Telecommunications Terms – a glossary


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A  key system has multi-line phones with keys that you  press to get dial tone on a specific line from the phone company’s Central Office  (CO), or to answer a call. 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 throughout a large area.

– With  a PBX (“Private Branch Exchange”), you usually use a single-line  telephone (“SLT”) and have to dial 9 to get dial tone.  Incoming calls usually go to a receptionist, attendant or operator,  who transfers the call to the appropriate person.
– CO,  by the way, is pronounced see-oh. It’s not “company”  or “co.”
– KTS is the abbreviation for Key Telephone  System, often called just a Key System.
– 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.
– An  individual module inside a KSU used to be called a KTU (Key  Telephone Unit), but this term is disappearing.
– Our  Panasonic 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-80’s, but they  seem 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 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 is called the finger wheel.
– Rotary  has another 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 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.

  What normal people call a “bell,” phone pholks call a ringer.  Traditional electromechanical phones, the dominant life form until  the mid-1980s, used mechanical bells. The oldest phones had  externally-mounted ringers, sometimes on a box separate from the actual  phone. Phones generally had two separate gongs with a vibrating hammer  that moved from one to another, until the compact size of Princess and  Trimline phones necessitated space-saving single-gong ringers. 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. The rhythm  of the ringing you hear is not necessarily synched with the real ringing at  the other phone.

– 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.
– Ring  up just means to make a  call, as in “I’m going to ring up my mother after breakfast.”

Where’s your OCTOTHORPE?
“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.
*The asterisk under the 7 and to the left of the 0, is called Star.
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 be synonymous with  “wire,” and might eventually replace it.
– The  name of the British long-distance company, Cable & Wireless, Ltd.  comes from the undersea cables that run around the world, and  “wireless,” the Brit term for radio. Cable & Wireless installed  the first telegraph cable between the US and Britain. Some cellphone  service providers, such as AT&T and Verizon, refer to their services  as wireless. That’s silly.
– 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. Operators broadcast multiple channels of  television at microwave frequencies from an antenna located on a tower, tall  building, or mountain.
– Wire  running from the phone company 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 now considered  inadequate, was called D-station wire and 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 strapped  or lashed 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.)
– 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.
– Modern  wire without a jacket is usually cross-connect wire, and is generally  used in short lengths to make connections  between two terminal blocks (also called punch-down blocks). A  group of punch-down blocks near the main phone system control unit may be  called a main distributing frame (MDF). A block or blocks  farther away, closer to the phones, is an intermediate distributing frame (IDF).
– 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 and mice.
– 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 or Cat-6, and phone systems Cat-3  or Cat-5.
– Cat-5  wire and above is capable of higher data transmission speeds, and must be  installed properly to avoid loss of speed and data glitches. Special  jacks and other hardware items are available for use with Cat-5 and Cat-6  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 parts  of an old-fashioned telephone switchboard plug.
– Multi-pair  phone and data wire use an industry-standard color code, to  distinguish one pair from the others. Each wire usually has a base color and  a contrasting stripe, and the other wire in the pair is the opposite. The  first pair of wires usually has a white wire with blue stripes, and a blue  wire with white stripes. There are codes for 25 different pairs. When cables  have more than 25 pairs, each group of 25 pairs is 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-runwiring. Computer guys call it  star topography.
– Loop-through is a less-expensive wiring scheme, often  found in homes, where one piece of wire goes from jack to jack to jack.
– 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 that  accept patch cords.
– When  a piece of 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 7′ long. Other common lengths are 12′ and 25′.  You may also find 50′, 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 6 feet long. 12 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.
– 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. Or study Michelangelo’s “Temptation and  Fall” on the Sistine Chapel ceiling in Rome. Modular plugs are made in  three standard sizes. The smallest plug, known as 4-position/2-wire, is used  for handset cords. The middle-size plug is the most common. It has six  positions, 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 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, a connector can be male or female. In the phone  world, a connector is female. A CPC adapter has one (male) plug and  two (female) connectors.
– CPE  used to mean customer-provided  equipment (in the ATT empire) or its opposite, company-provided  equipment (in the GTE empire). Now it’s customer premises equipment, like  a phone or a modem; so CPE can be either CPE or CPE.
– ETE is the abbreviation for employee telephone  equipment, often freebie CPE. 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 electricians — call wall outlets and wall jacks…plugs.  That’s stupid. Plugs go on wires, not on walls.
– Even  though almost all phone jacks go on the wall, the term wall jack is reserved for jacks that are designed to  support a wall phone. Wall jacks can have plastic or stainless steel  covers. The mushroom-like pieces on a wall jack that fit into slots on the  backs of wall phones are mounting studs.
– Other jacks include surface jacks that stick out from the wall, and flush jacks that are nearly flat, like an electrical outlet (also called a receptacle).
– 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 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 8-wire jack used for a phone or a computer network an RJ-45.  That’s a mistake, because an RJ-45 is 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.
– 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 Website, we use the term line to refer to an  individual two-wire circuit (a pair) between your office or home and  the phone company, that generally provides service for one phone number.

– There  are ways to get more out of a 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 dialtone where there is insufficient wire running through the street. It can  provide up to 96 derived lines. The smallest unit 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 this technology.
– ISDN stands for Integrated Services Digital  Network, a package of voice and data channels that can use just one pair  of wires. 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 the broadband  data speeds provided through cable and DSL.
– DSL (Digital Subscriber Line) is a  technology that moves data at frequencies higher than normal speech 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, and there  are no busy signals.
– 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  is up to 120 times faster than dialup service and 100 times faster than ISDN.  ADSL enables voice and high-speed data to be sent simultaneously over the  existing telephone line. This type of DSL is the most predominant in  commercial use for business and residential customers around the world. It’s  good for general Internet access and for applications where downstream speed  is most important, such as video-on-demand.
– 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. Keep in mind that a T-1 circuit does not use 24  pairs of wire. It is able to carry multiple streams of voice and data on on  just two pairs.
– VoIP stands for Voice over Internet Protocol and  is also known as Internet Telephony. It’s a money-saving method 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  phone call, and better than many cellular calls.
– 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 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 CentraNet and Plexar.
– Fiber-optic  cables use very thin  strands of glass, instead of copper wire, and can carry a huge number of  conversations, as well as data and video.
– Microwave  uses extremely high  frequency radio transmission to carry voice, data, and video between  dish-shaped antennas, and is used by phone companies in private networks. The  “M” in MCI, stands for Microwave, which the company used in  its early days as an alternative to AT&T long distance service.

In this Website, we use phone to mean an individual telephone instrument.
– 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.
– 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 model numbers. An  old-fashioned rotary-dial desk phone is a 500-set. An ordinary  touch-tone phone is a 2500-set. A 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 code 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. (Thanks to Ray Keating for  his help on this.)
– 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 “Joe’s in  K-Plant.”
– 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, NJ. Even today, 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.
– ATT (now Lucent and Avaya) sometimes likes to call its phones voice terminals. I think that’s silly and pompous and confusing.
– Inter-Tel likes to call its phones endpoints. YUCK! I think that’s worse than voice terminals.
– Some people call phones handsets, which is not very pompous, but is even more confusing.
– Phones used in or around your house or business, that don’t need wires between the  handset and base, are called cordless phones.
– Completely self contained phones that work without wires are called cellphones,  or cellular phones, wireless phones, mobile phones or  handyphones.
– Various  radio frequencies have been used over the years for cordless phones.  The newest frequencies used in the US are in the vicinity of 5.8GHz and  1.9GHz, selected to avoid interference with 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 (formerly  European) Cordless Telecommunications.


The handset is the part of the 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 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.
– Some people even 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).
– 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 uses for some phones that have headset jacks.

When you hang-up briefly to get dialtonewaiting 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 above. Some phones have buttons labeled flash  and some fax machines have hook buttons.

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