Foreign exchange service (telecommunications)
Encyclopedia
In telecommunication
, foreign exchange service (FX) is a network
-provided service in which a telephone
in a given exchange area is connected, via a private line
, to a central office in another foreign exchange, rather than the local exchange area where the device is located.
To call
originators, it appears that the called party
having the FX service is located in the foreign exchange area.
Customers who want a telephone number provided by a neighboring telephone central office, lease a "foreign exchange" line. With the old two-wire loop technology, this would require an engineered circuit with increased costs. The practice is rare except in big cities.
, or "plain old telephone service". It generates the off-hook
and on-hook
indications (loop closure/non-closure) at the FXS's end of a telephone circuit. Analog telephone
handset
s, fax
machines and (analogue) modem
s are FXO devices, though the term is rarely used except in connection with Foreign exchange service
(FX).
FXO interfaces are also available for computers and networking equipment, to allow these to interact directly with POTS systems. These are commonly found in devices acting as gateways between local Voice over Internet Protocol (VoIP) systems and the public switched telephone network
(PSTN).
, appears to be a regular telephone. As such, it should be able to accept ringing signals, go on-hook and off-hook, and send and receive voice frequency
signals. It may use loop start
or ground start
signaling. FXO channel units were invented and named in the middle 20th century for service at the "Office" end of an FX line via carrier system
.
, a Foreign eXchange Station, or FXS, is a telephone
interface
that supplies battery power, provides dialtone, and generates ringing voltage. A device that connects to such an interface contains an Foreign exchange office (FXO) interface and could be a standard analog telephone or a private branch exchange (PBX) to receive telephone service.
Any telephone exchange
is an example of an FXS, as is the telephone jack
on the wall, though the term is rarely applied except in connection with foreign exchange service
.
An FXS interface utilizes an FXO protocol to detect when the terminating device (telephone) goes on-hook
or off-hook
, and can send and receive voice signals.
An FXS interface provides service at the "station" end of a foreign exchange line.
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
, foreign exchange service (FX) is a network
Telecommunications network
A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...
-provided service in which a telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
in a given exchange area is connected, via a private line
Private line
In wired telephony, a private line or tie line is a service that involves dedicated circuits, private switching arrangements, and/or predefined transmission paths, whether virtual or physical, which provide communications between specific locations. Most private lines connect only two locations...
, to a central office in another foreign exchange, rather than the local exchange area where the device is located.
To call
Telephone call
A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...
originators, it appears that the called party
Called party
The called party is a person who answers a telephone call. The person who initiates a telephone call is the calling party....
having the FX service is located in the foreign exchange area.
Purpose
In basic telephony there are two types of offices: local and foreign. A local office was assigned a specific area, and all telephone services provided to that area came from that central office. Each central office had its unique identifier. In the early days names were used, such as "Jackson" or "Newton". The office names were changed to three-digit numerical exchange codes (NNX), prefixed to the local phone number (not the area code).Customers who want a telephone number provided by a neighboring telephone central office, lease a "foreign exchange" line. With the old two-wire loop technology, this would require an engineered circuit with increased costs. The practice is rare except in big cities.
Foreign eXchange Office
In telecommunications, Foreign eXchange Office, or FXO, designates a telephone signaling interface that receives POTSPlain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
, or "plain old telephone service". It generates the off-hook
Off-hook
In telephony, the term off-hook has the following meanings:# The condition that exists when a telephone or other user instrument is in use, i.e., during dialing or communicating. Note: off-hook originally referred to the condition that prevailed when telephones had a separate earpiece , which hung...
and on-hook
On-hook
In telephony, the term on-hook has the following meanings:# The condition that exists when a telephone or other user instrument is not in use, i.e., when idle waiting for a call. Note: on-hook originally referred to the storage of an idle telephone receiver, i.e., separate earpiece, on a switchhook...
indications (loop closure/non-closure) at the FXS's end of a telephone circuit. Analog telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
handset
Handset
On a telephone, the handset is a device the user holds to the ear to hear the audio sound. Modern-day handsets usually contain the phone's microphone as well, but in early telephones the microphone was mounted directly on the telephone itself, which often was attached to a wall at a convenient...
s, fax
Fax
Fax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...
machines and (analogue) modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s are FXO devices, though the term is rarely used except in connection with Foreign exchange service
Foreign exchange service (telecommunications)
In telecommunication, foreign exchange service is a network-provided service in which a telephone in a given exchange area is connected, via a private line, to a central office in another foreign exchange, rather than the local exchange area where the device is located.To call originators, it...
(FX).
FXO interfaces are also available for computers and networking equipment, to allow these to interact directly with POTS systems. These are commonly found in devices acting as gateways between local Voice over Internet Protocol (VoIP) systems and the public switched telephone network
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
(PSTN).
In a nutshell
An FXO device is any device that, from the point of view of a telephone exchangeTelephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
, appears to be a regular telephone. As such, it should be able to accept ringing signals, go on-hook and off-hook, and send and receive voice frequency
Voice frequency
A voice frequency or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech.In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz...
signals. It may use loop start
Loop start
In telecommunications, a loop start is a supervisory signal given by a telephone or PBX in response to the completion of the loop circuit, commonly referred to as 'off-hook'. When idle, or 'on-hook', the loop is at 48V DC...
or ground start
Ground start
In telephony, a ground start or GST is a method of signaling from a terminal or subscriber local loop to a telephone exchange, in which method a cable pair is temporarily grounded to request dial tone...
signaling. FXO channel units were invented and named in the middle 20th century for service at the "Office" end of an FX line via carrier system
Carrier system
In telecommunication, a carrier system is a multichannel telecommunications system in which a number of individual channels are multiplexed for transmission...
.
Foreign eXchange Station
In telephonyTelephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....
, a Foreign eXchange Station, or FXS, is a telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
interface
Network interface
Network interface may refer to:* Network interface controller, the device a computer uses to connect to a computer network* Network interface device, a demarcation point for a telephone network...
that supplies battery power, provides dialtone, and generates ringing voltage. A device that connects to such an interface contains an Foreign exchange office (FXO) interface and could be a standard analog telephone or a private branch exchange (PBX) to receive telephone service.
Any telephone exchange
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
is an example of an FXS, as is the telephone jack
Telephone plug
A telephone plug is a type of male connector used to connect a telephone to the telephone wiring in a home or business, and in turn to a local telephone network. It is inserted into its female counterpart, a telephone "jack", commonly affixed to a wall or baseboard...
on the wall, though the term is rarely applied except in connection with foreign exchange service
Foreign exchange service (telecommunications)
In telecommunication, foreign exchange service is a network-provided service in which a telephone in a given exchange area is connected, via a private line, to a central office in another foreign exchange, rather than the local exchange area where the device is located.To call originators, it...
.
An FXS interface utilizes an FXO protocol to detect when the terminating device (telephone) goes on-hook
On-hook
In telephony, the term on-hook has the following meanings:# The condition that exists when a telephone or other user instrument is not in use, i.e., when idle waiting for a call. Note: on-hook originally referred to the storage of an idle telephone receiver, i.e., separate earpiece, on a switchhook...
or off-hook
Off-hook
In telephony, the term off-hook has the following meanings:# The condition that exists when a telephone or other user instrument is in use, i.e., during dialing or communicating. Note: off-hook originally referred to the condition that prevailed when telephones had a separate earpiece , which hung...
, and can send and receive voice signals.
An FXS interface provides service at the "station" end of a foreign exchange line.
External links
- Differences between FXS and FXO
- Thinkquest.org, Telecommunication Glossary