larry@uunet.uu.net (Larry Lippman) (03/30/91)
In article <telecom11.247.1@eecs.nwu.edu> 0004133373@mcimail.com (Donald E. Kimberlin) writes: > Needless, to say, you could often > hear your ringer click or buzz when another party's frequency sailed > down the line, anyway! I was told by a WECo engineer some years ago that the above was the reason why the [late, great] Bell System felt that frequency-selective ringing was "inelegant". Since the WECo method of polarity-controlled superimposed ringing to ground provided four selective ringing codes, and the frequency-selective methods provided only one more code, Bell felt that their method - which required no tuned ringers and had little propensity for bell tapping when used with the 425A and 426A cold cathode electron tubes - was the optimum choice. > Unanswered to my satisfaction is that Bell employees many > times over the years told me that "Bell companies had 8-party service, > too," but they were always evasive about *how* 8 parties could be rung > with only 20 Hertz. And, I personally did some work replacing WECo > 350/355 CDO's in rural Mississippi last year, to hear these stories > proliferated. Yet, the old CDO's there had no evidence of ever having > had anything but 20 Hertz ringing generators. You must bear in mind that the WECo 8-party method is a semi-selective method involving four "electrical" codes and two ringing "cadence" codes, for a total of eight codes. The ringing supply was solely 20 Hz. There was really no "secret" nor any reason for anyone to have been "evasive". > So, my question to this forum, where someone certainly knows, > is *how* did Bell accomplish 8- party ringing if they used only one > frequency? Or, is it one of those bits of lore that had some truth > someplace where perhaps Bell had acquired an Independent using > frequency-selective ringing ... and then got the story embellished > with retelling and retelling? It's not at all a bit of lore. While it is indeed true that the Bell System maintained a wide diversity of non-WECo CO apparatus in telephone companies which they had acquired, this has little bearing upon the present discussion. > So far, I never met anyone who could tell me just *how* Bell > did eight-party with WECo-built apparatus. (No weasel stories now, > about apparatus WECo bought, resold and installed in some places. I > know they'd do that if they had to!) You have now met (electronically, at least) such a person. :-) My WECo experience in multi-party lines was limited to SxS, so that's what I will tell you about. There were *many* WECo SxS connectors that supported multi-party ringing. An example is the connector per SD-30862-01. I quote from the CD-30862-01 circuit description: "This circuit is used for extending a call from a toll or local selector to a subscriber line of either an 8-party semi-selective ringing rural line group or a 10-party 3-code ringing line group". This connector was used in No. 1, No. 350A and No. 355A SxS CO's. As previously discussed, WECo provided 4-party full selective ringing using either positive or negative battery superimposed upon ringing from tip-to-ground or ring-to-ground, summarized as: PARTY 1 negative superimposed battery ring lead to ground PARTY 2 negative superimposed battery tip lead to ground PARTY 3 positive superimposed battery ring lead to ground PARTY 4 positive superimposed battery tip lead to ground The party code number is an *absolute* number which corresponds to the precise condition above. The party code number was used in plant records and apparatus drawings. There is actually some rhyme and reason to the numbering, which I'm certain astute readers will notice. Eight parties could be achieved by using coded ringing; i.e., the parties 1 to 4 used the above scheme with a "one-long" ringing cadence, and parties 5 to 8 used the above scheme with a "two-short" cadence. This meant that a given telephone set rang for two of eight possible parties. By adding a third ringing cadence, 10 parties could be signaled (note reference to 10-party ringing in above quoted CD section). The differences between multi-party connectors and regular connectors were comparatively minor, and included: (1) provision for a ringing synchronization lead "PKU" which assured that ringing was started at a precise time so that a false, partial cadence would not be sent; and (2) greater flexibility in ringing control and ring-trip relay wiring options to accommodate the variations in polarity. Multi-party ringing in a WECo SxS CO was set up so that two connector shelves of 100 numbers each were required, resulting in a commitment of 200 directory numbers. One shelf had the connectors wired for tip-party ringing, and the other shelf had the connectors wired for ring-party ringing. The SxS connector wiper had 4 contacts: the standard tip, ring, sleeve, plus a fourth "A-lead" for ringing selection. On the connector bank multiple wiring block, the A-terminal corresponding to each directory number was strapped to one of five terminals: (1) resistance ground interrupted with a "one-long" cadence to provide negative superimposed battery; (2) resistance ground interrupted with a "two-short" cadence to provide negative superimposed battery; (3) resistance ground interrupted with a "three-short" cadence to provide negative superimposed battery; (4) solid ground interrupted with a "one-long" cadence to provide positive superimposed battery; and (5) solid ground interrupted with a "two-short" cadence to provide positive superimposed battery. While the above scheme was the most common for implementation of 8-party and 10-party lines in a WECo SxS office, it was not the only method. The WECo 35-E-97 (actually modified Automatic Electric Company apparatus) SxS CO used a connector per SD-30909-01 which accepted and decoded an *additional* digit to select one of ten possible ringing codes. These ten codes corresponded to the same ten possibilities outlined above. So, now you know how the [late, great] Bell System did 8-party and 10-party semi-selective ringing. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note: ub=acsu.buffalo.edu] uunet!/ \aerion!larry