Signaling (telecommunications)

Signaling (telecommunications)

In telecommunication, signaling (signalling in British spelling) has the following meanings:

Signaling systems can be classified according to their principal properties, some of which are described below:


In-band versus out-of-band signaling

In the public switched telephone network (PSTN), in-band signaling is the exchange of call control information within the same channel that the telephone call itself is using. An example is dual-tone multi-frequency signaling (DTMF), which is used on most telephone lines to customer premises.

Out-of-band signaling is telecommunication signaling on a channel that is dedicated for the purpose and separate from the channels used for the telephone call. Out-of-band signaling is used in Signaling System 7 (SS7), the standard for signaling among exchanges that has controlled most of the world's phone calls for some twenty years.

Line versus register

Line signaling is concerned with conveying information on the state of the line or channel, such as on-hook, off-hook (Answer supervision and Disconnect supervision, together referred to as supervision), ringing current (alerting), and recall. In the middle 20th Century, supervision signals on long distance trunks in North America were usually inband, for example at 2600 Hz, necessitating a notch filter to prevent interference. Late in the century, all supervisory signals were out of band. With the advent of digital trunks, supervision signals are carried by robbed bits or other bits in the E1-carrier dedicated to signaling.

Register signaling is concerned with conveying addressing information, such as the calling and/or called telephone number. In the early days of telephony, with operator handling calls, the addressing information is by voice as "Operator, connect me to Mr. Smith please". In the first half of the 20th century, addressing information is by using a rotary dial, which rapidly breaks the line current into pulses, with the number of pulses conveying the address. Finally, starting in the second half of the century, address signaling is by DTMF.

Channel-associated versus common-channel signaling

Channel Associated Signaling (CAS) employs a signaling channel which is dedicated to a specific bearer channel.

Common Channel Signaling (CCS) employs a signaling channel which conveys signaling information relating to multiple bearer channels. These bearer channels therefore have their signaling channel in common.

Compelled signaling

Compelled signaling is the case where receipt of each signal needs to be explicitly acknowledged before the next signal is able to be sent.

Most forms of R2 register signaling are compelled (see R2 signaling), while R1 multi-frequency signaling is not.

The term is only relevant in the case of signaling systems that use discrete signals (e.g. a combination of tones to denote one digit), as opposed to signaling systems which are message-oriented (such as SS7 and ISDN Q.931) where each message is able to convey multiple items of information (e.g. multiple digits of the called telephone number).

Subscriber versus trunk signaling

Subscriber signaling is between the telephone and the telephone exchange. Trunk signaling is signaling between exchanges.

Classification examples

Note that every signaling system can be characterized along each of the above axes of classification. A few examples:

  • DTMF is an in-band, channel-associated register signaling system. It is not compelled.
  • SS7 (e.g. TUP or ISUP) is an out-of-band, common-channel signaling system that incorporates both line and register signaling.
  • Metering pulses (depending on the country, these are 50 Hz, 12 kHz or 16 kHz pulses sent by the exchange to payphones or metering boxes) are out-of-band (because they do not fall within the frequency range used by the telephony signal, which is 300 through 3400 Hz) and channel-associated. They are generally regarded as line signaling, although this is open to debate.
  • E and M signaling (E&M) is an out-of-band channel-associated signaling system. The base system is intended for line signaling, but if decadic pulses are used it can also convey register information. E&M line signaling is however usually paired with DTMF register signaling.
  • By contrast, the L1 signaling system (which typically employs a 2280 Hz tone of various durations) is an in-band channel-associated signaling system as was the SF 2600 hertz system formerly used in the Bell System.
  • Loop start, Ground start, Reverse Battery and Revertive Pulse systems are all DC, thus out of band, and all are channel-associated, since the DC currents are on the talking wires.

Whereas common-channel signaling systems are out-of-band by definition, and in-band signaling systems are also necessarily channel-associated, the above metering pulse example demonstrates that there exist channel-associated signaling systems which are out-of-band.

See also


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • Signaling System 7 — Signaling System #7 (SS7) is a set of telephony signaling protocols which are used to set up most of the world s public switched telephone network telephone calls. The main purpose is to set up and tear down telephone calls. Other uses include… …   Wikipedia

  • Signaling System 7 — Signaling System #7 (SS7) ou système de signalisation #7 est un ensemble de protocoles de signalisation téléphonique qui sont utilisés dans la grande majorité des réseaux téléphoniques mondiaux. Sa principale application est l établissement et la …   Wikipédia en Français

  • Telecommunications Services of Trinidad and Tobago — Limited (generally known as TSTT) is the largest telephone and Internet service provider in Trinidad and Tobago. The company, which is jointly owned by the Government of Trinidad and Tobago and Cable Wireless, was formed out of a merger of Telco… …   Wikipedia

  • Signaling Transport — SIGTRAN est le groupe de travail, au sein de l IETF, chargé de définir une infrastructure de signalisation au dessus de IP. Le but principal est le transport de message de type SS7 ou RNIS. Le groupe a défini les RFC suivantes : RFC 2719… …   Wikipédia en Français

  • Telecommunications network — Example of how nodes may be interconnected with links to form a telecommunications network A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the… …   Wikipedia

  • telecommunications media — Introduction       equipment and systems metal wire, terrestrial and satellite radio, and optical fibre employed in the transmission of electromagnetic signals. Transmission media and the problem of signal degradation       Every… …   Universalium

  • Signaling Connection and Control Part — Sous systèmes SS7 Couche Protocoles Application CAP MAP INAP ISUP TUP DUP OMAP Util. TC (TCAP) Gest. TC (TCAP) Transport SCCP …   Wikipédia en Français

  • Telecommunications device for the deaf — Miniprint 425 TDD. The acoustic coupler on the top is for use with telephone handsets. The printer records the conversation. The specific GA and SK keys allow for speedier use of common abbreviations. A telecommunications device for the deaf… …   Wikipedia

  • Signaling End Point — In telecommunications, a Signaling End Point (SEP) is an SS7 endpoint. This is to be contrasted with a Signal Transfer Point (STP).Examples include: *Intelligent network components such as Service Control Points (SCPs) and Service Switching… …   Wikipedia

  • Maximum user signaling rate — In telecommunication, maximum user signaling rate, synonymous to gross bitrate or data signaling rate, is the maximum rate, in bits per second, at which binary information can be transferred in a given direction between users over the… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”