Telephone Network

                    A connection between two people - a caller and the called person - is the basic service of all      Telephone networks. To provide this service, the network must be able to set up and maintain a call, which involves a number of tasks: identifying the called person, determining the location, routing the call, and ensuring that the connection is sustained as long as the conversation lasts. After the transaction, the connection is terminated and the calling user is charged for the service he has used. In a fixed  Telephone network, providing and managing connections is a relatively easy process, because telephones are connected by wires to the network and their location is permanent from the networks’ point of view. In a Telephone network, however, the establishment of a call is a far more complex task, as the wireless connection enables the users to move at their own free will providing they stay within the network's service area. In practice, the

    Telephone Network has to find solutions to three problems before it can even set up a call:

- Where is the subscriber

- Who is the subscriber

- What does the subscriber want

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