Path: utzoo!attcan!uunet!husc6!bu-cs!kwe
From: kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England))
Newsgroups: comp.dcom.lans
Subject: Re: Does anyone rent TDR's?
Message-ID: <24956@bu-cs.BU.EDU>
Date: 19 Sep 88 16:41:04 GMT
References: <425@aoa.UUCP> 
Reply-To: kwe@buit13.bu.edu (Kent England)
Followup-To: comp.dcom.lans
Organization: Boston Univ. Information Tech. Dept.
Lines: 43

In article  ron@topaz.rutgers.edu (Ron Natalie) writes:
>The Ethernet TDR's are generally cheaper.  [...]
>
>I actually have a Cabletron unit.  We've had it out a couple
>of times, but we haven't actually found a problem that it
>would have solved.  Usually just serves to point out that
>the physical cable is NOT what is causing the failure.
>
>-Ron

	Just a follow-up to this:

	You should have a cable TDR'ed before installation when it is
still spooled and TDR'ed after installation.  The first test is the
"cable acceptance" test and the second is the "installation
acceptance" test.  You can have the installer do both TDRs as part of
his contract.  Any contractor with Ethernet experience can do that.

	You usually won't need to TDR a cable again, unless you let
just anybody install stuff on it.  :-)  You might be able to do
without one, unless you have miles and miles of cable.

	However, another trick we use is strategically placed barrel
connectors.  We usually have floor cables run into a closet to access
a riser.  There are barrel connectors placed in the closets that let
us physically partition a segment for diagnostics.  It's actually
easier and less disruptive than a TDR, for to TDR a cable you have to
disrupt traffic on it.  Ideally you want the cable completely shutdown
to traffic, which may be impractical.

	We do all the transceiver installs ourselves and rarely find
the need for a TDR beyond acceptance testing, but we do have one
because they are relatively cheap.  If you don't have an Ethernet
analyzer, buy that first, then buy a LAN-MD (or other), buy the TDR
last.  Hope this helps.

	Upon further reflection [pardon that pun], a TDR would be nice
when some other contractor damages your cable, but again we usually
find it faster by inspection and by asking questions.  The bright
yellow color we use saves a lot of damage.  I guess contractors will
waste anything black or aluminum/steel colored (like broadband coax)
before they'll touch that funny yellow stuff.  (Anybody know a vendor
that sells orange broadband coax?)