

The AUI slide-locks were a bit insecure even when new; most of us used wire ties or such to secure the cabling into the connector.

With ThinWire, you need an external power source and (typically) an external hub to get from 10Base2 ThinWire to 10BaseT Twisted Pair RJ45.

The DEMPR is a multiport repeater; you probably don't want that. That box was analogous to the DELNI; of an Ethernet cable plant in a box. (And IIRC, the DEMPR was all-ThinWire. The DELNI was all AUI.)

There are various small hubs with a ThinWire connection; here, you'd need a couple of 50 ohm terminators, a length of RG-58A/U coax with BNCs, and two T connectors.

For example, the Compaq HB1111, or the Blackbox "Compact Media Converter, 10BASE-T/10BASE2" widget.

Or scrounge up a DELQA or DESQA or such; an AUI Q-bus Ethernet adapter, and use your existing AUI transceiver.

I'd probably look to switch the VAX 4000 model 300 over to simh or to CHARON-VAX or other emulation; to trump the whole problem. Or to move the application(s) forward to OpenVMS Alpha; you might find a used Alpha at not that much more than the cost of some hubs I've seen around over the years.

Boy those are some old brain-cells that just got dusted off. Thanks for the trip down Ethernet memory lane....

Re: Connecting Thinnet to 10Base5

Hein van den Heuvel — Wed, 30 Jul 2008 03:51:06 GMT

I would think mechanical first.
Is the slider in place?
A squirt of fresh air / brush contacts?
Can you support it with a piece of wire, nylon cable tie or rubber band, to stay at a 90-degre angle?

Do you really mean 10Base5? As in THICK-WIRE Ethernet?
http://en.wikipedia.org/wiki/10BASE5

Do you not have Twisted-pair (10base-T) connectivity nearby? Or a 10base2 - Thinwire segment?

My VAX 4000/60 also has an AUI and Thinwire.
I used to a cigarette pack size blob called |d|i|g|i|t|a|l| DETPM AUI on one side, T0base-T on the other side.
I have a similar blob from HP: EtherTwist MAU

I since use an old Compex MicroHub/8 for my 'control'/monitor network. It has a 8 10Base5 ports (one up) and a Thinwire.

btw... for yucks I just tried whether the thinwire on my DECserver 90m was 'live', the feed being Twisted-Pair. No luck.
It's owners manual (EK-DSRVH-OM. A01) already suggested that would not work: "You should choose only a ThinWire or 10BaseT connection. If you connect to both, the connection will not function properly."

fwiw,
Hein.

Re: Connecting Thinnet to 10Base5

Steven Schweda — Wed, 30 Jul 2008 03:51:47 GMT

> [...] Thanks for the trip down Ethernet
> memory lane....

I'll say. My basement hardware collection
includes a few unlikely-ever-to-be-used
gizmos with BNC on one end and AUI on the
other. They sold for about $20 the last time
I cared. Junk bins (or land fills)
everywhere are probably filled with them,
now. Mine say Allied Telesis and CentreCom
on the side. The corresponding genuine DEC
gizmos always cost more, so I never learned
all the DExxx names, but I'd guess that
almost anything with the right connectors
would do the right thing. BNC "T" adapters
and 50-ohm terminators are also must-haves.

> The AUI slide-locks were a bit insecure
> [...]

The right-angle connector on a BNE4D-02
(Hmmm. Looks more like 2 meters than 2
feet.) cable works just fine on my VAX 4000
model 200. (It goes to an AUI-twisted-pair
gizmo, and on to the switch from there. I
haven't seen a DELNI under power for many
years.) Not having buggered the AUI
connector on the CPU console by cantilevering
some horse's-leg straight-out cable from it
probably helps.

Re: Connecting Thinnet to 10Base5

Jon Pinkley — Wed, 30 Jul 2008 06:57:09 GMT

As others have asked, is the 10Base5 cable still being used? That's the 1/2 inch diameter stiff coax cable.

If all you want to do is prevent the AUI cable from falling off the AUI connector, and you don't frequently remove it from the VAX, I would unscrew the "posts" that the cable latch connects to (from the VAX's AUI), and replace them with jack-screws like those used for serial connections (DB25 and DB9). Then remove the latch and use machine screws to hold the connector on. That was standard practice at our shop when we were using 10Base5 25 years ago. The only disadvantage is that it takes a bit longer to disconnect the cable, but that is much better than it coming loose when someone bumps the cable.

Jon

Re: Connecting Thinnet to 10Base5

Robert Gezelter — Wed, 30 Jul 2008 11:39:39 GMT

Duane,

The "cigarette pack" transceivers that convert AUI to 10BaseT are still available last time I checked (at least on the web and through mail order).

Cable to cable connection (Thinnet to Thicknet) requires a powered box that in effect acts as a repeater. This is also subject to the "maximum repeaters" rule in the IEEE 802.3 specification.

Is it absolutely certain that the 10Base5 (Thickwire) is the actual backbone at this point? It seems surprising, as that would seem to limit the backbone bandwidth.

- Bob Gezelter, http://www.rlgsc.com

Re: Connecting Thinnet to 10Base5

Kelly Stewart_1 — Wed, 30 Jul 2008 13:19:56 GMT

Duane,

Yes, a DESPR will work just fine. A DEMPR will also work, although as Hoff pointed out it is overkill since it has 8 Thinwire ports instead of just one.

A more modern version of the DESPR/DEMPR is the DECRepeater 90; it requires a piggy-back power supply or a DEChub. But there were a few variations and not all of them had AUI ports. I think the DECREpeater 90FA did (it also had a fiber port).

Of course, with these solutions all you'll do is move the AUI connection from the back of the VAX to the DESPR or whatever else you wind up using.

If I remember correctly, a DESTA will not work. It needs power from the AUI connection and the tap will not supply it.

Kelly

Re: Connecting Thinnet to 10Base5

Richard Brodie_1 — Thu, 31 Jul 2008 12:09:06 GMT

Hoff: "I'd probably look to switch the VAX 4000 model 300 over to simh or to CHARON-VAX or other emulation; to trump the whole problem."

I would say the biggest problem is having a 10BASE5 network. Otherwise you are going to end up trying to connect a 1000BASE-T CHARON-VAX to an AUI connector.

Kelly "If I remember correctly, a DESTA will not work. It needs power from the AUI connection and the tap will not supply it."

Yes, although that is merely the most obvious reason why it wouldn't work.

Re: Connecting Thinnet to 10Base5

Hoff — Thu, 31 Jul 2008 14:13:16 GMT

I guess whether the biggest problem here is the 10Base5 or 10Base2 network or the VAX is a matter open to some debate; barring a massive installed cable plant and no means to upgrade same, I'd assume that it's the VAX that is driving the cable plant and network technology selection and not the other way around.

Accordingly, replacing the VAX with an emulation is often a quick and compatible and easy way to have a VAX on a Gigabit 10baseT network, and to replace the VAX and its ancillary I/O and storage hardware with newer (and faster) hardware.

The one technical reason to keep one of these VAX 4000 boxes is the Q-bus, and particularly some unusual I/O widget and/or software tied to a widget. (There can be a seemingly infinite number of administrative restrictions that mandate retention of the VAX box; red tape is like that.)