The main objective of this dissertation is to investigate the performance characteristics of a broadcast star network with collision avoidance switch and a multichannel local lightwave network with grouping property.
So far, quite a few attempts have been made to model the broadcast star network with collision avoidance switch. Most of those models assumed constant message length and random selection policy at the central hub. If the central hub can choose the oldest message among the messages which are transmitted at the same slot, then the service discipline becomes first-come first-served (FCFS). Although the FCFS discipline has many desirable features such as fairness and lowest variance of message delay, this discipline is not easy to implement since the central hub does not know the arrival times of messages. If the central hub chooses one message randomly among the messages which are transmitted at the same slot, then the service discipline becomes random-order of service (ROS). While the ROS discipline is easy to implement, the message delay is not bounded and the variance of message delay becomes large in this discipline.
For this reason, we first proposed a service discipline which is relatively easy to implement and which has the variance characteristics of message delay almost the same as the FCFS case (ideal case). The proposed service discipline is a combination of FCFS and ROS disciplines and it uses reservation and priority fields in the message header. Using the proposed service discipline, we presented models for a broadcast star network with collision avoidance switch separately in two cases: a broadcast star network with small propagation delay and a broadcast star network with large propagation delay. We assumed that the network consists of an infinite population of stations which collectively generate new messages according to a Poisson distribution and that the size of each message is distributed according to a general distribution. We also assumed that the network is symmetric and that the channel operation is slotted so that each ready station can start transmission only at the beginning of a slot. Then the ready stations were modeled as a distributed queue, and the entire system was modeled as an M/G/1 queueing system with multiple server vacations. Here the vacation lengths are equal to the slot length. Then we presented performance analyses of the models to obtain distributions of the message delay for the proposed service discipline, and compared the results with that for other service disciplines. We found that the broadcast star network with collision avoidance switch has the potential of combining the benefits of random access.(low delay with light traffic, simple, distributed, and therefore robust) and controlled access with excellent network utilization. We also found that the proposed service discipline is suitable for the broadcast star network with collision avoidance switch in that it is easy to implement and it exhibits relatively low variance of the message delay.
In addition, we presented a model for the broadcast star network with collision avoidance switch and with multiple priority classes of messages. We assumed that the network consists of an infinite population of stations which collectively generate new messages according to a Poisson distribution and that the size of each message is distributed according to a general distribution. Here, each message belongs to one out of n classes. We also assumed that the network is symmetric and that the channel operation is slotted so that each ready station can start transmission only at the beginning of a slot. Then the ready stations were modeled as a distributed queue, and the entire system was modeled as a priority M/G/1 queueing system with multiple server vacations. Here the vacation lengths are equal to the slot length. Then we proposed a service discipline which is used to select one message among the same class messages which are transmitted at the same slot. Also, we analyzed the model to obtain distributions of the message delay for the proposed service discipline, and compared the results with that for the FCFS discipline. From numerical results, it was shown that the variance of message delay for the proposed service discipline is almost the same as that for the FCFS discipline (idea case) for any distribution of message length and also for any value of normalized propagation delay.
Finally, we proposed a multichannel local lightwave network with a grouping property which exhibits better channel efficiency as the traffic is more likely within groups and also avoids both wavelength agility and pretransmission coordination problems. Two network topologies were considered. One was a multichannel lightwave network with full connection within groups, and the other was a multichannel lightwave network with minimal connection within groups. For performance analysis the network capacities and the mean queueing delays for the two network topologies were obtained. We observed that the network with full connection within groups outperforms the network with minimal connection within groups in respect of delay-throughput characteristics. However, in a situation where the cost of the receiver may cause a major restriction on network construction, the network topology with minimal connection within groups may be preferred.
