Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!gem.mps.ohio-state.edu!usc!apple!motcsd!hpda!hpcupt1!hprnd!pat
From: pat@hprnd.HP.COM (Pat Thaler)
Newsgroups: comp.dcom.lans
Subject: Re: Any experience using commercial cable TV as a MAN?
Message-ID: <2230026@hprnd.HP.COM>
Date: 11 Oct 89 16:24:18 GMT
References: <160@ursa-major.SPDCC.COM>
Organization: HP Roseville Networks Division
Lines: 40

Kent W. England writes:
> 	Now for the gotchas:
> 
> 	1) Cable TV cable plants are not necessarily designed to
> support two-way high quality communication as required by a LAN (MAN).
> What the viewer sees as degraded, but watchable, television translates
> into useless bandwidth for data.  The cable TV operator must support
> the cable plant to meet data requirements.  If you call him and say
> that the system isn't working, he might respond that all the TV
> signals look fine, so the trouble must be in your equipment.  I know
> of one campus where the data guys try to run a LAN channel pair on a
> system operated by TV people, and they are unable to convince the TV
> people that there are serious signal problems.  So much for exploiting
> existing technology.

This is very true. In fact the degradation might not even be noticeable 
when watching the TV signal.
> 
> 	2)  The IEEE 3 channel broadband repeater technology is too
> restrictive for use in a MAN scale network.  It takes too many
> channels and does not have the necessary diameter.  You must use a
> *proprietary* vendor technology to build a MAN sized network.
> Something like the Ungermann-Bass Buffered Repeater or one of the
> Applitek devices would work.  To my knowledge, there are no standard
> interoperable broadband technologies except for the unacceptable IEEE
> standard.
>
I think Kent is refering to the IEEE 802.3 10BROAD36 standard which
runs Ethernet over broadband at 10 Mb/s and uses three channels.
There is also an IEEE 802.4 broadband token bus standard. It allows 5 Mb/s
on one channel or 10 Mb/s on two.  Both of these are intended as LAN
or campus backbones, rather than public MANs.

There has been some discussion of MANs operating over cable for purposes
such as home shopping.  However, most MAN work seems to be going to 
fiber for the higher data rate.  Cable has a lot of bandwidth, but 
it is already used and not available for data. I think maintenance 
costs are lower on fiber than to maintain data-quality broadband.

Pat Thaler