Digital Switching Systems

5.1. INTRODUCTION

Various facilities of digital switching and transmission is the reason why the analog switching is slowly getting replaced by digital switching. The incorporation of digital switching and transmission technique into telecommunications altered the whole telecommunication industries setup. The reliability of digital switching system is becoming increasingly important for users of telephone services. Voice and/or data can be represented using digital signals efficiently than analog signals.

A switching system is called digital when the input to and output from the switching system can directly support digital signal. Many basic elements of the digital switching system and its operation are very similar to the stored program control (SPC) switching system. The cost of an analogue switch is roughly proportional to the number of cross points, but the cost relationship in digital switching is different.

The functions of the digital switching network is to connect pairs of channels. So that information arriving at the switching centre in a particular channel on one PCM multiplex system can be passed to some other channel on an outgoing PCM multiplex systems. To achieve this switching, two processes referred to as time switching and space switching are used. The principles of these two switching process are described in this chapter.

In digital data communication (analog or digital signal), a fundamental requirement is that the receiver should know the starting time and duration of each bit that it receives. To meet this requirement a synchronous and synchronous transmission are used. These two transmission techniques are described in this chapter.

5.2. EVALUATION OF DIGITAL SWITCHING SYSTEM

The early version of electronic switching system is the stored program control (SPC). The SPC systems have temporary memory for storing transient call information and to carry programming information. The SPC performs line control, trunk control, ancillary control, maintenance control etc. The instructions required for performing these operations are resided in a single processor. For reliability or high availability, the processor may be duplicated. Thus SPC uses a centralised software and hardware architectures.

A modern digital switching system employs a number of processors not uses distributed softwate and hardware architectures. The digital switching system also referred as Electronic Switching System-III generation is purely electronic in operation, the switching process is by time division/digital transmission, the type of control is stored program common control and the network uses pulse code modulation. Fig. 5.1 shows the evaluation of digital switching system and is self explanatory.

Switching office

Analog incoming trunks

Subscriber inlets

Switching office

Analog incoming trunks

Subscriber inlets

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Analog switching

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Responses

  • girma
    What are the types of analog and digital switching?
    2 years ago
  • Pimpernel
    What is needed to write a project on didgital and switchong system?
    1 year ago

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