Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!think!ames!dftsrv!hq!illgen
From: illgen@hq.af.mil (Keneth..Illgen)
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet over twisted pair: a summary of the "whys"
Message-ID: <672@hq.af.mil>
Date: 1 Dec 89 13:45:32 GMT
Reply-To: illgen@hq.af.mil (Kenneth..Illgen)
Organization: Air Force HQ, Air Staff LAN, The Pentagon
Lines: 45


     What I find, typically, as one who provides different media-services
to a wide range of applications is that most of those who are tied into
a twisted pair network immediatly question the future need for increased
bandwidth. At this point they start looking at various ETHERNET forms.
     In most buildings twisted pair is already there with only the occasional
jumper needed. Even if it isn't installed it is easily the simplest to 
install. The attractiveness to me is that it takes an act of God to kink the
stuff so the need to replace a good shielded twisted pair is rare after the
initial installation.
     On the down-side is noise susceptibility. Fortunatly for most of you 
there isn't the RF floating through your buildings as we here in the Pentagon
experience; but it can weigh heavily depending on where you run the cable and
how well the cable is shielded. Also twisted pair is easy to tap; if some-
one so desires.
     My overall 2 cents on twisted pair is that it's overrated. The pluses
are in cost savings and installation. That makes it easier for a network 
planner to go with it (especially if it is already installed). But as a 
network grows the data transfer reliability will drop, the noise suscept-
ibility will get higher, security will be harder to maintain and you can't
run long legs; even if you fan-out.

     As an alternative I would suggest fiber. Of course that isn't always
agreeable with the budget. So the next best thing would be to run a riser
with thick E-NET and legs of either thick E-NET or thin net. Thick E-NET is
not difficult to install. As one who has done more then my share of E-NETs
I can tell you that the primary concern of a data cable installer is not the
weight of the cable but whether or not it's going to kink up going
around corners and through walls. A small cable like TWINAX is a lot harder
to run then thick E-NET (IMO). I also feel that people shouldn't be so hard
on thinnet. Granted adding taps can be a pain but if the run is planned right
'T' connectors can be installed at points where cables can be moved or 
eliminated with little difficulty.



"Where there's a will...There's an 'A'" - John Ritter

Ken Illgen
HQ USAF LAN
The Pentagon
Washington, DC

Phone: (202) 695-5090        Mail: illgen@hq.af.mil
 Autovon: 224-6136