Quiz 8: The Telephone System
The difference between telephone network and a broadcasting network in terms of meaning, type of communication, basic network is tabulated. The Differences between Telephone Network and Broadcasting Network is tabulated as shown.
There is a hierarchy of toll stations connected for routing long distance calls of telephony network. This is termed as hierarchical switched networks. At the bottom of hierarchy is the local central office. Calls could be completed at various levels of hierarchy as many as five layers up and down the hierarchy and go through many switches. Hierarchical switched network is shown in figure 8.2 in the text book. Flat switched networks are constructed by long distance switching centers that are connected to every other one in mesh formation. Here the system finds a direct route from one area to the other. Hence there is no more than one intermediate switch between switching centers. Flat network is shown in figure 8.3 in the text book. The hierarchical switched networks are suitable for a network of minimum computation with electromechanical switches. But with modern computer controlled switches, a flat switched network is efficient that allows direct connectivity between end stations with not more than one intermediate switch. Hence modern networks are flat.
In Public Switched Telephone Network (PSTN), the central office represents one exchange to which the subscribers are connected. These central offices themselves are connected through trunk lines for connectivity among subscribers within a local calling area. When there is scarcity of available trunks between central offices during peak traffic, a tandem office is used for connecting these central offices. This tandem office connects central offices without having any direct connection to individual telephones.