John S. Vardakas

Performance Analysis of OCDMA PONs Supporting Multi-Rate Bursty Traffic

Optical Code Division Multiple Access (OCDMA) provides increased security communications with large dedicated bandwidth to end users and simplified network control. We analyse the call-level performance of an OCDMA Passive Optical Network (PON) configuration, which accommodates multiple service-classes with finite traffic source population. The considered user activity is in accordance with the bursty nature of traffic, so that calls may alternate between active (steady transmission of a burst) and passive states (no transmission at all). Parameters related to multiple access interference, additive noise, user activity and number of traffic sources are incorporated to our analysis, which is based on a two-dimensional Markov chain. An approximate recursive formula is derived for efficient calculation of call blocking probability. Furthermore, we determine the burst blocking probability; burst blocking occurs when a burst delays its returning from passive to active state. The accuracy of the model is completely satisfactory and is verified through simulation. Moreover, we reveal the consistency and necessity of the proposed model.

On the End-to-End Delay Analysis of the IEEE 802.11 Distributed Coordination Function

The IEEE 802.11 protocol is the dominant standard for wireless local area networks (WLANs) and has generated much interests in investigating and improving its performance. The IEEE 802.11 medium access control (MAC) is mainly based on the distributed coordination function (DCF). DCF uses a carrier sense multiple access with collision avoidance (CSMA/CA) protocol in order to resolve contention between wireless stations and to verify successful transmissions. In this paper we present an extensive investigation of the performance of the IEEE 802.11b MAC protocol, in respect of end-to-end delay. The end-to-end delay analysis of the IEEE 802.11b has not been completed, because no adequate queuing delay is provided. Our delay analysis is based on Bianchis model for the DCF, while a more comprehensive model could be used as well. We use z-transform of backoff duration to get mean value, variance and probability distribution of MAC delay. From the mean value and the variance of the MAC delay we determine the mean queuing delay in each station. Our analysis is validated by simulation results for both the Basic and RTS/CTS access mechanisms of the DCF. The accuracy of the analysis found to be quite satisfactory. We assume data rates of 1, 5.5 and 11 Mbps, in order to highlight the effect of the bit rate on delay performance for both access mechanisms.

Dual-Band Resistance Compression Networks for Improved Rectifier Performance

In this work, the concept of dual-band resistance compression networks is introduced and applied to the design of rectifier circuits with improved performance. The use of resistance compression networks (RCNs) minimizes the sensitivity of rectifier circuits to variations in the surrounding environment, such as input power level and changes in the rectifier load. The proposed dual-band RCN can be used as the matching network located between the antenna and the rectifying element of a dual-band rectifier for energy harvesting applications. A dual-band ( 915 MHz /2.45 GHz) rectifier based on RCN is designed and characterized showing improved performance in comparison with a conventional dual-band envelope detector by exhibiting improved RF-dc conversion efficiency and reduced sensitivity versus output load and input power variations.

Performance behaviour of IEEE 802.11 distributed coordination function

The authors present an extensive investigation of the performance of the IEEE 802.11 medium access control (MAC) protocol, with respect to throughput and delay. For the protocol analysis, a new model, which describes the protocols behaviour to a great extent by incorporating and extending the existing models, is proposed. The authors also present a detailed analysis of the end-to-end delay through the study of the MAC delay and the queueing delay. The authors use the Z-transform of backoff duration to obtain the mean value, the variance and the probability distribution of the MAC delay. For the queueing analysis, first the authors consider an M/G/l queue in order to provide a first look at the queueing delay. Second, the authors modify the input process of the queue so that the packet arrival process is described by an ON- OFF model, which expresses the bursty nature of traffic. In the investigations, data rates of 1, 5.5 and 11 Mbps are assumed to highlight the effect of the bit rate on network performance for both Basic and request-to-send/ clear-to-send access mechanisms. The throughput and delay analyses are validated by simulating the distributed coordination function, whereas the models are compared with the existing models based on their results. The accuracy of the analyses was found to be quite satisfactory.

Congestion probabilities in a batched Poisson multirate loss model supporting elastic and adaptive traffic

The ever increasing demand of elastic and adaptive services, where in-service calls can tolerate bandwidth compression/expansion, together with the bursty nature of traffic, necessitates a proper teletraffic loss model which can contribute to the call-level performance evaluation of modern communication networks. In this paper, we propose a multirate loss model that supports elastic and adaptive traffic, under the assumption that calls arrive in a single link according to a batched Poisson process (a more “bursty” process than the Poisson process, where calls arrive in batches). We assume a general batch size distribution and the partial batch blocking discipline, whereby one or more calls of a new batch are blocked and lost, depending on the available bandwidth of the link. The proposed model does not have a product form solution, and therefore we propose approximate but recursive formulas for the efficient calculation of time and call congestion probabilities, link utilization, average number of calls in the system, and average bandwidth allocated to calls. The consistency and the accuracy of the model are verified through simulation and found to be quite satisfactory.

An Analytical Approach for Dynamic Wavelength Allocation in WDM–TDMA PONs Servicing ON–OFF Traffic

Optical access systems are now considered a feasible alternative to the predominant broadband access technologies, while, at the same time, passive optical networks (PONs) are viewed as an attractive and promising type of fiber access system. In this paper we present and analyze three basic dynamic wavelength allocation scenarios for a hybrid wavelength division multiplexing-time division multiple access (WDM-TDMA) PON. We propose new teletraffic loss models for calculating call-level performance measures, like connection failure probabilities (due to unavailability of a wavelength) and call blocking probabilities (due to the restricted bandwidth capacity of a wavelength). The PON accommodates bursty service-classes of ON-OFF traffic. The proposed models are extracted from one-dimensional Markov chains, which describe the wavelength occupancy in the PON, and two-dimensional Markov chains, which describe the bandwidth occupancy inside a wavelength. The accuracy of the proposed models is validated through simulation and is found to be quite satisfactory. Moreover, these models are computationally efficient because they are based on recursive formulas.

Performance metrics of a multirate resource sharing teletraffic model with finite sources under the threshold and bandwidth reservation policies

The authors propose a new multirate teletraffic loss model of a single link with certain capacity that accommodates different service-classes whose calls come from finite traffic sources. Calls compete for the available link bandwidth under the combination of the threshold (TH) and the bandwidth reservation (BR) policies. The TH policy can provide different quality of service among service-classes by limiting calls of each service-class up to a certain number, which is a predefined TH, which can be different for each service-class. The BR policy reserves part of the available link bandwidth to benefit calls of high bandwidth requirements. They show that the proposed model, without the BR policy, has a product form solution (PFS) and prove recursive formulas for the efficient calculation of the call-level performance metrics, such as time and call congestion probabilities as well as link utilisation. The combination of the TH and BR policies destroys the PFS of the model. However, they show that approximate but recursive formulas still exist for the efficient calculation of the call-level performance metrics. The accuracy of the proposed formulas is verified through simulation and found to be very satisfactory.

QoS guarantee in a batched poisson multirate loss model supporting elastic and adaptive traffic

In this paper, we consider a single link that supports both elastic and adaptive traffic of Batch Poisson arriving calls, under the Bandwidth Reservation (BR) policy, whereby we can achieve specific QoS per service-class. Arriving batches have a generally distributed batch size, and can be serviced either as a whole or in part (partial batch blocking discipline), depending on the available link bandwidth. Blocked calls are lost. Accepted calls of a batch can compress or expand their bandwidth; elastic calls expand or compress their service time accordingly, while adaptive calls do not alter their service time. This system does not have a Product Form Solution. For the efficient calculation of time and call congestion probabilities as well as link utilization, we derive approximate but recursive formulas. The accuracy of the model is completely satisfactory and is verified together with the models consistency, through simulation. Comparison of the new model with existing models reveals its necessity.

Congestion probabilities of elastic and adaptive calls in Erlang-Engset multirate loss models under the threshold and bandwidth reservation policies

In this paper, we consider a single link of fixed capacity that accommodates calls of different service-classes with different bandwidth-per-call requirements. The link behaves as a multirate loss system. Calls of each service-class arrive in the link according to a Poisson (random) or a quasi-random process and have an exponentially distributed service time. Poisson or quasi-random arriving calls are generated by an infinite or finite number of traffic sources, respectively. Service-classes are also distinguished according to the behavior of in-service calls, in elastic and adaptive service-classes. Elastic calls can compress their bandwidth by simultaneously increasing their service time. Adaptive calls tolerate bandwidth compression without affecting their service time. All calls compete for the available link bandwidth under the combination of the Threshold (TH) and the Bandwidth Reservation (BR) policies. The TH policy can provide different QoS among service-classes by limiting the number of calls of a service-class up to a predefined threshold, which can be different for each service-class. The BR policy reserves part of the available link bandwidth to benefit calls of high bandwidth requirements. The proposed models, for random or quasi-random traffic, do not have a product form solution for the determination of the steady state probabilities. However, we approximate both models by reversible Markov chains, and prove recursive formulas for the efficient calculation of the call-level performance metrics, such as time and call congestion probabilities as well as link utilization. The accuracy of the proposed formulas is verified through simulation and found to be quite satisfactory.

Performance evaluation of IEEE 802.11e based on ON-OFF traffic model

We investigate the performance of the IEEE 802.11e while emphasizing on the end-to-end delay performance. In our MAC delay analysis, we are based on elementary conditional probabilities, avoiding the complex Markov Chains method. For a thoroughly study of the MAC delay, we take the Z-transform of the backoff duration in order to provide higher moments of the MAC delay distribution. The first moment corresponds to the mean MAC delay, while the second moment to the Standard Deviation of the MAC delay, which depicts the jitter. We also estimate the Probability Mass Function (PMF) of the MAC delay through the Lattice Poisson Algorithm. For the queuing delay, we consider a queue for each Access Category (AC) with one common server and an input process which is described by an ON-OFF model depicting the bursty nature of traffic. The service time follows the MAC delay distribution. Analyzing this queue, we provide results both for saturated and non-saturated channel condition. The end-to-end delay is estimated by the sum of queuing and MAC delay. The analytical results are validated through simulation.