Registers are used in common control exchanges to store and analyze routing data. They are provided on a common basis is a single register provides routing data for a number of speech circuits. Once a call has been setup, the register is then made available to set up other calls. Inter register refers to signaling between two registers of different exchanging. Signaling systems link the variety of switching systems, transmission systems and subscriber equipments in telecommunication network to enable the network to function as a whole. Three forms of signaling are involved in a telecommunication network:
1. Subscriber loops signaling.
2. Intra exchange or register signaling
3. Interexchange or inter register signaling
In a telephone network, subscriber loop signaling depends upon the type of a telephone instrument used. The inter exchange signaling is internal to the switching system and is heavily dependent upon the type and design of a switching system. It varies from one model to another even with the same manufacturer. This signaling does not involve signaling system of the type required on the switching network. When interexchange signaling takes place between exchanges with common control subsystems, it is called Inter register signaling. The main purpose of Inter register signaling is the exchange of address digits which pass from exchange to exchange on a link by link basis. Network wide signaling also involves end to end signaling between the originating exchange and the terminating exchange. Such a form of signaling is called line signaling. CCS does not use the speech or the data path for signaling. It uses a separate common channel for passing control signals for a group of trunks or information paths.
For a multi link connection in a network of register- controlled exchanges, a register in the originating exchange receives address information from the calling customer and sends out routing digits. Each succeeding register both receives and sends out routing digits, until the terminating exchange is reached. This sequence of operation introduces post-dialing delay. An inter-register signaling system cannot be used for seize, answer and clear signals. No register is connected when an incoming seize signal is received, since it is the signal which initiate a connection to a register. The register is released after it has set up a connection through its exchange and sent out routing digits; therefore, it cannot receive answer and clear signals. Either in-bloc or overlap signaling may be used. In enbloc signaling, the complete address information is transferred from one register to the next as signal string of digit. Thus, no signal is sent out until the complete address information has been received. In overlap signaling, digits are sent out as soon as possible. Thus, some digits may be sent before the complete address has been received and signaling may take place before the complete address has been received and signaling may take place simultaneously on two links (i.e. the signal overlap). The enables subsequent registers to start digit to analyses earlier than is possible with en-bloc signaling and this reduces post-dialing delay. Either link-bylink signaling or end-to-end signaling may be employed. In link-by-link signaling, information exchange only between adjacent registers in a multi link connection as shown by Fig. In end-to-end signaling, the originating register controls the setting up of a connection until it reaches its final destination, as shown in Fig. Each transit register receives only the address information required to select the outgoing route to the next exchange in the connection. Having performed its task, it is released and the originating register signals to the next register.