The authors present an algorithm to provide local fairness for ring and bus networks with spatial bandwidth reuse. Spatial bandwidth reuse can significantly increase the effective throughput delivered by the network. The proposed algorithm can be applied to any dual ring or bus architecture such as MetaRing. In the dual bus configuration, when transporting ATM cells, the local fairness algorithm can be implemented using two generic flow control (GFC) bits in the ATM cell header. In the performance it is shown that this local fairness algorithm can exploit the throughput advantage offered by spatial bandwidth reuse better than a global fairness algorithm. This is accomplished because it ensures fair use of network resources among nodes that are competing for the same subset of links, while permitting free access to noncongested parts of the network. The performance advantage of the local fairness scheme is demonstrated by simulating the system under various traffic scenarios and comparing the results to that of the MetaRing SAT-based global fairness algorithm. It is also shown that under certain traffic patterns, the performance of this algorithm achieves the optimal throughput result predicted by the known Max-Min fairness definition.>

The output queues of an M*N packet switch are studied using a Markov-modulated flow model. The switching element is a central server which sequentially routes packets from the inputs to the outputs. The focus is on systems in which the server speed is such that the bulk of the queuing takes place in the output queues. The conventional point process approach neglects the impact of switching and transmission time. An attempt is made to account for these finite system speeds by using a Markov-modulated continuous flow to approximate the arrival process to an output queue. This model captures the dependency between arrivals at different outputs and reflects the fact that packet arrivals and departures are not instantaneous. The output queue content distribution is obtained, for both infinite and finite buffer systems, from the spectral expansion of the solution of a system of differential equations. Numerical examples and comparisons with the results of an M/M/1 approximation are presented.>

MetaRing is a Gigabit/second local area network architecture based on a dual(bi-directional) optical fiber ring with spatial reuse mechanism. The paper uses simulation to study the performance of MetaRing in the buffer insertion mode with variable length packets. It shows through various delay-throughput curves the major performance aspects of the MetaRing architecture. The results indicate that the combination of a full-duplex ring spatial reuse, and a simple and reliable fairness mechanism of the MetaRing architecture exhibit an excellent delay-throughput performance.>

A general model is presented to study the performance of a family of space-domain packet switches, implementing both input and output queuing and varying degrees of speedup. Based on this model, the impact of the speedup factor on the switch performance is analyzed. In particular, the maximum switch throughput, and the average system delay for any given degree of speedup are obtained. The results demonstrate that the switch can achieve 99% throughput with a modest speedup factor of four. Packet blocking probability for systems with finite buffers can also be derived from this model, and the impact of buffer allocation on blocking probability is investigated. Given a fixed buffer budget, this analysis obtains an optimal placement of buffers among input and output ports to minimize the blocking probability. The model is also extended to cover a nonhomogeneous system, where traffic intensity at each input varies and destination distribution is not uniform. Using this model, the effect of traffic imbalance on the maximum switch throughput is studied. It is seen that input imbalance has a more adverse effect on throughput than output imbalance.>

An N*N nonblocking packet switch with input queues and two priority classes that can be used to support traffic with different requirements is described. The switch operation is slotted and, at each time slot, fixed-size packets arrive at the inputs with distinct Bernoulli distributions for both the high- and low-priority classes. Two policies are discussed. In the first policy, packets of both priority classes are queued when waiting for service. In the second policy, only low-priority packets are queued, and high-priority packets not delivered at the first attempt are dropped from the system. Under both policies, high-priority packets prevail over low-priority packets at the inputs as well as the outputs. An approximate analysis that is based on independence assumptions and uses an equivalent queueing system to estimate the service capability seen be each input is presented. Using this approach, an expression for the input queue length distribution is obtained. The maximum system throughput is derived and shown to exceed that of a single priority switch. Numerical results are compared to simulations and are found to agree.>

A study is made of the output queues of an M*N packet switch using a Markov-modulated flow model. The switching element is a central server which sequentially routes packets from the inputs to the outputs. The authors focus on systems where the server speed is such that the bulk of the queueing takes place in the output queues. For such systems, accurate sizing of the output buffers is an important design issue and requires a correct characterization of the arrival processes to the output buffers. The conventional point process approach neglects the impact of switching and transmission time. An attempt is made to account for these finite system speeds by using a Markov-modulated continuous flow to approximate the arrival process to an output queue. This model captures the dependency between arrivals at different outputs and reflects the fact that packet arrivals and departures are not instantaneous. The output queue content distribution is obtained, for both infinite and finite buffer systems, from the spectral expansion of the solution of a system of differential equations. Numerical examples and comparisons with the results of an M/M/1 approximation are presented.>

An N*N nonblocking packet switch with two priority classes which can be used to support traffics with different requirements is analyzed. Real-time traffic such as voice is assigned high priority to satisfy its strict delay requirement, while data traffic uses a lower priority and utilizes the remaining system capacity. The switch operation is slotted, and at each time slot packets arrivals at the inputs have Bernoulli distributions with different probabilities for high-priority and low-priority classes. Packets of both priority classes can be queued when waiting for service; the service discipline is FCFS (first-come first-served) within each priority class. The authors provide explicit expressions for blocking probabilities and average delays. They also study system stability and show that the maximum throughput can in fact be higher than with no priority.>