Q. Explain working of Public Switched Telephone Network?

Public Switched Telephone Network (PSTN) accommodates two kinds of subscribers: private andpublic. Subscribers to private sector are customers who lease equipment, transmission media (facilities) and service from telephone companies on a permanent basis. Leased circuits are configured and designed for their use only and are generally referred to as private line circuits or dedicated line circuits. For instance, large banks don't wish to share their communication network with other users, however it's not effective for them to create their own networks. So banks facilities and lease equipment from public telephone companies and basically operate a private telephone or data network within PSTN. Public telephones companies are sometime called providers because they lease equipment and provide service to other organizations, private companies and government agencies. Most wide area networks (WANs) and metropolitan area networks (MANs) utilize private line data circuits and one or more service provider. Subscribers to public sector of PSTN shareequipment and facilities which are available to all the public subscribers to network. This equipment is appropriately termed as common usage equipment, which includes telephone switches andtransmission facilities. Anyone with a telephone number is a subscriber to public sector of PSTN. As subscribers to public network are interconnected only temporarily through switches, network is often appropriately known as the public switched telephone network (PSTN) and sometimes simply as dial-up network. It is likely to interconnect telephones and modems with one another over great distance in fraction of a second by an elaborate network comprised of central offices, cables (optical and metallic), switches and wireless radio systems which are connected by routing nodes (a node is a switching point). When someone talks about public switched telephone network, they referring to combination of switches and lines that from a system of electrical routes through the network.