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From: lars@spectrum.CMC.COM (Lars Poulsen)
Newsgroups: comp.dcom.sys.cisco,comp.dcom.lans,comp.dcom.modems
Subject: Re: V.35 null modems
Message-ID: <1991Jan5.062616.7340@spectrum.CMC.COM>
Date: 5 Jan 91 06:26:16 GMT
References: <1991Jan4.145007.22904@sobeco.com>
Organization: Rockwell CMC
Lines: 25

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.
>
>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?
>Do I need one of these V.35 modem eliminators that I see advertised?

Yes. As in any other synchronous serial modem interface, the question is
"Who supplies the clock?", and the answer is "The modem does".

>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 :-).

The V.35 breakout boxes tend to be expensive because they need to have a
power supply to drive the lights. V.35 uses a differential signal with
less than 1 Volt drive. I never understood why the phone companies liked
it so much when we already had RS422 which had +-5V drive which is
enough umph to drive lights directly and even to interoperate with RS232
in a pinch. But you still need somebody to supply the clock.
-- 
/ Lars Poulsen, SMTS Software Engineer
  CMC Rockwell  lars@CMC.COM