So, how does a panel office work ??

The Panel Office

This will describe the basic components of the typical panel central office. In our next installment, we'll trace a call through a panel office, showing exactly what happens in each stage of the process. We'll also describe the 'revertive pulsing', the method by which panel offices communicate with eac other, in some depth in a subsequent article.

I've been fascinated with the panel offices ever since being served by one and discovering some of its quirks. In the 1970s I was actually able to schmooze my way in for a late-night off-the-record tour of one, which only increased my interest.

In the 1970s, the panel switch was the Rodney Dangerfield of telecom. It got no respect! It was considered to be crufty, unreliable, low-tech, old, antiquated, a Rube Goldberg machine, and the like.

For the 1920s, however, the panel switch was high-tech. It was bleeding-edge for its time. In those days the practicality of providing machine-switched telephone service to large metropolitan areas was unproven, and the Panel installation in Omaha, beginning in 1921, was the proof of concept.

The term 'panel' comes from the panels of contacts which make up the frames which comprise a panel switching office. Each 'frame' consists of a panel of contacts, arranged normally in 5 banks of 100 contacts each, or in 10 banks of 40 contacts each for the (newer) linefinder frames. Each frame has 60 selector rods, 30 on the front, 30 on the rear, with each rod having normally 5 contact 'brushes', with the rods on the linefinder frames having 10 contact brushes.

The selector rods are positioned over the correct contacts on the panels by motor-driven cork rollers located toward the bottom of the frames. Clutches for up-drive, down-drive (and slow up-drive on the final frame) control the movement of the selector rods.

The brushes are the movable contacts which connect to the fixed contacts upon the banks of the panel switch.

Let's take a quick overview of what comprises (or comprised, this is all in the past tense here, actually) the typical real-world panel office and discuss the various parts.


In the diagram above we show the various frames of the panel office, plus some of the major ancillary components.

Five types of panel switching frames existed, with four of them appearing in all full-blown panel offices and a fifth type existing in those in the largest metropolitan areas.

• Linefinder frames
  
  A complete full-scale panel office will have 25 linefinder frames, each serving a group of 400 subscriber lines, for a total of 10,000 lines. (Researching the proverbial 10,500 line panel offices will be an exercise for the student.)
  
  The linefinder frame provides the connection to the subscriber's telephone set when the receiver is taken off hook, and routes that connection first to the register-sender and then to a corresponding district frame.
  
  
• District frames
  
  District selector frames appear in all panel offices. In panel offices in smaller communities (ya know, it's difficult for me to write all of this in the past tense, so if you don't mind, I'll do this in the present tense as if these things still exist today, ok?) the district selector frames provide the outgoing connection from the subscriber, via the linefinder, to either inter-office trunks to other central offices, or intra-office trunks to incoming frames in the same central office.
  
  Each district frame can connect to 500 trunks, so there is a practical limit, and in larger communities a second stage of outgoing selectors is provided.
  
  
• Office frames
  
  In the largest communities where there are many central offices, 500 outgoing trunks from a panel office is inadequate, so a second stage of outgoing selection is provided by 'office' frames. These frames only appeared (there I go mixing tenses again) in the largest metropolitan areas, such as New York City, Chicago, etc. It's believed that Omaha's panel offices used only the district frames for the outgoing connections.
  
  The district and office frames select the particular central office of the call to be completed.
  
  
• Incoming frames
  
  The incoming frame of a panel office is the first stage of selection of the called station. The incoming frame connects the incoming inter-office or intra-office trunk to the particular final frame which serves the called subscriber.
  
  The incoming frame consists of five banks, each with 100 contacts. Each bank is served by one brush on each of the selector rods. This allows a maximum of 25 connections between the incoming frame and the final frame. These sets of 25 connections are referred to as a 'group', and there are four groups within each bank, for a total of 20 groups within the incoming frame.
  
  
• Final frames
  
  Each final frame can serve 500 subscribers, therefore there will be 20 final frames in a complete panel office serving 10,000 subscriber lines. The final frame connects the incoming call to the subscriber's station, and provides the logic to test for line busy, to supply ringing voltage to the called line, to return the ringback tone (or busy tone) to the calling subscriber, and to remove ringdown/ringback and complete the talking path when the called subscriber answers.
  

Besides the actual switching frames, other important parts of the panel office included:

• The Register-Sender. (Sometimes called just 'sender'.)
  
  Think of this as the 'brain' or the 'CPU' of the panel office. It's actually a collection of electromechanical relay-logic circuitry. This is the main 'Common Control' section of the panel office. The register-sender records the digits dialed by the calling subscriber and gives the commands to the various frames, both in the originating office and the terminating office, as to how to position the brushes against the banks of contacts, in order to complete the call.
  
  The register-sender is only needed at the initial call set-up phase. It is dismissed once the selector rods are all in place and the call is in the ringing or the line-busy state.
  
  A full-scale panel office would have anywhere between 3 and 6 or so register-senders depending on the volume of calls anticipated.
  
  
• The Translator or Decoder.
  
  While the positions of the selectors on the incoming and final frames are easily determined by the called subscriber's number, the connections to various intra and inter-office trunks are quite arbitrary and vary considerably from community to community.
  
  The register-sender calls upon the Translator (earlier panel offices) or Decoder (later panel offices) to determine how to route the call through the district frame and, if used, the office frame.
  
  
• The Sender-Link circuitry.
  
  Each connection between the linefinder frame and the district frame has a set of multi-contact relays and associated circuitry which allows it to 'seize' an idle register sender when the subscriber goes off hook.
  
  Note that the register-sender is only needed for a few seconds for each call. It receives the digits, does some lookups via the translator/decoder, sets up the call, and is then available for another call.
  
  'Slow dial tone' on a panel office is almost always due to the fact that all register-senders are busy at the time.
  
  
• The Tone Plant.
  
  In the typical panel office, this is a rotary electromechanical device about the size of and in some ways resembling a metal lathe. This contains rotary generators for the low-voltage tones which make up dial tone, busy tone, etc., and the high-voltage (90-100 v 20Hz) ringing signal.
  
  Interrupters are driven by a step-down gear train. These provide the cadences for such things as ringdown, ringback, busy tone, etc. Some of these would use a rotary brush arrangement, while others used mercury-filled rotating drums to interrupt the signals.
  
  The various tones and signals which come from the tone plant are:
  
  
  
  
  • Dial tone. This would be the older non-precise dial tone for panel offices not converted for touch-tone service.
    
    
  • Busy tone. This would be the older somewhat rude and raucous 'BAWW BAWW BAWW BAWW' tone, interrupted at 60 impulses per minute, returned to the calling subscriber for a line busy condition. Even panel offices which were converted to touch-tone retained this tone for busy-back.
    
    
  • Ringback tone. For most panel offices this would be the non-precise 'metropolitan ring' tone, electromechanically generated and interrupted normally with a [corrected] two seconds on, four seconds off cadence.
    
    
  • Reorder tone. Same as the busy tone, but interrupted at 120 impulses per minute. 'Fast busy'. Used for various all trunks/circuits/equipment busy conditions.
    
    
  • No such number or 'vacant code' tone. A deprecated intermittent fast busy type tone used to indicate numbers, prefixes, etc., which did not exist. This was phased out as recorded 'The number you have reached is not in service' announcements were phased in.
    
    
  • Permanent signal, or 'receiver off hook' tone. No, this was not the very loud and obnoxious 'CLANK CLANK CLANK' receiver off hook sound of today. It was a single high-pitched tone, returned to the calling subscriber when the register sender got tired of waiting for dialed digits and routed the call to be 'parked' on a 'permanent signal trunk' on the district frame.
    
  
  
  
• The Intra-Office trunks.
  
  From the perspective of the register-sender, a call within the local central office is identical to that going to a remote central office, or to another panel office within the same building. Each panel office would have a certain amount of hard-wired connections reserved for intra-office calls, connected between the local office (or district) frames and local incoming frames.
  
  
• The Inter-Office trunks.
  
  These were the outgoing and incoming connections to and from distant central offices. In the early days of panel offices, these were simply loaded two-wire circuits with a frequency response of DC through 3kHz or so. When setting up a call to a distant panel central office, it was the register-sender of the originating CO which controlled the operation of the incoming and final frames in the terminating CO.
  
  
• The batteries and power plant (not shown).
  
  Primary central office power is provided by huge lead-acid cells, which are continuously charged by motor-generator sets (MGs) or rotary converters. This is very typical of central offices today, except that solid-state rectifiers now replace the former electromechanical devices. In the heyday of panel offices, commercial power was normally used to run the MGs or converters, supplanted by on-site diesel, gasoline, or LP generators to be used for commercial power outages.
  

This is a basic overview of a typical panel central office. In the next installment we'll show the progress of a call from receiver off hook to receiver off hook as it works its way through the panel switches.

Updates

Thanks to those who sent in updates, additional information, and corrections.

These can be sent in either via e-mail or as comments.

Two updates of some significance have been reported.

• A recently-retired long-time TPC employee has stated that in his recollection the Elkhorn and Waterloo CDOs were separate, discrete, and each located in their respective towns prior to 289 and 779 going ESS in the mid 1970s. I do recall that at one time prior to the cut, the same numbers could be dialed using either prefix. We may have to agree to disagree on this factoid until something in writing can be located.
  
  
• A person 'in the know' reports that the Internorth Centrex on 633 was Centrex-CU using a local WECO Definity, as opposed to a Centrex-CO hosted off of the main switch as I had erroneously reported.
  
  
• Late update: Another former TPCer reports that Council Bluffs did not use the Omaha time announcement service on 844-8111 and the 844 prefix was not dialable from Council Bluffs. Instead they had their own similar time announcement machine on 328-8116. This time announcement machine could also be reached from Glenwood, which at the time was not within the Council Bluffs calling area.
  

Thanks, gang, and keep those cards and letters coming.

The CDO's

Historically speaking, in the 1950s and 1960s the small towns surrounding Omaha in Douglas and Sarpy counties had local dial service, but very limited local calling areas. These communities were served by 'Community Dial Offices' consisting of smaller direct-control Step-By-Step (Strowger) facilities. These typically served anywhere from a few hundred to a few thousand subscribers.

The switches in these offices were typically configured to allow 'permissive' 5 or 7 digit dialing. For a call within the office, the full seven-digit number could be dialed, but only the last five digits were actually required. 'Digit absorbing' first selectors in these offices permitted dialing plans such as this.

Party lines were very common in these offices until the 1970s, with the far rural areas having availability of four-party fully-selective service (ringer is silent except for calls to that particular subscriber) if they were lucky, but often times eight-party semi-selective (one long ring or two short) service only.

Ma Bell chose to avoid the frequency-selective ringers used by independent telcos which allowed fully-selective ringing for up to 12 parties on a single line. Instead they chose a system where the ringing voltage was applied to either one conductor or the other, in either a positive or negative polarity, giving four possible fully-selective combinations. To service eight parties, one-long and two-short ringer cadences were used.

The advent of Subscriber Carrier ('AML') in the late 1960s provided some relief for far rural subscribers, but the result was often that one lucky subscriber on each rural line received a private line, while all others were stuck with eight-party semi-selective service.

Bare copper open-wire lines, supported on wooden crossarms with glass insulators were still in use into the 1970s. As these were upgraded to either multi-conductor aerial or underground lines, the availability of single-party private lines became common in rural areas.

Around 1970, several nearby communities with existing CDO's were integrated into Omaha's toll-free local calling area. This made significant use of the 19th. St. Crossbar Tandem office. As phone 'enthusiasts' know, Step offices do not easily interface directly with Panel and some #1 Crossbar offices, making either a tandem office or a toll office a necessity to provide direct dial service between them.

Calls from metropolitan Omaha to these extended-area offices required the usual seven digits, and except in a very few cases, these calls were routed through the Crossbar Tandem. The outpulsing of dial pulses from the Crossbar Tandem to the Step CDO was clearly audible after dialing was finished.

Calls from these CDO's to Omaha numbers or other CDO's required the dialing of an access code, usually 5 or 7, in addition to the seven-digit number. The dialing of this access code caused the first selector in the CDO to seize a trunk to the downtown Tandem's dial-pulse receiver.

One-plus Direct Distance Dialing from these offices was available, but DDD calls were routed to a 'CAMA Intercept' operator to verify and record the calling number, since automatic number identification of the calling number was not possible with the Step type CDO equipment.

Trunking from the Tandem to the CDOs at the time used analog medium-haul trunks with hissy analog repeaters, and background noise and 'singing' on calls to and between these offices was not uncommon.

In the mid 1970s, these offices were converted one by one to smaller WECO ESS units, but it most cases the calls were still routed via the 19th. St. Tandem.

Although calls to metropolitan Omaha (including Carter Lake) were toll-free, calls to Council Bluffs were long-distance to and from these communities until the 1990s.

• Elkhorn and Waterloo
  
  Originally, Elkhorn and Waterloo, neighboring communities separated by the Elkhorn River, each had their own local Step CDO. These were combined just prior to the extended calling area, resulting in the Elkhorn office serving both the 289 and 779 prefixes.
  
  An access code of 5 was required to dial numbers other than Elkhorn or Waterloo.
  
  Although residents of Elkhorn continued to be assigned 289 numbers, and residents of Waterloo continued to be assigned 779 numbers, the prefix codes were interchangeable and 'aliased' to each other as long as the office remained on the Step equipment.
  
  Due to the aliasing, the digit absorbtion, and the tandem connection, a local call from a 289/779 number to another could be dialed with 9 plus the last four digits, either 289 or 779 and the last four digits, or 5 plus either 289 or 779 and the last four digits.
  
  The Elkhorn CDO was cut to a #2 ESS around 1975. Some subscribers expressed dismay at losing the 5-digit 'shortcut' for Elkhorn and Waterloo calls. At this time 289 and 779 became discrete offices.
  
  
• Bennington
  
  The Bennington CDO had a very large service area but only a few hundred subscribers in the Step CDO days, including the town of Elk City, and extending as far north as some parts of Washington County, including the unincorporated community of Washington.
  
  Only two levels of the 238 prefix were actually in service, with the 9000 level aliased to the 2000 level, allowing for only 1000 total lines.
  
  It was rumored, but not substantiated, that Ma Bell put the Bennington CO and facilities up for sale to another telco during the 1990s.
  
  An access code of 7 was required for calls to other communities.
  
  
• Valley
  
  The Valley CDO was the most northwest in Douglas County, but the service area extended far south to the communities of Two Rivers and Venice.
  
  Several auto dealers in Fremont subscribed to FX service out of Valley to provide flat-rate toll-free service from Omaha customers, prior to the inclusion of Fremont in the Omaha toll-free calling area.
  
  The Valley CDO hosted the 359 prefix.
  
  An access code of 7 was required for calls to other offices.
  
  
• Springfield
  
  Springfield was the smallest of the CDOs with only the 2000 and 9000 levels provisioned, again aliased to each other. An access code of 7 was required for calls to other offices.
  
  A somewhat controversial decision by the Ma Bell powers that be was to cable the upstart community of Hawaiian Village, literally a stone's throw away from Springfield, to the far-more-distant 84th. and Harrison office.
  
  The Springfield CDO hosted the 253 prefix.
  
  
• Gretna
  
  The Gretna CDO had the distinction of hosting the most distant local calls from metropolitan Omaha, those being in the Linoma Beach and Beaconview communities, halfway between downtown Omaha and Lincoln.
  
  During the Step days, an access code of 7 was required for calls to other offices.
  
  The Gretna office hosted the 332 prefix. Due the similarity of 332 to other west Omaha prefixes, this was sometimes perceived as being 'more urban' than the other CDO's.
  
  

All of these CDO's were converted to ESS in the mid 1970s, allowing for Touch-Tone and various calling features, but toll-free calling to and from Council Bluffs would not come for another two decades.

The Expansions - The New Prefixes

Omaha's growth and increased telecom usage sparked the equipment upgrades and addition of the following prefixes to existing COs between our timeline start in 1953 and our checkpoint of 1977.

Douglas:

In the mid 1950s, a new #5 Crossbar system was installed at 19th. and Douglas, replacing much of the aging Panel installation, part of which was Ma Bell's first Panel roll-out, serving ATlantic and JAckson. The first new prefix was EXpress, originally serving as Ma Bell's own internal Centrex. EXpress (and later 344) served some of the very first IMTS (direct-dial) mobile phones.

A recorded time service was launched out of the Douglas Crossbar with a listed number of TIme-8111. See further notes on 844 below.

At the time of the Great Renumbering 348 was added to the 19th. St. #5 Crossbar, becoming Omaha's first prefix not to have descended from a legacy named exchange. There is some evidence that what became the 348 prefix was originally scheduled to be launched prior to the Great Renumbering (tentative name of BLackstone), but that various circumstances delayed the roll-out until September of 1960.

At the same time, 347, serving Carter Lake, was added to the Crossbar, giving Carter Lake its own dedicated prefix. See separate article for more details on this.

271 and 281 were an enigmatic pair of prefixes, and elicited hours upon hours of talk, experimentation, and speculation among telephone 'afficianados'. :) These served the Union Pacific Headquarters exclusively at the time. Whether the UP installation was Centrex or DID-PBX is really a question of semantics. It was basically an on-premesis Step installation driven by the #5 Crossbar at 19th. and Douglas.

The only listed number on the 281 prefix was the main UP incoming number, 281-5822. All other listed numbers for UP were on 271. The two prefixes 271 and 281 were 'aliased' to each other and could be interchangably dialed. You could dial either prefix plus the last four digits. Consensus was that this was done to 'balance the load' somewhat, directing the calls to the main number over one set of trunks, and direct-dialed calls to various UP offices to another.

221 was another Centrex-or-DID-PBX which served the Federal offices in Omaha. Again, a Step installation off of the #5 Crossbar.

536 and 541 were set up on the #5 Crossbar to serve mainly 101 ESS Centrex-Cu customers, some of which were also served by 348. Original Centrex-CU customers out of these offices were Norwest Bank, Lutheran Hospital, UNMC, and Lozier Corporation, among others.

Phone 'enthusiasts' were quick to note that of these new prefixes, access to 536 from many other Omaha offices was via the downtown Crossbar Tandem, and a distinctive burst of MF could often be heard when calls to 536 were placed.

The big addition to the 19th. and Douglas office was a very significant #1 ESS, commissioned around 1970. This replaced the last of the Panel (345, 346) and added 422, 444, 449, and eventually 633, 636, 977, and 978, among countless others as the facilities were expanded..

Ma Bell's internal Centrex was then converted to 422 on the ESS, and Centrex-CO for Eppley Airfield was added to 422 as well.

The main customer on 444 was the Douglas County offices, including County Hospital, a Centrex-CO installation. 444 also served some IMTS mobile phone customers.

The then-new St. Joseph hospital on north 30th. was the first major customer on 449, Centrex-CO.

633, 636, 977, and 978 were added during an expansion in the late 1970s, mostly intended to serve large Centrex-CO customers. OPPD, originally a Centrex-CU customer on 536, eventually spilled over to 636 as well. InterNorth (nee' Northern Natural Gas) was the first major customer on 633, a Centrex-CO replacing the former #101 Centrex-CU on 348. Omaha Public Schools was the first major customer on 978. 977 was at first mainly used for pagers and some pre-cellular mobile phones.

844 was hosted out of Douglas, used exclusively for the automated 'Time' service. 844-8111 was the published number, but anyone with any kind of curiosity knew that the time recording could be reached equally well by dialing 844 and any four random digits.

No, I haven't forgotten about 894. Yes, at the turn of the 21st. Century, 894 is a general service prefix out of 156th. and Harrison. However, 894 began life as a somewhat red-headed-stepchild 'choke' prefix out of Douglas.

Only two published numbers ever appeared on the orignal 894 prefix, one being a recorded weather announcement, sponsored by a radio station, and another a medical advice recording, sponsored by a local hospital.

894 was originally hosted on the #5 crossbar, as an 'alias' for 344. You could dial either 344 or 894 plus the four digits and get the same number.

However, when the #1 ESS came to life, shortly after the 894 prefix was moved to ESS and 'aliased' to 444.

341, 342, 344, 347, 348, 536, and 541 remained on the #5 Crossbar well into the 1980s.

So, at our 1977 checkpoint, we have the following out of Douglas Street:

221, 271, 281, 341, 342, 344, 345, 346, 347, 348, 422, 444, 449, 536, 541, 633, 636, 844, 894, 977, and 978.

Izard:

The Panel office serving 551 and 553 remained in service well into the 1970s, until a new #1 ESS replaced it. Along with 551 and 553, 554 and 559 were added to the new #1 ESS.

556 and 558 remained on the #1 Crossbar into the 1980s.

An interesting quirk was that while the Izard #1 ESS was being installed, what would become the 551 and 553 sections were temporarily accessible from several other Omaha offices via 531 and 533. Many phone 'afficianados' became 'acquainted' with the Izard ESS this way.

'Bay 1, circuit 2, Centrex Direct Inward Dialing intercept.' :)

1977 checkpoint prefixes were: 551, 553, 554, 556, 558, and 559.

Fowler:

KEnwood was the last remaining Omaha office to have manual ('Numberrr Pleeze') service. KEnwood was added to the Fowler #1 Crossbar in about 1957, finally bringing dial service to all of Omaha. 457 was added as an expansion in the late 1960s.

Prefixes as of the checkpoint: 451, 453, 455, and 457.

O Street:

The only major expansion to the long-lived O Street #1 Crossbar was the addition of the 734 prefix around 1970. O street was the only one of Omaha's #1 Crossbar offices which was converted to MF signaling on the interoffice trunks. The others (Izard, Fowler) used revertive pulsing throughout their lives.

The O Street #1 Crossbar lived on until around 1985.

1979 prefixes: 731, 733, 734.

Bellevue:

I admit. I don't really know too much about the Bellevue CO. The earliest I remember this CO was in the early 1970s, and it was a #5 Crossbar. It was a bit quirky in that it had a tone plant which gave a ringback tone which could best be described as a 'low rumble', with not very much in the way of tones or harmonics as were typical in the 'metropolitan' ringing machines which were common on Panel, #1, and #5 Crossbar offices, or the newer 'precise' tones.

The nuances of the connections indicated that it was most definitely a #5 Crossbar.

At the time of the Great Renumbering, the only prefix in Bellevue was 291. 292 and 293 were added in the early and late 1970s respectively as the community expanded.

I'm not really sure if the 294 prefix, which served Offutt Air Force Base exclusively at the time, was actually hosted out of Bellevue, or out of Douglas. I've heard some 'in the know' people say one, and some say the other.

Prefixes at the 1977 checkpoint: 291, 292, 293. Honorable mention: 294.

Council Bluffs:

The area's first #1 ESS switch was installed in Council Bluffs ca. 1970, replacing the Step offices serving 322 and 323. An additional prefix, 328, was added at the time of the cut, and 325 followed several years after, giving the main Council Bluffs downtown CO a total of four prefixes at the time of our checkpoint.

In 1971, toll-free direct seven-digit dialing was established between Council Bluffs and metropolitan Omaha.

Along with metropolitan Council Bluffs, the Manawa CO, serving prefix 366, was added to the Omaha dialing area. The Manawa office was unique in that it used 'directorized' Step switches. This was a typical up-and-around Strowger-switch type office, but with a common-control 'Director' device added. The Director was between the linefinder and the first selector. The Director returned dial tone to the subscriber, received the dialed digits, and then drove the switches appropriately to set up either an intra-office or inter-office call. This also allowed true Touch-Tone service on this Step office, as opposed to a simple tone to pulse converter. The Manawa office was the only Director Step office in the Omaha area.

Council Bluffs also had toll-free calling to a few nearby rural CDO's, all on the Iowa side, in Silver City/Mineola (526), Crescent (545), and Underwood (566), but these remained toll calls from Omaha (and Carter Lake, Iowa) until the 1980s.

Prefixes as of the 1977 checkpoint: 322, 323, 325, 328 downtown CB and 366 in Manawa.

Carter Lake

The community of Carter Lake, Iowa is a geographic oddity as well as a telecommunications oddity.

Carter Lake, an incorporated village, lies physically on the Nebraska side of the Missouri River, but remained politically in Iowa when a flood, ca. 1880s, caused the river to shift.

Carter Lake has an Iowa Zip Code, residents vote in Iowa elections, and students attend Iowa public schools. Carter Lake is in Iowa, except for one telecom-related quirk.

In the subscriber dial era, Carter Lake has always been served from Omaha's Douglas Street office, and has always been toll-free to and from Omaha. Carter Lake's original dial prefix name was LAke, and those who are observant can easily see that this is simply a renamed JAckson, which was the second Panel office out of Douglas.

For some unknown reason, at a date I'm unable to precisely determine, Carter Lake subscribers were moved from the LAke prefix to the 'new' YEllowstone prefix. YEllowstone was implemented sometime prior to our 1953 beginning of the epoch. Again, those who have been paying attention will notice that YEllowstone is simply a renaming of WEbster, rinse, repeat.

At the date of the Great Renumbering in 1960, Carter Lake was spun off to its own distinct prefix, 347, in anticipation of Direct Distance Dialing.

Carter Lake, politically in Iowa, was within area code 712 and was dialable as such. However, anecdotal evidence persists that at one time the 347 prefix was dialable from outside the area as either 402-347 or 712-347.

Carter Lake has always received the short end of the stick as far as local calling area is concerned. Carter Lake's toll-free dialing options into nearby rural Iowa communities have always been fewer than those from Council Bluffs or Omaha proper.

An interesting quirk of the 347 office, noted by many phone 'enthusiasts', was that the 5000 and 9000 levels were interchangeable. You could dial any 347-5xxx or 347-9xxx number using either 5 or 9. Yes, this facilitated some game-playing with 'check for coin' procedures. :)

Toll-free seven-digit dialing remains between Omaha and Carter Lake to this day, with Carter Lake still being served out of the Douglas office.

The New Offices

Let's discuss Ma Bell's newer physical offices which came about between our timeline start (1953) and 1977, which is a good 'checkpoint' at which things were reasonably stable again.

The westward and southwestward expansion and sprawl of the Omaha area required the construction of several new offices, beginning in the mid 1950s. A total of six new CO buildings, three of them originally #5 Crossbar and the other three #1 ESS appeared within a 20 year span between the mid 1950s and the mid 1970s.

• 90th. St. and Western Avenue
  
  The first of the newer central office buildings in Omaha was the 90th. and Western Avenue office, ca. 1955. This was a brand new #5 Crossbar office which served two new prefixes, HUdson and TErrace prior to the Great Renumbering.
  
  The service area of the 90th. and Western office began at approximately 72nd. St. and reached westward past Boys Town. This relieved part of the load from the Izard St. office and allowed westward expansion without as many issues due to long loops.
  
  It covered the newer suburbs such as Rockbrook, Maple Village, and Tomahawk Hills and replaced the Izard St. service in Irvington, which was still a disjoint unincorporated community.
  
  TErrace became 391 and HUdson became 393 in September of 1960.
  
  A third prefix, 397 was added in the late 1960s and 392 was added to the #5 Crossbar in the mid 1970s.
  
  496 and 498 were temporarily hosted on the 90th. and Western #5 Crossbar as the 132nd. and Fort office (see below) was constructed and subscribers in part of the area to be served by the Fort St. office were migrated.
  
  A major addition, an eastward expansion of the building and a new #1 ESS switch appeared in the late 1970s. When this was complete, 397 was moved to the ESS, 399 and 390 were added, and 398 was moved from the 135th. and Center office (below) to 90th. and Western.
  
  At our checkpoint of 1977, the 90th.and Western office served 391, 392, and 393 on the #5 Crossbar and 397, 398, 399, and 390 on the #1 Ess.
  
  
• 84th. and Harrison and 135th. and Center
  
  'The Twins'
  
  Two similar and very significant #5 crossbar offices were constructed in the early 1960s to expand the Omaha dialing area and to serve the westward and southwestward expansion. These were at 84th. and Harrison and at 135th. and Center.
  
  84th. and Harrison originally hosted the 331 and 339 prefixes and served the Ralston (formerly served by O Street), La Vista, and Papillion areas, all of which had explosive growth in the 1960s and 1970s. 592 was added to the office in the late 70s, bringing our prefix count for this office at our 'checkpoint' to 3: 331, 339, and 592. 593 was eventually moved to 84th.
  
  135th. and Center originally hosted the 333 and 334 prefixes and served a very large area of West Omaha, roughly west of I-680 from just north of Dodge south past the community of Millard, then an independent town. 330 was added in the mid 1970s.
  
  The 398 prefix, originally used mainly for Centrex-CU for Bergan Mercy Hospital was temporarily hosted out of 135th. until it was moved to the new ESS at 90th. in the late 1970s.
  
  Another significant temporarily-hosted prefix, 895, was temporarily served out of 135th., as the 156th. and Harrison office was constructed.
  
  At our 'checkpoint' of 1977, 135th. hosted 333, 334, and 330. (691, 697 and others were yet to come.)
  
  
• 78th. and Girard
  
  The first of the new stand-alone ESS offices was commissioned in 1971 at 78th. and Girard and was intended to serve the somewhat-sluggish northwest expansion of Omaha. It took its service area from existing subscribers served by 90th. (391, 393, 397 at the time), Izard (551, 553, 556, 558 at the time), and Fowler (451, 453, 455, 457 at the time).
  
  571 and 572 were the original prefixes out of 78th.
  
  The service area was large and stretched northwest from approximately 60th. and Ames. It originally included sections of what was to be served by the 132nd. and Fort St. office (below). The 493 prefix was temporarily hosted at 78th. as the new Fort St. CO was constructed and customers for that area were migrated.
  
  Due to the less than predicted northwest expansion, the 78th. St. office held a permanent prefix count of two (571 and 572) for almost two decades.
  
  
• 156th. and Harrison
  
  The next office was the 156th. and Harrison office, hosting the 895 and 896 prefixes. This served the Millard area, recently annexed into the city of Omaha with significant angst. 156th. took a large chunk of its service area from the 135th. and Center office and some (Westmont, etc.) from the 84th. and Harrison office.
  
  895 had been temporarily hosted out of 135th. and Center and many of the customers in the new office's service area were migrated prior to the actual turn-up of the 156th. and Harrison office.
  
  156th. and Harrison also 'temporarily' (for several years, actually) hosted the 593 prefix, used mostly at the time for the Centrex-CU installations at Midlands Hospital in Papillion and the Sarpy County offices, also in Papillion.
  
  At our checkpoint in 1997, 156th. hosted 895 and 896 for general service and at the time hosted the 593 prefix for the Centrex-CU installations.
  
  
• 132nd. and Fort
  
  The third of the large ESS installations was at 132nd. and Fort, coming on line in the late 1970s. This new office took its service area mostly from portions of 135th. and Center (333, 334), and 78th. and Girard (571, 572).
  
  A 'choke' prefix, 962, used mostly for radio call-in lines, was added to the Fort office in the late 1970s.
  
  At our checkpoint of 1977, Fort. St. hosted 492, 493, 496, 498, and 962, three of which had been temporarily hosted by neighboring COs during the construction period.
  
  

The Great Renumbering

September 10, 1960 was a red-letter date in Omaha's telephone history!

Late Saturday night, Omaha went from a two-letter, four digit, to a seven-digit numbering plan, to allow Omaha to join the nationwide Direct Distance Dialing plan.

This was a 'hard cut' with no period of permissive dialing when old and new numbers would work.

Lettered exchange names were totally eliminated (All-Digit Dialing), and there was no attempt to retain any of the legacy prefix numbers. The legacy prefixes were reassigned as follows:

• Douglas Street:
  
  ATlantic - 341
  JAckson - 342
  EXpress - 344
  HArney - 345
  WEbster - 346
  YEllowstone - 347
  TIme - 844
  
  
• Izard Street:
  
  WAlnut - 551
  GLendale - 553
  REgent - 556
  CApital - 558
  
  
• Fowler Street:
  
  PLeasant - 451
  PRospect - 453
  KEnwood - 455
  
  
• O Street:
  
  MArket - 731
  ORchard - 733
  
  
• Bellevue:
  
  BEllevue - 291
  
  
• Millard:
  
  334 (Joined Omaha toll-free calling area)
  
  
• Papillion:
  
  339 (Joined Omaha toll-free calling area)
  
  
• Council Bluffs (still long distance to/from Omaha):
  
  COuncilBluffs: 322
  CouncilBluffs-3: 323
  

I was told that some, not all Omaha offices, were able to identify and 'trap' misdialed calls to some old numbers and route them to an appropriate intercept for some time.