Thicknet (was Re: BBS's)

From: Eric J. Korpela <korpela_at_ellie.ssl.berkeley.edu>
Date: Wed Nov 22 11:14:28 2000

> >
> > > For older (classic) computers, the bus bandwidth won't support 100Mbps
> > > ethernet, so you have to go with one of the 10Mbps standards (I'll ignore
> > > the original 3Mbps.. :-)).
> >
> > I've only found one place where it's a problem so far, with an NE2000 card
> > in a slow XT compatible the data rate (even at 10 Mbps) was too high for it
>
> I would be suprised if a PDP11 or PERQ or D-machine or... would manage
> anything close to 100Mbps. In fact I know it won't.

They don't need to. Nothing stops machines from talking 10 Mbps over
10baseT. That's what the 10 stands for. As long as you've got appropriate
hardware, they can commingicate with a 100 Mbps machine elsewhere on the net.
I've got 4 machines on the desk behind me on a 10 Mbps hub. The hub is
connected to the 100 Mbps switch that the machine on my desk is connected to.
I have no problems with my 100 Mbps full duplex machine talking to 10 Mbps
half duplex machines. I don't claim to know how the switch negotiates
rates and duplex. I just know that it does.

> Of course another issue is that some of these machines have built-in
> ethernet interfaces (PERQs do, for example), and there's no way of adding
> a 100Mbps card to them.

If you've got 10base2 nothing stops you from connecting it to a 100baseT
network through a repeating hub or switch. There's no need to cripple the
fast machines to support the old machines.

> Or because older, larger, hardware is often easier to maintain. Put it
> this way, the DELNI (8 port AUI 'hub') is a lot easier to repair than
> most of the 10baseT hubs I've seen. The DELNI is mostly 10K ECL. The
> 10baseT hub uses a single AMD chip that while standard (I have the
> datasheet somewhere), is not easy to get as a 1-off.

But at $80 a new 100 Mbp hub doesn't break the bank. (I also have never had
a hub or switch fail. Except at work a cheap 100 Mbps switch that we were
pumping a continuous 40 Mbps through was getting intermittent failures.
We replaced it with a better one and put the old one on a lower traffic line,
no problems since.)

My guess is that my switches will be replaced by gigabit equivalents before
they fail. My hubs will probably be replaced from surplus stores as people
upgrade their hubs to gigbit.

> > Another general complaint is that 10BaseT to 10Base2 media converters are
> > too damn expensive. You can't swing a live cat without hitting a coax
>
> The media converter has to be a repeater IIRC, and has to correctly
> handle collisions on both sides. That makes it more complex than a simple
> transceiver. And I guess they're less used than transceivers so there's
> less 'economy of scale'.

That's probably true. With 100baseT the fast side probably needs to be able
to do the speed/duplex negotiation properly as well.

On a related note, are there standards for wiring an RJ45 for phone use?
For localtalk? (I would assume that it would be possible to put both
in one.) It would be nice to have the wired such that a misconnection
(ethernet into phone) won't fry anything. It would also be nice to sprinkle
RJ45 sockets around the house and decide what to use them for later.

Eric
Received on Wed Nov 22 2000 - 11:14:28 GMT