Wireless Networking in the Developing World

The next most commonly encountered network layout is point-to-multipoint. Whenever several nodes are talking to a central point of access, this is a point-to-multipoint application. The typical example of a point-to-multipoint layout is the use of a wireless access point that provides a connection to several laptops. The laptops do not communicate with each other directly, but must be in range of the access point in order to use the network.

Point-to-multipoint networking can also apply to our earlier example at the university. Suppose the remote building on top of the hill is connected to the central campus with a point-to-point link. Rather than setting up several point-to-point links to distribute the Internet connection, a single antenna could be used that is visible from several remote buildings. This is a classic example of a wide area point (remote site on the hill) to multipoint (many buildings in the valley below) connection.

Note that there are a number of performance issues with using point-to-multipoint over very long distance, which will be addressed later in this chapter. Such links are possible and useful in many circumstances, but don’t make the classic mistake of installing a single high powered radio tower in the middle of town and expecting to be able to serve thousands of clients, as you would with an FM radio station. As we will see, data networks behave very differently than broadcast radio.