Xref: utzoo comp.dcom.sys.cisco:777 comp.dcom.lans:6879 comp.dcom.modems:7847
Newsgroups: comp.dcom.sys.cisco,comp.dcom.lans,comp.dcom.modems
Path: utzoo!utgpu!cunews!bnrgate!bwdls61.bnr.ca!bwdls56!fortinp
From: fortinp@bwdls56.bnr.ca (Pierre Fortin)
Subject: Re: V.35 null modems
Message-ID: <1991Jan6.061857.28933@bwdls61.bnr.ca>
Sender: usenet@bwdls61.bnr.ca (Use Net)
Organization: Bell-Northern Research, Ottawa, Canada
References: <1991Jan4.145007.22904@sobeco.com>
Date: Sun, 6 Jan 91 06:18:57 GMT

In article <1991Jan4.145007.22904@sobeco.com>, stacy@sobeco.com (s.millions) writes:
> 
> Well, I finally got the cisco pancake routers I have been waiting
> for. Now, for my first batch of silly questions...
> 
> I want to test these things before they get installed (call me
> crazy, but this is my first experience with routers and V.35). My
> problem is, how do I connect the two beasties together? Is it
> as simple as a V.35 null modem cable? Do I need one of these V.35
> modem eliminators that I see advertised? Could I do the same
> job with a V.35 break out box, they seem to be as expensive as
> the modem eliminators, but provide a little more info (I might not
> know what is going on, but I like to _see_ what is going on :-).

Your not crazy, you'd be surprised how extensively we test all equipment 
which goes on our network; sure gets a vendors attention when they are not
allowed to have their equipment connected until they fix any major 
non-conformance problems...  :^}

With V.35, I highly recommend you test with the _same_ cables you plan to 
install in the field.  No, you can't just make up a null cable; you _will_
need a modem eliminator.  Better yet, if you plan to use T1, use the CSU/DSU
itself; you'll be surprised to find that 1.544M will *not* work due to T1's
one's-density requirement.  The break-out boxes are handy, but now that
cisco has gotten the V.35 interface straight, these shouldn't be necessary
unless you've got a physical problem.

Oh yeah:  get high quality cables.  We've resorted to designing our own
which gave us slightly more than 10dB improvement in noise/crosstalk
immunity.  Our cables have individually shielded pairs with an overall shield.
The pair shields are grounded (drained) at the signal-source end only.  The 
outside shield is grounded to the cisco and the modem.  This may seem like 
overkill, but if you had seen the problems we suffered through a year ago
with our older cables, you'd understand why I CUT (really) any old cable 
I find *anywhere* (stockroom, parts cabinet, etc.)

If you really like to _see_ what's going on, then you'll want a V.35 datascope 
(up to sub-rate T1) of some sort.  Full T1 datascopes are rare beasts however.
> 
> -stacy
> 
Good luck!

Cheers,

Pierre Fortin       Bell-Northern Research     I know, my postings are
Internet Systems    P.O.Box 3511, Stn C        terse and humourless. So?
(613)763-2598       Ottawa, Ontario            RIP: aptly named protocol
fortinp@bnr.ca      Canada    K1Y 4H7          AppleTalk: Adam&Eve's design