Mustafa Mehmet-Ali

Performance analysis of a multicast switch

The performance of a multicast switch, a space division switch in which a packet at an input port is routed to a subset of the output ports, is discussed. The delay under the assumption of input port buffering is determined. The system is modeled as an independent set of M/G/1 queues. A key assumption in the analysis is that output port contention is settled by random selection among the contending input ports. In order to justify this as well as the other assumptions, a Monte-Carlo simulation of the system is devised. Numerical results from the analysis and simulation of the system are presented. >

Performance Modeling of Message Dissemination In Vehicular Ad Hoc Networks with Priority

In this paper, we present an analytical study for the performance of message dissemination in vehicular ad hoc networks (VANETs) at the steady state. First, we find the probability that a receiving node is exposed to collisions and hidden terminal activities in a multi-hop VANET using a novel approach. Based on this result, we then derive the distribution of the number of concurrent transmissions in the system at the steady-state, through a birth-death process analysis. The distribution has a simple product form solution. Numerical results are provided, along with simulation results that confirm the accuracy of the analysis. In particular, it is shown that the distribution of the number of concurrent transmissions has a bell-shape curve. Results also show that the probability that a receiving node is exposed to interference increases as a function of the transmission range, an increase which becomes faster for networks with higher node densities.

Performance comparison of two input access methods for a multicast switch

A comparison of the performance of two input access mechanisms for multicast switching is presented. The first of these-a cyclic priority input access method-is a derivative of the ring token reservation method which eliminates the unfairness of the ordinary ring token reservation. It has the advantage of being relatively simple and easy to implement. A second approach employs a neural network to resolve output port conflict. While more difficult to implement, it has a delay-throughput performance advantage over the cyclic priority approach. The primary performance measurements are the switch throughput and the packet delay. A key assumption is that all copies of the same packet must be switched in the same slot. >

The performance analysis and implementation of an input access scheme in a high-speed packet switch

The performance analysis of an input access scheme in a high-speed packet switch for broadband ISDN is presented. In this switch, each input port maintains a separate queue for each of the outputs, thus n/sup 2/ input queues in an (n/spl times/n) switch. Using synchronous operation, at most one packet per input and output will be transferred in any slot. We derive lower and upper bounds for the throughput which show close to optimal performance. The bounds are very tight and approach to unity for switch sizes on the order of a hundred under any traffic load, which is a significant result by itself. Then the mean packet delay is derived and its variance is bounded. A neural network implementation of this input access scheme is given. The energy function of the network, its optimized parameters and the connection matrix are determined. Simulation results of the neural network fall between the theoretical throughput bounds. >

Traffic analysis of a local area network with a star topology

Two forms of fast circuit switching are modeled and studied through mathematical analysis and Monte Carlo simulation. The two examples described use the switching technique in an optical-fiber-based local area network with a star topology. The technique is compatible with time-division multiplexing techniques that are used for a range of traffic classes. Further, the technique trades transmission capacity for processing power, which is the critical limitation of the system. By means of a certain independence assumption, the first form of fast circuit switching is modeled as an M/G/1 queue. The results of the analysis show excellent agreement with simulation. The general result is that there is good system throughput, despite simplicity of processing. The second form, in which rather than first-come first-served the discipline is to search for a message whose destination queue is free, is studied by means of simulation alone. The results indicate an improved performance with a modest increase in processing power. >

Analysis of Continuous Communication Availability in Vehicular Ad Hoc Networks

In this paper, we study the steady-state statistical properties of continuous communication path availability in vehicular ad hoc networks. We assume a network of highways with arbitrary topology. The mobile nodes arrive at the network through one of the traffic entry points following a Poisson process and move along a path according to a mobility model with a state-dependent mean speed. First, the joint distribution of the number of nodes in the highway segments of the network is determined. Then, the number of clusters in the node population of a network path is modeled as a Markovian birth-death process where a cluster is defined as a group of nodes that may communicate with each other directly or indirectly. Thus, the probability distributions of the number of clusters in a path and duration of continuous communication path availability time are derived as functions of mobility and traffic arrival parameters. We present mean durations of continuous availability and unavailability times and mean packet delay for end-to-end communications in a path. The given numerical results illustrate the effects of mobility and traffic arrival process on continuous communication path availability and packet delay. The results show that the mean durations of path availability and mean packet delay increase with the increasing transmission range. Clearly, while high path availability duration is desired but not high packet delay. Thus, the transmission range should not be chosen higher than needed for acceptable communication path availability, so as to maintain an acceptable mean packet delay. In practice, an adaptive transmission range may be required to achieve the right balance between the communication path availability and delay. The analytical results have also been compared with some available experimental studies and verified by two different simulation approaches.

Delay Optimization and Cross-Layer Design in Multihop Wireless Networks With Network Coding and Successive Interference Cancelation

Network coding (NC) and multipacket reception with successive interference cancellation (SIC) have been shown to improve the performance of multihop wireless networks (MWNs). However, previous work emphasized maximization of network throughput without considering quality of service (QoS) requirements, which may lead to high packet delays in the network. The objective of this work is minimization of packet delay in a TDMA-based MWN that is jointly utilizing NC and SIC techniques for a given traffic demand matrix. We assume conflict-free scheduling and allow multipath routing. We formulate a cross-layer optimization that assigns time slots to links in a way that the average packet delay is minimized. The problem formulation results in a difficult mixed integer nonlinear programming (MINLP) that the state-of-art software can only solve for very small-sized networks. For large networks, we develop a heuristic approach that iteratively determines the optimal solution. We present numerical results, which show that the average packet delay and traffic handling capacity of a network, using w/o NC+SIC, NC, SIC and NC+SIC schemes, improves from left to right. The traffic capacity of NC+SIC is double of the w/o NC+SIC. Thus, combined utilization of NC and SIC techniques results in significant performance improvement.

Delay optimization in multi-hop wireless networks with network coding

Network coding (NC) has been shown to improve the throughput of multi-hop wireless networks (MWN). Prior work on performance modeling of NC mainly addresses the maximization of throughput. However, these works fail to capture the complete picture since there may be paths in the network for which end-to-end packet delay is prohibitively high. In this paper, we address the problem of delay minimization in MWNs with NC. The objective has been assignment of wireless node capacities in a way that the average packet delay is minimized for a given network topology and the traffic demand matrix. We develop a performance analysis of the system, which models network nodes as M/G/1 queues and takes into account wireless interference. The proposed model is valid both with and without opportunistic listening for any wireless network topology. The model also incorporates network coding-aware routing that routes the flows in a manner that increases coding opportunities. We present numerical results, which show that NC reduces the average packet delay in the network and extends the stable operating region of the network. We also present simulation results, which confirm the accuracy of the analysis.

Performance modeling of message dissemination in vehicular ad hoc networks

In this paper, we present an analytical study for the performance of message dissemination in vehicular ad hoc networks (VANETs) at the steady state. First, we find the probability that a receiving node is exposed to collisions and hidden terminal activities in a multi-hop VANET using a novel approach. Based on this result, we then derive the distribution of the number of concurrent transmissions in the system at the steady-state, through a birth-death process analysis. The distribution has a simple product form solution. Numerical results are provided, along with simulation results that confirm the accuracy of the analysis. In particular, it is shown that the distribution of the number of concurrent transmissions has a bell-shape curve. Results also show that the probability that a receiving node is exposed to interference increases as a function of the transmission range, an increase which becomes faster for networks with higher node densities.

An approximate performance analysis of interconnected token-passing rings

An analysis of the performance, in terms of average message delay, is presented for a system of interconnected ring networks. The system is hierarchical, with local rings served by a high-speed backbone ring through gateway queues. In both the local and the backbone rings, the access technique employed is token passing. Service disciplines, with and without priority, have been studied. In the former, priority is given to inter-ring traffic over local traffic. The study makes use of certain results on average delay in systems where the customer initiating a busy period receives special service for the M/G/1 queue with nonpreemptive priority and for the G/G/1 queue. The analysis, which involved several approximations, was verified by simulation. >