Explain Common channel signalling.

Common channel signalling: Signaling systems connection the variety of transmission systems, switching systems and subscriber equipments, in the telecommunication network to allow the network to function as an entire. Three forms of signaling are involved in a telecommunication network:

a.      Subscriber loops signaling.

b.      Intra exchange or register signaling

c.       Interexchange or inter register signaling

Within a telephone network, subscriber loop signaling depends on the type of a telephone instrument utilized. The intra exchange signaling is internal to the switching system and is heavily based upon the type and design of a switching system. This varies from one model to other even with similar manufacturer. Such signaling doesn't involve signaling system of the type needed on the switching network. While interexchange signaling takes place among exchanges with common control subsystems, this is termed as Inter register signaling. The main reason of Inter register signaling is the exchange of address digits that pass from exchange to exchange upon a link by link basis. Network broad signaling also includes end to end signaling in between the terminating exchange and the originating exchange. This form of signaling is termed line signaling. CCS does not utilize the speech or the data path for signaling. This uses a separate common channel for passing control signals for a group of trunks or information paths. This gives the advantages as follows:

(i) Information can be exchange in between the processors much more quickly than when channel connected signaling is used.

(ii) Accordingly, a much wider repertoire of signals can be utilized and it enables more services to be given to customers.

(iii) Signals can be added or changed through software modification to give new services.

(iv) There is no longer any require for line signaling equipments on every junction that results in a considerable cost saving.

(v) Because there is no line signaling, the junctions can be utilized for calls from B to A as well to calls from A to B. Both way working needs fewer circuits to carry the traffic than if divide groups of junctions are given from A to B and from B to A.

(vi) Signals associating to a call can be sent while the call is in progress. It enables customers to change connections after they have been set up. For illustration a customer can transfer a call elsewhere or may request a third party to be associated in to an existing connection.