Olden form of phone systems involved manual exchanges which involved a great task in switching and routing of calls to various subscribers that increased network traffic and longer setup times. Also, fault checking and identification was very difficult. With the introduction of electronic exchanges which used a stored program concept of switching and routing of calls and automatic error checking, the manual tasks involved in such operations has reduced, network traffic has reduced and call setup times has reduced.
There was a transformation from the stream of electronic exchanges to digital exchanges which uses Pulse code modulation (PCM) techniques to transmit speech signals in digital form between two digital exchanges. Such digital exchanges provide multiplexed speech channels, latest fibre optic technologies for signal transmission, reduced network traffic, least call setup time, better error checking and control and better customer support.
An example for a digital exchange setup is E-10B digital exchange. The organization of an E-10B exchange is shown below –
The main features of E-10B digital exchanges are as below –
Stored program control (SPC)
Time-division multiplexing (TDM)
Use of Pulse Code modulation (PCM)
Separation of switching functions from exchange management functions
Distributed common control structure for switching using functionality dedicated control units
Centralized management of E-10B exchanges through the Operation and Management center (OMC)
Could be used for implementing subscriber exchanges, tandem / tax exchanges (Transit exchanges) and Hybrid exchanges combining qualities of subscriber and transit exchanges.
Supports more subscribers and provides better customer support by detailed (itemized) billing, alarm calls, identification of malicious calls and hot-line facilities.
Having a modular architecture, E-10B exchanges could be expanded to meet increased demand by mere insertion of hardware equipment.