Path: utzoo!attcan!uunet!husc6!think!ames!pasteur!ucbvax!proteon.COM!jas
From: jas@proteon.COM (John A. Shriver)
Newsgroups: comp.sys.proteon
Subject: Serial Line Problems
Message-ID: <8807251526.AA26421@monk.proteon.com>
Date: 25 Jul 88 15:26:46 GMT
References: <8807242148.AA14996@violet.berkeley.edu>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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We are indeed listening to this discussion very carefully, you may be
assured.  We want to see this problem solved.

We certainly recommend that your cables be built correctly.  The pairs
just have to be twisted correctly.  I guess a lot of vendors are silly
and pair the RS-449 cables 2-3, 4-5, 6-7, instead of the correct (but
more subtle) 2-20, 3-21, 4-22, 5-23, 6-24.  There are some specs on
cable in RS-422 in sections 4.3 and 7.1.  However, they never
explicitly say that you should pair the wires of one differential
pair, they assume common sense here.

V.35 is not as explicit about cables (in fact, the pinout is not in
V.35, only AT&T PUB 41450).  PUB 41450 says about the same thing about
cables as RS-422 does.  The V.35 voltages are much lower than RS-422
(+/- 0.55V as compared to +/- 6.0V).

Individual shields might be overkill, but it would depend on your
electrical environment, cable length, and common-mode rejection ratio
of the DSU/CSU.  Our DDS line works fine with just twisted pairs, but
our cable is maybe 5 or 10 meters long.  We use a "genuine Bell" AT&T
2556 DSU/CSU.

Obviously, everything is more critical at T1.