Resequencing control and analysis in computer networks

This dissertation is concerned with the design and analysis of efficient scheduling policies to minimize resequencing problems occurring in computer communication networks, distributed systems, and manufacturing systems. In packet switched networks, messages are often transmitted from source nodes to designation nodes over paths called virtual circuits. For efficiency and reliability reasons, logical channels connecting adjacent nodes of a virtual circuit may consist of multiple physical links. Due to different link speeds and variable packet size, packets may arrive at the destination node in an order different from that in which they were originally generated at the source node. Given that First-In-First-Out delivery is required, out of sequence packets must wait at the destination node to be placed back into proper sequence. Consequently, out of sequence packets experience delay called resequencing delay, in addition to queueing delay. This dissertation examines the impact of threshold type policies on the resequencing delay. Various methods for analyzing resequencing problems are developed and exact expressions for the resequencing delay distributions are obtained. These techniques are applicable in many other contexts where the resequencing problem arises. The analytical results reveal that the resequencing delay is affected by the way customers are dispatched to the servers. A general class of dispatching policies called Fixed Position Policies is presented. This dissertation investigates the problem of the judicious selection of the system parameters so as to achieve certain performance requirements. This dissertation also addresses the resequence buffer design issue. The appropriate buffer size is determined by the distribution of the number of packets in the resequence buffer. This distribution in turn depends on the scheduling policy being employed. This relation is explored and the policies which keep the system performance within specified design limits are obtained. The resequencing problem is also studied in a system of two parallel queues with multiple classes. The system controller dispatches arriving messages to the queues randomly. This dissertation examines the load balancing problem when resequencing delay is taken into account. The optimal routing probabilities that minimize the average system response time are derived.