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From: juraschek@gmuvax.gmu.edu
Newsgroups: sci.electronics
Subject: Re: "spiking" of cable-TV descramblers
Message-ID: <1991May28.133901.51379@gmuvax.gmu.edu>
Date: 28 May 91 18:39:01 GMT
References: <13867@exodus.Eng.Sun.COM> <1991May23.190150.3982@rodan.acs.syr.edu> <1991May27.150924.3482@jts.com> <4207@jethro.Corp.Sun.COM>
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Organization: George Mason University, Fairfax, VA.
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In article <4207@jethro.Corp.Sun.COM>, acm@Sun.COM (Andrew MacRae) writes:
> In article <1991May27.150924.3482@jts.com>, gil@jts.com (Gil Hauer ) writes:
>  > It was my impression that cable television service is basically a one
>  > way communication channel (i.e. out from the head-end). Is this not
>  > the case any more? If it is one way, how can the descramblers be
>  > "polled"?
>  
>  
> The repeating amplifiers used in cable systems are all two way.  At least
> that is what I was told back in '73 when we used to broadcast our own shows
> over the community access channel at college.
> 
> I've always thought that cable would make a nice way for underground groups
> to communicate.

In the Northern Virginia area, the cable system (Media General - Magnavox
boxes, I think) definitely uses a two way system.  In fact, the converters
are essentially "modems".  Each one has a unique address (id) pinned into
it.  The nice side effect of this is that you can go anywhere in the network
with your convertor box, and your customer profile follows you - since it's
keyed to the box id.  The bad thing is that occasionally some neanderthal in
the home office will key in the wrong address (id) when changing a profile,
and after power failures, it occasionally necessary to call the guys in the
home office to have them deliberately poll your unit so that it handshakes
with the home computer to refresh itself.  (That is, after a power failure,
you sometimes end up with no options, so you have to be "reset".  This implies
a kind of handshaking.)  I've been told that future plans for this system
include allowing response polling (The cable guys ask you a question and
you punch a button in reply) and the system already will support this.  
That definitely implies two way communication.

-Dave