Scope and purposeQueueing theory is an important subject in computers and operations research. Buffers/queues are used, e.g. in telecommunication networks, to store information that cannot be transmitted instantaneously. The study of the buffer behavior is important since network performance is directly related to it. Queues with a priority scheduling discipline are an important subject in queueing theory. As a result, these type of queues are thoroughly studied in the past, especially in continuous time. In discrete-time queueing models on the other hand, this type of queues is not as widely studied. Discrete-time queueing models are suitable for the performance evaluation of Asynchronous Transfer Mode (ATM) switches. In ATM, different types of traffic need different Quality of Service (QoS) standards. The delay characteristics of delay-sensitive traffic (e.g., voice) are more stringent than those of delay-insensitive traffic (e.g., data). We can thus give priority to delay-sensitive traffic over delay-insensitive traffic, thus trying to reduce the * Corresponding author 1 delay of the delay-sensitive traffic. This paper studies the impact of a priority scheduling on the buffer characteristics. AbstractIn this paper, we consider a discrete-time queueing system with head-of-line (HOL) priority. First, we will give some general results on a GI-1-1 queue with priority scheduling. In particular, we will derive expressions for the Probability Generating Function of the system contents and the cell delay. Some performance measures (such as mean, variance and approximate tail distributions) of these quantities will be derived, and used to illustrate the impact and significance of priority scheduling in an ATM output queueing switch.

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In this paper, we investigate a simplified head-of-the-line with priority jumps (HOL-PJ) scheduling discipline. Therefore, we consider a discrete-time single-server queueing system with two priority queues of infinite capacity and with a newly introduced HOL-PJ priority scheme. We derive expressions for the probability generating function of the system contents and the packet delay. Some performance measures (such as mean and variance) of these quantities are derived and are used to illustrate the impact and significance of the HOL-PJ priority scheduling discipline in an output queueing switch. We compare this dynamic priority scheduling discipline with a FIFO scheduling and a static priority scheduling (HOL) and we investigate the influence of the different parameters of the simplified HOL-PJ scheduling discipline.

Abstract:We develop power series approximations for a discrete-time queueing system with two parallel queues and one processor. If both queues are non-empty, a customer of queue 1 is served with probability β and a customer of queue 2 is served with probability 1 − β. If one of the queues is empty, a customer of the other queue is served with probability 1. We first describe the generating function U (z 1 , z 2 ) of the stationary queue lengths in terms of a functional equation, and show how to solve this using the theory of boundary value problems. Then, we propose to use the same functional equation to obtain a power series for U (z 1 , z 2 ) in β. The first coefficient of this power series corresponds to the priority case β = 0, which allows for an explicit solution. All higher coefficients are expressed in terms of the priority case. Accurate approximations for the mean stationary queue lengths are obtained from combining truncated power series and Padé approximation.

In the past, many researchers have analysed queueing models with batch service. In such models, the server typically postpones service until the number of present customers reaches a service threshold, whereupon service is initiated of a batch consisting of several customers. In addition, correlation in the customer arrival process has been studied for many different queueing models. However, correlated arrivals in batch-service models has attracted only modest attention. In this paper, we analyse a discrete-time D-BMAP/G l,c /1 queue, whereby the service time of a batch is dependent on the number of customers within it. In addition, a timing mechanism is included, to avoid that customers suffer excessive waiting times because their service is postponed until the amount of customers reaches the service threshold. We deduce various useful performance measures related to the buffer content and we investigate the impact of the traffic parameters on the system performance through some numerical examples. We show that correlation merely has a small impact on the service threshold that minimizes the mean system content, and consequently, that the existing results of the corresponding independent system can be applied to determine a near-optimal service threshold policy, which is an important finding for practitioners. On the other hand, we demonstrate that for other purposes, such as performance evaluation and buffer management, correlation in the arrival process cannot be ignored, a conclusion that runs along the same lines as in queueing models without batch service.