Message Delays with Prioritized HOLP and Round-Robin Packet Servicing

Three disciplines for prioritized transmission of messages in packet switching systems are considered. Messages from a finite number of classes having their lengths drawn independently from general service time distributions are assumed to arrive to the system according to independent Poisson processes. After entering the switch, the messages are divided into packets, overhead is added, and then the packets join a queue to be served according to one of the following disciplines: head-of-the-line (HOL), HOL with message preemption, and prioritized round robin (RR). Preemption of packet transmission is not allowed in any of the disciplines, and the service disciplines of different classes need not be the same. One result of the work presented here is a model to assess delays in the case of the prioritized RR; this work appears to be the first in which messages are not of fixed length and all quanta from a given message are served at the same priority. Numerical results which illustrate effects of choice of packet lengths and service disciplines upon delay of messages from the different classes are presented.