peter@uunet.uu.net (06/07/89)
I'm curious anout this terminology. Why two symbols for unspecified digits, here? Why N1X rather than N1N or X1X? And why NXX rather than any other combination on Ns and Xes? Does this mean anything, or is it just traditional? --- Peter da Silva, Xenix Support, Ferranti International Controls Corporation. Business: uunet.uu.net!ficc!peter, peter@ficc.uu.net, +1 713 274 5180. Personal: ...!texbell!sugar!peter, peter@sugar.hackercorp.com.
cmoore@brl.mil (VLD/VMB) (06/08/89)
N means any single digit EXCEPT 0 and 1. X means any single digit, to INCLUDE 0 and 1. Until 1973, area code-prefix combinations were of the N[01]X-NNX form. In July 1973, area 213, which includes Los Angeles and which has since split to form area 818, went over to NXX prefixes (in other words, it allowed for new prefixes of the form N0X and N1X), so that for the first time some 3-digit numbers could serve both as a prefix and as an areacode.
deej@bellcore.bellcore.com (David Lewis) (06/12/89)
In article <telecom-v09i0189m05@vector.dallas.tx.us>, ficc!peter@uunet.uu.net writes: > I'm curious anout this terminology. Why two symbols for unspecified > digits, here? Why N1X rather than N1N or X1X? And why NXX rather than > any other combination on Ns and Xes? Does this mean anything, or is it > just traditional? In telco shorthand, N = any digit from 2 through 9; X = any digit from 0 through 9. Before the advent of common control switches (where a single controller, either electronic or electromechanical, reads the whole number and then sets up a path through the switch fabric), the first three digits of a phone number were used to determine what sort of treatment to give a call. Special treatment was recognized by a 0 or 1 for the first digit. An "N" -- 2 through 9 -- in the first digit therefore meant "handle normally". A long-distance (out of area code) call was recognized by a 0 or 1 in the second digit, so an "N" in the second digit meant "inside this area code -- expect only 5 more digits". I don't know why 0/1 were chosen as the special numbers; it may have been tradition or it may have been some operations research whiz at Bell Labs doing some T&M studies... Anyway, the result of this is that, to date, office codes are generally of the pattern NNX and area codes (or Numbering Plan Area codes, NPA codes for short) are of the pattern N0/1X. If you've been following the discussion here lately, this all becomes moot over the next five or six years as the lack of codes leads to interchangeable CO/NPA codes. Both CO codes and NPA codes will be of the format NXX. -- David G Lewis ...!bellcore!nvuxr!deej "If this is paradise, I wish I had a lawnmower." [Moderator's Note: I think 0/1 were chosen probably because at the time this first came up for consideration, telephone companies were just beginning to move away from Pennypacker, Pennsylvania, Sheldrake and Buckingham style exchange names into ANC (All number calling). And which two numbers on the rotary dial did NOT have letters associated? Zero and one. I have seen exactly *one* very old, circa 1920's instrument which had the letter 'Z' on the zero-operator hole. '1' was always held out as a special sort of digit. PT]