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One last topology deserves to be mentioned since it historically was one of the first, though it suffers from many obvious problems. That is the star topology where one central computer, the hub, acts as the main switching center, accepting all incoming messages from the other hosts and rerouting them to the appropriate destination. Fig. 23.11.7 shows a star topology. Obviously stars suffer from a vulnerability in the central hub which, if it dies, takes the whole network with it. Some early WANs were stars, such as CSNET which linked all the Computer Science Departments in academic institutions in the US for many years. Also, early mainframe and terminal networks were stars. A bus based topology is essentially a star if the hub is taken to be the coaxial cable instead of a distinct computer. |
