telecom terminology

telecom terminology

(From Phone Systems & Phones for Business & Home by Michael N. Marcus. Copyright 2008. All rights reserved.)

In this book, we generally use key system, rather than PBX terminology.

A key system has multi-line phones with keys (buttons) that you press to get dial tone on a specific line from the phone company's Central Office (CO), or to answer a call. “CO” is pronounced “see-oh.” It's not “company” or pronounced “koh.” Some of those phone buttons may be used for features such as intercom, paging or speed-dial.

A soft key is a feature button located near a display screen on the phone and its function changes, depending on what the display shows at the moment. These changing buttons are also called context-sensitive keys or buttons.

In smaller key systems, incoming calls usually ring at several or all phones. In bigger key systems, calls usually go to the receptionist or attendant, who will then tell someone that he or she has a call on a particular line, often using the intercom to call one phone, or by making a paging announcement to several people, or to many people.

With a PBX (“Private Branch Exchange”), you usually use a single-line telephone (“SLT”) and have to dial 9 to get dial tone to make an outside call. Incoming calls usually go to a receptionist, attendant or operator, who transfers the call to the appropriate person.

The word “branch” was used in “Private Branch Exchange” because originally these systems were thought of as branches or subsidiaries of the phone company’s main Central Office switching exchange — the hardware, wire and programming that directs and connects phone calls. Together, these elements are often called a switch or a wire center. Sometimes an office PBX system is called a switch, particularly by old phone guys.

The term “exchange” can also be used to refer to a physical area (a neighborhood, or sometimes a whole town or several towns) served by a particular switch. Sometimes “exchange” refers to the first three digits, or two letters and a digit, of the local phone number. Other old telecom terms for those first three digits are office code and NXX.

In the United States, the word exchange can also mean a local access and transport area (LATA) under the 1982 “Modification of Final Judgment” antitrust suit that required the divestiture of the Regional Bell Operating Companies (RBOCs) from AT&T.

The word “exchange” was originally used because the central office was a spot where wires and conversations came together. It was analogous to “stock exchange,” “mercantile exchange” or “Post Exchange” (PX).

A PABX is a Private AUTOMATIC Branch Exchange that allows many functions without assistance by an operator. Since virtually all PBXs in use today are PABXs, the terms are used interchangeably, except when referring to ancient hardware.

An IPBX is a PBX designed to use VoIP. It may also be able to use ordinary analog lines. The “I” stands for “Internet.”

One type of predecessor ancient hardware is the PAX (Private Automatic Exchange), a telephone system used solely for internal communication in offices, factories, hospitals and on ships, with no connection with the outside world. It’s basically a large intercom system, and seldom found today. When PAXes were popular, many business people had two phones on their desks, one for internal use, and one for connecting with the outside world.

KTS is the abbreviation for Key Telephone System, often called just a Key System, the most popular type of phone system for small business and residential use.

The heart (or brain) of a KTS is its KSU (Key Service Unit). Some telecom newbies say Key System Unit. Computer guys often call it a Central Processing Unit, or CPU. Old telecom guys call it a switch. Cardiologists call it a “heart.” Neurosurgeons call it a “brain.” Guess what urologists call it.

An individual module inside a KSU used to be called a KTU (Key Telephone Unit), but this old Bell System term is fading away, just like the Bell System.

Many phone systems combine features of key systems and PBXs, and can use both multi-line and single-line phones, so they are considered to be hybrid systems.


It's OK to say “dial,” even if you make your calls by tapping buttons on a touch-tone pad. “Touch-Tone” was originally a trademark of AT&T, but they let the trademark lapse. A maker of cheapie phones used “Touch-Tone” as a brand name in the mid-1980's, but the company seems to have disappeared. Most phones and phone systems can be switched to produce either touch-tones or dial pulses (clicks), like old rotary dial phones, for use with the rare ancient central offices that don't accept touch-tones. The technical term for touch-tone is DTMF (dual-tone/multi-frequency).

The actual “dial” on rotary dial phones, the disk with the holes where you put a finger or pencil, is called the finger wheel.

Rotary has another ambiguous meaning in the phone business — the feature that lets a caller who dials a busy phone number, to automatically connect through another number. This feature may also be called hunting or ISG (Incoming Service Group) or Call Forward on Busy.

Phone company features such as Call Forwarding, Conference Call, Speed-Dial, Call-Waiting, Re-Dial, Call Return and Caller ID, are often called Custom Calling Services, as distinct from POTS (Plain Old Telephone Service). Pot, on the other hand, is not a plain old telephone.

Wireline service is also a term for POTS, generally using copper wire or fiber-optics, as opposed to wireless radio to carry voice and data. The term is frequently used to describe the type of phone service someone has.


What normal people call a “bell,” phone folks call a ringer. Traditional electromechanical phones, the dominant form until the mid-1980s, used mechanical bells. Many ancient phones had externally-mounted ringers. Phone ringers generally had two separate metal gongs with a vibrating hammer that moved from one to the other, until the compact size Princess and Trimline phones necessitated space-saving single-gong ringers.

Many people confuse the Princess and Trimline phones, or even speak of a “Princess Trimline.” The Princess is a compact oval-shaped table phone with its dial in the base. The Trimline is a compact table or wall phone, with dialing in the handset. Princess and Trimline were AT&T designs made by Western Electric.

Nearly identical phones have been made by other companies under license from Western Electric, including IT&T, Stromberg-Carlson and Northern Telecom. GT&E developed its own designs, “inspired by” Western Electric, but they apparently did not pay for a license to copy Western.

Strangely, the GT&E versions of Western Electric phones were always uglier, just like Mercury cars have generally been uglier than the Fords they were based on. If you disagree, don’t complain — just enjoy your ugly Capri, Sable, or Bobcat. At least there was no uglier Mercury version of the Edsel. By the way, the Mercury name was thought up by Edsel Ford in 1939.


OK, back to the phone business.

Modern electronic phones use internal electronic ringers, which can sound like warbles, chirps, chimes, beeps, buzzes or almost anything else. In a noisy area you can use a loud alert signal, which can sound like a horn, gong, bell, whistle, etc.

Ringback tone is the artificial ringing sound that you hear on your phone when you call someone else. The rhythm of the ringing you hear is not necessarily synched with the real ringing at the other phone.

Sidetone is a little bit of your own voice that is fed into your own ear when you speak to someone on the phone. Years ago, Alex Bell himself came up with the idea. Without sidetone, people tend to yell into the phone, or might doubt that their phone is working.

A ringdown circuit lets you make a call to a pre-determined phone just by picking up a handset on another phone. It can be provided by your local phone company, or you can use your own equipment and wires.

A hotline phone is often used with a ringdown circuit to make an automatic call, particularly in an emergency situation. Some hotline phones use pre-programmed internal memory instead of ringdown circuits. Hotline phones can generally be answered, but not dial calls manually. The BatPhone is a hotline phone. You can get a BatPhone and other hotline phones at

Ring up is not the opposite of “ringdown.” It just means to make a call, as in “I'm going to ring up my mother after breakfast.” The term is more common in the remnants of the British Empire than it is in the United States.

Some people say “give me a buzz” when they want a phone call. Most phones ring, or at least warble. Very few buzz.


Octothorpe is one of many names for the # key — usually found below the 9 and to the right of 0 on a touch-tone phone. It's also called the “tick-tack-toe sign,” “cross-hash,” “cross-hatch,” “enter,” “hash,” “number-sign,” “noughts-and-crosses,” “octothorp,” “pound,” “pound-sign” and probably other things I haven’t heard of. The Þ (asterisk) under the 7 is called Star in the phone business.


Just as a ship is a big boat, cable used to mean thick wire. Computer people have affected telephone vocabulary, and now “cable” seems be synonymous with “wire”, and might eventually replace it.

The name of the British long-distance company, “Cable & Wireless, Ltd.” comes from the undersea telegraph and telephone cables that were run around the world to unite the British Empire, and “wireless”, the Brit term for radio. The company also installed the first telegraph cable between the U.S. and Britain. Some cellphone service providers, such as AT&T and Verizon, refer to their services as “wireless.” That's silly. They use many miles of wire. I’ve even sold wire to Verizon Wireless. I’ve also sold wire that was made by Lucent, to Lucent. Life is strange.

Wireless Cable refers to cable-like TV programming sent over-the-air to an antenna on your roof or in your attic. It is NOT satellite TV. Multipoint Multichannel Distribution Service (MMDS) is the technical term for it. MMDS companies use microwave frequencies to transmit television channels from an antenna located on a tower, tall building, or mountain. The service is fading away as cable TV becomes more available.

Years ago, phone equipment, local phone service and long distance service were all provided by one company that had a government protected natural monopoly in each city. Today you can choose from many companies and many types of companies.

A LEC (pronounced “leck”) is a Local Exchange Carrier (or Company), a business that provides local telephone service. It may be a tiny independent, or a giant RBOC (pronounced “are-bock”), Regional Bell Operating Company like Verizon. Most LECs face competition from ILECS or BLECs (see below). An ILEC (pronounced eye-leck) is an Independent Local Exchange Carrier, a non-Bell phone company. They vary in size from companies with dozens of customers to hundreds of thousands of customers.

ILEC also means Incumbent Local Exchange Carrier, a phone company in business at the time of the AT&T breakup.

A Rate Center is the geographic area used by LEC or a cellphone carrier to set rate boundaries for billing and for issuing phone numbers. Generally, a call within a rate center is a local call, while a call from one rate center to another is a long-distance call.

Sometimes an RBOC is just called a BOC (Bell Operating Company). When AT&T was split up at the end of 1983, the long distance business was separated from the local service business. The local business was divided into seven regional companies that included what had been 22 former Bell System phone companies. They did not all use the Bell name before or after the split.

The new companies were originally known as Regional Holding Companies, or RHCs, and later as RBOCs, but were commonly called Baby Bells — the offspring of Ma Bell. Less affectionate cynics called them the Seven Dwarfs. Cincinnati Bell was independent and not considered an RBOC. As of 2008, the seven RBOCs have merged into just three mega-BOCS (Verizon, AT&T and Qwest). The company that now calls itself “AT&T” is not the original AT&T. It’s made out of several Dwarfy Bells, such as Southwestern Bell (“Taco Bell”) — which bought AT&T in 2005 and preferred its name.

Southwestern Bell Corporation was originally headquartered in St. Louis. In 1993, it moved to San Antonio and became SBC Communications, Inc. The name change was an effort to reinforce the company's global reach and the company stated that “SBC” was not the initials for Southwestern Bell Corporation. SBC then gobbled up fellow Baby Bells Pacific Telesis, Ameritech and BellSouth, and former independent Southern New England Telephone Company.

Verizon includes major former Bell companies like New England Telephone, New York Telephone and New Jersey Bell, as well as the biggest non-Bell phone company, GTE, and long distance company MCI. Cynics like me assume there is a plan in a file cabinet or PC somewhere for putting the three remaining RBOCs together to restore the situation that existed in 1983.

A CLEC (pronounced “cleck”) is a Competitive Local Exchange Carrier, a company or person authorized to provide local telephone services in competition with the traditional local phone company. There are two CLEC types: facilities-based and non-facilities-based (also known as switchless resellers), where the CLEC re-sells services provided by the traditional company under the CLEC’s name. Some large cities have several CLECs, but rural areas often have no competition for local service. Some CLECs provide phone service only to businesses, and others serve both residential and business customers.

A BLEC is a Building Local Exchange Carrier. Also known as Real Estate Carriers, BLECs allow building tenants to get phone service from their landlords. Real estate developers frequently install phone and data wiring in new or remodeled buildings, and try to get additional monthly income by reselling phone services from the local phone company or its competitors.

You can also get local telephone service from a cellphone company, a VoIP company, or a cable TV (CATV) company. A Multiple System Operator (MSO) runs several cable television systems. The term is usually reserved for big companies like Cablevision and Comcast.

The cable companies and some phone companies sell bundles of discounted services including telephone, Internet access and television, frequently marketed as Triple Play. Some of them also offer cellphone service in bigger bundles as Quadruple Play. (Fourplay sounds like more fun.) Bundling saves money in billing and customer service and increases customer loyalty. Verizon CEO Ivan Seidenberg — who started splicing cables in manholes in the Bronx — said bundles “make our offerings sticky.” It’s hard for customers to break away to sign up with competitors. Several companies are trying to take my phone and Internet service away from Cablevision, but I’ll still need Cablevision for television, so I’m not likely to change.

Unbundling, on the other hand, is the regulatory process that allows multiple telecom companies to use wiring between a phone company’s central office and a customer's premises. The actual wire on the poles and in the ground is owned by the incumbent local exchange carrier, but it must be made available to competitors who pay rent for it. The procedure is called unbundling because traditional phone company customers paid for a bundle of services that were not broken down into separate items with individual costs.

Cable company phone service is similar to VoIP, and is called PacketCable. People who have Internet service from their cable companies don’t have to get phone service from them. They can also have VoIP telephone service by using a VoIP specialist such as Vonage or Skype.

Companies that traditionally were providers of phone service, such as Verizon and AT&T, have felt the threat from the cable TV companies, and responded by getting into the TV and Internet business, sometimes using fiber-optic cable for faster data transfer than has been possible with the metallic coaxial cable used by the cable companies.

Higher speeds will be increasingly important for downloading movies and television shows, particularly in high definition. Verizon was so aggressive in marketing its FiOS fiber-optic service, that Comcast, Time Warner Cable and Bright House Networks filed an FCC complaint in early 2008 against Verizon for improperly trying to retain customers who wanted to try cable phone service.

Cable companies are fighting back with technology. Docsis 3.0 is supposed to enable them to match or even beat Verizon’s FiOS. Comcast, which had been offering maximum speeds of about 16 megabits per second, expected to boost speeds to 50 megabits to some homes by late 2008; and over the next two years, planned to offer speeds over 100 megabits. This compares with the FiOS download speed of up to 50 megabits per second. As of springtime 2008, AT&T’s U-verse service could provide a maximum data speed of only 10 megabits a second, 40% better than its best DSL service, and close to cable companies’ data speeds.

There are businesses like CLECs and BLECs in the cellphone business, called MVNOs. A Mobile Virtual Network Operator is a company that provides cellphone service but does not have its own radio license from the FCC or the antennas and infrastructure to provide service.

MVNOs buy wholesale minutes from other cellular carriers and resell them to their customers. Virgin Mobile is a successful MVNO operating in the United Kingdom as a reseller of T-Mobile service and in the United States where it uses Sprint Nextel. Walt Disney Company failed with a cellphone service aimed at families, called Disney Mobile, which also used Sprint Nextel’s network. They planned to try again outside the USA.

At one time there were no options for long distance service, other than not making long distance calls. Everything changed in 1969 when the FCC allowed MCI to compete with AT&T, which owned most of the national long lines facilities. Soon after that, Sprint and many other competitors appeared. Some had their own microwave, satellite, copper or fiber-optic networks; others were switchless resellers that re-sold excess capacity of the major companies.

Prices seemed to drop every few months, and there was a confusing batch of ever-changing discount deals, including MCI’s famous “Friends & Family” loyalty program. AT&T offered a complicated array of WATS (Wide Area Telephone Service) discounted calling services. In the 1980s, there were books, lectures, magazine articles, college courses, computer programs and consultants who specialized in helping business owners and consumers make the right long distance choices.

Initially, it was much less convenient to use an alternative long distance carrier. Callers had to enter a long string of digits before the destination phone number to switch their call away from AT&T. If a caller only had a rotary dial phone, a touch-tone adapter called the Soft Touch could be screwed onto the handset or held against the mouthpiece to allow the transmission of the vital tones needed to direct a call. If a customer spent enough money each month, the long distance carrier would send a technician to install a pre-programmed device to automatically spit out the needed digits before each long distance call.

It eventually became possible for every customer of a local phone company to designate a long distance carrier for each phone line. The local phone company’s central office computer would be coded with a PIC (Primary Interchange Carrier) code, which indicates which long-distance carrier you chose, and it directs your long distance calls to that carrier. If you change long-distance carriers, the PIC code is updated.

Casual PIC-ing is a procedure that allows you, or a visitor to your business or home, to temporarily override your PIC code to select another carrier for a call. To route the call through the alternative, the caller dials that carrier’s PIC code before entering the telephone number. Some long distance carriers will not accept casual PIC-ing, and will only let you use them if you have pre-registered. When you travel, casual PIC-ing may allow you to avoid the exorbitant telephone rates in many hotels and resorts. You can also save money by using your cellphone instead of the room phone.

Some phone systems could be programmed to dial carrier selection codes, or to select specific phone lines based on the destination area code, sometimes even considering the time of day. In fact, the ability to “memorize” complex rate tables for least cost routing was a major reason businesses invested in new phone systems in the 1980s.

Changes in technology and pricing and new business alliances have made things much simpler now. Former competitors are now partners. MCI combined with corrupt rival WorldCom and nearly went bust, and is now part of Verizon.

Sprint has had an even more complicated history. It started as a provider of internal communications for the Southern Pacific Railroad. Then it offered service to everyone. It was bought by GTE, and then by US Telecom, a large independent phone company based in Kansas. It later bought Centel to provide service in 18 states, tried to merge with MCI, and bought Nextel to expand its cellphone service. That move killed its stock price and alienated many customers and employees.

Today it doesn’t make much difference whom you get long distance service from. Just don’t pay more than $25 a month for it. Lots of people make all of their long distance calls from cellphones that have free long distance service.

Wire running from the phone company, whoever it may be, to your place is called the local loop.

Loop plant includes the local loop, plus all the telephone poles and underground conduit and assorted hardware used to connect them to you.


Wire running around inside your place is station wire, or station cabling.

The common phone wire that was used for decades, and is now considered inadequate, was called D-station wire or JK. It was also classified as IOW, because it could be used Inside and Outside. Wire designed for inside use only, is IW. Most of this wire had four conductors (with green, red, black and yellow insulation), and was also called quad.

Some of the oldest wire used in and on walls, with three or four conductors twisted together, but with no outer jacket, is called bridle wire. Newer bridle wire does have an outer jacket, and can be used between a telephone pole and a building. Wire designed to go in the air is called aerial cable. It can be attached to a supporting cable, or might be made with an integral support strand in a figure-8 configuration (a cross section looks like the number eight.) Wire that goes from a telephone pole to a building is called drop wire.

When wire is installed underground, it may be placed in a protective conduit or duct, or it may be designed for direct-burial, and filled with a moisture-resistant gel and equipped with protective layers of gopher-proof aluminum and plastic. Gophers have sharp teeth. Aluminum, copper and vinyl have no nutritional value and probably don’t taste very good; but gophers, mice, squirrels and even birds love to chew on phone wiring.

Alpeth is a common type of cable used both in the air and underground. It is protected with aluminum and polyethylene. When a layer of steel is added for more strength, it’s called stalpeth. Cupeth cable has a copper shield. Lepeth uses lead. Don’t chew on it. Save it for the gophers.

Modern wire without a jacket is usually cross-connect wire, and is generally used in short lengths to make connections between two terminal blocks (often they are punch-down blocks). A group of punch-down blocks near the main phone system control unit is often called a main distributing frame (MDF). A block or blocks farther away, and closer to the phones, is an intermediate distributing frame (IDF). There are several types of punch-down blocks in use that allow easy connection of wires without stripping the insulation off the wires and then wrapping them around screws. The most common types are designated as 66 and 110 blocks. Special punch-down tool blades are made for each type.

Most phone installations now use multi-pair station wiring inside the walls, usually with four twisted pairs. The general description is UTP (unshielded twisted pair). It's a good idea to install more pairs than you think you'll need, for adding more phones and gadgets, and to compensate for damage by plumbers’ torches and mice teeth after the installation.

Twisted-pair wire varies in the number of twists per inch. Wire with more twists is better and more expensive. UTP is classified in various levels or categories (“Cats”).

Computer networks generally use Cat-5, Cat-5e, Cat-6, or Cat-7, and phone systems Cat-3 or Cat-5e. Cat-5 has largely been replaced by Cat-5e, and many people say “5” when they really mean “5e.”

Cat-5 wire and above is capable of higher data trans-mission speeds than phone system wiring, and must be installed properly to avoid loss of speed and data interruptions. Special jacks and other hardware items are available for use with data category wire.

Each phone circuit consists of two wires in a pair. One wire, with positive electrical polarity, is called the tip and is traditionally green within a phone jack. The other is negative, called ring, and is red. The tip and ring terms come from the old-fashioned telephone switchboard plug.

Multi-pair phone and data wire use an industry-standard color code, to distinguish one pair from the others, and the wires within a pair. Each wire usually has a base color and a contrast-ing stripe; and the other wire in the pair is the opposite.

The first pair of wires should have a white wire with blue stripes, and a blue wire with white stripes. A recent trend in wire manufacturing, particularly for data wire, is to have one half of a pair solid and one half striped. With this method, the first pair would consist of a white wire with blue stripes, mated to a solid blue wire.

There are codes for 25 different pairs. When cables have more than 25 pairs of wires, the colors repeat, and each group of 25 pairs is separated and wrapped with colored nylon thread, in a binder group.

With most phone systems, you need a direct path from the central control unit to each phone. Phone guys call this home-run wiring. Computer guys call it star topology. Sometimes you’ll see the term star topography. The terms are not identical, but are close enough.

Loop-through is a less-expensive wiring scheme, often found in homes, where one piece of wire goes from jack to jack to jack. It’s also known as daisy chain wiring.

A cord used to mean a short, flexible, and perhaps temporary piece of wire — such as the one between the base of a phone and a jack on the wall. Here, too, computer lingo is taking over. Patch cable is now more common than patch cord. A patch panel is an array of jacks in a metal slab that accept patch cords.

When wire is cut to a specific length and has specific connectors or plugs attached, it is usually called a “cord” or a “cable,” as in “extension cord,” or “modem cable.”

A cord/cable/piece of wire that connects a phone to a jack is normally called a line cord or sometimes a base cord or a mounting cord. A standard line cord is seven feet long. Other common lengths are 12 feet and 25 feet. You may also find 50 feet, particularly in dollar stores.

The coiled cord between the base of a phone and the handset is usually called a handset cord. The standard handset cord is six feet long. Twelve feet and 25 feet are also common, and if you want your dog or cat to have a lot of fun, you can get a 50-footer at the dollar store. Don’t trip on it.


The little plastic tips on the ends of cords and cables are plugs. Plugs fit into jacks. Despite their male name, jacks are female. Plugs are male. If you don't understand this, find someone of the opposite sex, get naked, and look in the mirror. You might get lucky later. Or go to Rome and study Michelangelo's “Temptation and Fall” on the Sistine Chapel ceiling.

Modular plugs are made in three standard sizes. The smallest plug, known as 4-position/4-wire, is used for handset cords. The middle-size plug is the most common. It has six positions (meaning that there are six positions or grooves where connecting pins could possibly be placed) and either two, four, or six wires. It is used for most line cords, for connecting phones, modems and other devices to phone jacks. The largest commonly used plug, with eight positions and eight wires, is usually used for LANs (Local Area Networks) and sometimes for four-line phones.

In the computer world, and in most kinds of hardware, a connector can be male or female. In the phone world, the word “connector” is reserved for females. A CPC adapter has one male plug and two (female) connectors. There is a vulgar mnemonic device for remembering this, but I won’t print it here.


CPE used to mean customer-provided equipment (in the AT&T Empire) or its opposite, company-provided equipment (in the GT&E Empire). Now it's customer premises equipment, like a phone or a fax machine. Therefore, CPE can be either CPE or CPE. There’s also WCPE, Wireless Customer Premises Equipment.

ETE is the abbreviation for employee telephone equipment, often freebie CPE provided by the company. Could ET phone home with ETE?

People sometimes say they “jack-in” a phone. That's silly. You plug-in a phone.

Some people — even many electricians — call wall outlets and wall jacks “plugs.” That's beyond silly. It’s absolutely stupid! Plugs go on wires, not on the walls.

Even though almost all phone jacks go on the walls, the term wall jack is reserved for jacks that are designed to support a wall phone. Wall jacks have either plastic or stainless steel cover plates. The mushroom-like pieces at the top and bottom of a wall jack that fit into holes on the back of a wall phone and support the weight of the phone are mounting studs.

The original modular wall phones (below left) had metal backs with slots and modular plugs in them that slid up and down and mated with wall jacks. Many recent models — particularly phones that can be used on a table or on a wall — have a jack in their back inside a recessed space, and connect to the wall jack with a short cord that has plugs on both ends.

Other jack types include flush jacks that are nearly flat, like an electrical outlet (also called a receptacle); and surface jacks that stick out from the wall. Surface jacks are often called baseboard jacks or biscuit jacks. In modern houses, the baseboard is often replaced by a small strip of molding that is too small to hold a jack, so the jack goes on the wall above the baseboard.

Jacks that connect directly to the phone company have RJ designations. RJ stands for Registered Jack, and refers to FCC-established standards. A single-line jack for a wall phone is an RJ-11W. A two-line jack for a desk phone is an RJ-14C. The RJ designation refers to the way a particular piece of hardware is connected at a particular time. It is not a part number. An RJ-11C, RJ-14C, and RJ-25C can be physically identical, but differ in the number of phone lines connected to them.

Most people call an eight-wire jack used for a phone or a computer network an RJ-45. That's a mistake, because an RJ-45 is really a jack used to connect a data terminal to a phone line; but since the same piece of hardware can be used for terminals, networks and phones, any 8-wire jack is commonly called an RJ-45. I’m not happy about it, but I’ve probably lost this battle.

The W in RJ designations stands for “wall.” Nobody seems to know what the “C” stands for. There are other suffixes, including “X.”

RJ21X is a common phone company demarcation point (demark) for up to 25 lines. In this book, we use the term line to refer to an individual two-wire circuit (a pair) between your office or home and the phone company, which generally provides service for one phone number.


The most common type of line is Loop Start, used for ordinary analog phones and many phone systems. A call is started by going off-hook, which closes a circuit (“completing the loop”) which signals the phone company’s central office switching equipment that you want dial tone, to make a call.

Some phone systems, particularly large PBXs, use Ground Start lines (often called trunks) to signal the central office that you want dial tone by momentarily connecting the “tip” side of the phone line to ground. This is done to avoid call collision or glare, the condition when you pick up the phone to make a call just as a call comes in, but before ringing starts, and you are both confused.


There are ways to get more than one conversation out of one pair of wires, and alternatives to wire.

SLC (pronounced slick, and standing for Subscriber Line Carrier) is used by phone companies when they need to provide dial tone where there is insufficient wire running through the street. A SLC can provide up to 96 derived lines. The smallest SLC can squeeze two calls out of one pair of wires. The line voltage on derived lines is usually much lower than the 48 volts on normal lines, and may confuse simple multi-line phones. Hold circuits may not work, and in-use lights may be on, even when the phone is hung up. SLCs may limit modem speeds, too.

Some phone companies use “SLC” to mean Subscriber Line Concentrator or Subscriber Line Carrier, and you may also encounter SLCC (Subscriber Line Carrier Circuit). And, to make things even worse, some people say “slick” when referring to SLIC (Subscriber Line Interface Concentrator). PairGain, once a trademark, has become a generic term for SLC technology, but it’s spelled as pair gain. (Thanks to an anonymous tipster at Telcodata for this.)

And, if all of those SLCs are not bad enough, SLC also means Subscriber Line Charge, the monthly fee paid by customers to compensate the local telephone company for part of the cost of the telephone wire, poles, and other facilities used to connect a business or home to the national telephone network.


ISDN stands for Integrated Services Digital Network, a package of voice and data channels that can use just one pair of wires. Some people say it stands for It Still Doesn’t Work. Data speeds are usually 56k or 128k, which was a big improvement over the modem speeds common in the early 1990s, but is much slower than broadband data speeds provided by cable and DSL.

Modem comes from MOdulator-DEModulator, the two opposite functions of a device used to prepare digital data for transport as analog sound over phone lines, and reconstruct the sounds into digital data when received at the other end. Modems are generally rated for the quantity of data they can send in a given time, in bits per second, or “bps.”

Bit is the abbreviation for binary digit. Eights bits makes one byte, enough information to represent a letter or a number. A thousand bytes is a kilobyte (KB) A million bytes is a megabyte (MB). A billion bytes is a gigabyte (GB).

<b>Here’s a comparison of file sizes</b>

Short email: about 2KB

One-page letter: about 30kB

10 megapixel color photo (JPG, compressed): about 6MB

10 megapixel color photo (TIF, uncompressed): about 31MB

Words and pictures in this book: about 6MB

3-min. song, compressed: about 4MB

30-min. video, compressed: about 500MB.

57-sec. high-def Harry Potter trailer, compressed: 169MB

87-min. The Simpsons movie, compressed: 1.64GB

90-min. high-def movie, compressed: 15 – 50Gb

<b>Here’s a comparison of download speeds</b>

Dial-up modem: 28kB per second

ADSL: 6MB per second

Cable: 10MB per second

FiOS: 50MB per second

Speeds above are approximate.

People also refer to devices used to connect a computer to cable and DSL Internet services as cable modems and DSL modems, but this is not technically correct, because the data is kept in the digital mode and not modulated or demodulated.

DSL (Digital Subscriber Line) is a technology that moves data at frequencies higher than normal voices on copper telephone lines to transmit traffic typically at multi-megabit speeds. DSL can allow voice and high-speed data to be sent simultaneously over the same line. Because the service is always on, you don't need to dial in as you would with a modem, and there are no busy signals or un-answered calls.

ADSL (Asymmetrical DSL) uses different upload and download speeds and can be configured to deliver up to six megabits of data per second (6000K) from the network to the customer — that’s up to 120 times faster than dial-up service and 100 times faster than ISDN. This type of DSL is the most common for business and residential customers. It's good for general Internet access and for applications where download speed is most important, such as receiving music or video files.

SDSL (Symmetrical DSL) is more common in Europe than in the United States. Unlike ADSL, it provides the same upload and download speeds, but can’t coexist simultaneously with voice connections over the same wires.

There are other types of DSL including High Bit Rate Digital Subscriber Line (HDSL) and Very High DSL (VDSL). They can provide fast data transmission speeds over short distances, and the shorter the distance, the higher the speed. As a group, all types of DSL are referred to as xDSL.

A T-1 circuit can provide 24 conversations (or data transmission paths) using two pairs of wire. It is commonly used to connect several offices of one company, or to allow a business to connect directly to a long-distance provider, without passing through the local phone company’s facilities. Some phone systems can connect directly to a T-1 line; others use an adapter called a channel bank. The standard T-1 data speed is 5.44MB per second.

VoIP stands for Voice over Internet Protocol and is also known as Internet Telephony. It's a money-saving method used to transport voice via the Internet, rather than the Public Switched Telephone Network (PSTN). Initially VoIP calls were made from computer to computer, then computer to phone, and now can use conventional phones on both ends of a call. VoIP can also be used to link branches of the same company, even thousands of miles apart; and allows people to work at home with the same type of phone they'd use at the office. Analog voice signals are converted to a digital format that can be sent as Internet Protocol (IP) packets, and the process is reversed at the receiving end. Early VoIP calls sounded lousy. Now they can sound as good as a conventional call, and better than many cellular calls. In the future, they may sound better than regular calls, as special phones are developed.


Centrex is a package of features provided to business customers by the local phone company that may replace — or duplicate — features in your own phone equipment. The package may or may not save you money, may or may not save you space, and is often a major PITA (pain in the ass) to use, because you'll probably have to dial 9 before each phone call. Sometimes you can get assumed dial nine to avoid the PITA, but you may have to pay extra. Centrex is good for uniting multiple branches of a company that are spread around a metropolitan area. In some places, Centrex has other names such as Plexar and CentraNet.


Fiber-optic cables use very thin strands of glass or plastic instead of copper wire, and can carry a huge number of conversations, as well as data and video. Some companies such as AT&T and Cablevision use fiber-optic cables in the street, but connect them to conventional copper to reach customers’ homes and offices. Verizon’s FiOS service uses fiber all the way to residential customers to provide television, phone calls and Internet service.

Microwave uses extremely high frequency, extremely short wavelength, radio transmission to carry voice, data, and video between dish-shaped antennas, and is used by phone companies and private networks. The “M” in MCI, stands for Microwave, which the company used in its early days as an competitor to AT&T’s long distance service.


In this book, we use phone to mean an individual telephone instrument, the thing you talk and hear with. In PBX lingo, a line is called a trunk and a phone can be called a line, or an extension. In both key systems and PBXs, phones are often called stations.

The general term for a physical connection on a phone system, and the circuitry that makes it work, is a port. The two main types of ports are line ports or CO ports, which connect to the phone company, and extension ports or station ports, which connect to phones.

Sometimes there are specialized ports for devices and accessories such as paging amplifiers, music-on-hold, voicemail, and door intercoms. Some phone systems have different types of station ports, such as analog, digital, and hybrid. Some phone systems can support an Off-Premises Extension (OPX).

People who have worked in offices for a long time often call a phone line a wire, as in “I'm sorry, but Mr. Witherspoon is on another wire.”

Old phone guys often call phones, sets. A wall phone is a wall set and a desk phone is a desk set and a multi-line phone is a key set.

You may also hear phones referred to by their traditional generic model numbers. An old-fashioned rotary-dial desk phone is a 500-set. An ordinary touch-tone phone is a 2500-set. A basic touch-tone wall phone is a 2554.

Phone company customers used to be called subscribers, and telco (telephone company) old-timers often called phones, subsets.

Old electromechanical key telephones sometimes were referred to with generic numbers, such as K-10 for a key phone with 10 buttons.

In Bell-Talk, single-line phones were often called CVs (pronounced “see-vees”) and key phones were called KVs (pronounced “kay-vees”). If they went on the wall, they'd be a CVW or KVW.

CVs were sometimes called C-sets.

These terms were part of the Bell System USOC (Universal Service Ordering Code) which consumer and business customers have seldom encountered since the AT&T breakup in 1983. The codes included standardized abbreviations for a huge number of hardware items, and were listed on installation orders. The USOC is now used in the wholesale side of the telecom business, where, for example, a competitive local exchange carrier (CLEC) orders service from a telco for resale to its customers. In this situation, USOCs are also referred to as Uniform Service Order Codes and Field Identifiers (FIDs) (Thanks to Ray Keating for his help on this paragraph.)

An installation order for a key system was called a K-Plan, and had a chart that showed the functions of each button on each phone.K-Plan is different from K-Plant, which was all the key system equipment and support and distribution facilities owned by a phone company. K-Plant almost became a “place” in the minds of phone guys, as in “Joey's working in K-Plant now.”

Bell's actual hardware items (jacks, adapters, transformers, etc.) often carried a KS designation. KS stood for Kearney System, a parts numbering scheme developed for a Western Electric factory in Kearney, New Jersey. Future actress, poet, playwright, screenwriter and journalist Ruby Dee worked there in the early 1940s. Even today, long after the factory was closed, some common pieces of telecom hardware are marked with KS numbers. You might also find pieces of telecom gear with a ComCode, another Bell/Western Electric part number scheme. One 50-cent part can have a dozen different identifiers.

Phones are often refurbished after being removed from service, so they will look and work like new for other customers. In the old Bell system, refurbished phones and gadgets were known as C-Stock. In the consumer electronics industry, B-stock products are usually items that were returned by customers and may have cosmetic defects, but still work fine. They are usually sold at a discount. A-stock products are brand-new and presumably perfect.

ATT (now Lucent and Avaya) sometimes liked to call its phones voice terminals. I think that's silly and pompous and confusing. Inter-Tel likes to call its phones endpoints. YUCK! That's even worse than voice terminals. It’s a phone, dammit!

Some people call phones handsets, which is not very pompous, but is confusing. A handset is not a phone. It’s a part of a phone. Unless the phone is a cellphone. Then the handset is the phone.

There are also some corded phones where the entire phone is the handset, such as the original GTE Flip Phone from the 1980s, and various one-piece phones.

Phones used in or around your house or business, that don't need wires between the handset and base, are called cordless phones, or wireless phones or sometimes portable phones. Some people use the brand name of one of the original makers, Freedom Phone, as a generic term for all cordless phones. Cordless and wireless phones are not actually cordless or wireless. The bases need cords or wires to provide power and to connect to the phone line. And there are lots of wires inside the wireless phones.


Various radio frequencies have been used over the years for cordless phones. The newest frequencies used in the United States are in the vicinity of 5.8GHz and 1.9GHz, selected to avoid interference to and from wireless computer networks and other devices and systems operating in the 2.4GHz band.

The 1.9GHz radio band is known as DECT or Digital Enhanced (once “European”) Cordless Telecommunications.

Completely self-contained phones that work without wires are called cellphones, or cellular phones, wireless phones, mobile phones, mobiles or handyphones. AT&T and Verizon call their cellphone services “wireless,” the old British term for “radio.”

Cellphones use different radio transmission technologies and different frequency bands within a section of the radio frequency spectrum designated as Ultra High Frequency, or UHF. The UHF band is also shared with television, Wi-Fi and Bluetooth transmissions.

Frequencies used for cellular networks are different in the Western Hemisphere, Europe, and Asia. The first commercial standard for cellphones in the United States was American Mobile Phone Service (AMPS), which was in the 850MHz frequency band. In Europe, the first widely used network was in the 450MHz band. When cellphones became more popular, providers could not furnish service to all of the customers who wanted it, and developed new technologies, often based on other frequencies and required government sanction.

A satellite telephone, satellite phone, or satphone is a mobile phone that communicates directly with orbiting communications satellites that in turn downlink to an earth station. Coverage may include the entire Earth, or only specific regions. A satellite phone handset is as bulky and heavy as a 1990-vintage cellphone, usually with a long and thick antenna. They are popular for scientific explorations and news reporting where conventional wired or cellphone service is unavailable. Some shipboard satellite phone systems use large steerable antennas that keep moving to maintain contact with satellites, and can support multiple conversations and data transmissions.

PCS or Personal Communications Service is the official name for the 1900MHz radio band, but the name is seldom used in marketing anymore. Code Division Multiple Access (CDMA), Global System for Mobile communications (GSM), and Digital-American Mobile Phone Service (D-AMPS) systems can be used on PCS frequencies. The FCC set aside the frequency band of 1850-1990MHz for cellphones in 1994, because the original 850MHz phone band was becoming too crowded. Dual-band GSM phones are capable of working in both the 850 and 1900MHz bands. Time Division Multiple Access (TDMA) is a technology that divides each cellular channel into three time slots in order to increase the amount of data that can be carried. CDMA takes the entire allocated frequency range for a given service and multiplexes information for all users across the spectrum range at the same time.

Third-generation or 3G is the once futuristic technology that lets cellphone companies carriers provide high-speed data.

Television stations were ordered to end analog broadcasting in 2009, and some of their 54 – 216MHz VHF frequencies may be used for cellphones.

Analog cellphones have not been made since about the late 1990s, and most cellphone carriers planned to stop providing network coverage for them in 2008.

In the early days of cellphones, and in pre-cellular mobile phones, there were no national wireless networks. If you needed to use your phone outside your local area, you had to pay the local carrier for roaming service, and often had to make arrangements days in advance. With today’s national networks and automatic roaming, this is not an issue within the U.S., but it can be outside the country. To roam when you’re vacationing in Rome, Italy instead of at home in Rome, New York can cost you $4 per minute.


The handset is the part of a conventional phone that goes in your hand, and includes the parts you listen to and talk into. The plastic shell that holds the parts is the handle.

If those parts were attached to something that attached to your head or ear instead of being held in your hand, it would be called a headset, instead of a handset.

The important components inside a headset or handset are the transmitter (or microphone) and the receiver (or speaker). What some people call receivers, are really handsets. This is a holdover from the early days of telephones when transmitters were on the wall and people actually did hold the receivers.

Some people call their entire phone a receiver. Yuck. Some people, particularly Brits and Aussies, call an entire phone a handset. Double-Yuck (unless it's a cellphone or a one-piece wired phone).

Headphones have miniature speakers (also known as drivers and transducers and receivers and receiver elements) and are mainly used for listening to music. It's unusual to hear the word “headphone.” The word almost always has an “s” at the end. It's a contraction for “pair of headphones,” like “pants” is short for a “pair of pants” and “scissors” is short for “pair of scissors.” Headphones are sometimes called cans.

An earphone is a tiny speaker that fits in or on your ear, commonly used for listening to a portable radio. EarPhone® is a tiny ear-mounted speaker with a short microphone boom (sort of a mini headset), made by Jabra for phones. EarSet® is an all-in-the-ear speaker/microphone, also made by Jabra. Similar products from other companies are called ear buds. HeadPHONE is an advertising label that Panasonic has used for phones that have headset jacks.

When you hang-up briefly to get dial tone for a new call, or to activate call-waiting or another feature, you flash the hookswitch.

“Flash” refers to a light on an old-fashioned switchboard that would let the operator know that you need help. The “hookswitch” refers to the actual on-off switch inside the phone that would be activated by hanging up or picking up the handset. When you pick up the handset, you go off-hook. When you hang up, you go on-hook. “Hanging up” refers to the actual switchhook on old phones, where you would hang the receiver.

A lot of our current telecom vocabulary is based on the parts of ancient phones, like the candlestick phone. Some phones have buttons labeled flash and some fax machines have hook buttons.

The switchhook’s connected to the hookswitch, and the headbone’s connected to the neckbone, and that’s all right with me.