In this paper, we present an exact analysis for the performance of wireless LANs which support real-time and data communication using a carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In the system, a user with a packet ready to transmit initially sends some pulse signals with random intervals within a collision avoidance period before transmitting the packet to verify a clear channel. The system consists of a finite number of users to share a common channel. Each user can be a source of both voice and data traffic. The time axis is slotted, and a time frame has an arbitrary large number of slots dependent on the chosen durations of the collision avoidance period and packet transmission period. A discrete-time Markov process is used to model the system operation. Numerical results are shown in terms of channel utilization and average packet delay for various packet generation rates. They indicate that the network performance can be improved by adequate choice of ratios between collision avoidance periods and transmission periods, and pulse transmission probability.

This paper presents the output and delay process analysis of integrated voice/data slotted code division multiple access (CDMA) network systems with random access protocol for packet radio communications. The system model consists of a finite number of users, and each user can be a source of both voice traffic and data traffic. The allocation of codes to voice calls is given priority over that to data packets, while an admission control, which restricts the maximum number of codes available to voice sources, is considered for voice traffic so as not to monopolize the resource. Such codes allocated exclusively to voice calls are called voice codes. In addition, the system monitoring can distinguish between silent and talkspurt periods of voice sources, so that users with data packets can use the voice codes for transmission if the voice sources are silent. A discrete-time Markov process is used to model the system operation, and an exact analysis is presented to derive the moment generating functions of the probability distributions for packet departures of both voice and data traffic and for the data packet delay. For some cases with different numbers of voice codes, numerical results display the correlation coefficient of the voice and data packet departures and the coefficient of variation of the data packet delay as well as average performance measures, such as the throughput, the average delay of data packets, and the average blocking probability of voice calls.

There is a growing interest in studies on high-speed unidirectional fiber-optic bus networks to be used in metropolitan area networks (MANs). It is well known, however, that the original IEEE 802.6 MAN standard may exhibit an unfairness property depending on the position of stations. To cope with this problem, the p/sub i/-persistent protocol has been proposed. In fiber-optic bus networks various kinds of traffic are supposed to be carried, so that detailed analysis of the delay process is highly desired. However, the interdependence between station queues makes exact analysis intractable. We consider the p/sub i/-persistent protocol used in unidirectional fiber-optic bus networks and present a novel approximation method to evaluate the packet delay. First we model each station as a Geo/sup [X]//SBP/1 queueing system with p/sub i/-persistence and carry out an exact analysis. To take into account the correlation of occupied slots floating from upstream, we use the switched Bernoulli process (SBP) with two states for the service process. Then a moment matching procedure is developed to approximate the output process of occupied slots to the downstream neighbor station. The analysis exhibits good accuracy in the numerical examples.>

This paper deals with the problem of scheduling a server in a polling system with multiple queues and complete information. We represent the polling policy by a neural network; namely, given the number of waiting customers in each queue, the server determines next queue he should visit according to the output of the neural network. By using the simulated annealing method, we improve the neural polling policy in such a way that the mean delay of customers is minimized. Numerical results show that the present approach is especially valid for asymmetric polling systems whose analytical optimization is considered intractable.

An exact analysis is presented of an asynchronous (unslotted) multipacket CSMA/CD-DFT (carrier-sense multiple-access/collision detection with delayed first transmission) model and used to derive (1) the Laplace-Stieltjes transform of the probability distribution function (PDF) of the packet interdeparture time, (2) the LST of the PDF of the message interdeparture time, (3) the moment generating function (MGF) of the message response time, and (4) the MGF of the message response time conditioned on the number of packets necessary for transmission of a message. Higher moments as well as averages of these performance measures are important for performance evaluation of interconnected networks or integrated networks of voice and data. As the performance model allows each message to consist of a geometrically distributed number of constant-length packets, the result is also useful in examining the performance of error-prone CSMA/CD systems as well as the impact of random message sizes on the system performance. Numerical examples include comparisons between the DFT model and the IFT (immediate-first-transmission) model.>

An unslotted model of the nonpersistent CSMA/CD protocol is considered, and the effect of different packet size distribution functions on the system performance is investigated. Under the assumption that packet sizes obey a general distribution function, an exact analysis of the packet output process on the CSMA/CD channel and the packet delay process at each homogeneous station is presented. Statistics analyzed are the following: (1) the Laplace-Stieltjes transform (LST) of the probability distribution function (PDF) of the packet interdeparture time, (2) the autocorrelation coefficient of the packet interdeparture time, (3) the LST of the PDF of the packet delay, and (4) the LST of the PDF of the waiting time. In addition, explicit expressions for the LSTs, averages and variances of the interdeparture time, packet delay, and waiting time distribution functions are given under the heavy-traffic assumption. In numerical results, typical packet size distribution functions are applied to the analytical result, and their effects on the autocorrelation coefficient of the interdeparture time as well as the averages and coefficients of variation of the interdeparture time, packet delay, and waiting time are examined.>

A single CSMA/CD (carrier sense multiple access with collision detection) local area network which is connected to other networks by a gateway with finite buffer capacity is described. Its performance is analyzed by using an embedded Markov chain. For the service discipline of packets queuing at the gateway, three cases are considered: G-limited service discipline, E-limited service discipline, and G-decrementing service discipline. The state transition of the system is analyzed, and the Laplace-Stieltjes transforms of the probability distribution functions of idle and busy periods are derived. Equations for average performance measures are formulated. Numerical examples are used to examine the effect of external traffic on the packet delay and throughput at terminals as well as at the gateway for each service discipline. The results show that as a service discipline at the gateway, the limited service disciplines are preferable to the decrementing service discipline in that they more fairly allocate the channel bandwidth to terminals and the gateway. The numerical results also show that the performance of the gateway is substantially improved by using a higher retransmission rate at the gateway.>