ctual service time. It is equal (S) and offered traffic (G) is as in Figure 13.2. The traffic throughput to the time between an arrival into the end of the queue and its increases linearly, as more traffic is presented to the network, until departure from the queue, with service having been completed. It is it reaches the maximum capacity of the transmission medium, at given by Equation 13.3 and, for a transmission channel capacity of which stage the throughput flattens out. C bits per unit time, it may be rewritten as in Equation 13.4. (13.3) (13.4) 13.3 Performance parameters This section introduces some of the concepts which need to be Offered traffic (G) considered when comparing the performance of different multiple access techniques. These will then be used in the following sections Figure 13.2 Idealised curve of S/G or medium utilisation which describe the methods in more detail. The key performance measures are: 1. The elapsed time between a packet of information being ready The length of the medium in bits is give by Equation 13.5 and it is a measure of the number of bits which are in transit between for transmission at a transmitting node and when it is success- fully received at the receiving node. This is referred to as the communicating nodes at any time. delay and is usually denoted by D. The total rate of information flow, the carried load, between the (13.5) nodes on the network. This is referred to as the throughput, S. As will be seen later, throughput is also a measure of utilisation. 3. The fraction of the total capacity of the transmission medium A very important dimensionless parameter used in the definition which is used to carry information between nodes. This is of the performance of multiple access systems is denoted by a as in referred to as the utilisation, U. Equation 13.6. Several parameters need to be considered when defining the Length of medium between nodes (in bits) (13.6) performance of a network. These are: Length of data frame (in bits) 1. The number of nodes (N) on the netwo