he assumption is also made that no arrivals (a) point-to-point; (b) star; (c) ring or loop; (d) bus; (e) tree; are lost, i.e. leave or are rejected from the queue because of long (f) mesh; (g) fully interconnected waiting times. Arrivals are also assumed to be served on a first come first served basis, unlike, for example, a hospital queue where the most urgent cases are served first. 13/4 Multiple access techniques If a is the arrival rate in number per unit interval of time and u is 6. The offered traffic (G), i.e. the total rate of information the service rate in number per unit time, then the traffic intensity presented to a network for transmission. Whereas the average (p is given by Equation 13.1. arrival rate is a measure of the data traffic, the offered traffic includes items such as control data (e.g. acknowledgements), p = ALL (13.1) packets destroyed due to collision, retransmissions, etc. 7. The length (1) of the communication path. The average number (N) in the queue is given by Equation 13.2. Generally the throughput (S) and offered traffic (G) are nor- malised, i.e. expressed as a fraction of the capacity of the trans- N = 1 p p (13.2) mission medium. For example, if the successful transmission between nodes totals 10Mbit/s, and the capacity of the medium is 100Mbit/s, then the throughput S is stated to be 10/100 or 0.1. As the traffic intensity grows, i.e. the arrival rate approaches the Therefore S is also a measure of the utilisation of the medium, as service rate, the value of the traffic intensity factor p approaches stated earlier. For stability the steady state arrival rate at a network unity, and the number in the queue rapidly increases towards in- must not exceed the rate at which this data can be transmitted over finity. The queue is now said to be unstable. the network, otherwise the queue would grow without control. The total waiting time (T_) in the queue for any arrival is equal to Under ideal conditions the relationship between the throughput the time before service begins and the a