bill@toto.info.com (Bill Cerny) (01/07/91)
In the local switching environment, if two end offices are connected by interoffice trunks, how many digits are passed between offices when completing an interoffice call? (assumptions: electronic offices, inband signalling, same NPA, same telco) Side trivia: were #5 crossbar offices capable of supporting DID? Bill Cerny bill@toto.info.com | attmail: !denwa!bill
floyd@ims.alaska.edu (Floyd Davidson) (01/07/91)
In article <15840@accuvax.nwu.edu> bill@toto.info.com (Bill Cerny) writes: >In the local switching environment, if two end offices are connected >by interoffice trunks, how many digits are passed between offices when >completing an interoffice call? (assumptions: electronic offices, >inband signalling, same NPA, same telco) >Side trivia: were #5 crossbar offices capable of supporting DID? I can't answer the xbar question. Because you specified the same NPA they would most likely pass only the last four digits. But also it is unlikely that there would be two switches and only one NPA. With digital switching it can be arranged in almost any manner that will uniquely identify the correct routing. Usually the minimum number of digits are sent (but not less than four). There are times when for some oddball reason more than the minimum required are sent. Usually that is either future planning, or bad planning. The same is true of toll trunks to end offices. Inter-toll trunking almost always requires all digits to be passed. With mechanical switches there were other considerations because the switch may not have been configured to handle some given set of numbers. Strange things could happen. Before digital switches made it impossible there was such a quirk here in the Fairbanks area. The Fairbanks telco (45x), the North Pole (488), and the Eielson AFB telco all had EAS (Extended Area Service) trunks between each other. But there was a grand total of only six from Eielson to North Pole (one way trunks, six went the other direction too). From Eielson AFB if you dialed 488-nnnn you most likely got an all trunks are busy signal. But for those who knew about it (almost everyone), you dialed 458-nnnn instead. It went 26 miles up the road to Fairbanks, grabbed a trunk to 488 land, and went ten miles back down the same road to North Pole. It worked because the Eielson switch stripped the first digit, selected N.P. or FBK for a second digit of 8 or 5, and sent the last five digits down the line. The Fairbanks switch looked at the first of those five digits and selected either itself (a 6), the other Fairbanks switch (a 2), or an 8 would send it to North Pole. For some reason they did absorb a 7, so it could never be routed back to Eielson (372 and 377). Digital switching came in '82 and it became almost impossible to call between North Pole and Eielson until more trunks were in place. And now the Fairbanks telco is using 458 for one of their remotes. Floyd L. Davidson floyd@ims.alaska.edu Salcha, AK 99714 paycheck connection to Alascom, Inc. When I speak for them, one of us will be *out* of business in a hurry.
john@bovine.ati.com (John Higdon) (01/07/91)
bill@toto.info.com (Bill Cerny) writes: > In the local switching environment, if two end offices are connected > by interoffice trunks, how many digits are passed between offices when > completing an interoffice call? (assumptions: electronic offices, > inband signalling, same NPA, same telco) It varies, but usually works out like this: KP + Prefix code (one digit) + Number (four digits) + ST for a total of seven tones. Omission of the prefix code would be interpreted to mean the "0" prefix; possibly the first CG0 or MG0 prefix in the office. Since the stream is bracketed by KP/ST, variable length is easy. > Side trivia: were #5 crossbar offices capable of supporting DID? Absolutely. I remember many DID installations long before ESS had any significant penetration. The "CHUNK-KA-TUNK" when connected into the end office was unmistakable. Decades ago, the San Jose city offices used DID on a very crossbar switch. The first digital pagers were served via DID on crossbar here. There were some large Silly Valley firms who also made use of DID long before their COs were equipped with stored program equipment. Mind you, virtually all DID in those days was rotary signaling from the CO to the premise switch. In fact, when I put in an ITT 3100 for a customer that had DID service, Pac*Bell tried to talk me out of using DTMF. "Everyone uses rotary signaling." That was in 1984. Now DTMF is quite common. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !
dave@westmark.westmark.com (Dave Levenson) (01/07/91)
In article <15840@accuvax.nwu.edu>, bill@toto.info.com (Bill Cerny) writes: > In the local switching environment, if two end offices are connected > by interoffice trunks, how many digits are passed between offices when > completing an interoffice call? (assumptions: electronic offices, > inband signalling, same NPA, same telco) Anywhere from four to ten digits are sent between central offices as described. In most cases, five digits are sent. Because most central offices serve more than one prefix, but seldom more than ten, it is customary to send a single-digit prefix-index followed by the last four-digits of the called number. > Side trivia: were #5 crossbar offices capable of supporting DID? Some #5 crossbar switches were, and indeed still are, capable of providing DID service. They generate dial-pulse signaling toward the customer equipment, unlike some of the more recent switch designs which can send DTMF over such trunks. Dave Levenson Internet: dave@westmark.com Westmark, Inc. UUCP: {uunet | rutgers | att}!westmark!dave Warren, NJ, USA AT&T Mail: !westmark!dave Voice: 908 647 0900 Fax: 908 647 6857
grayt@uunet.uu.net (Tom Gray) (01/08/91)
In article <15840@accuvax.nwu.edu> bill@toto.info.com (Bill Cerny) writes: >In the local switching environment, if two end offices are connected >by interoffice trunks, how many digits are passed between offices when >completing an interoffice call? (assumptions: electronic offices, >inband signalling, same NPA, same telco) The answer is that as many digits are tranmitted as are requred to do the routing in the distant office. The number of digits would or could be different on different trunks between the same offices or for different calls on the same trunk. Normal subscriber calls could transmit different numbers digits than maintenance connections on the same trunks.
floyd@ims.alaska.edu (Floyd Davidson) (01/08/91)
In article <15850@accuvax.nwu.edu> floyd@ims.alaska.edu (Floyd Davidson) writes: >In article <15840@accuvax.nwu.edu> bill@toto.info.com (Bill Cerny) >writes: >>In the local switching environment, if two end offices are connected >>by interoffice trunks, how many digits are passed between offices when >>completing an interoffice call? (assumptions: electronic offices, >>inband signalling, same NPA, same telco) >Because you specified the same NPA they would most likely pass only >the last four digits. But also it is unlikely that there would be two >switches and only one NPA. My statement above is a bit brain damaged. I was thinking of office codes, not area codes when I wrote that. Guess I gotta stop posting at 3 AM. Floyd L. Davidson floyd@ims.alaska.edu Salcha, AK 99714 paycheck connection to Alascom, Inc. When I speak for them, one of us will be *out* of business in a hurry.