History--old MIT dial-up directory [telecom]

And if you yank hard enough, this tab is perfectly designed to > bend and back and snap off, rendering the whole cord useless.

Later in the thread, Jeff or Lisa noted:

... One big change was that the Bell System would no longer > own and be responsible for the cord and plug--it would be the > customer's problem.

And that includes customer-owned portable wall-mounted phones. Such phones were attached to a telco-provided backplate fitted with a modular jack and two mounting studs to provide physical support for the phone. The backplate was permanently installed on the premises. The whole interface was identified by USOCs RJ11W (single line), RJ14W (two lines) or RJ18W (single line with make-busy feature).

In order for this arrangement to work, it was necessary to design a plug-and-jack interface that would make the proper electrical connection when the phone was installed, but would disconnect without damage when the phone was removed.

Wall-mounted modular jacks also had to accept wired phones so the jack had to be equipped to accept the "little plastic locking tab" that AES mentioned.

And, of course, the whole concept--plug, jack, and cord--had to be designed so that plugs could be attached by non-telco personnel (including the general public) with inexpensive tools.

It's easy to criticize the whole modular concept, but if you consider the requirements I've noted above, you begin to understand why the industry and the FCC chose it.

Modular interfaces were defined in Part 68 of the 1997 (and earlier) editions of the FCC Rules and Regulations. A PDF of the 1997 edition is posted at

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USOC configurations are defined in Section 68.502, beginning on page 394 (PDF page 134).

Neal McLain

Reply to
Neal McLain
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Interesting to read this add'l information.

However, I wasn't criticizing the modular concept per se. I was criticizing the design of the "lever" on the modular connector, which in many (most?) cases was angled _outward_ pointing back along the cord -- a perfect "fishhook" to catch on anything it came close to.

Surely some other "snap-in" design or level design would have possible.

Reply to

Surely it would have.

that said, the answer to why something else wasn't chosen is covered by the (mildly cynical);

'The answer to _any_ question that starts off "Why didn't they.." is *always* "Money."' -- Maureen Johnson Smith, 'To Sail Beyond The Sunset', by R.A.H.

The 'phone cord' -- no longer being permanently attached to _either_ the telephone instrument, or the rest of the premises wiring -- was now being considered as a 'replaceable' element, a "consumable', if you will, rather than part of the durable ('capitalized expense') physical plant. As such, the economic touchstone was 'minimize the amortized cost over the projected lifetime', *without* requiring any specific guaranteed lifetime. If you can make something for 1/10th the cost (or less) that will deliver a 5-year projected life-span, vs. the traditional '40 years', you go with the low- cost version.

The other half of the answer is that in the early 1970s, when the standard was being developed, the 'rats nest' of wiring that commonly exists near the modern phone/computer/fax/scanner/printer/etc. was simply _not_ anticipated. 'In isolation', or in a 'managed' high-density wiring environment (e.g. 'patch-panels', with 'dressed' wiring harnesses). the modular jack works well.

The drawbacks of the 'fishhook' as you put it, manifest themselves primarily in _undisciplined_ wiring environments, and it is arguable the problems =there= are more a result of said lack of discipline, rather than any inherent failing if the modular design.

The fact is that there are a fairly limited number of ways to make a 'durable' multi-wire connection. you can use 'friction fit', like a standard 120V electrical plug does, but this places requirements on conductor mass and rigidity that are 'far beyond' what is needed for a telephone circuit. use of 'twist-lock' (like a 'BNC' connector) or screw- thread (like a coax TV 'F' connector) has numerous issues -- orientation is problematic for more than a 2-conductor configuration, the connector has to be manufactured as multiple separate/distinct pieces and assembled, building 'flush-mount' jack is tricky (and, on one where the jack pro- trudes, the jack is much more vulnerable to physical damage), etc.

This essentially leaves you with the 'spring clip' design, in some form or other. There are only 3 basic ways to build the spring clip -- hinge on the inside end, hinge on the outside end, or hinged/attached on -both- ends, requiring some sort of 'expansion' mechanism. 'Hinged on both ends' is significantly more complicated than a single-ended mechanism. "hinged on the outside" has to either be fairly rigid -- so you _can't_ plug it in without the tab _fully_ depressed -- or you have something that _can_ be plugged in with the tab _not_ engaged, whereupon the tab is acting as a spring to force the plug =out= of the socket. Not a good thing.

There is a "possible' alternative -- where the tab lever is 'hinged on the inside', but the outside end is somehow 'contained' (e.g. between a couple of 'walls' or 'boxed in' ) and can't 'snag' things -- but this requires that the 'back side' of the plug extend considerably further out from the surface of the jack. Which makes it _much_ more vulnerable to damage from side blows.

"Building a better connector" seems like it should be easy enough -- until you actually try to design it.

Reply to
Robert Bonomi

I suspect that some advocates of Bell System Divesture expected the traditional Bell System heavy-duty standards to continue and that competition would reduce only the price, not the quality. They didn't realize that Divesture would eliminate the economic reasons to build components to last a long time.

I also suspect that other advocates of Divesture did understand the economic changes, and saw an opportunity to get in on the action for themselves. That is, they knew they could build telephone components much cheaper than Western Electric had been building them. Thus the market was flooded with cheap phones that broke if you merely hung up too hard or business systems that didn't work very well. Further, as discussed in the past on this newsgroup, some equipment and service vendors were outright dishonest.

The Bell System itself suffered from "rats nests" wiring, particularly in cities where there were constant service changes. In the late

1960s people began to move their location much more frequently and this resulted in central office distrubting frames getting quite messy and backups in executing installation orders. (There were other issues at work as well, such as trouble finding qualified staff in certain areas). In addition, the service panel in larger buildings became quite cluttered. These contributed to the service crisis of that era.

A Bell Labs Record article of that era described a new service panel for buildings using pink and blue backplates and other aides to keep wiring clean.

However, generally speaking Bell System crews were pretty careful. That was one advantaged of the high-priced network--the crews had the time to spend to do things right.

Side note: At a worksite in the 1990s the patch panel had _new_ old- style four prong plugs and jacks for some connections. I was told this was for "test purposes", but I could not find out anything more why they installed something 20 years after it became obsolete.

Reply to
Lisa or Jeff

On Mon, 11 Oct 2010 21:38:02 -0500, Neal McLain

Well, it kind of bugs me when the FCC requires you to install jacks that are not best suited to your purpose.

When I was working for SkyTel, I proposed the implementation of a Homaco distribution frame in the new office we were about to open. I knew that Telco was going to require RJ21s, which are totally unsuitable for a distribution frame.

When we met with our sales rep from the phone company, I told them I wanted them to mount the RJ21s in a closet near the frame. We'd put Amphenol connectors to them. run the cable to the frame, and punch down the wires.

Telco objected. They wanted to drop our cable pairs on our frame. I told them that the only way we would allow that is if they guaranteed that they would use split sixty-six blocks instead of RJ21s.

They agreed.

Some weeks later, Telco showed up unannounced and went to the distribution frame. Guess what they did? You're right. They dropped RJ21s on the frame.

I showed up at the new office several days later and found them. I went straight to our director of engineering and we initiated a conference call with our Telco sales rep. I asked her to explain why they had put the RJ21s on our frame (eighteen of them, by the way) against our agreement. She was speechless for a moment.

She looked over the paperwork and said that it clearly instructed them not to use RJ21s but the sixty-six blocks instead. She arranged for the installers and his supervisor to meet me the next morning. I had to cancel a dental appointment to meet them.

When I explained the problem, the supervisor told me that no one had given him any such instruction. I got the standard, 'The FCC requires it'. I told them that I didn't care what the FCC required when it came to our distribution frame. And I further pointed out that since we were a telecommunications carrier that that rule didn't apply to us, anyway. That rule was for COAM equipment, not equipment owned by a carrier.

The supervisor removed the Amphenol connectors and the wires from the blocks and converted them into sixty-six blocks. It was nice looking and neat so I said OK.

It worked out quite well. When finished, we had a very nice distribution frame that expedited our work. I got a nice writeup in the letter the board of directors sent commending our systems cutover. They also paid me a two hundred dollar bonus. Normally, anyone other than sales got only a Christmas bonus and nothing else. That was very unusual for them to do that.

Personally, I would like to kick the guy that came up with the requirement for those things to be on distribution frames.



***** Moderator's Note *****

I'm surprised that you'd want "66" blocks on a DF: Ma Bell never used them for that AFAIK, at least not inside CO's. Why would you prefer them to punch or solder blocks?

Bill Horne Moderator

Reply to
Fred Atkinson

While not exactly a rat's nest, ...

While working for Bell Labs in the 1960's, several times I had occasion to visit a major Long Lines microwave and L3 coax junction station in Colesville, NJ where NJ, NY and PA meet. The station had lots of microwave equipment, and lots of frequency-multiplexing equipment (group, supergroup, mastergroup, etc.). One day, I arrived to see workmen on tall ladders pulling coaxial cable from the overhead racks. There was cable strewn all over the floor. Asking what was happening, I was told that they were "mining" for coax: In normal operation. circuits were continually being rerouted. The regular station personnel simply disconnected the old cable, left in the rack, and ran new cable to make the new connections. Every once in a while, the cable rack overflowed. So the hired a crew to come in and remove (i.e, mine) the no-longer-used cable.


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