From ptownson Thu Dec 26 17:24:25 1996 Return-Path: Received: by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id RAA21539; Thu, 26 Dec 1996 17:24:25 -0500 (EST) Received: from mailhost.tcs.tulane.edu by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id RAA21528; Thu, 26 Dec 1996 17:24:22 -0500 (EST) Received: from MARK ([129.81.26.141]) by mailhost.tcs.tulane.edu (8.7.6/8.7.3) with SMTP id QAA12409 for ; Thu, 26 Dec 1996 16:28:36 -0600 Message-ID: <32C31774.7663@mailhost.tcs.tulane.edu> Date: Thu, 26 Dec 1996 16:25:24 -0800 From: "Mark J. Cuccia" X-Mailer: Mozilla 2.01 (Win95; I; 16bit) MIME-Version: 1.0 To: ptownson@massis.lcs.mit.edu Subject: History - 1960 Numbering Document Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Status: RO The following is a transcript of several mimeographed pages of notes, from a Bell System conference on the US/Canada Nationwide Numbering Plan. It is 'unauthored' as well as undated, but I assume it is from 1959 or 1960. In the following, there are several references to material presented on a "Vugraph", i.e., an overhead transparency projector. I don't think that any of those "Vugraph" charts are 'themselves' included here, but are probably somewhat described in the notes. An original copy of the following was recently *loaned* to me by a man who is now retired from Bellcore, and who had been with Bell Labs since the late 1950's. Any additional notes of mine are enclosed within square brackets []. MARK J. CUCCIA PHONE/WRITE/WIRE/CABLE: HOME: (USA) Tel: CHestnut 1-2497 WORK: mcuccia@mailhost.tcs.tulane.edu |4710 Wright Road| (+1-504-241-2497) Tel:UNiversity 5-5954(+1-504-865-5954)|New Orleans 28 |fwds on no-answr to Fax:UNiversity 5-5917(+1-504-865-5917)|Louisiana(70128)|cellular/voicemail ----------------------------------- NUMBERING PLANS The first numbering plan crisis occurred in 1917 when dial service was started for large cities. A numbering plan was needed then that would handle a mixture of manual and dial offices. W.G. Blauvelt provided the solution with the 3-letter/4-number plan. Later this became the present 2L-5N plan. The historical need for a lettered dial ceased when the large cities became substantially all dial. However, the present DDD numbering plan has extended the usefulness of the lettered dial. The present plan of numbering for DDD was devised in the later 1930's and early 1940's. In 1947, 86 area codes were assigned in the U.S. and Canada. By 1957, 113 area codes were assigned. This is a growth factor of 27 codes in 10 years. As of December 1959, 117 codes were assigned from a possible maximum of 152. If growth continues at the same rate, all codes will be used up about 1972, and in the year 2000, 229 codes will be in use. This does not include an allowance for dialing to other parts of the world. The demand for NPA codes can be estimated by a more logical process, that is, by basing it on population forecasts. We have several estimates based on forecasts by the AT&T Co. statisticians, by Fortune Magazine, and by George Washington University. They are shown on this first Vugraph. An interesting side issue developed out of this analysis. Bell System Central Office station fill in 1925 was slightly under 2000 stations per central office, including [PBX] extensions. By 1957, 32 years later, the fill was slightly above 5000 stations. This 2.5 fold improvement in fill indicates that a large part of the telephone growth was absorbed by additions, rather than by the opening of new offices. The telephone industry in 1957, Bell and Independent, in the U.S. and Canada, had a fill of slightly under 3000 stations, including [PBX] extensions. At the past rate and type of growth, this will result in a fill of 10,000 stations by the year 2000. Since a large part of this fill (residence extensions) does not have a requirement for line numbers, this figure is quite plausible. The implication drawn from this is that it is likely that most of the telephone growth of the next 40 years will also be absorbed by additions to central offices at existing wire centers. The present ABX [NNX] numbering plan for local offices provides a maximum of 640 codes per [NPA] area. If each code must have a useable name, the maximum is about 600. If, in addition, codes cannot end in [the numerical zero] "0" because of possible customer confusion with the letter "O", the maximum is 540. On the basis of present code assignments to NPA's, in the DDD Reference Guide the fill averages 134 central office codes per [NPA] area. When DDD is fully implemented, the Guide will list about 60% more names. By the year 2000, the fill will average about 390 codes per NPA. Thus there does not appear to be an immediate necessity for planning for more codes per NPA. All this is premised only on the needs we see now and includes consideration of arrangements for PBX in-dialing, national Enterprise service [what would become automated 800 Toll-Free Service], data transmission [new dial-up services using modems over the DDD network; also automation of existing manual TWX Service, using N10 form NPA codes], and similar items. There is a definite need for more area codes, however, as already shown on the first graph. The present 152 capacity will exhaust sometime between 1967 and 1975 depending on the forecast used. Plans for expanding this capability are as numerous as individuals consulted. A few years ago, it was proposed to add the 1XX series to the present series to gain added capacity of at least 64 codes. This would move the congest dates out to a period from 1980 to 1996. Another possible added series is the AB0 [NN0] series, of which 19 have already been assigned to central office codes, but which can be recaptured. This moves us out to from 1989 to beyond the year 2000. If the AB1 [NN1] series were recaptured for area codes, the earliest exhaust date would be 1997. There is one additional possibility, namely the 0XX series. This would add 64 more codes, but would require either a delay on all "0" Operator calls, or a changed operator code. This kind of approach we have just been discussing was dropped because of the feeling that we should set up a plan that would carry us a long way into the future - well past the year 2000. New numbering plan arrangements are expected to provide for more than increased capacity. Examples are: 1. Barrier codes to prevent locally intended calls from reaching toll points in error. [i.e. the use of 1+] 2. Access codes to provide access to the centralized CAMA equipment in SxS areas. [i.e. the use of 112+ initially, later to become simply 1+] 3. Reduction in six-digit translation. This [six-digit translation] has been costly and is desirable [than] to split areas to reduce the amount of six-digit translation. 4. Elimination of non-uniformity in service codes [i.e. conversion of 11X service codes in SxS areas to the "common-control type" of N11 service codes] and provision of a code for DDD information. [i.e. the use of (NPA)-555-1212] 5. A code for dialing person and collect calls. [i.e. 0+ dialing] 6. Arrangements that will be compatible with mechanized Enterprise Service, a special type of collect call [i.e. future 800 Toll-Free] 7. Possible codes for dialing to foreign countries. [809 for the Caribbean; 903 for the northwest Mexican border; 90-5 access to Mexico City; proposed inclusion of Europe, Latin America, Australia into the Bell System DDD network and numbering plan. The latter proposed inclusion of countries was dropped, as Europe, and later the CCITT was developing a worldwide 'country code' numbering plan of its own. 011+ would become the access code for dialing out of the NANP] This brings us up to recent history, the plans that have been proposed, and the present favorite plan. Work was started in 1956 to provide more uniformity in dialing, and reduced effort in calling nearby NPA's. As a result of this work, the "11" plan was presented to the President's Conference of October 1956. This plan proposed the use of "11" instead of "112" in SxS areas, and the allied use of "1X" for calling nearby NPA's. There was no consideration of person dialing. An important consideration was to get uniformity without senderization of SxS. The plan was covered in an AT&T Co. letter to the field on January 28, 1957. It didn't take - but here it is on this Vugraph. During 1957, study work was started on an expanded numbering plan. This work was stimulated by Mr. Turner's SER-48 [Switching Engineering Report] issued February 1, 1957, which included that more capacity would be needed in about 15 or 20 years. In May 1957, a conference was held by AT&T Co. people to discuss the need for co-ordinated development of certain items. Among the items discussed were access, area, and service codes. Increased area code capacity was one of the items. It was pointed out that the Laboratories were handicapped by lack of a plan. The O&E conferees agreed that quick action was necessary and that a plan would be forthcoming in a few months. A formal committee of O&E and Laboratories people (O. Myers from Labs.) was set up on March 4, 1958 to recommend a plan. The outcome of the committee's work was the presentation of 3 plans to which a fourth was later added at the request of the New York Telephone Company. These were to be appraised and priced and one was to be selected. The plans are shown on these Vugraphs. On September 8, 1958, Mr. C.A. Armstrong wrote Mr. F.J. Singer to confirm the formation of a joint O&E-Labs. working group to estimate cost factors of the three basic dialing plans. This group farmed out the job of determining what changes were required to implement the several plans. A group of development and systems engineers studies the nature of the changes required and wrote a memorandum on the subject. Pricing on the detailed basis suggested by this memorandum would have taken too much time and effort. It was, therefore, agreed with the O&E that short-cut methods would be employed. A group of four O&E and Labs people, therefore, priced out the plans using these short-cuts. Here is a summary of the results on this Vugraph. The important thing is that they are all roughly a stand-off if person-to-person dialing is included. A series of three meetings was held in February and March of this year for presenting the report of the pricing committee. At the last, held on March 23, 1959, Messrs. Busch, Singer and Ritchie were present. As a result of these meetings, Plans 2 and 4 were dropped, and Plan 1 was agreed upon for common control [Panel, Crossbar, and at-that-time still experimental/developing Electronic Switching] areas. For step-by-step areas, the long term plan was left open but it appeared that the "112" access code should be dropped at the time person dialing was started. An option was suggested that would permit retaining the "112" access code until pushbutton dialing with the "d" button was introduced. [There was a proposal for a touchtone button labeled 'd' which would have probably been the present '*' or '#' button. It would have been entered as an access code for all ten-digit DDD calls. This would have allowed probably all one-thousand possible XXX format codes to be used as area codes, however this plan was dropped, since it would have taken way to long for everyone in the US and Canada to be cut-over to touchtone, before any 'additional' format area codes could have been assigned.] It was also suggested that a conference be held with the New York Telephone Co. to acquaint them with the study results and the tentative decisions. This was held and the New York Co. objected to the proposed plans. Their objection was based on N.Y.Co. plans to publish area codes in directories. The Manhattan directory to be issued this June will list the area code for each foreign listing instead of the statement "ask operator for [location name], etc." By January 1, 1963, there will be 100% area code listing for the New York City area. PBX attendants are being trained to accept area code placement and the commercial people have agreed to billing on an area code basis, i.e., there will be no place names. Customers will be urged to print their complete telephone numbers on letterhead and in advertising. [THAT LAST SENTENCE CAN *NEVER* BE UNDERSTATED, IMO.] There are several advantages to this, as follows: 1. Rate and route effort will be reduced. About $2,000,000 per year will be saved in New York City. 2. Operating effort will be saved on foreign listings. 3. It takes care of the boundary problem, i.e. telling the customer what to dial when the called customer is on or near an NPA boundary. In order for the plan to work properly, the New York Co. feels that the person prefix must be placed *ahead* of the area code, not after the first digit. [There was another proposal that "10+" would be dialed for collect and person type calls. This was changed to "0+" before actually being implemented. Maybe this is what was referred to with the 0+ prefix being dialed 'first'?] On March 5, 1959, or just before, Mr. Singer called Mr. Mapes who promised to get out a letter with a tentative answer very shortly. The answer the letter will contain is shown on this Vugraph. We do not have the letter as yet, however. If we do not get an answer by the middle of the year, the person project will be delayed. [end-of-document] ---------------------------------- From ptownson Thu Dec 26 17:24:29 1996 Return-Path: Received: by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id RAA21572; Thu, 26 Dec 1996 17:24:28 -0500 (EST) Received: from mailhost.tcs.tulane.edu by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id RAA21548; Thu, 26 Dec 1996 17:24:25 -0500 (EST) Received: from MARK ([129.81.26.141]) by mailhost.tcs.tulane.edu (8.7.6/8.7.3) with SMTP id QAA34176 for ; Thu, 26 Dec 1996 16:28:38 -0600 Message-ID: <32C31777.58EF@mailhost.tcs.tulane.edu> Date: Thu, 26 Dec 1996 16:25:27 -0800 From: "Mark J. Cuccia" X-Mailer: Mozilla 2.01 (Win95; I; 16bit) MIME-Version: 1.0 To: ptownson@massis.lcs.mit.edu Subject: History - 1970 Numbering Document Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Status: RO The following document is a transcript of a memo from Mr. Charles Clos to to Mr. F.J. Turner of Bell Labs. It is dated May 15, 1970, and it regards some of the history behind the dialing plan used in the Bell System, and how individual local switching systems shaped the dialing plan. A copy of this document was recently *loaned* to me by one of my contacts who is now retired from Bellcore/Bell-Labs. Any notes of mine are enclosed in square brackets []. MARK J. CUCCIA PHONE/WRITE/WIRE/CABLE: HOME: (USA) Tel: CHestnut 1-2497 WORK: mcuccia@mailhost.tcs.tulane.edu |4710 Wright Road| (+1-504-241-2497) Tel:UNiversity 5-5954(+1-504-865-5954)|New Orleans 28 |fwds on no-answr to Fax:UNiversity 5-5917(+1-504-865-5917)|Louisiana(70128)|cellular/voicemail -------------------------------- The Bell System's future numbering plan which is currently being implemented was approved in 1959. It is the best plan that the study committee was able to arrive at and obtain universal approval. When I became chairman of that committee, I stopped the sniping on all other plans. I have arrived at three Numbering Plan Principles: 1. Everyone is an expert on numbering. 2. Everyone's numbering plan has a twist to it that makes it better than everyone else's plan. 3. Future Requirements are always underestimated. The committee met to consider one plan at a time, assuming it to be the most desirable plan. At such sessions, the objective was to make to plan viable. To everyone's surprise, we found that the four major plans under study required equivalent central office modifications and each cost about the same. The decision then hinged on choosing that plan which was least objectionable. Before delving into some details of the numbering plan, a bit of historical and philosophical background seems desirable to show how prior decisions and switching hardware developments shaped the numbering plan. MANUAL SYSTEMS: It appears that manual systems left no visible effect on the numbering plan, unless we consider that the "B" operator's reach, with the old plugs and jacks, limited the size of a manual office to 10,500 numbers. This limitation probably carried over and resulted in the 10,000 number limitation in common control offices. STEP-BY-STEP SYSTEMS: Step-by-step systems almost produced a lasting effect on the numbering plan, in that these systems cater to open-ended numbering. The invention of the digit absorbing selector made it economically tolerable to convert step-by-step systems using fewer than 7 digits and/or open-ended numbering to a closed system of 7 digits. OPEN VS. CLOSED NUMBERING: The great debate between open-ended and closed numbering was settled in favor of the latter (except in Germany where it was settled in favor of the former), chiefly because the switching hardware in common control [Panel, Crossbar, ESS, etc] systems needs an indication when the last digit has been dialed. The cheapest way to provide this indication is to fill up the register and immediately advance the call. If, however, one digit less might be permitted, the register must wait for a prescribed time awaiting another possible digit. This is costly for two reasons, namely, because of the timing circuit and due to the need to provide extra registers to allow for the waiting times. There are other solutions, such as the use of pre-translators, the recognition of certain digits in certain places, etc. But these likewise are costly. BLAUVELT'S INVENTION: In 1917, Mr. W.G. Blauvelt got a patent on the use of letters on the dial (other than for party-line letters). He made it possible to introduce dial offices in an orderly fashion in the larger multi-office manual cities. Imagine the customer problems if, in 1922, all manual offices in New York City had suddenly become known by numerical prefixes. Blauvelt showed how to get the equivalent of a numerical prefix by the simple expedient of dialing "letters suggestive of the office name." The first dial office in New York City was named PENnsylvania and existing manual offices became known as BEEkman, ORChard, etc. 2L-5N NUMBERING: The size of New York City in the early 1920's was such that a 3-letter prefix sufficed. In fact, this was thought to last for a long time to come. However, in the early 1930's, the New York Telephone Company started to exhaust its supply of suitable central office names. According to Mr. Chester E. Brooks, Mr. H.C. Carpenter (Staff V.P.) called a conference at which all sorts of solutions were debated. The choice narrowed down to 2L-5N or [completely numerical] 7D, with the former winning by one vote. THE LETTER "Z": In the early 1940's, the New York Telephone Company studied toll dialing for the Greater New York Metropolitan area. One plan assumed the use of toll directing codes, such as JZ, LZ, and WZ for dialing calls to New Jersey, Long Island, and Westchester, respectively. Since J and L are in the same pull [of the dial, namely the '5'], this plan was not viable. However, for several years, dials were manufactured with a 'Z' in the tenth [zero] pull. [Another reason for the letter 'Z' on the digit '0' is that some people might have tried to dial operator-connected manually translated toll-free reverse charge "Zenith" calls. By putting the 'Z' on the dial with the '0'/zero for Operator, customers trying to *dial* ZEnith would be dialing '03', which would connect them with the operator on the first digit dialed, '0'. Same applies for customers trying to dial 'ZEro' for the Operator.] AB1X [NN1X] CODES: Another plan studied by the New York Telephone Company assumed a great big dialing area, out to Brewster in the North, and Riverhead in the East. To make this plan viable, Mr. K.E. Bassett proposed the use of ABX [NNX] and AB1X [NN1X] type central office codes. At that time, there were a great many manual offices still in existence in the suburbs. Bassett's idea was to name the offices "CArmel Eleven", "WHitehall Twelve", etc. and at the same time, keep [existing New York City] designations, such as WHitehall Four. The use of "teens" designations was for operators when passing calls manually. The presence of a "1" in the third-pull [of the dial] would alert the dial office to expect 8 digits. All dial offices in New York City had a capacity for 8 digits. [Party-lines in manual offices in the city would have seven-digits of the 2L-5N format, plus a single letter to identify the particular party on that line. All eight digits would be pulled out on the dial by a calling party from a dial central office.] His plan was proposed years before the first AB1 [NN1] type codes were assigned anywhere in the Bell System, which occurred in Pittsburgh around 1950. [Actually, there were some seven-digit 2L-5N cities using NN1 central office codes in the 1930's. Some places even had some NN0 central office codes at that time, although this was highly discouraged.] Bassett's proposal would have doubled the number of available local codes in an NPA. When he presented his plan to '195' [AT&T's Headquarters office building was at 195 Broadway in New York City], Mr. C.G. Miller of Bell Laboratories objected because the dial offices in Chicago did not have a capacity of 8 digits. The proposal was dropped. I cite this incident in support of Mr. R.W. Ferguson's viewpoint that sometimes a small insignificant decision, made in a casual way, has a far-reaching effect. If Bassett's idea had been adopted, we would never have had to make the big study in 1958-9. However, in 1944, there were only a few people who foresaw DDD and the early congestion of the numbering plan. DDD CODES: The first mention of A1X [N1X] and A0X [N0X] type NPA codes seems to have been made by Mr. F.F. Shipley in a memorandum dated July 28, 1944. In a second memorandum dated January 16, 1945, he grossly underestimates the future NPA code requirements. He says, " ... it has been estimated that 53 numbering areas are sufficient." Yet, in 1947, 86 codes were initially assigned to the NPA's in the USA and Canada. ANC: All Number Calling was studied by the Laboratories around 1956. Once a large multi-office city is on an all dial basis, there is no real need to continue with the use of Blauvelt's invention, namely, the lettered dial. ANC makes more local codes available because it removes the restriction of impossible names for certain of the codes. The use of arbitrary letters would, of course, accomplish the same thing. The opposition to ANC came chiefly from customers who had a fond attachment to a particular name, e.g., BUtterfield-8, RIverside-9, etc. SER No. 48: In 1957, Mr. W.O. Turner, in Switching Engineering Report No. 48 estimates that 130,000 central office codes would be required in the year 2000 for the United States, Canada and Mexico. He estimated that 23,800 codes would be needed for in-dialing to PBX's. The underlying concern in his report was that the NPA codes may be expected to exhaust at about the year 1975. No concern regarding an early exhaust of NNX codes was indicated, yet today it seems that NNX codes in two NPA's will exhaust before the supply of NPA codes exhausts. LOCAL OFFICE CODES: When I undertook the big study in 1958, I obtained from earlier correspondence, so-called ultimate central office code requirements for each NPA. The following were the ten NPA's having the highest future code requirements: Number of Local Office Codes as State/ Shown in the DDD Number of Projected Ultimate NPA Province Reference Guide Local Central Office Codes 305 FL 249 634 504 LA 155 622 519 ON 059 596 705 ON 029 586 312 IL 319 575 404 GA 126 570 617 MA 357 555 813 FL 073 547 217 IL 048 530 314 MO 209 525 Note the gross underestimate for the 212 and 213 NPA's which are missing from the above list. CAMA SENDERS: In the mid 1950's, the CAMA senders were being developed for crossbar tandem. Mr. M.E. Maloney got quick acceptance from someone in '195' Traffic that the CAMA senders can be limited to 10-digits. Actually, Maloney asked if the Laboratories could ignore the stations delay digit, the 8th-digit in areas where manual numbers exceeding 10,000 still existed or where party line letters were used. He should have asked: will we ever need 11-digits? By 1958, that "innocuous" decision helped to keep us from studying an 8-digit local code plan. [However, there were situations in the 1960's and 70's where eleven-digits total were MF keypulsed between switches in the network, or MF keypulsed by operators, including: routing of calls to Mexico (using 180+ the eight-digit Mexican national number), and routing of certain TWX calls (conversions from 4-row terminal to 3-row terminal connections, where a leading digit '0' is internally keyed to the ten-digit "3-row" TWX number NPA-NNX-XXXX.)] "112" PREFIX: CAMA in step-by-step areas was made feasible with the "112" prefix. Thus, on a ten-digit call, the customer dialed 13 digits, three of which were needed to route to the CAMA tandem. There was considerable public criticism of this arrangement. The development of a double headed trunk made it possible to dial CAMA calls in step-by-step areas by means of the single digit prefix "1+". [i.e., if the second digit following the initial '1' is another '1', the call would have routed to the 11X miscellaneous or service codes, while if the second digit were an 'N' i.e. a '2' through '9', it would indicate the first digit of an NPA code. However, many SxS areas began to reconfigure their local switch routings to adopt the traditionally 'common-control' style N11 service codes, thus eliminating the use of all 11X form service codes, and able to adopt the 1+ toll prefix without having to use this 'double-headed' trunking method.] PLANS STUDIED: Each of the four plans studied in 1958-9 assumed 7-digit local numbering. No serious consideration was given to any plan involving more digits. In retrospect, this indicates that there was a lack of adequate information that the local office codes in New York City and Los Angeles would exhaust before the supply of NPA codes ran out. One of the plans studied provided for 4-digit NPA codes, but did not provide for local codes beyond the present limit of 640. The other three plans assumed a common supply of 792 codes, used interchangeably as NPA or as local office codes. They differed amongst themselves with respect to the prefix to be used when a code is used as an NPA code. As long as the number of NPA codes plus the number of local office codes in the fullest NPA do not exceed 792 codes, there is no need for a prefix or indicator to clear up the ambiguity created when an interchangeable code is dialed. Timing after the 7th-digit is one way to resolve the ambiguity. The operation of an end-of-dialing button ['#'] is another. 1+ DIALING: The simplest possible prefix is the digit "1". Since it dovetailed into the replacement of the "112" Prefix in step-by-step areas by the Prefix "1", "1+" dialing became the plan accepted in 1959. Basically, "1+" dialing should be used only on ten-digit calls, and not on 7-digit calls. However, the use of "1+" dialing in step-by-step CAMA areas is for the purpose of gaining access to the toll billing equipment, and, in common-control areas, to reduce toll-billing errors - not to discriminate between ten-digit and 7-digit calls. Hence, the "1+" dialing plan has an anomaly that can only be resolved, when interchangeable codes come into being, by timing after the seventh digit to await an eighth digit. This is perhaps the weakest spot in the "1+" dialing plan, namely, the use of "1+" on 7-digit toll calls, with timing delaying the completion of such calls. We have looked at this problem as one that will eventually go away when local charging areas are expanded to include a whole NPA. [To this day, the debate continues of what the '1+' *really* means, and how/when/where/if it should/could/must/might be used; i.e. whether "1+" is permitted or required.] 0+ DIALING: The "1+" dialing plan assumed "10+" dialing for person-to-person, etc. type calls. This was changed to "0+" dialing by a management decision. To discriminate between "Dial-0" calls to Operators and "0+" calls, timing is employed after [dialing] the "0". This delays completion of calls to the assistance operator. CONTEMPORARY PERIOD: This concludes the narrative, bringing it to the period with which you are familiar, namely, the decisions and events concerning emergency codes [which was originally planned to be "00" to reach the Operator, so as to avoid delaying for a time-out if a single "0" had been dialed; however, 911 to reach an "emergency center" was later implemented], international access codes [011/01+], the directory assistance code [use of "555-1212" in each and every NPA, for customer dialing to a distant city's directory information operator/center], and the unblocking of the 'E' digit for dialing into Mexico City. [Mexico City had numbers also of the form N1X-xxxx and N0X-xxxx in the early 1970's, when 90-5+ was proposed for customer DDD calling to there, well before Los Angeles (213) and New York City (212) had such local codes in the later 1970's. All Common-control toll switches, as well as such local #5XB, #1XB, etc. switches, had to allow a '1' or '0' in the 'E' or fifth position dialed by a customer for dialing to 90-5 Mexico City. i.e. The fifth position of: 905-N0X or 905-N1X. Unblocking of customer access to a 'E' digit of '0' or '1' also meant that certain internal and operator dialed 0XX/1XX codes had to be modified, as there could have been a code conflict -- i.e. Kp+312+115X+St had indicated a "115X" leave-word operator in the Chicago (312) area code, as there would have been no local central office codes of the N0X/N1X format. However, when a local area started to have such N0X/N1X central office codes, 312-115X could be a local seven-digit number. So, all 'leave-word' operator codes had an extra "dummy digit of '1'" tacked onto the end -- 115X-1. So, Kp+312-115X+St would indicate a local seven-digit number for the operator to dial, while Kp+312+115X-1+St would indicate a "115X-1" leave-word operator in Chicago to be reached.] [end-of-document] --------------------------------------------------------------- From ptownson Thu Dec 26 17:24:30 1996 Return-Path: Received: by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id RAA21590; Thu, 26 Dec 1996 17:24:29 -0500 (EST) Received: from mailhost.tcs.tulane.edu by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id RAA21530; Thu, 26 Dec 1996 17:24:23 -0500 (EST) Received: from MARK ([129.81.26.141]) by mailhost.tcs.tulane.edu (8.7.6/8.7.3) with SMTP id QAA35438 for ; Thu, 26 Dec 1996 16:28:31 -0600 Message-ID: <32C3176C.458E@mailhost.tcs.tulane.edu> Date: Thu, 26 Dec 1996 16:25:16 -0800 From: "Mark J. Cuccia" X-Mailer: Mozilla 2.01 (Win95; I; 16bit) MIME-Version: 1.0 To: ptownson@massis.lcs.mit.edu Subject: History - 1957 Numbering Document Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Status: RO The following is a transcript of SER (Switching Engineering Report) No.48, prepared by W. O. Turner of the Systems Engineering Department of the Bell Telephone Laboratories, dated February 1, 1957. It regards the Bell System Telephone Numbering Plan - Case 38931. A copy was recently *loaned* to me by one of my contacts who is now retired from Bellcore, and who had started with Bell Labs in the 1950's. Any additional comments of mine are enclosed in square brackets []. MARK J. CUCCIA PHONE/WRITE/WIRE/CABLE: HOME: (USA) Tel: CHestnut 1-2497 WORK: mcuccia@mailhost.tcs.tulane.edu |4710 Wright Road| (+1-504-241-2497) Tel:UNiversity 5-5954(+1-504-865-5954)|New Orleans 28 |fwds on no-answr to Fax:UNiversity 5-5917(+1-504-865-5917)|Louisiana(70128)|cellular/voicemail -------------------------- S.E.R. No. 48 February 1, 1957 SWITCHING ENGINEERING REPORT COVERING THE BELL SYSTEM TELEPHONE NUMBERING PLAN - Case 38931 W.O. Turner Systems Engineering Dept. Bell Telephone Laboratories, Incorporated [the first page is a cover letter from Mr. M.L. Almquist, Director of Systems Engineering, Bell Telephone Laboratories, 463 West Street, New York 14, N.Y., CHelsea-3-1000, to Mr. C.M. Mapes, Assistant Chief Engineer, American Telephone & Telegraph Co., 195 Broadway, New York 7, N.Y., dated March 26, 1957.] Dear Mr. Mapes: The attached S.E.R. No. 48 covers a study of the Bell System telephone numbering plan to determine its adequacy and to explore methods of economically adapting the plan to meet long-range future requirements. The study indicates that: 1. The existing numbering plan will reach capacity in about 20 years. 2. Introduction of a pushbutton telephone instrument with suitable features would permit an economical transition to a new numbering plan with entirely adequate capacity at such time as all users of direct distance dialing service are equipped with the new telephone set. 3. Additional capacity will be needed before transition to the final plan can be made economically. To meet this need, the use of additional numbering plan area codes of the form 1XX is suggested. 4. The additional code capacity which can be gained by adopting an all-numeral numbering plan is not essential, but would be of advantage, particularly to the largest cities. In preparing this report, we have had the benefit of valuable comments and suggestions of your people and of many other members of the AT&T Co. general departments. (signed) M.L. Almquist [the report itself now follows] NOTE: This report has been prepared to record the results of a Systems Engineering investigation that has been conducted primarily to provide background information for use by and guidance of Bell Laboratories technical organizations. It is not intended that the information be used as a guide for development as such information, when and if required, will be contained in a Prospectus. Copies of this report are being distributed within the Laboratories and, on a limited basis, to the American and Western Companies. ACKNOWLEDGEMENT: The writer wishes to express his appreciation of the helpful comments and suggestions contributed by many members of the Laboratories and AT&T Co. staffs during the preparation of this report. In particular, the advice and assistance given by Mr. L.K. Palmer of the AT&T Co., O&E Department, and the data on possible growth in population and telephones furnished by W. Hodgkinson, Jr. of the AT&T Co. Chief Statistician's Division, have been invaluable. TABLE OF CONTENTS: I. Purpose of Study II. Requirements III. Capacity of Present Plan IV. Proposed Action V. The All-Numeral Numbering Plan VI. Summary Attached: Appendix - Capacity Requirements Figure 1 - United States - Population and Telephones Projected to Year 2000 Figure 2 - Bell System Numbering Plan - Number of Office Codes Required Projected to the Year 2000 I. PURPOSE OF STUDY: The study covered by this report estimates the possible future requirements of the Bell System telephone numbering plan, reviews the adequacy of the present plan in the light of these requirements, and suggests a course of action which will economically adapt the present plan to care for long-range future requirements. II. REQUIREMENTS: The future requirements of the Bell System numbering plan will be determined by the geographical area covered by the plan, and by the number of telephones and number of office codes required for all purposes in that area. This study assumes that the Bell System plan will include the United States, Canada, Mexico, Alaska, and the Hawaiian Islands. In addition, it is assumed to be desirable, if not essential, that capacity be provided within the plan for at least operator dialing to Great Britain and perhaps the rest of Western Europe. The number of office codes required in this area at a given time will depend upon the total number of telephones, the percentage of these telephones identified by telephone numbers, and the average number of telephone numbers per telephone office. In order to plan a course of action which will economically care for future requirements, an estimate must be made of the rate of growth in office codes. Then the probable exhaust date of the present plan may be estimated and used as the basis for a program which will provide additional capacity when needed without unreasonable inconvenience to telephone users or heavy expenditures by the Telephone Companies in modifications of plant. The rate of growth selected should be a safe upper limit rather than a minimum, since the penalties to customers and to the telephone industry are small if the growth is overestimated, but might be great if requirements increase much faster than planned for. With this in mind, a compound annual rate of growth in office codes of 4.0% has been assumed. This is based on an estimated annual rate of growth of 1.8% in population and 5.1% in telephones, and assumes inward dialing to all PBX extensions except those of hotel PBX's. At this rate of growth there will be by the year 2000 a total of 130,000 office codes in the United States, Canada, and Mexico, for a development of 550-million telephones. (See the report, "Population and Telephones in the Year 2000", memorandum dated July 16, 1956, by W. Hodgkinson, Jr., of the AT&T Co., Chief Statisticians Department.) This compares with approximately 22,000 office codes serving 56-million telephones in the United States and Canada at the beginning of 1955. The rates of growth in population and telephones are shown on Figure 1, and the corresponding rate of growth in office codes in Figure 2. The derivation of the estimate of growth in office codes is given in the Appendix. III. CAPACITY OF PRESENT PLAN: The present plan is a 10-digit numbering plan, consisting of a 3-digit area code, a 3-digit office code and a 4-digit station number. Area codes are all-numeral. They are distinguished by having either the numeral "0" or the numeral "1" as the second digit. There are 152 of these codes available after eliminating those starting with the numerals "0" and "1", and those conflicting with existing service codes. Office codes comprise the first two letters of the central office name followed by a numerical digit. There are 640 possible codes of which 40 do not correspond to suitable office names and are used only for radiotelephone service. Of the remaining 600, the 60 ending in the numeral "0" are considered less desirable because of possible confusion with the letter "O". The maximum number of office codes per area is thus between 540 and 600. In practice, the average number of office codes per area is well below the maximum for several reasons: 1. Numbering plan area boundaries follow state boundaries. The state is the basic area; less populous states each comprise one area and the larger states are subdivided into as many areas as necessary to accommodate their telephone development. This, of course, reduces the average number of codes per area well below the capacity. 2. Where a telephone community of interest crosses an area code boundary, the codes of the offices involved may be reserved in both numbering plan areas. 3. An adequate reserve of unused codes should be available in each area for future growth. At present, the average number of offices per area is about 200. In the Companies' 20-year view, this will grow to about 300, and should increase further to a level of about 350 in the ultimate. The ultimate capacity of the present numbering plan is estimated as: 152 x 350 = 53,000 offices. At the assumed rate of growth in requirements, this capacity will be reached by 1977 if no area codes are reserved for Great Britain or Western Europe (see Figure 2). If some 20 codes are so reserved, capacity will be reduced to 46,000 offices in North America, and this capacity will be reached in 1973. This estimate is in close agreement with the Companies' own view. In a forecast for the year 1975 approximately, they estimate that 42,000 office codes in 128 numbering plan areas will be required. This does not include 5000 codes which would be required for in-dialing to all PBX extensions, except at hotel PBX's, nor any reservation of codes for Mexico, Alaska, Hawaii or Great Britain. Adding 17 area codes for in-dialing to PBX's and one each for Alaska and Hawaii to the Companies' estimate results in a need for 147 area codes exclusive of Mexico and Great Britain. To sum up: Assuming as high a rate of growth in code requirements as can reasonably be expected, and expansion of the area covered to include Mexico, Alaska and the Hawaiian Islands with some modest provision for operator dialing of calls to Western Europe, the capacity of the present numbering plan may be expected to exhaust at about the year 1975. IV. PROPOSED ACTION: If the rate of growth in office code requirements in the year 1975 and beyond turns out to be the order of magnitude assumed in this study, a major increase in the number of office codes available will be necessary to prevent frequent changes in customer dialing procedures and modifications of telephone plant as more capacity is needed. It is proposed that this increase be achieved by providing a "Distance" button on all telephones. Customers will be instructed to operate this button before dialing 10-digit calls. The local switching systems, on receiving the signal generated by this button, will recognize the first three digits following as an area code and the second group of three as an office code. In this way, identical codes can be used as area codes and also as office codes. With this plan, it naturally follows that switchboard operators as well as customers will have to take some action on each call to permit the switching system to distinguish between area and office codes. It is therefore assumed that each switchboard position at which distance calls are completed will be equipped with two KP keys, one for 7-digit and the other for 10-digit calls. The provision of this "Distance" button has been agreed upon as a requirement for the pushbutton telephone now under study by the Laboratories and American Company. When pushbutton telephones with this feature are in use by all customers having direct distance dialing privileges, the number of area codes available will be increased from the present 152 to a total of 872. This total is made up as follows: Codes starting with the digits 2 to 9, inclusive ............... 800 Codes starting with the digit 1, excluding those reserved for Plant and Traffic Administrative purposes (*) ..... 72 --- TOTAL ..... 872 (*) The access code "11", and the various local service codes, will not conflict with area codes, since they will not be dialed following the operation of the "Distance" button. The availability of these 72 "1XX" codes is also dependent upon the provision in standard electronic switching systems (using pushbutton telephones) of some means of indicating repertory calls, sequence calls, and inter-PBX extension calls other than by the initial digit "1" which is proposed for the Morris trial. [The Morris trial was an experimental Electronic Central Office (ECO) which eventually became ESS. There were experiments and plans being developed even as early as the 1950's for "Custom Calling" features and their dialing and numbering codes to be used in the Electronic office.] Assuming an average of 350 office codes per area, the plan would have capacity for about 300,000 offices, which is adequate for some decades beyond the year 2000. Introduction of the "Distance" button as a feature of the pushbutton telephone rather than as an addition to present dial telephones avoids very heavy modification costs, but it also imposes a delay of some 25 to 35 years before the new telephones are in universal use and the potential additional code capacity can be realized. Since it has been estimated that area code relief may be required in about 20 years, some inexpensive means of obtaining a moderate increase in available area codes with the present dial telephone must be found. for this purpose, it is proposed that all local and toll common control systems be arranged to accept three-digit area codes starting with the numeral "1". No modification of non-senderized step-by-step systems is required, since users of these systems will be required to precede all distance calls with the code "11" or "112", and the area code digits will be registered in a toll system instead of the local system. Of the 100 possible 3-digit codes starting with the numeral "1", there will be available 72 for use as area codes after eliminating those conflicting with the "11" access code, with local service codes, and with codes used by Plant and Traffic in administering toll systems [i.e., the ten 10X system codes Plant Test, the ten 11X local service codes as well as the 11XX system codes for "leave word" operators, and the eight 1N1 system codes for operators (such as 121 Inward, 131 Information, 141 Rate & Route, etc.)] These 72 added to the present 152 will make available a total of 224 area codes, which at an average of 350 offices per area will give capacity for 70,000 to 80,000 offices, depending upon the number of area codes used for transatlantic calls. This capacity should last until 1984 or 1987, affording an interval of almost 30 years for economical transition from the present to the new telephone. If service codes and test codes of the type "1NN" [where the second and third digits are *identical*, such as] (122, 133, 144, etc.) are adopted for common control systems, the number of "1XX" codes available as area codes will be reduced to 64. However, 8 codes of the "N11" type now used as service codes in common control systems would be released for use as area codes, bringing the total net gain back to 72. V. THE ALL-NUMERAL NUMBERING PLAN: It is evident from the foregoing that it is not necessary to take advantage of the greater code capacity of all-numeral numbering in order to expand the Bell System numbering plan to meet requirements of the year 2000 and beyond. However, Laboratories' studies suggest that the all-numeral plan may have advantages other than increased code capacity. It therefore seems worthwhile to outline in this report a possible program based on the adoption of an all-numeral plan. (See the report, "An Evaluation of All-Numeral Dialing", by A.H. Inglis, J.E. Karlin, and W.O. Turner, dated March 1, 1956). The full advantage of the all-numeral plan in speed and accuracy is realized when the letters can be eliminated from the dial plate of the dial telephone, or from the buttons of the pushbutton telephone. If a new pushbutton set is to be introduced, and if an all-numeral plan is to be adopted, the buttons of the new set should therefore preferably be engraved with numbers only. Letters cannot be dispensed with until central office names are eliminated in all communities which can be dialed from any offices equipped for direct distance dialing. Such a conversion, involving among other things, resetting of type in telephone directories serving these communities, extensive publicity, and customer education, requires times for adequate planning and careful execution. In order to keep at a minimum the number of pushbutton telephones which must display both letters and numerals if all-numeral dialing is adopted, an early decision in this matter is obviously desirable. Were all-numeral dialing adopted, the increase in office codes per area would be as follows: 1. Present dial telephones: the 60 codes ending in "zero", now considered undesirable, would be fully useful. The 40 codes for which no suitable office names are available would also become available. The average number of offices per area might increase from 350 to 400. 2. Pushbutton telephones with "Distance" keys: all 872 codes available as area codes could also be used as office codes. The average number of offices per area would of course be well below this maximum because of the factors discussed in Section 3, but an average of 575 per area should be realizable. A comparison of possible programs with and without all-numeral numbering follows: PRESENT PLAN ALL-NUMERAL PLAN Office Exhaust Office Exhaust Capacity Date Capacity Date 1. Present 152 Area Codes 46,000-53,000 1973-76 53,000-60,000 1976-80 2. Add 72 "1XX" Area Codes 70,000-80,000 1984-87 80,000-90,000 1987-90 3. Adopt Pushbutton Telephone with 300,000 beyond 2000 500,000 beyond 2000 "Distance" Button >From a numbering plan standpoint, the added capacity gained through adoption of all-numeral numbering would be of advantage in two ways. The excess over-all capacity of the system beyond a safe reservation for North American needs could be assigned to other continents, thus permitting a universal 10-digit numbering plan covering as much of the world as wished to participate in the plan. The expansion of the maximum number of office codes per area from 600 to almost 900 will become important to rapidly expanding metropolitan areas. At the average rate of increase in office code requirements assumed in this report, the following metropolitan exchange or zone areas will each outgrow the capacity of one letter-numeral numbering plan area before the year 2000: Boston, Chicago, Cleveland, Detroit, Los Angeles, New York, Philadelphia, San Francisco-Oakland One additional point in favor of an all-numeral numbering plan should be mentioned. It appears to be practically essential if customer dialing is ever to be extended to reach non-English speaking countries, since differences in the arrangement of letters on the telephone instruments, in pronunciation and spelling, and in the alphabets themselves, appear otherwise to be insurmountable. VI. SUMMARY: Action suggested as a result of this study is as follows: 1. Proceed with the development of a pushbutton telephone equipped with a "Distance" button to be operated before pulsing 10-digit numbers. When these telephones are in use by all customers who have the direct distance dialing privilege, the supply of area codes can be expanded to a number adequate for a period well beyond the year 2000. 2. As an interim measure to provide adequate area code capacity until the new telephones are in general use, introduce a new series of area codes of the form "1XX". Use of these codes in addition to existing area codes will provide an interval of some 30 years for economical transition to the new telephone. 3. Consider the advisability of adopting an all-numeral numbering plan, in order to gain the full capacity inherent in the adoption of the new telephone with the "Distance" button. Continued use of central office names would permit realization of only part of the potential capacity of the plan. APPENDIX - CAPACITY REQUIREMENTS 1. FACTORS DETERMINING REQUIREMENTS: The requirements a numbering plan must meet are determined by the period of years it is designed to last; by the geographical area to be covered; and by the number of telephones and number of office codes required for all purposes in the area at the end of the period. The following sections outline the basis for estimating these factors for the purposes of this study. 2. YEAR SELECTED FOR CAPACITY ESTIMATE: The year 2000 was selected for the basis of the capacity estimate. Forecasting for such a long period ahead is unusual in the Bell System, but there are good reasons for doing so in this instance: Number changes are annoying and frequently expensive to customers. Business stationery and advertising must be changed. Orders for products or services may be delayed or lost. Lists of frequently called numbers must be revised. If the number or type of characters in the telephone number are changed, customers must change their dialing habits. Until customers become accustomed to the new plan, telephone service in general deteriorates. Customers will undergo these inconveniences with good grace if they are convinced that the change is necessary and in their own best interests. Frequent changes, however, must appear capricious or due to poor planning on the part of the telephone company. If the present system has to be changed, it is only fair to present customers to adopt a plan which can reasonably be expected to last for a generation. The objective is not to make a second change until the inconvenience of the first has been forgotten. The telephone industry itself needs a numbering system which will be stable for a long period as a background for current and future planning in order to avoid frequent and costly changes. Numbering plans have impact upon operating procedures, accounting methods, the design of switching equipment and of the telephone instrument itself. Considering only the telephone instrument, if a new numbering system requires a new instrument, the planning, development and early trials leading to production may well take 5 years; and the replacement of all outmoded instruments on an economical basis 20 years more. Thus, planning for such a numbering should start at least 25 years before the capacity is exhausted, and the new system itself must be adequate for a period of at least 50 years in the future. 3. AREA COVERED BY THE NUMBERING SYSTEM: The area covered by this study consists of the United States, Canada, Mexico, Alaska, and the Hawaiian Islands. Direct distance dialing from San Diego into Mexico would be desirable now, if the numbering system permitted. As Mexico and the United States increase their community of interest, dialing across the Mexican border will become more and more attractive. Codes are now reserved for Alaska [907] and Hawaii [808]. In addition, the plan should provide for the inclusion of area codes for Great Britain and perhaps other parts of Europe. This requirement is impossible to estimate with any precision at this time, but an adequate margin for intercontinental dialing is a very real requirement. 4. NUMBER OF TELEPHONES IN THE YEAR 2000: It is well to point out that what is needed for this purpose is an _outside_ figure. An under-estimate of growth would advance the date when a new major change would have to be made, and the economic penalty to the telephone industry might be enormous. The estimate used for this study is a total of 550,000,000 telephones in North America in the year 2000. This compares with 57,000,000 telephones in 1955. Of these, 500,000,000 are assumed to be in the United States and about 50,000,000 in Canada and Mexico. The source of the estimate given above is a memorandum prepared by Mr. W. Hodgkinson, Jr., of the Chief Statistician's Division of the American Telephone and Telegraph Co., dated July 16, 1956. It should be emphasized that these data were furnished as safe outside limits for use in designing a numbering plan. The use of the data as estimates of telephone development is the writer's own responsibility. In case any reader feels that the assumed number of telephones in the United States at the year 2000 is too optimistic, he is referred to Mr. B.T. Miller's article "The Course of America is Upward", in the Spring 1956 issue of the {Bell Telephone Magazine}. The following excerpts from Mr. Miller's article are pertinent: "We in the telephone business have ... geared our activities to customers' _needs_ ... We have done very little to cater to this huge market in the sense that other businesses have ... We have not tried to find out ... what are the communication possibilities of the average family ... When we have done so, we have made an honest effort to meet their _wants_, we shall certainly be amazed at the potential ... This could mean that by 1965 or 1970, when we have 45 million homes in Bell System territory, we could have a hundred million (*) telephones in these homes instead of the thirty million or so that we now have." (*) Assuming the present ratio of business to residence telephones, this is equivalent to a total of 140 million telephones. The estimate used as a basis for this study forecasts a total of 115 million telephones in the United States in 1970, including non-Bell as well as Bell territory. 5. NUMBER OF OFFICE CODES IN YEAR 2000: 5.1 United States: Both the existing and the proposed numbering plans limit the number of telephone numbers per central office to a maximum of 10,000. In urban areas, the average number of working telephone numbers per office will be less than this maximum, since recently changed and disconnected numbers numbers cannot be immediately reassigned and since in each building, there will be partially equipped growing units which will bring down the average per office. A review of the 1955 edition of "Metropolitan Exchange Data", published by the O&E Dept. of the AT&T Co. shows that under actual conditions, the average telephone office in urban areas has 7000 working numbers. For the purposes of this study, it is assumed that in the year 2000, the average office in urban areas will serve 7000 telephone numbers. In rural (*) areas, it will not be possible to approach the average number of telephones per office found in urban areas, since a high percentage of the exchanges will serve areas with a hundred or a few scores of households. In these rural areas, the average number of telephones per office will be affected more strongly by the average size of the community served than by the maximum capacity of any one office. (*) The word "rural" here is used as defined by the Census Bureau, and includes places of under 2500 population. These offices will therefore serve many telephones not classified as "rural" by the telephone industry. The average number of telephones per office in rural areas for the year 2000 is estimated as follows: a. In 1954, the average number of telephones per office in the United States, considering only "rural" places of less than 2500 population, was 175. b. The estimate for the year 2000 assumes that the average number of residential telephones per household will increase from the 1954 figure by a factor of 4.5. c. The average number of telephones per office in places under 2500 population in the year 2000 will be 175 x 4.5, or 800. In order to use the figures of 7000 telephone numbers per office in urban areas, and 800 telephones per office in rural areas, some estimate must be made for the year 2000 of the number of telephones in the two types of areas, respectively. For this study, it is assumed that there will be 40 million rural population in the year 2000. This amounts to 12% of the total population compared with 36% rural population in 1950, and assumes a decline of 14 million in total rural population. It is further arbitrarily assumed that there will be no business telephones in rural areas. The average number of residence telephones per hundred population for the year 2000 has been estimated at 106. This gives a total of 42,500,000 telephones in rural areas. At 800 telephones per central office, this would require 53,000 central offices to serve the rural areas. Of the remaining 457,500,000 telephones in urban areas, 143 million are assumed to be business and the rest residence. For the purpose of this report, it is assumed that all business telephones [including "extensions" in a PBX] will require numbers, but that in the residence classes, only main telephones will be numbered. It is further assumed that the kinds of residence service offered, perhaps Visiphone [i.e. Picturephone] and other new services, will result in the equivalent of 1.5 residence main telephones per household, or a total of 144 million residence main telephones in urban areas. Inward dialing to PBX extensions is assumed. Of the 143 million business telephones, 76.5 million will be non-PBX, requiring a number per telephone. In addition, 12.5 million PBX trunks will occupy numbered terminals in the central offices. This total of 89 million business numbers, added to the 144 million residence numbers, will require 33,300 office codes in urban areas exclusive of those required for in-dialing to PBX extensions. Numbers for PBX extensions are assumed to be supplied in blocks of 100. According to a study by Mr. C.M. Conway, of the AT&T Co., O&E Department, 2500 office codes would be required for the 1955 telephone development, were in-dialing to extensions in effect in all cases, except hotel PBX's. On this basis, 23,800 office codes will be required for this purpose in the year 2000. The following table summarizes office code requirements for the year 2000, compared with 1955 requirements: 1955 2000 ---- ---- Rural 10,505 53,000 Urban 10,400 33,300 In-Dialing to PBX Extensions 0 23,800 ------- ------- Total 20,905 110,100 Obviously, not all the factors which will determine the actual number of office codes in the year 2000 have been included in this estimate. The use of line concentrators with electronic switching systems to serve small communities might drastically reduce the number of office codes required in rural areas. However, the vast preponderance of these rural communities will be served by non-Bell companies, and it is not possible now to forecast the extent to which these companies will adopt the line concentrator principle. On the other hand, new services not even on the horizon now may be in common use by the year 2000, and result in a much greater demand for office codes than forecast here. For purposes of this study, then, the estimate of 110,000 office codes will be used. 5.2 Canada and Mexico: According to the estimates used for this study, Canada and Mexico will have less than 10% of the telephones in North America in 2000. Since data for Canada and Mexico are not entirely reliable, a "broad-brush" estimate for these two countries seems as likely to be correct as the more detailed computations made for the United States. Canada had 3.9 million telephones and about 2860 office codes in 1955, or 1400 telephones per office code; about half the average for the United States. In view of the vast undeveloped areas yet to be settled, it is not likely that development in terms of telephones per central office will catch up with that of the United States in the next 44 years. A more reasonable assumption is that Canada's development in this respect in the year 2000 will equal that of the United States today. For want of a better assumption, this may be applied to Mexico as well. On the above basis, the 51.6 million telephones in Canada and Mexico would require 19,000 office codes in the year 2000. Perhaps 1000 more codes would be required for in-dialing to PBX extensions, for a total of 20,000. 5.3 Summary: It is estimated that there will be 100,000 office codes required for the United States, and 20,000 for Canada and Mexico in the year 2000, for a total of 130,000. [There are two "figures" -- graphical charts -- as indicated in the table of contents, as well as mentioned in the main text. They are not included in this text-based transcription for TELECOM-Digest, however.] [end-of-document] ............................................................... From ptownson Thu Dec 26 17:24:32 1996 Return-Path: Received: by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id RAA21617; Thu, 26 Dec 1996 17:24:31 -0500 (EST) Received: from mailhost.tcs.tulane.edu by massis.lcs.mit.edu (8.7.4/NSCS-1.0S) id RAA21526; Thu, 26 Dec 1996 17:24:21 -0500 (EST) Received: from MARK ([129.81.26.141]) by mailhost.tcs.tulane.edu (8.7.6/8.7.3) with SMTP id QAA35443 for ; Thu, 26 Dec 1996 16:28:33 -0600 Message-ID: <32C31772.7BC6@mailhost.tcs.tulane.edu> Date: Thu, 26 Dec 1996 16:25:22 -0800 From: "Mark J. Cuccia" X-Mailer: Mozilla 2.01 (Win95; I; 16bit) MIME-Version: 1.0 To: ptownson@massis.lcs.mit.edu Subject: History - 1958 Numbering Document Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Status: RO The following is a transcript of a Technical Memorandum from Bell Telephone Laboratories. It is dated April 28, 1958, and authored by Mr. W.O. Turner. It's reference code is MM-58-312-1, and carries the subject: History of the Bell System Telephone Numbering Plan - Case 38931. A copy was recently *loaned* to me by one of my contacts now retired from Bellcore who had started with Bell Labs in the late 1950's. Any additional comments of mine are noted enclosed within square brackets []. MARK J. CUCCIA PHONE/WRITE/WIRE/CABLE: HOME: (USA) Tel: CHestnut 1-2497 WORK: mcuccia@mailhost.tcs.tulane.edu |4710 Wright Road| (+1-504-241-2497) Tel:UNiversity 5-5954(+1-504-865-5954)|New Orleans 28 |fwds on no-answr to Fax:UNiversity 5-5917(+1-504-865-5917)|Louisiana(70128)|cellular/voicemail --------------------------- The history of the Bell System telephone numbering plan is not well documented, and not many individuals are left in active service who have had long continuous contact with this problem. There is renewed interest currently in the numbering plan situation because the capacity of the present plan is rapidly being approached and because discussion of the pushbutton telephone naturally leads to consideration of the environment in which it will be used. For these reasons it has seemed appropriate to the writer to set down this account. Events antedating 1927 are based on documents in the files; subsequent history is based on the writer's personal recollections and those of Mr. L.K. Palmer of the AT&T Co., who since about 1930 has had the responsibility for the administration of the plan. By the summer of 1916, work on the Western Electric power driven full mechanical telephone switching system [Panel] had progressed to the point where preliminary cost comparisons could be made with the Strowger [SxS] system which was in use in a number of cities and towns operated by [*non* connecting competitive] independent telephone companies. These comparisons indicated that the Strowger system would be cheaper for the small single office towns. The Western Electric [Panel] system would be more economical in the multi-office cities where its large access switch and flexible trunking arrangements were of most advantage. This conclusion was disheartening to the Bell System people, because there was uncertainty in their minds whether telephone customers in large cities would be willing to dial their own telephone calls, and if not, there would be very little demand for the Western Electric system. In a small city served by one office, no telephone number needed to consist of more than 4-digits, but in the multi-office cities, it would be necessary to prefix office codes to the 4-digit station numbers to distinguish between offices, and as many as 6 or 7 digits might need to be dialed on each call. Two questions worried the planners: Would the customers be willing to dial as many as 7 digits in placing a telephone call, and if so, could they do this accurately enough so that the grade of service they would get would compare favorably with manual service? Obviously, a favorable answer to these two questions depended largely upon the ability of the planners to evolve a numbering plan which the customers could use easily and accurately. Existing dial communities operated by independent companies were small enough so that telephone numbers of 4 or 5 numerical digits were sufficient to designate all the telephones. A small number of telephones operated by the [independent] Home Telephone Co. in Los Angeles [even] had [as long as] 6-numeral listings. Therefore, the Bell System people could not depend upon independent company experience for guidance in solving their problem. The most obvious course would be to follow independent company practice and number telephones in the larger cities with 5, 6, or 7-numeral telephone numbers depending on the size of the city. One school of thought, however, held that only the line number should be designated by numerals and that the added office code digits should be made up of arbitrary letters. [Actually, in the early decades of the century, some cities with local dial step-by-step systems of competitive non-connecting independent telephone companies were using a combination of both letters and numerals on five or six digit local numbers. The first digit was represented by a letter, and it identified the particular central office in that city, of the independent telephone company's dial system. Most of these used 'unique' lettering on the dial, and not standardized until much later, beginning in the 1920's, when the independent and Bell companies began to co-ordinate and consolidate their local dial systems. Some of this continued into the mid-40's, when Bell of Pennsylvania took-over the non-connecting competitive Keystone System in Philadelphia, which had its own unique lettered dialface. Calgary (Alberta) in Canada also continued to have its own unique lettered dialface until the 1950's, when it changed over to the North American standard dialface, as it needed to be properly incorporated into the DDD network of the USA and Canada.] Proponents of the all-numeral scheme argued that it was just an extension of the existing all-numeral scheme used by [some] of the independent companies, and that the addition of letters on the dials would result in more errors, since the space would have to be shared by letters and numerals, thus making all [of the] characters less legible. Proponents of the letter-numeral scheme felt that a combination of letters and numerals would be easier to remember and dial, and that this advantage would outweigh the decrease in legibility. There was general agreement that there would not be room for more than one-letter-per-fingerhole on the dial, so that all office codes would be made up by suitable selections from the ten available letters. A suggestion that the number of fingerholes be increased to 15 with letters only in the additional 5 holes appears not to have been seriously received. [Most of the independent systems using letters had such one-letter-per- digit on their dialfaces at that time. Sometimes, it represented the first letter of the 'name' of a central office building or neighborhood; others were simply 'arbitrary' letters which had no 'attachment' to a 'name'. Some systems had 'sequential' or 'increasing' letters - i.e. 1=A, 2=B, etc.; others had 'arbitrary' arrangements - i.e. 1=A, 2=M, 3=S, 4=W, 5=E, etc. There were some independent dial systems which had *more* than ten finger- holes on their dials, where the 'additional' fingerholes (and associated dialpulses) above the 'ten' were for reaching the operator, long-distance, or other special functions.] It was obvious that the full mechanical system would have to be introduced in multi-office cities on an office-by-office basis, so that for the period of transition, provision would have to be made for dial customers to dial manual telephone numbers as well as dial numbers. Because the proposed form of numbering for dial offices was different from that used for manual offices, the situation appeared to present a difficult stumbling block to the smooth introduction of the new dial system. One possible plan was to change all telephone numbers in the city to the full mechanical form before the first dial office was put in service. This would mean abandoning the traditional central office names, and substituting letter or numeral codes for them. This wholesale change of numbering affecting customers not to be cutover to dial as well as those who were, might be extremely distasteful to the public and would create a bad environment for the introduction of the new system. Moreover, it was felt that telephone operators would have more difficulty in understanding and passing arbitrary codes than central office names so that the service would become less satisfactory. A second possibility was to retain the present form of numbering, using central office names for existing and new offices, but in addition, to assign to all stations both manual and dial, a second number made up of all numerals, or arbitrary letters and numerals. With this plan, it would be necessary either to show two numbers for every customer in the directory, or to provide two separate directories, one for use by dial customers, and one for use by manual customers. The inconvenience to the public, and expense to the telephone company of either plan are obvious. While debate was continuing on the merits and demerits of the various numbering schemes, it was decided to attempt to get some experimental evidence as to the accuracy with which customers might dial numbers containing more than 5 characters. Accordingly, in the Fall of 1916, there was set up at 195 Broadway equipment which would be recorded by a printing telegraph circuit so that the accuracy of dialing might be checked. Numbers of 4 to 8 digits inclusive were dialed by test subjects. In the early stages of the trial, the digits dialed were all numerals. In a report on the preliminary phases of the trial, dated November 13, 1916, it was stated that dialing of numbers consisting of letters and digits was about to start. The files do not contain, however, any comparisons of accuracy as between all numerals and letter-numerals, nor do they state specifically that the letter-numeral combinations were in fact tried. The results of the trial were summarized in a memorandum dated July 25, 1917. This is of some historical interest since it may be a record of the first experimental test of customer dialing performance made by the Bell System; therefore, it is attached in full as Appendix I. Conclusions were that the overall error rate ranged from 1.3% with 4-digit numbers, to 4.1% with 7-digit numbers, and then fell to 2.5% for 8-digit numbers. The low rate of errors with 8-digit numbers was explained as follows: "Up to and including the 7-digit numbers, the majority of the people dialing looked up the number and then dialed it without looking back in the directory or on the list, while on the 8-digit numbers, nearly everyone took the number in two parts". It was noted that a large fraction of the errors were caused by sending in a preliminary digit caused by a quick movement of the switch-hook before dialing, and when these were deducted from the total, the per-cent dialing errors reported as follows: No. of Digits % Dialing Errors 4 0.82 5 0.95 6 1.80 7 3.14 8 1.95 By the Summer of 1917, the early concept that all ten-positions on the dial were available for use as office code digits had been modified. Agreement seems to have been reached that the zero digit should be reserved for calling the operator, and that the "1" digit should not be used to start office codes, because of the danger of reaching the wrong office inadvertently when preliminary pulses were caused by careless operation of the switch-hook. The desk-stand ["candle-stick" phone] in use at that time was particularly vulnerable to this kind of error. While there is no explicit statement to this effect in the files, it might be reasonable to assume that the results of the dialing tests given above were the basis for the decision to protect against preliminary pulses. While the dialing tests indicated that there was hope that customer dialing accuracy might be sufficient so that dial service would compare favorably with manual service, no progress had been made by the middle of 1917 on the problem of devising a smoother way of introducing dial numbering into a multi-office city. On September 7, 1917, a major break-through occurred. Under this date, Mr. W.G. Blauvelt wrote a memorandum outlining a plan of retaining central office names and instructing customers to dial the first 1, 2, or 3 letters of the central office name, in addition to the digits of the station number. The number of digits dialed would, of course, depend on the number of offices in the city. This plan would avoid the problem of double listings or the alternative problem of complete abandonment of central office names. Mr. Blauvelt admitted that it would be necessary to change a large proportion of the existing central office names in each city, since with only one-letter-per-fingerhole (he assumed a [single] letter in each of the ten holes), the codes corresponding to many of the existing central office names could not be dialed. During the year following the date of Mr. Blauvelt's suggesting, the AT&T people held discussions with interested officials of most of the Bell System Operating Telephone Companies, and the ultimate decision reached almost unanimously was that the Blauvelt scheme should be adopted in spite of the penalty involved in changing a large portion of office names. It was felt that the plan using central office names was inferior to a plan using arbitrary code letters, or to an all numeral plan; but the relative ease of transition from manual to dial outweighed all other disadvantages. It was pointed out that if dialing errors due to mis-spelling of names remained at a high level, the names could be dropped once all manual offices [in that city] were eliminated [i.e. cutover to dial]. On August 30, 1918, a memorandum was written by Mr. W.D. Sargent which contained the first proposal to associate more than one letter with each fingerhole in the dial. Mr. Blauvelt's original numbering plan proposal was modified by this suggestion, and was eventually patented (Pat. 1,439,723, issued December 26, 1922). Mr. Sargent's specific proposal was to associate two letters with each of the ten fingerholes and, in addition, to use the numeral zero as the letter "O" ("oh"), thus getting a total of 21 letters. This proposal directed thinking and experiment in the direction of various arrangements of letters and numerals on the dial to obtain maximum legibility, and out of these experiments, there evolved the conviction that it would be feasible to associate 3 letters with each of the numerals 2 to 9, inclusive, thus obtaining a total of 24 letters which could be used in office codes. By leaving out only the letters Q and Z, it was found that central office name changes could be reduced to a minimum, the changes being made only in those codes where two names started with the same letters or with letters equivalent to the same numeral code. A good deal of discussion took place as to the best arrangement of letters and numerals, and the best coloring of background and characters to promote legibility; but by August 14, 1919, a memorandum was written submitting samples of dial markings employing black letters and red figures on a white background with the dial arrangement almost identical with that ultimately adopted for multi-office cities. Thus, the pattern of the Bell System numbering plan was set, and because of the ingenuity of the early planners, our large cities have gone through the transition from all manual to all dial, with a minimum of inconvenience to the customers. The general pattern was about as follows, although there were exceptions: Number of Number of Type of Offices Digits in Number in a City a Number 1 4 4321 more than 1, 5 2-4321 less than (and mixed (and (ultimate) 8 4 and 5) 4321) more than 5, less than 6 ADams-4321 (ultimate) 64 more than ultimate 64 7 ADAms-4321 One further major change was made in the 7-digit numbering plan. In the 1920's, New York City found itself badly cramped for office code combinations for its rapidly expanding number of offices, and the New York Company suggested that 3-letter/4-numeral listings be changed to 2-letter/ 5-numeral listings. ADA-4321 became AD-2-4321. This would permit one name to serve eight offices; in fact, if the numerals "0" and "1" were used as the third office code digits, each name could be used ten times, and the maximum code capacity for a 7-digit city would increase from 512 to 640. Moreover, some codes hitherto unusable could now be used; for example, the code 777 is unusable with a 3-letter system, but forms the perfectly good central office name PResident-7 with the 2-letter/5-numeral system. [Actually, 777 was used for SPRing, one of the earliest *manual-era* central offices used/named in New York City. It became SPring-7, when New York City went to 2L-5N circa 1930.] Other advantages, such as the possibility of retaining community names for suburban communities served by more than one office, were evident. This plan was adopted by New York City and Northern New Jersey in 1930, and eventually all 7-digit cities followed suit. [However, even earlier, in the early 1920's, Los Angeles and the Southern California area had 7-digit numbers of the 2L-5N format, without ever having gone through the 3L-4N phase. In addition to 2L-5N seven dialpull numbers, the Los Angeles metro area also had mixed six dialpull 2L-4N numbers.] As telephone growth outstripped early predictions, many local numbering systems burst at their seams. Four-numeral cities grew to 4 and 5, then to straight 5 numerals. When 5-numeral cities outgrew this plan, 2-numeral office codes were added and the plan became 5 and 6-numeral. Six-digit cities with 2L-4N numbers evolved into 6 and 7-digit cities with 2-letters and 4 or 5 numeral [station] numbers. By 1940, there were some 12 different varieties of local numbering in the Bell System, including some using only one letter and 4 or 5 numerals. With the end of World War II, the Bell System plunged into a program of extending operator toll dialing to nationwide proportions. Early attempts at extended operator toll dialing were limited not only by inadequate equipment design, but by the necessity for dialing an arbitrary code to route the call through each intermediate switching point in its path. Thus, an operator might have to dial as many a 12 digits before dialing the called number if there were 4 intermediate switching points on the route. Satisfactory dialing accuracy under these conditions seemed to be too much to hope for. The No. 4 type toll crossbar system could be given the ability to translate, change, and spill-forward codes dialed into it, and this made possible a universal nationwide numbering plan with each subscriber station given its own unique code and number in the national plan. At the AT&T Co. the writer and Mr. L.K. Palmer were charged with the responsibility of evolving this universal nationwide numbering plan, in co-operation with the Bell Laboratories' engineers. Requirements set up for the plan were: Minimum number of digits to cover the United States and Canada and provide for 40 years' growth. Uniform number of digits to be dialed on long-distance calls. All existing local numbering plans to fit into the national plan without significant change in local numbering, which would increase the difficulty of dialing local calls. In addition, it seemed highly desirable that the plan be suitable for direct distance dialing by customers at such time as facilities for this became available. This additional requirement was accepted by management, but only on the basis that the ease and simplicity of operator dialing was not to be reduced thereby, and that no local number changes were to be forced to gain this objective alone. The nationwide plan which was evolved is the now familiar ten-digit plan consisting of a three-numeral area code preceding a seven-digit number. Local telephone numbers of less than 7-digits were to be built up to 7-digit numbers by the toll operators by following these rules: 4-numeral numbers: dial arbitrary 3-numeral code assigned to the town, and 4 numerals 5-numeral numbers: dial [first] 2-letters of the town name, and 5-numerals 6-numeral numbers: dial initial letter of the town name, and 6-numerals 2-L/4-N numbers: dial 3-letters of the office name, and 4-numerals Thus, for the bulk of the traffic, to all but the smaller towns, the full 7-digit telephone number could be built up by the operator from the town name and number furnished by the calling party. Considerable thought was given to the problem of dividing the United States and Canada into numbering plan areas. Using the basic 2-L/5-N numbering plan, there would be capacity in each area for a maximum of 640 offices with no conflicts between office codes. There were something under 20,000 telephone offices in the area to be covered by the nationwide plan. One hundred areas could be designated by a 2-digit area code series; and if area boundaries could be arbitrarily set so as to allocate an average number of offices to each area regardless of density of telephone development, these 100 codes would suffice until the number of offices had increased three-fold. This would permit adoption of a 9-digit universal numbering plan. It was immediately apparent, that this ideal was impossible of attainment, for several reasons. In toll operating practice, it is customary to maintain on the switchboard keyshelf adequate information to permit the operators to determine the route for 90% or more of the calls they handle without reference to the special route operator. If the boundaries of numbering plan areas were to be purely arbitrary, without relation to any natural or political boundaries, the job of determining the area code for a particular called point would be immensely complicated, and would almost certainly increase the delay and cost involved in handling toll calls by making it necessary to refer to the route operator on more than 10% of the calls. Moreover, there are definitely outlined local calling areas around the larger cities, and numbering plan area boundaries should not be drawn to cut across these areas. As an aid to memory in determining the area code of a called place, the device obviously most useful was to establish a relationship between the area code and the state or province in which the office is located. One area would cover each of the less populous states, while the larger states would have to be divided into two or more areas each. This was the plan adopted; early estimates indicated that the number of codes needed over a 40-year period would be about 100. The form of numbering plan area code adopted was dictated, in the last analysis, by past history. Because of the decision, back in 1918, not to assign letters to dial positions one and zero, since these digits would not be used to start office names, it followed that the second letter of office codes never corresponded to the numerals "1" and "0". Therefore, if numbering plan area codes included a "1" or "0" as their second digit, the toll switching equipment could readily be designed to examine the second digit received, and if it were a "0" or "1", to recognize that the first three digits received were to be translated as an area code, not an office code. This meant a 3-digit area code instead of a 2-digit area code; but after conflicts with codes reserved for other purposes were set aside [the eight "N11" 3-digit local service codes], there remained 152 such codes available for numbering plan area use. The 100 code capacity of a 2-digit code system had seemed perilously limited, so the 3-digit code pattern seemed amply justified. Thus the present pattern evolved: From any place in the United States and Canada where the necessary facilities are available, the number CHelsea-3-1000 in New York City can be reached by dialing 212-CH3-1000. Hardly had the pattern been set for nationwide operator toll dialing, when the decision was made to press forward with the development of facilities to permit nationwide customer direct distance dialing. Because this possibility had been kept in mid throughout the development of the nationwide numbering plan, no major changes in the plan itself needed to be made. Customer use of the plan, however, did emphasize certain difficulties which the operators had already encountered, and sparked the next stage in the evolution of the Bell System numbering plan. The next stage of evolution consisted of two innovations: the adoption of universal 2L-5N numbering for all local offices reached by direct distance dialing, and the introduction of a standardized list of central office names, chosen on the basis of ease of spelling and pronunciation. Although the rules for building-up the existing 4, 5, 6, and 7-digit telephone numbers to uniform 7-digit numbers were relatively simple for trained operators to use, customers could not be expected to remember them. No more should be asked of the general public than to dial the called area code followed by the called number as listed. This meant uniform listings of 7-digits across the continent, in small towns as well as large cities. And as local dialing areas were expanded to conform to the widening areas of social and business interest in growing communities, the 7-digit local numbering plan simplified the dialing of calls to nearby communities as well as distant ones. By changing at one move to the 7-digit plan, the gradual shifts from 4-digits, to 5, to 6, and to 7, with the attendant annoyance to customers and expense to telephone companies, were stopped once and for all. Almost from the inception of operator toll dialing, difficulty was experienced with the spelling of unfamiliar office names, which may have had rich local significance, but were virtually unknown away from their immediate locality. An early example of the need for a standardized list of names came at the time the Indianapolis toll crossbar switching machine was placed in service. An analysis of the calls which were misrouted through the toll office showed that some 70% to 80% were due to mis-spelling two Indianapolis office names: IMperial and RIley. The name IMperial was frequently [mis]spelled [and mis-dialed as] EMperial; and as for the RIley office, named after the famous Hoosier poet, it was apparent that outside his home state, most people were more familiar with the good Irish name Reilly than with the poet's name. There was no recourse but to give these two offices new names which would be mis-spelled less frequently. Another difficulty that had to be straightened out was the existence of three central offices in different cities of the Bell System spelled HIland, HYland, and HIghland, respectively. Even the traditional office name CYnwyd, near Philadelphia, was abandoned. As experience with distance dialing accumulated, it became apparent that another difficulty had to be straightened out. That difficulty arose from the use of town names as central office names. Lafayette, California is a relatively small town, just outside Oakland. The name is in the approved list of central office names, so why not use the town name as an office name? But consider the plight of an operator asked to complete a call to "Lafayette, California, 3-1211." Has she complete information? Is the town name missing, or the office name? To avoid the chance of mis-routing the call, she must cross-examine the customer, which annoys the customer, and delays the call. So an arbitrary name is added; the customer asks for: "Lafayette, California, ATlantic-3-1211" and the call goes through without delay. Obviously, the name ATlantic has no significance in a town overlooking San Francisco Bay, but uniformity has been achieved, and uniformity helps eliminate errors. Much local pride in historically significant names has had to be put aside, and telephone office names, for the sake of mechanical progress, are becoming colorless and standardized. Even with much progress in eliminating hard-to-spell names, sources of confusion remained. One of the most frequent errors was substitution of the numeral "0" for the letter "O" as the second letter of names as "MOntrose," In 1955, a group of Bell Laboratories' engineers and scientists met at the request of Mr. A.B. Clark to consider whether anything might be done to improve dialing accuracy. As a result of this meeting, a program of laboratory tests was organized to compare the speed and accuracy of dialing of two systems - the existing system using central office names, and an all-numeral system. The all-numeral system was selected for comparison rather than one using arbitrary letters and numerals, because it is, of course, essentially the simplest possible numbering system. Results of the Laboratories' tests were published on April 2, 1956, in the form of a report "An Evaluation of All-Numeral Dialing", by Messrs. A.H. Inglis, J.E. Karlin, and W.O. Turner. Conclusions were that with the all-numeral system, errors would be fewer and dialing faster; and that from a memory standpoint, there was little choice between systems except that the average person would take a few days longer to memorize a 7-numeral number than one consisting of an office name and 5-numerals. With pushbutton telephones, the speed and accuracy advantage of the all-numeral system becomes relatively greater. The tests did not include dialing of ten-digit numbers, as in direct distance dialing. Since the establishment of the nationwide numbering plan, new numbering plan areas have been created at such a rate that in 1957, there are 113 in existence. This increase in area requirements is partly the result of inefficient use of office codes in the less developed parts of the country, and partly due to accelerated growth, particularly in the fast developing territory of the U.S. south and west, and Canada. A 1956 survey of the Companies' own forecasts indicated a requirement of some 130 area codes by the time telephone development doubles again. This estimate did not take into account three factors which by this time were definitely in the picture: The probable extension of the numbering plan into Western Europe and possibly beyond; increased numbers of office codes required for inward dialing to PBX extensions and other new services [paging, mobile, datasets/ modems]; and the possibility of greatly stimulating the demand for telephone numbers by aggressive merchandizing of telephone service. Obviously, the 152-area capacity of the numbering plan, which had looked so safe 10 years before, required re-examination. This re-examination was undertaken by the writer, and resulted in S.E.R. No.48, "The Bell System Telephone Numbering Plan," released on March 26, 1957. Conclusions of the study were as follows: Capacity of the present numbering plans may be reached in about 20 years. Limited additional capacity can be provided on a temporary basis by using 3-digit area codes beginning with the numeral "1". For permanent relief, the pushbutton telephone, when introduced, should be equipped with a "Distance" key, to be operated before setting up all 10-digit calls. With this means of identifying 10-digit calls, all combinations of three numericals can be used for area codes - a total of 1000. Further relief could be obtained by adopting all-numeral telephone numbers. The maximum number of office codes per area would be substantially increased, which would particularly benefit the larger cities. These proposals have the obvious weakness that long-term expansion of the numbering plan capacity depends upon the universal substitution of pushbutton telephones for dial telephones within a 20-year period. This might turn out to be uneconomical for both the Bell and non-Bell telephone companies. Discussions of this point among AT&T Co. and Laboratories' engineers gave rise to a suggestion which is under review by the AT&T Co. at the time this memorandum is written; that is, that when further code capacity is needed, either the digit "1" or the digit "0" be set aside for use as a prefix to be dialed before all 10-digit calls. The arguments for and against each of these digits have been summarized by AT&T Co. engineers and discussions leading to agreement on a choice of digits are currently under way. This prefix would serve the same purpose as preliminary operation of a "Distance" key at pushbutton telephones, and would be applicable to both types of sets. Additional code capacity would no longer be dependent upon the elimination of dial telephones, but the total number of available office codes would be reduced. For example, use of the digit "1" as a prefix to indicate a 10-digit number to follow would preclude its use as the first digit of an office code. Meanwhile, in the Directory Departments of the telephone companies, there has spread an innovation which has a bearing on the evolution of the numbering plan. As cities grow and telephone directories get bulkier, each fraction of an inch of directory space becomes more precious. The directory people looked with covetous eyes on the space taken up by the central office name, repeated for each listing in the directory. Cautiously at first, they dropped out all but the first two letters of the central office name in directories covering but a few offices, showing in a box on each page the list of office names and their two-letter codes. The saving in space could be taken in less pages per directory, or it could be translated into larger and more legible type. No adverse reaction came from the public - who use the 2L-5N system in advertising and other public displays anyhow - so the system is being extended to the larger cities, and the list of names and corresponding codes is being moved to the information section at the front of the directory. This development may well lead to further changes in central office names, or their abandonment entirely. Consider two perfectly good central office names, ADams and ATlantic, both on the approved standard list. Now, drop the names, and continue to use the code letters AD and AT. On passing these by word of mouth between customers, and between customers and operators, how many times will "AD" come out as "AT"? Each such translation prepares the ground for one or more dialing errors. It seems inevitable that if names are dropped, letters too must be dropped, or else the list of permissible letters reduced to eight or so that are not easily confused phonetically with each other or with numerals. The Australian Post Office has already started the transition from a combination of arbitrary letters and numerals in their large cities, to a straight 7-numeral plan. In Europe, elimination of letters from local numbers is being considered as a means of minimizing the language difficulties accompanying the introduction of direct international dialing. The arguments for all-numeral dialing are compelling enough so that the AT&T Co., early in 1958, embarked upon a full-scale trial in Witchita Falls, Texas. This moderate-sized city has had a 5-numeral numbering plan and was scheduled to be changed to the conventional 2L-5N plan. Instead, it has been changed to 7-numerals. Indications so far are that the customers are satisfied with the 7-numeral plan and that their performance compares favorably with that of customers in other similar places where the transition has been to the 2L-5N plan. [It might have been possible that the first digit of the two new initial digits didn't conflict with the first digit of the five-digit local number. I assume that Witchita Falls was a SxS city at that time, and installed 'digit-absorbing' equipment in its SxS first selectors to 'absorb' the first two new dialed digits. Customers might have continued to be able to dial only the five-digit portion of the telephone number for many more years, as occurred in many mid-sized SxS situations.] Further experience with the 7-numeral plan is, of course, desirable, and the acid-test of acceptability will be to convert to this plan, some city now accustomed to dialing 2L-5N. Plans for such a trial are under discussion. [However, in the mid-1960's the "Anti-Digit-Dialing Leagues" were formed, the first one in the San Francisco Bay Area. It went as far as even involving a lawsuit against Pacific Telephone & Telegraph, with the ADDL plaintiffs using attorney Marvin Belli.] And so, central office names have become a vestige of the past, without significance to the people who use them, and a source of errors and confusion. If we try to project the lessons of 40 years of history into the future when international dialing may well be common-place, it seems to the writer, at least, that the evolution of the Bell System numbering plan will not be complete until we arrive at the ultimate simplicity of an all-numeral numbering plan. (signed) W.O. Turner NY-312-WOT-BC Att. Appendix APPENDIX: Tests in Dialing Telephone Numbers with Varying Numbers of Digits. July 25, 1917 (Taken from O&E Department File 1606, Vol. I) An automatic telephone with the usual dial at its base was connected with a printing telegraph machine located in a room on the floor below the one in which the telephone was located. Two sets of tests were made. On the first set of tests, lists of numbers with four, five, six, seven, and eight digits were pasted in a New York City telephone directory, and lists of the names and addresses corresponding to the names and addresses in the directory associated with the lists, were also prepared. A number of different people were selected approximating as nearly as possible an average group of telephone users. These people were given lists of names and addresses containing 25 names with four-digit numbers, 25 with five-digit numbers, etc., copies of which are attached. They were also given the attached set of instructions on how to operate the automatic telephone. The numbers as sent were recorded on the printing telegraph machine, and a record was kept of the accuracy with which the numbers were sent, together with the time required to send the lists with the varying number of digits. A quick movement of the switch-hook caused digit one to be printed by the machine, and it was not possible to decide in many cases, whether these digits would have resulted in wrong numbers under ordinary operating conditions of an automatic telephone system. These extra digits are shown separately below, but are included in the total errors and the per-cent total errors. The results of the first set of tests are shown in the following table: Time per No. of Number to people Calls Digits Dialing Extra Total Percnt Look up in using Dialed in Errors Digit Errors Total Directory telephone Number Errors and Dial 18 450 4 5 4 9 2.0 % 44.3 17 425 5 4 6 10 2.4 % 43,5 19 475 6 8 2 10 2.1 % 42.3 17 425 7 17 5 22 5.2 % 51.5 16 400 8 7 5 12 3.0 % 53.0 ---- -- -- -- AVG: TOTALS: 2175 41 22 63 2.9 % The second set of tests were made similar in every way to those summarized above, with the exception that the calling parties were given lists with the telephone numbers associated with the name, rather than being instructed to look up the numbers in the telephone directory. A copy of the lists used in this second set of tests is attached and the results of the tests is summarized below: Time per No. of Number to people Calls Digits Dialing Extra Total Percnt Look up in using Dialed in Errors Digit Errors Total Directory telephone Number Errors and Dial 21 525 4 3 1 4 0.8 % 15.3 21 525 5 5 4 9 1.7 % 20.7 21 525 6 10 1 11 2.1 % 21.7 20 500 7 12 4 16 3.2 % 24.3 21 525 8 11 0 11 2.1 % 26.4 ---- -- -- -- AVG: TOTALS: 2600 41 10 51 1.9 % The two sets of tests are combined below: No. of people Calls Digits Dialing Extra Total Percnt Percent using Dialed in Errors Digit Errors Total Dialing telephone Number Errors Errors 39 975 4 8 5 13 1.3 % 0.82 % 38 950 5 9 10 19 2.0 % 0.95 % 40 1000 6 18 3 21 2.1 % 1.80 % 37 925 7 29 9 38 4.1 % 3.14 % 37 925 8 18 5 23 2.5 % 1.95 % The extra digit errors were undoubtedly independent of the number of digits in the numbers dialed, so that the final column "percent dialing errors" is the one giving the best data as to the effect on the accuracy of the number of digits per telephone number. Up to and including the seven-digit numbers, the majority of the people dialing, looked up the number and then dialed it without looking back in the directory or on the list, while on the eight-digit numbers nearly everyone took the number in two parts - the first five-digits were dialed, and then the calling party looked in the directory or on the list for the last three numbers and dialed them. This, I think, accounts for the lesser number of errors on the eight than on the seven-digit numbers. (no signature shown) Attached: Lists of Names and Addresses Set of Instructions Copy of Lists used in Second Test (None of these attachments are included in the file) [end-of-document] ------------------------------------------------