Signaling (telecommunications)

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

Signaling systems may be classified based on several principal characteristics.

In-band and 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 dedicated channel separate from that used for the telephone call. Out-of-band signaling has been used since Signaling System No. 6 (SS6) was introduced in the 1970s, and also in Signalling System No. 7 (SS7) in 1980 which became the standard for signaling among exchanges ever since.

Signal

Signal, signals, signaling or signalling may refer to:

Science

Computing

Communications

Signalling (economics)

In contract theory, signaling (or signalling: see American and British English differences) is the idea that one party (termed the agent) credibly conveys some information about itself to another party (the principal). For example, in Michael Spence's job-market signalling model, (potential) employees send a signal about their ability level to the employer by acquiring education credentials. The informational value of the credential comes from the fact that the employer believes the credential is positively correlated with having greater ability and difficult for low ability employees to obtain. Thus the credential enables the employer to reliably distinguish low ability workers from high ability workers.

Introductory questions

Signalling took root in the idea of asymmetric information (a deviation from perfect information), which says that in some economic transactions, inequalities in access to information upset the normal market for the exchange of goods and services. In his seminal 1973 article,Michael Spence proposed that two parties could get around the problem of asymmetric information by having one party send a signal that would reveal some piece of relevant information to the other party. That party would then interpret the signal and adjust her purchasing behaviour accordingly — usually by offering a higher price than if she had not received the signal. There are, of course, many problems that these parties would immediately run into.

Signalling theory

Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals, both within species and across species. The central question is when organisms with conflicting interests, such as in sexual selection, should be expected to communicate honestly (no presumption being made of conscious intention) rather than cheating. Mathematical models in which organisms signal their condition to other individuals as part of an evolutionarily stable strategy are important for research in this field.

Signals are given in contexts such as mate selection by females, which subjects the males' signals to selective pressure. Signals thus evolve because they modify the behaviour of the receiver to benefit the signaller. Signals may be honest, conveying information which usefully increases the fitness of the receiver, or dishonest. An individual can cheat by giving a dishonest signal, which might briefly benefit that signaller, at the risk of undermining the signalling system for the whole population.