Date   : Thu, 18 Feb 1993 10:52:26 GMT
From   : "M.J.Ebourne" <M.J.Ebourne@...>
Subject: Re: Cheapo network

> I agree that flat-out you can get very high bandwidth (though I must say I'm
> impressed that the olde wurlde tech. in the beebs can manage nearly 80Kbaud)
> The trouble is that if you start playing with that sort of speed in a network
> application you need a 100us interrupt cycle (remember that you're going to
> want to do something with the machine at the same time as being on the net!)
> you're doing well if you can get a 400us cycle out of a 6502 and even that
> will need a lot of bitdiddling if you're going to have a workable system.

The high baud rates are not that hard to achieve. During actual file transfer
you are not going to want to do anything else - filing systems don't
multitask on the beeb. I've written a Viewdata bulletin board system which
can pump menus out at over 40kbaud, and that is without doing anything
silly like disabling interupts. Indeed, the reason I know the baud rate,
is because the in & out baud rates are measured continuously to the
nearest 25baud, and displayed on the scrolling bar at the bottom!

During the menu display, the screen is updated as normal, and the sysop can
be busy doing other things with built in mouse controlled windowing type
system! And we still get 40Kbaud.

> As for coax, I would have thought that above about 10kbaud you're better off
> with screening. The company I was working for was Sollac, the largest steel
> production outfit in Europe. The net was supposed to work next to electric
> arc welders ;-) as it was to help control a steel rolling plant.

For that application, I think I'd recommend coax, too. :-)

> If the beeb ACIA can do simultaneous I/O (which I think it can as I remember
> testing mine by wiring out to in) then you have a chance of an ethernet

Indeed it can.

> Don't underestimate the speed problem. I was using a 486 at Sollac and we
> had to install special device drivers to get 95% efficiency (after framing
> & CRC) at 19k2. Does anyone know how Econet work(ed/s) ??

Ah, well that's a pc. Its only to be expected. These baud rates are all
achieveable - what I am saying is based on practical experience. The BBs
is running 24hours a day...

-- 
Martin Ebourne                             Email: mje@...        
Electronics, Southampton University