Path: utzoo!telecom-request Date: Sun, 26 May 91 13:39 EDT From: Macy Hallock Newsgroups: comp.dcom.telecom Subject: Re: Why a Twist in Modular Cables? Reply-To: macy@ncoast.org Message-ID: Organization: Hallock Engineering and Sales Medina, Ohio USA +1 216 722 3053 Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 403, Message 3 of 3 Lines: 78 >> Can anyone tell me why there is an electrical twist in most (US) >> modular cables? >> I got to thinking about this recently when I started using these >> cables for RS-232. If you're clever about pin assignments, this twist >> can be useful for RS-232. > If the plugs are crimped on so the wires go straight through, and all > adapters are wired that way, you will have no problems. Not always true. Phone people generally think in terms of all punch on type jumper wiring up to the wall jack. This is straight thru type operation ... until the base cord to the instrument is reached. Now, most telecom equipment is designed to take this type of wiring scheme and reflects it in their documentation. If the phone system is using direct connections to its terminating blocks, then the system is setup for one reversal ... the one in the base cord to the set. If the system uses RJ11 or RJ14 type connectors, it usually expects two reversals (one at the system's connection to the building wiring and one at the instrument base cord). Use of intermediate patch panels has been a problem to many, including my company. We have tried using staight thru path cords on intermediate panels with some success ... and try to use an oddball length (read short) to help make them easy to tell from standard base cords. Our unofficial policy is: two and four conductor cords are always standard reversal type base cords. Six and eight conductor cords are either, but straight thru cords are to be labeled "DATA" or "STRAIGHT" or "PATCH" at both ends. Most straight thru patch type cords are three feet long here. We are looking for a source of reasonably priced cord stock in a distinctive color for use in making up straight thru cords ... red or blue would be ideal ... we have a lead on getting black, white and brown stock, but have not yet received pricing. Bear in mind that some electronic phones and data equipment can be messed up by a reversal. > That is the way the DATA industry generally does it. In many sites > 'PHONE" cords have caused needless confusion and are BANNED. With > polarity guards built into modern TT dials, and ringing being across > the line and not to ground, many sites make life simple and ALL > modular cords, both EIA DATA and 'phone' cords are wired straight > through. FWIW most folks use six or eight wire cords for everything, > and cords that come with phones are generally four or even two wire, > so the problem ones are easy to spot. This may be true on sites manned and operated by data people who are not trained/acclimated to the telecom way of things. Here, we find we must live with both worlds. Frankly, I would like to see us use DEC type RJ connectors exclusively for data, but this is not really practical ... much of the wiring we install is set up to be used either way. I have a high regard for AT&T's standards and many of the WE designs, but I think they blew it on this one ... of course I think we all only thought in terms of phone lines and tip/ring when modular phones first came out in the 70's ... and WE though only in terms of its own production efficiency. I have spent many an evening working out RS-232 DB-25 to RJ-45 adaptor wiring schemes with the operations guys ... I'd like to see how others are setting up their RJ type wiring schemes, especially in multiuse wiring schemes involving LAN, RS-232, balun and phone operations. I will happily publish a summary ... email me at macy@ncoast.org ... fax is +1 216.778.6239 Macy M. Hallock, Jr. N8OBG 216-725-4764 Home macy@fmsystm.UUCP macy@NCoast.ORG Note: macy@ncoast.org is best reply path to me. uunet!aablue!fmsystm!macy [No disclaimer, but I have no real idea what I'm saying or why I'm telling you]