Telecommunications Network

Chapter III Telecommunication networks The rapid developments in telecommunications technology over the years has brought a sea change in long-distance communication. With the use of advanced technologies like the internet , intranet , VSAT (Very Small Aperture Terminal), ISDN (Integrated Services Digital Network), ADSL (Asymmetric Digital Subscriber Line), cellular telephony and video conferencing, distance is no longer a barrier to communications. Telecommunication systems have proved immensely beneficial for business operations. IT has enabled the control and exchange of information across business units that are spread across the globe. This sections aims at providing a basic understanding of various aspects of telecommunications like enterprise-wise collaboration, electronic commerce and internal business systems. Apart from this, you will learn about the various media used in information transmission and the manner in which telecommunications helps build internetworked enterprises.

UNDERSTANDING THE TELECOMMUNICATIONS SYSTEM The first telecom network to be developed was PSTN (Public Switched Telephone Network). Most of the telephone lines provided by PSTN have analog connections, which transmit data in the form of electrical pulses. However, a gradual shift from analog to digital connections can be observed. Digital connections transmit data in the form of 0’s and 1’s. It is much faster and clearer when compared to analog transmission. The followings points will provide a better understanding of telecommunications systems :

Quality of service Modern telecommunication systems use advanced switching technology to create an end-to-end circuit between two telephones. The amazing factor about this system is the number of telephones that can be directly and almost instantly connected. PSTN ensures good audio quality over the network.

Local Exchange Carriers (LECs) LECs provide wired services for subscribers. A network of local connections is called the local access and transport (LATA). Within LATA, the subscribers can place a call without accessing a long distance carrier. Telephones are analog devices, which continuously transmit and receive electrical signals that mach the human voice. LATA’s are linked to Subscribers Loop Carriers

(SLCs) by means of copper wires, called twisted pair cables. These are used to prevent any disturbance (called noise) from electrical circuits. The area served by an SLC is called the local loop.

Long-Distance Transmission Media An Inter Exchange Carrier (IXC) comes into play when a user places a call outside the local transport area. A variety of transmission media are used to provide regional and long distance services between local telephone exchanges. These include copper wires, fibre-optic cables, microwaves, and satellites. A technique called multiplexing has been developed for long distance transmission. Multiplexing is the process of designating a system for the simultaneous transmission of two or more messages or signals over the same channel.

Standards and Regulations Since there are many companies offering telecommunications services, it is essential that certain standards be enforced. Standards ensure smooth transmission of calls placed by subscribers of two different companies. Telecommunications standards are governed by ITU (International Telecommunications Union), a division of United Nation, based at Geneva, Switzerland.

Access Alternatives Systems access the network using various access alternatives. Few alternatives are discussed in detail below. Private Branch Exchange (PBX) Large organizations and universities, install their own internal digital telephone systems called Private Branch Exchanges (PBX). This access method provides cost effective telecommunication networks. Cellular Telephones These telephones enable subscribers to place calls through wireless communications systems. Prior to cell phones, walkie-talkie enabled mobile, twoway communications. But a major disadvantage was that they worked only in a limit range. In 1971, AT&T built a network of automatic repeating transmitters (called a cell site), which enabled long distance telephony that was free from disturbance and provided a wider range.

Leased lines Companies need long-distance data communication lease lines to get rid of the analog limitations of the local loop. These specially set-up telephones lines provide direct signal access to long distance carriers and are connected permanently.