TELEPHONE SYSTEM

INTRODUCTION

Telephone Network is used to provide voice communication. Telephone Network uses Circuit Switching. Originally, the entire network was referred to as a plain old telephone system (POTS) which uses analog signals.

• With the advancement of technology, i.e. in the computer era, there comes a feature to carry data in addition to voice. Today’s network is both analogous and digital.

MAJOR COMPONENT OF TELEPHONE NETWORK

• There are three major components of the telephone network
• Local loops
• Trunks
• Switching Offices

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There are various levels of switching offices such as end offices, tandem offices, and regional offices. The entire telephone network is as shown in the following figure

• Local Loops: Local Loops are the twisted pair cables that are used to connect a subscriber telephone to the nearest end office or local central office. For voice purposes, its bandwidth is 4000 Hz.

• It is very interesting to examine the telephone number that is associated with each local loop. The office is defined by the first three digits and the local loop number is defined by the next four digits defines.

• Trunks: It is a type of transmission medium used to handle the communication between offices.

• Through multiplexing, trunks can handle hundreds or thousands of connections. Mainly transmission is performed through optical fibers or satellite links

Switching Offices: As there is a permanent physical link between any two subscribers. To avoid this, the telephone company uses switches that are located in switching offices.

• A switch is able to connect various loops or trunks and allows a connection between different subscribes.

Advantages of Telephone Network:

• It is a circuit-switched network.
• There is no transmission delay as any receiver can be selected.
• It is cheap in price because it is a widely spread network.

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Disadvantages of Telephone Network:

• It requires a large time for connection.
• It has a low transmission speed

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Applications of Telephone Network:

• It is used by business organizations to advertise their products.

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• It helps to connect people.
• It is also used around the world for recreational purposes.

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Structure of the Telephone System��

• The telephone system model is organized as a highly redundant, multilevel hierarchy. It comprises of the following components −
• Telephone of the subscriber or end user
• End office − Local central office directly connected to end user at a distance of 1 – 10km.

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• Local loop − A two-way connection between the telephone and the end office.
• Toll office − switching centres which are called tandem offices when located within the same local area.
• Toll connecting trunk − Lines that connect end offices with toll offices.

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• Intermediate switching offices − Interconnected non-hierarchical switching offices for connecting toll offices.
• Inter toll trunk − Very high bandwidth channels that connect either two toll offices via intermediate switching offices.

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• There are a number of different types of telephone network:
• A landline network where the telephones must be directly wired into a single telephone exchange. This is known as the public switched telephone network or PSTN.

• A wireless network where the telephones are mobile and can move around anywhere within the coverage area.
• Integrated Services Digital Network (ISDN)

• A private network where a closed group of telephones are connected primarily to each other and use a gateway to reach the outside world. This is usually used inside companies and call centres and is called a private branch exchange (PBX).