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Date: Sat, 6 Jul 1996 20:10:21 -0400 (EDT)
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: your mail
To: "Jacob M. Parnas" <jparnas@jparnas.cybercom.net>
cc: Richard Foulk <richard@pegasus.com>, hardware@freebsd.org,
        bsdi-users@bsdi.com
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> >Our cable company here in Honolulu is apparently going to use modems that
> >provide 6Mb in both directions.  The promise is $50/month.  The cable
> >modem connects to your ethernet.  The cable company is becoming an ISP,
> >in a big way.
> 
> Is it bidirectional (ie can you send) or does that have to go through some
> other channel?

That's what people are trying to tell you:  CABLE DOES NOT HAVE TO BE
ONE-WAY.  When he says "both directions", he really does mean both, as in
bidirectional. 

Some places with old cable systems are stuck with unidirectional 
transmission, and that means going the other way by phone modem, which
is marginally satisfactory at best.  Modern cable systems can do better.

> ...that 3-8 mbits/second,  Usually without putting a whole new
> set of cables underground (or above), its bandwidth would be split by many
> users and the for 1000 users, on average, that's the same as 3-8 Kbits per
> second...

The bandwidth is indeed split, but the question of "by how many users"
does not have a simple answer -- it depends on what the cable company has
done.  Note that the splitting is *not*, in general, over the entire
metropolitan area -- the cable company can and does subdivide.  The folks
in the Rogers Toronto-area experiment say that the net effective data rate
did vary depending on load, but it was always a lot faster than phone
modems. 

> And if you have to move, you may be out of luck.

ISDN has the same problem.

                                                           Henry Spencer
                                                       henry@zoo.toronto.edu