Telephony 101: Key Telephone System (KTS)

The first on site customer systems was the PBX, but later on in the 1920s into the 1930s, brought a specific solutions to customers, called the Key Telephone System.

The “key” to this was to have hard wired lines for users who wanted to get to someone directly. This also fused with Intercom systems, acting as a separate “service” for the time. Intercoms for this context was a private circuit to enable telephone calls to work within the system. Most often, the Intercom line was on the fifth button of say a 564 telephone.

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Telephony 101: Private Branch Exchange (PBX)

You may have heard this phrase a number of times in your life, “PBX”, the “PBX number”, “our PBX” something along those lines.

It’s called a Private Branch Exchange. A PBX has been mostly in the last ten years coined by Information Technology professionals who don’t even use phones often to define it as a “premise based” or “a phone system inside a business”. This is a blatant over-simplification and re-writing history which is very common in the IT industry.

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Telephony 101: On Voice Mail

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.

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Enhanced 9-1-1

TRIGGER WARNING: The following is mostly an accurate narrative, however editorial statements are featured in the latter paragraphs that could offend people personally.  Trigger words include “Part 68”, “Enhanced 911”, “Avaya”, “Kari’s Law”, etc.

This is a work in progress. Expansion of this subject will occur as time progress to focus on earlier generation 9-1-1 services.

9-1-1 in the United States is a three digit telephone number to access emergency services to report a fire (fire), stop a crime (police) and save a live (emergency medical services). When it first came out in some markets in 1968; all it was provided a hotline to a dispatch center of the local municipality, country or even statewide. The first generation of 9-1-1 was around for more than two decades, and in some locales in the US it was not abnormal for some to still have seven digit emergency numbers instead of 9-1-1. While switching services routed calls to dispatch centers and also provided redundancy and failovers in case one dispatch center was overloaded; one of the major failures was location.

The origins of Enhanced 9-1-1 began in the early 1980s. The technology required digital switching; and in some markets step-by-step switching was still a common system going up till the mid 1990s. Also the advancement of digital PBX and Key systems for local dispatch centers provided call-center grade quality. With all these advancements would be enable location information. Essentially, if your phone company didn’t provide Caller ID, then your service was analog.

For consumers, information would automatically be passed over to the local Public Safety Answering Point. This would come from the database of the telephone company and would be confidential between the telephone company and the PSAP authorities; as some customers choose to have numbers unlisted. The database would include the physical address because some billing addresses could go elsewhere.

For businesses, with the change of technologies moving from hard wired digital systems to a bit and byte, cyber based technologies; instead of regulating the services, regulations went against the customer. As a result, this may be the reason why so many customers in the enterprise world have cut the cord and gone to mobile or cloud based phone systems.

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Telephony 101: Centrex

Central Exchange (or Centrex) is a service provided by many telephone carriers to deliver PBX or Key-like services via the telephone company (or Telco.) Little to no hardware is required at the customer end, unless its special adjuncts for digital telephones for power, etc. Regardless of the hardware, the “brain” lives out in the “cloud” so to speak at the central office. If it’s a government, or a large corporation, rarely are these actually installed on site.

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Telephony 101: Teletypewriter/TTY/TDD

A teletypewriter is a special device that was typically known as the Telecommunications Device for the Deaf or TDD. These devices act as typewriters that can carry special signals to provide text based communications over voice telephone lines. This was the beginning of using data over the telephone lines.

This technology was invented in the 1960s, nearly a century after Alexander Graham Bell attempted to invent the telephone for this audience, which obviously went for the masses who could speak or hear. The Teletypewriter (known as TTY) was initially referred to leased line that provided automatic printing such as news wire services or even for a console access to mainframes. (In fact, if a customer was very frugal dumb terminals for some were too expensive so computing would result in the typewriter that would automatically “printout” what was coming off the “screen”. A user would respond to commands by typing it into the typewriter which then would relay it to the computer.)

TDD/TTY uses a standardized protocol that basically sends various tones through the telephone lines so the other end would receive the message. According to Wikipedia (use with caution) the change to IP in the traditional phone cloud, would make these devices unusable (including the 500 Rotary telephones) because the complexity of converting landline networks to work in “native” cyber (or packet) worlds. While VOIP enables some analog communications, the move to IP would be easier to service providers to tell users to just send iMessages, SMS, Tweet, IM or other text based technologies instead.

According to various sources, TDD is separate from TTY in the technological sense, and speech impaired users that may have acquired brain disorders; a non verbal, but high functioning form of the autism spectrum disorder; cerebral palsy or other types of speech disorders) are basically non existent users. Or so you think. It’s not to say that people who aren’t deaf can’t use this technology and people with speech impairments have ether used TTY or all the other IP based communications like IM, Web, social media and text messaging.

Because of the similarities of the two platforms, here at The Museum, I believe the term should be referred as TTY as non verbal people are actually disabled users to any telephony technologies as well. Using “TTY” in the generic sense would enable inclusion to all disabled users of this technology.

Telephone Network


This is basically the central processing unit to an old fashioned telephone. The “network” varies model to model, especially by generation.  The first picture,  made by Western Electric in the 1950s to late 70s, the network weighed a brick and they were sealed shut. Later models among all 500 and 2500 sets not just Western Electric moved to a PCB like unit. The phones themselves became more lighter because the move from a brick to a board. Modern analog phones have moved to chip based, so the units are much more lighter weight and use just a couple of chips. In short, this just another visual example of a critical component of a vintage telephone.