deej@bellcore.bellcore.com (David Lewis) (11/06/89)
In article <telecom-v09i0490m06@vector.dallas.tx.us>, U5434122@ucsvc.ucs. unimelb.edu.au writes: > Could someone please explain some North American abbreviations: > NXX-XXXX (why 'N' ) Warning: I started writing a response to this and ended up trying to provide a shorthand explanation of the North American Numbering Plan. The strict answer to the question provided is three lines down; the rest is further information.... lots further...] As to why "N" and "X", I don't know. "N" is ex-Bell System shorthand for a digit in the range 2-9; X for a digit in the range 0-9. They came into use, as far as I know, at the time that all-number dialing came into use (when exchanges became known by number, instead of NAme...) North American Numbering Plan (NANP) (that which defines the syntax for telephone numbers in North America) syntax for a telephone number is: N(0/1)X-NNX-XXXX OR N(0/1)X-NXX-XXXX. The first has been the syntax since the introduction of all-number dialing until the introduction of "interchangeable codes" -- 3-digit codes which can be either an exchange or an area code (NPA code, or Numbering Plan Area code, in NANP parlance). It made for simpler switches, since the switch can do a three-digit analysis -- if the second digit is 0 or 1, it has to collect seven more digits; if the second digit is 2-9, it has to collect four more digits. Unfortunately, it also restricts the number of available NPA codes and exchange codes. Therefore, the NANP has been modified to permit interchangeable codes. This is first being implemented according to the second syntax above -- the second digit of an exchange code, in areas which have implemented interchangeable codes, can now be 0-9 instead of being limited to 2-9. This adds 152 new available exchanges in each NPA (although practically the number is something less, because the "home NPA" and N00 codes are not recommended for use as exchanges). The second step, interchangeable NPA codes, will result in NPAs being of the format NXX as well, instead of N(0/1)X. That will come about when the available set of NPA codes is exhausted, predicted to happen sometime around 1995. This also gets into a discussion of dialing methods, which came up in another post. (I do seem to digress a bit, don't I...) Given the use of interchangeable exchange codes (I really should use the proper terminology -- "interchangeable CO codes"), switches can no longer simply examine the second digit dialed and determine whether it's an NPA code or CO code. This is the reason Bellcore is recommending the "Prefix method" of dialing -- 7D and 1+10D being allowable dialed numbers, 1+7D and 10D not being allowable. This is a "clean" technical solution -- leading 1 means collect 10 digits, no leading 1 means collect 7 digits (plus special cases like N11). Unfortunately, as has been pointed out, it's not so clean a solution when considering customer toll restriction. What is considered a "toll" call and what is considered a "local" call is not a strictly technical decision, and will become less and less easily mapped to home/foreign NPA considerations (particularly with more and more cases of multiple NPAs in a single city, for example). A leading 1 may or may not be toll; no leading 1 may or may not be toll. CO switches have the appropriate routing and billing tables loaded to keep track of that -- but CPE doesn't. I suppose the paranoid out there could argue that this is all a BOC plot to destroy competition with CPE in the Toll Restriction Service market, but I don't believe that's the case. Far more important an issue is that not using the Prefix method requires a timer after the seventh digit dialed to determine if end of dialing is reached. This adds to call setup time -- after dialing seven digits when you mean to dial seven digits, the CO switch has to wait and see if you intend to dial an eighth -- and increases the probability of error -- you forget the number halfway through, so dial NPA-NXX-X and stop to look up the remainder, and the switch times out and places the call to NPA-NXXX. Granted, that's unlikely given that the syntax is such that most people remember NPA-NXX- then stop to look up the XXXX. The call setup time considerations are most definitely not trivial, though -- consider trying to sell state regulatory agencies on increasing the call setup time by two seconds for *every* phone call placed by every Joe Random in the state, to make it easier for "all them big corporations with all their fancy equipment" to have toll restriction or other dialing plan services in CPE... I'd rather not, myself. Apologies for the digression. David G Lewis ...!bellcore!nvuxr!deej "If this is paradise, I wish I had a lawnmower."
jjd@necis.nec.com (Jeff DeSantis) (11/09/89)
In article <telecom-v09i0490m06@vector.dallas.tx.us>, U5434122@ucsvc.ucs. unimelb.edu.au writes: >> NXX-XXXX (why 'N' ) Quoting from the second edition of: Engineering and Operations in the Bell System Copyright 1977, 1983 by Bell Telephone Laboratories, Inc. Page 115. "The following set of symbols is commonly used in discussing the numbering plan and dialing procedures: N = Any digit 2 through 9. X = Any digit 0 through 9. 0/1 = Either 0 or 1." Page 118 footnote 11. "Although all-number calling is now the system standard, telephone numbers have an alphanumeric tradition. Despite the personal appeal of names (which often had local geographical significance, for example, MUrray Hill 7-1234) rather than all-number codes, letters were a basic barrier to the use of the full range of dial-code sequences and numbers were commonly referred to as "2L+5N" to call attention to the alphanumeric usage. It should be noted, though, that the alphanumeric format also used the "3-4" character subgrouping." No longer quoting. I also remember as a child (mid '50s) making my first phone calls by picking up the handset, waiting for the operator to say "Number please", and replying "RE8" followed by the four digit phone number I wanted. A few years later when we got rotary dial phones, the prefix was changes to AT4, then sometime in the sixties I remember the prefix changing to 284 (no real change since AT4 is 284).
johnw@gatech.edu (John Wheeler) (11/17/89)
Patrick, I don't think it would be such a bad idea to put out a glossary of telecom terms to stay on here all the time. I get lost myself when we start talking about all those cryptic acronyms. /* John Wheeler - Unix/C Systems Designer/Programmer/Administrator/etc... * * Turner Entertainment Networks * Superstation TBS * TNT * Turner Production * * ...!gatech!nanovx!techwood!johnw (404) TBS-1421 * * "the opinions expressed in this program are not necessarily those of TBS" */ [Moderator's Note: Well, the beginnings of the glossary are under construction now. I am trying to get a file transferred to me with quite a few terms defined. Stick around for a few days; I should have it installed. PT]