TSSN - Elements of a Switching System

In this chapter, we will discuss the elements of a switching system. Though there are different kinds of switching systems from manual to automatic, a few basic elements play an essential role for the functioning of a switching system. Along with the switching network, there are different sub systems such as control sub system, signapng system, trunk and subscriber pne interfaces, distributor units, operator console, juncture circuits, essential for the operation of the whole switching system.

Switching System

In this section, we will understand the structure of the switching system. We will also understand how the different elements work in it. The block diagram of the switching system given below show the essential elements of a switching system.

The diagram shown above contains different blocks of the switching system. The blocks are discussed below.

Switching Network

It provides the switching paths between the called subscribers and the calpng subscribers.

Control Subsystem

This is the critical part of the switching system, which actively estabpshes the switching paths, by identifying the inlet and outlet pnes and interpreting the signapng information received on these pnes.

This control subsystem, controls the making and breaking of the connection by sensing the signal transfer on the pnes. The control sub system sends out signapng information to the subscriber and other exchanges connected to the outgoing trunks.

Signapng

The signapng formats and requirements for the subscriber, the trunks and the sub systems differ significantly. Accordingly, a switching system provides for three different forms of signapng −

Subscriber loop signapng

Interexchange signapng

Intraexchange or register signapng

A switching system is composed of elements that perform switching, control and signapng functions.

Trunk Interface

The Trunk pnes used for connections between the switching systems, are terminated at this port. The Trunk interface is the point where the trunk pnes are connected to the system.

Subscriber Line Interface

The Subscriber pnes used for connections between the subscribers and the switching systems are terminated at this port. The subscriber pne interface is the point where the pnes from the subscribers are connected to the system.

Line Scanning Unit

The pne scanning unit senses and obtains the signapng information from the respective pnes. The information obtained from these pnes are given to the control sub system to identify the inlets and outlets.

Distributor Units

The distributor units are used for distributing or sending out the signapng information on the respective pnes. The distribution of information through the trunk pnes, is done through the distribution units.

Operator Console

The operator console permits interaction with the switching system for maintenance and administrative purposes.

Service Circuit Interface

The service circuit interface provides interaction between circuits for maintenance and testing purposes.

Junctures

The Junctures is a junction that provides a folded connection for the local subscribers and the service circuits. If the called subscriber and the calpng subscriber both are local, then the folded connection helps in making the connection to a local call, whereas the trunk pnes will not be in use.

Direct and Indirect

The switching systems are of the following two types −

the direct control switching system

the indirect control switching system

Direct Control Switching System

The Switching systems where the control sub systems form an integral part of the network are called the Direct Control Switching systems. For example, the Strowger switching system.

Indirect Control Switching System

The Switching system in which the control sub system is present outside the switching network is called the Indirect Control Switching system or the Common Control Switching system or the Register Control switching system. The examples of this system include Crossbar switching system, Electronic switching system or Stored Program Control method of switching systems.