8.1.1 Overview

Let us consider an ATM network that transfers information between users in cell streams over virtual circuits. A virtual circuit specifies a route of links and switches that connects the users. The cells in different virtual circuits share the transmission bandwidth and buffers that their routes have in common.The way in which those resources are shared is determined by the network's control strategy.

Because of fluctuations in the cell streams, there are periods of time when the cells arrives in a buffer faster than the transmitter empties that buffer. When this situation occurs, the buffer stores the excess cells. This temporary storage results in delays and, in case the buffer is full, in cell loss. Delays and losses affect the quality of service provided to the user.

With better control strategies, the network can carry more virtual circuits while maintaining the quality of service promised to the users. This possibility has long been known in the case of the telephone network, where improved routing algorithms enable the network to carry more phone calls with the same blocking probability. Thus, by improving the control algorithms, network managers can provide better service without additional hardware. In a public network that sells...