The Age of “The PBX” – 1970s-2000s

November 6, 2021February 20, 2025clickfoLeave a comment

The PBX really became something of an on site telephony product by the 1980s, even though the concepts began in the 1970s. The advent of the integrated circuit along with programs, made these ol electromechanical relics to become obsolete. And I say “become” because it would be a long time coming for that to happen. ROLM out of the left coast, had developed military spec computers and dabbled into telephony, they had gotten into the business by the early 1970s. They became successful, then came Northern Telecom (later Nortel).

a picture from Andy of a ROLM digital telephone from the mid to late 1980s — A standard looking ROLM telephone from the mid 1980s to even today at some sites.

The Computerized Branch Exchange or CBX was obviously a registered trademark to ROLM and brought the concept of a box making and answering calls and users would have devices that they could use to answer or place calls. Want to call out, you hit a button like 9 or 8 like you did in a Centrex setup. The system could route calls per to what a number was pressed, and block it or rout it to another set of trunks to save money on long distance.

Northern had introduced the SL1 PBX in 1975 (but not to be confused with the X11 platform since 1988 and the Avaya fusion of the 2010s). The SL stood for Stored Logic, or just code living on chips with a programed software. The SL1 was not friendly to a manager of machines, but for engineers, as well documented on this site for a number of years. This plagued into the Meridian 1 days. At this time most electronic and digital PBX systems were not as simple to choose. the SL1 PBX for an example came in about 12 varieties, between software options and hardware choices. It wasn’t like an Option 11 could cover 500 users, with 60 inbound lines today. Lot of this had to do with the computing of the 1970s.

Mitel was one of the first companies to introduce digital desk phones that allowed multiple line and feature access. Their system was called the Superswitch, and the phones were called Supersets (this is where the “Superkey” comes from even in their current VOIP carnation.) They wanted to make a PBX phone a bit more functional than a 2/500.

For some of the readers… you’re waiting on Ma Bell. Well AT&T’s Western Electric division was in no hurry to go digital, in fact some antidotes indicated that AT&T had plans to go into digital telephony by the 1990s… planned as far back as the 1960s. AT&T’s first PBX that was electronic in nature was the Dimension PBX, and Horizon PBX. For some lingering Avaya fanboys, the cabinets of these things were no modern marvel, unless you thought one cabinet holding 50 lines was a great engineering feat. A PBX scale from users/extensions to lines made sense from an economic scale for years, but when the electronics came in, boy did it take real estate. To power a 10 button Multibutton Electronic Telephone required 8 pairs of wiring. a far cry from the ol 25 pair, but certainly for what it could do was very limited.

Turn around for technology takes several years, by 1981 the researchers at Bell Labs started to develop a fully electronic telephone network that would make the Dimension/Horizon hot mess end. ROLM’s phone systems were mostly ol 2/500s and the fancy phones were for operators. Nortel had made digital phones as far back as the creation of the SL-1, but they made their phones mimic the infamous 1A2 Key telephone system (this explains why the Nortel Meridian phones have few line buttons, and are set up for a single phone number.)

Western wanted to be unique, and this uniqueness for users stood out from the competition, they opted for use Merlin-looking telephones, but instead of having 4 line buttons directing to the outside world, use the top left row to have by default 3 instances of personal line appearances to make the phone ring, page, etc. This would be considered “call appearances” and made these phones more attractive than the MET, which sent a bit of a mixed message in the technical sense. the MET had literally Multibuttons, but not multiple lines or appearances. One call to an MET phone at a time. Want to transfer? You had to press the Recall Button, and then press a button called Transfer, then hang up.. .and it had the infamous Red and Green color indications.

The transition away from “System 75 and 85” to Definity in a 1989 TV campaign in the mainstream media

By April of 1984, AT&T introduced the System 75 PBX, with 7400 Series Digital Voice Terminals, that were a bit superior to the MET and it took several years to fix user pet peeves with the quirks of the phones, but by 1995, the 8400 Series Voice Terminals really put AT&T on the mark leading into the Avaya years, and by 2020 Avaya became an also-ran company throwing the combined history of Nortel and Lucent and AT&T into a trashcan.

For the mainframes themselves, AT&T went to extra lengths to make the system be as efficient as possible, they developed the Information Systems Architecture (a nod to what became their enterprise/carrier services) developing a company standard of circuit boards and connectors and one large cabinet could hold 900 lines. But the System 85 was basically the Dimension PBX with with System 75 hardware. There was some differences in the Dimension-specific hardware. To run the PBX’s code, required it’s own cabinet, while the System 75 could run on a single circuit board. But to put lines and stations was equal though.

For a number of years, hospitality only used electronic PBX systems to monitor, route and direct calls per to numbers dialed, did customers get the same treatment in offices? No, they stuck to 2 wired analog phones, and the front desk typically had a digital set. Other industries may had many average users having low button phones, and more power users had the middle line, and assistants had multi buttons between 20 to 34, while the executives had the 5 to 10 button set.

The fun facts of digital PBX systems is a) the computer is technically a “phone” per to the FCC regulations on Part 68 b) and the desk phones I call just “sets” because they are regulated as Part 15 in FCC rules. c) these “phones” cannot use the regular Plain Ol Telephone provider, and are not engineered to work at home or remotely without some box. This is why I do not call these devices a “phone” but due to FCC regulation in 2018 and 2020, they see them as “phones”. The “PBX” is a computer, and it’s there where it dials out phone numbers, your “extension” is a device that tells the box what to dial using your dialpad.

Obviously by the 1990s a PBX of the 1970s that used to take an entire corner was miniaturized and could fit into a plastic “shoebox” and by taking some code and adapt it to a microcosm allowed Electronic Key Telephone Systems do function more like a PBX than an an EKTS itself. This is where the blur of what is a PBX and what should a KTS be.

By the 2000s, most VOIP vendors that had no experience in legacy voice really amped up PBX systems as opposed to Key systems. Everyone thinks a PBX, is anything that’s on site and can route a call is what everyone wants…

Why Private Branch Exchanges was overrated (Prior to the 1970s)

November 6, 2021February 20, 2025clickfoLeave a comment

The Private Branch Exchange… the No Frills Approach for Saving Money on your Telephone Bills!

In the wayback of time, in the days of electromechanical switching, and you had say a 500 users… what was your options?

There was two options. Centrex and a PBX. What was the difference? One was off prem at the phone company and the other was just an identical copy of a switch, just a bit modified for an on premise environment. I should also state, that back in those days, it was not abnormal for PBX systems to be in sites less than 200 phones. The role of a PBX at the time was to have less cabling going in, allowing users to call each other by a 3 to 4 digit numbers, and be able to access to the outside world… but in those days most of the PBX was done by humans…

an image of a western electric operator station taken at the NH Telephone Museum in 2015

The operator switchboard was basically the “PBX” while in the switchrooms, was all the switching of the time whether it was crossbar or Step by Step. There was not that many features, and that didn’t come till the days of ROLM, Northern’s SL1 and AT&T’s Dimension.

There was “Cordless switchboards” that resembled the Call Directors, but it was done in a similar fashion, a call would come into a bank of lines, and the operator would buzz the extension to then patch them in via buttons. But a cordless switchboard was still a very wiring intensive devices, with many, many pairs of wires that had to be tied directly to the console.

So what about outbound calling? Before the days of electronics, a user would “dial zero” and ask to dial out, the operator would patch that caller, and either s/he would dial, or if the operator was nice, would dial the number for that caller.

The cost of a PBX, to users to lines was still cheaper, but was mostly seen in hotels, and some businesses where handling calls were important. The 1970s that brought the ability to have multiple phones and few lines coming from the telco, also brought features like station IDs (internal caller ID), Automatic Routing Selections and Automatic Alternative Routing, and anything where a computer could hear the tones and or rotary pulses where the PBX could dial for the user, rather than an operator. This moved the dialing into an electronic mainframe, but the operator still had a role to play, to answer calls, to juggle calls, and to monitor the health of the electronic PBX, sometimes outside of the States it’s called “Private Automatic Branch Exchange”.

A lot of these PBX systems were phased out with the advent of electronics by the late 1970s, but there were holdouts up to the 90s. The White House had zero electronic systems until the Clinton administration that by the mid 1990s had installed then an AT&T Definity PBX; that only had a shelf life of 3 Presidents dual terms. By 2017, the Trump Administration had prided for having a “very secure” phone system that was a Cisco, which had been a secondary system since the latter end of the Bush administration.

If you are a Gen Xer and older, you could tell a system was a PBX or Centrex by telling it’s telephone.

Standard one line phones were common in PBX setups even in the days of electronic.

If you did see Key phones, most likely it was because they were the power users, and needed direct access to lines without operators or codes. While some say the 1A2 concept was dated by the advent of electronic systems, this was critical in places where calls couldn’t get dropped because a transfer failed. In the advent of VOIP, the physics of how a call can be captured or be answered or a line can be captured… and that can be blamed to the lack of listening to customers in the world of IP… but that happened many years later.

Why Key Telephone Systems Had Relevancy For So Long

October 14, 2021February 20, 2025clickfo

The Key Telephone System is becoming as obsolete as landline telephones and is becoming ill relevant like the rotary dial telephones. It’s being replaced not just with “the cloud” and Voice over IP; it’s the overall methodology how VOIP works today. The other factor is technical “professionals” who often trash customers for retaining older ideas and if anyone insists what they want they’ll be gaslighted as “stuck in the past”.

But this type of telephone system was the earliest type of system that had buttons, had the ability to buzz, ring, lock out another line if the other telephone was busy (privacy modes), and other dodads like Music On Hold and paging.

It’s easy from a historical point of view, that plain ol dial sets in offices were tied to PBX systems and multi button telephones were tied to Key Systems. Of course this is prior to the 1970s before these became electronic devices. Earlier key systems were known as “1A” series, followed by “1A1” and “1A2” systems as the years went on, these were originally developed by Western Electric, but was cloned by other vendors.

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Update! History of the Cisco 7900 Series IP Phones

December 20, 2018February 20, 2025clickfo

UPDATED & CORRECTED in December 2018

The 7900 series IP Phones from Cisco has now been in the market for 20 years this year! These sets were the first after the acquisition of Selius Systems, the publisher of CallManager.

These are the classic, default choice for the true Cisco install base, while newer versions, the 6900, the 9900 and 8900 (and in the last couple years, the 7800, and 8800s, 6800s those “second generation” Cisco sets will appear at a later post.) Also this site attempts to conform to Plain English and so over uses of “79xx” will not be tolerated.

A picture of 8 Cisco VOIP office terminals, 1 without a display (7905), and 1 with a full screen color screen (7970) — From Cisco’s website circa 2004 featuring most of the first generation of Cisco 79×0 series sets.

79×0 Series (1st Generation)

(where x indicates solely on it’s functionality, that latter “0” implies generation)

The first round of options at that time included

7902 (blank set), a display, single appearance (realistically);
7905 (a 7902 with a display) Both known by Cisco as “cubicle” sets
the 7910 (a black colored set, that looked like half the size of a full blown 7900s, but functions similar to a 7902 and 7905)
The infamous large screen sets known as the 7940, the 7960. The 7914 sidecar was available.)
And the 7970 (a Java based set with color and other goodies would roll out later in time; not available originally.) The LCD display had very low resolution, with a display for text; and graphics were primitive icons. Worse, these sets age, they don’t age well, due to its black and black display (I can’t say white per se, but the reader should understand.)

Cisco strongly sold these sets for their Skinny Call Control Protocol (SCCP or Skinny), as SIP and MGCP were available for downloadable firmware as an option. The SIP versions of this generation would not have the visual straight lines to separate appearances or features like Skinny, instead looking like softkey buttons. Also a SIP icon appeared on the top right with the S resembling a snake.

When the 7970 was released, it was a luxury set for executives or conferencing; as time would go one, each little feature in the 7970 would become standard in newer models with lower entry points. This “screen phone” was running with a Java applet to allow it to surf the web and do other fancy things.

Regardless, from the start, they licensed Polycom’s conferencing technology, according to archived pages, which was probably the strongest selling point of the Cisco IP Phones. In fact Polycom wouldn’t make VOIP sets till after the year 2000, of course they had the great sound quality on crappy software and flimsy hardware.

Cisco sold their 7920 mobile set, but the set wasn’t well used because of its dependence on WLAN, later WiFi. Wireless LAN at the time went so far, and could carry much less data and to extend the signal would be cumbersome. Many opted to stay with DECT (despite it being politically incorrect in the world of Cisco – because anything “digital” was deemed “analog”) ether using analog sets or IP (such as SIP) as the base unit. It wasn’t until 2013, Cisco settled on DECT – but offered such sets to the small market.

The 7980 was a video phone designed for the conferencing market. The set’s label on the front of the display indicates it used Tandberg technology, of which they acquired the company years later.

Formerly owned this 7960 which failed to register in a Call Manager Express. Partly because I didn’t realize “TFTP” in the Cisco world refers to the PBX/IP KSU the system will reside on.

79×1 Series (Second Generation)

(where “1” indicates the newer generation where the x indicates the set’s functionality as previously described.)

As time went on beginning in late 2005; Cisco introduced:

The 7941 and 7961 sets. Other than prettier text, and tri colored LEDs for lamp status, the set was in fact based on Java; of which was a critical difference unlike the first generation, except for the 7970 and 7980. This gave developers the ability to make your desk set check the weather, a package from UPS, etc. Whether it was widely used is debatable. Around this same time period, the 7971 was released, with slight improvements. A massive issue if you are not fully familiar to managing servers but managing traditional phone systems; was the inability to use the local Corporate Directory out of the box, requiring Cisco IP Phone Services server to run such feature as an app on some server or gateway and some experience in coding.
Gigabit models were available if you asked for a 79×1-GE part number.
The phone supported Power over Ethernet (POE) or Cisco’s Inline power standards natively.
Introduction of the 7912 set, similar to the 7905 but it runs the Java operating system to run the phone’s applications and services.

Not my Photo – Cisco 7961 with a 7915 Module

Cisco also introduced a graphical sidecar as well. The 7915 was a grayscale and the 7916 was color

large_photo_7916 — Cisco 7975 with the 7916 sidecar

79×2 (3rd Generation)

Where “2” indicates the third generation where “x” indicates the type of sets in the series

In the mid 2007, Cisco introduced the 7942, 7962 and a new set 7931.

A Cisco 7931 taken at a local Nashua, NH Staples. This replaced a Vertical Networks solution which used 24 button sets. Most Staples on the East Coast had already dumped Norstar systems with Vertical in the last 7 years. Cisco originally sold these and marketed these sets for the retail market.

In 2008, Cisco released the 7931. It looks like a traditional Key or PBX set with the old fashioned desi key strips, most likely responding to a shock to the system of end users who wasn’t ready to let go of the tried and true solution of paper designation strips. The set can support up to 24 lines/feature/URL keys and cannot support any sidecars.

The 7942, the 7962 sets had bitmapped display (that could handle graphics similar to the 797x, just in grayscale.)

Model of a Cisco 7962 taken at the NH Telephone Museum in their modern day collection. This can run bitmapped graphics, Gigabit Ethernet and Power over Ethernet.

Given the “cubicle” version of the 7900s, Cisco went back 1 digit, and introduced the 7911 at this same time. In short, the Cisco 7911 is the “latest” generation of the “cubicle” line

The phone has a large, 4-bit grayscale graphical LCD (Figure 2) that provides features such as date and time, calling party name, calling party number, digits dialed, and presence information. The crisp graphic capability of the display allows for the inclusion of higher value, more visibly rich Extensible Markup Language (XML) applications, and support for localization requiring double-byte Unicode encoding for fonts.

Cisco’s datasheet for the 7962 set

By this point Cisco shipped these sets with dual image firmware of Skinny or SIP, as many decided SIP was the future or “standard”, but massive tradeoffs occur when going to SIP. In these versions, the SIP and Skinny screens are the same (horizontal lines separating the line/feature keys.) Tradeoffs include, a half-duplex speakerphone, the ring tones sounding tinny and the voice quality isn’t like talking to a sea shell compared to using SCCP. But you can’t fix stupid with everyone defending “open” systems.

79×5 Series (4th and Final generation)

Example of a Cisco 7965 set at a Citi bank in New York City, taken in Midtown Manhattan in April 2015 by this publisher.

The 3rd generation and 4th generation was release concurrently. At the same time, Cisco released the 6900 series. When Cisco released the 79×5 sets in late 2007, they basically giving everyone a 797x, but on a smaller footprint. You can set up applications similar to the 797x on a similar size of the 796xs and 794xs. Gigabit Ethernet was standard. The sets have full color and touchable screens, multi colored LED buttons and a 4 direction with a center OK button in the middle. The 7975 reflected that latter change, as the 4 way buttons before had no center key. Also the last generation of the video conferencing set, the 7980 was released under 7985 (but end of life notifications for that set was settled in 2015)

The sets were not seen in many desktops till the teens, perhaps enterprise cutbacks due to the Great Recession and the 2008 Financial Crisis, of which Cisco had taken a direct hit, as many UC customers were in the financial industry

In short, as time would go on, the only “7900” sets one could order and acquire a license was:

Cisco IP Phone 7945
Cisco IP Phone 7965
Cisco IP Phone 7975
Cisco IP Phone 7985 (End of Life circa 2011)

The End

Remarkably, the millions of 7900s came to an end in the summer of 2018 where Cisco announced the End of Sale. The final End of Support will occur in 2022. At the time of the E.O.S. announcement, only the “4th generation” except for the 7985 was still on the market.

The reasoning is the age. Inside the Cisco 7900 IP Phone is a specialized computer designed to make and receive telephone calls. The original CallManager, was essentially as primitive as a consumer POTS service. The Cisco 7900 Series IP Phones have used H323 to make the phone tick. However SIP is software based, and a lot of it’s magic lives inside the phone, and for SIP to work effectively it needs more memory and CPU cycles. This isn’t to be officially known to the customer, all VOIP set makers just tell customers to upgrade to later generations, and as time went on Cisco added more processing, Flash memory, etc to handle a desktop smartphone for the lack of a better word.

Perhaps the makers of the hardware are ether no longer making chips, resisters, etc., or perhaps issues with licensing with those companies; leading Cisco to move onto different lines concurrent to the lifespan of the Cisco 7900s:

Cisco 6900 Series IP Phones
Cisco 8900 Series IP Phones
Cisco 9900 Series IP Phones

But lately Cisco has focused on a few newer models

Cisco 7800 Series IP Phones
Cisco 8800 Series IP Phones
Cisco 6800 Series IP Phones, as they are a bit more open to allow customers to buy phones and run them on their own call platforms (or phone systems)

Most importantly Cisco has focused on security. While the 7900 Series was “secure” in theory using firmware and secure versions of CallManager, the newer sets focus on using “signed” Cisco firmware that cannot be tampered by third party or companies outside of Cisco. With this scheme, the lifecycles could be shorter given how “certificates” have certain shelf life, so no one can try to tamper with the secure code.

Despite these newer offerings the 7900s are still very popular and sell well in the thirdhand market. These are perfect for hobbyists, home users, small businesses that depend on phones still and can last a long time. Security wise, shouldn’t be a serious issue till a few years after 2020, but a well designed multimedia network should be based with security in mind. Even though these sets are extremely overpriced in the firsthand for what little it can do, it’s has become a status symbol just like how AT&T was the status symbol with the Merlin (small systems) and 7400 (the large system) sets (albeit more superior!)

Telephony 101: On Voice Mail

February 20, 2017January 8, 2025clickfo

Some people love voice mail, many just hate it. Many are apparently so egotistical, they think it’s not worth listening to 2 minutes of a voice based message than a generic email.

People also think email is better, but do you know the history of voicemail?

if the answer is no, lets go down memory lane of Voice Mail.

Voicemail is often assumed to be an electronic answering machine on a server. While it’s true, its origins was almost similar to sending a letter or an email, just with spoken word.

The first indication of such language was in printed publications in 1877. A famous man named Thomas Edison with an invention called the phonograph. For the Gen-X audience and older, this is basically a record player. Millenials are probably familiar to just be cool for the latest trend. While it was well known for songs, the ability to record spoken word, as a way to replace letter writing had the possibility. The “voice mail” language was in the lexicon by the 1910s.

While the answering machine was invented in the 1960s, the ability to install these would be so cost prohibitive, and worse, a wiring nightmare. In the early 1970s, Motorola introduced pagers that provided one way voice messages that would be answered by an “answering center” (this in 2017 is completely archaic with the advent of digital telephony, automated attendants, in fact the size of these answering centers were the size of contact centers, which was not existent at the time.) These pagers used UHF signals and were often used for volunteer fire fighters, etc. In this sense, this could be considered as a voice message.