Muhammad Faisal Hayat

Burst switched optical networks supporting legacy and future service types

Focusing on the principles and the paradigm of OBS an overview addressing expectable performance and application issues is presented. Proposals on OBS were published over a decade and the presented techniques spread into many directions. The paper comprises discussions of several challenges that OBS meets, in order to compile the big picture. The OBS principle is presented unrestricted to individual proposals and trends. Merits are openly discussed, considering basic teletraffic theory and common traffic characterisation. A more generic OBS paradigm than usual is impartially discussed and found capable to overcome shortcomings of recent proposals. In conclusion, an OBS that offers different connection types may support most client demands within a sole optical network layer.

Engset loss models for an OBS/OPS node with shared wavelength conversion

Asynchronous bufferless OBS/OPS core nodes behave as loss systems and therefore, widely analyzed under traditional Erlang and Engset loss models. Additionally, it has been shown that the Engset traffic assumptions are more realistic with a correction in the offered load. This correction is proposed due to the fact that in case of loss, the source cannot offer a new packet while the input wavelength is busy in transmitting a lost packet. This effect is more evident in OBS switches which deals with large burst lengths compared with packets. In this study, Engset traffic model with and without correction in the offered load is used to analyze a switch using the shared wavelength conversion. We show that the degree of wavelength conversion also effect the blocking of the switch significantly and in the switches with small and medium port counts the effect of blocked inputs due to packets/bursts should not be ignored. Continuous time Markov chains have been used for analysis and expressions have been derived to evaluate the time, traffic and call blocking.

A simulative comparison of dynamic multi-path routing algorithms for OBS networks

This paper reports extensive simulations of the dynamic routing techniques for optical burst switching (OBS) networks. It gives a summary of the already proposed algorithms and describes more broadly some of them. It introduces also a new one called the Weighted Link Congestion and Frequency (WLCF) algorithm. Our comparative simulations are performed using an in-house developed environment in which all the OBS mechanisms are implemented in detail. Considering various network topologies and traffic scenarios, we show that basically WLCF performs better than other routing strategies in terms of mean burst blocking probability averaged over the whole network, and, thus, increases the overall network throughput.

Restricted intermediate buffering in OBS networks with combined nodes

This paper concerns optical burst switching (OBS) networks with combined nodes which function as both edge and core nodes. In such architecture, we propose intermediate electronic buffering of transit burst traffic. As our simulations show, this buffering, when applied in a restricted manner, decreases the overall burst blocking probability in the network and provides better fairness among short and long routes. We compare the performance of two versions of the proposed technique considering different network topologies. In the simulations, all the important mechanisms of OBS such as burst assembly, wavelength conversion, scheduling and routing, are implemented in detail.

Performance modelling of MAC protocol for GPRS

This paper presents the analysis and performance evaluation of the Radio Link Control/Media Access Control (RLC/MAC) protocol in General Packet Radio Service (GPRS) networks. The aim of our study is to model the Media Access Control protocol that provides coordinated access to the shared channels resources of GPRS radio interface. After describing a simple functional model for a single node in GPRS system, a detailed analysis is presented to model the behavior of a single GPRS cell. A Markov chain is developed to describe the single cell system and the expressions for the uplink throughput and mean transfer delay are derived using this Markov chain.

A normalized residual energy clustering for wireless sensor networks

This paper contributes to recent improvements in energy-efficient clustering algorithms for static and homogeneous wireless sensor networks. We propose a modified algorithm, called NREC, which considers information on the locally normalized residual energy of sensor nodes. This information is weighted with the probabilistic threshold used in standard algorithms for periodic election of cluster heads. The performance of our solution is compared with that of previously proposed variants by detailed simulation. Reduction of energy consumed per bit of useful data is shown.

Towards dynamic wavelength grouping for QoS in optical burst-switched networks

This paper concerns quality of service in optical burst switching realized by dynamic wavelength grouping. It reports detailed simulations of this method in presence of combined edge-core nodes using special scheduling algorithm. Specifically, we are interested in optimal partitionings of wavelengths among traffic classes of high and low priority. We observe certain tradeoffs between minimizing the overall blocking probabilities and providing service differentiation. We find that the scheme may be ineffective in varying traffic conditions unless traffic prediction is used to adapt partitioning of wavelengths on demand.

Performance modelling of a priority scheduling system with exhaustive service, finite capacity and switchover

In modern communication systems edge nodes serve the incoming traffic flows from a number of networks and act as traffic aggregators in technologies like optical burst switching and carrier Ethernet. To provide fairness to incoming flows scheduling systems are used as an integral part of these nodes. A scheduling system can be modelled as a multi-queue single-server system. Modelling is categorized on the basis of different factors in consideration and type of service. In this paper, an exhaustive service priority scheduling system is analyzed using state space modelling technique. The model assumes a system with finite capacity and switch-over time is taken into account. The interest of this model is fueled by applications in edge nodes. The performance measures such as mean flow time and blocking probability have been evaluated. To illustrate the accuracy of analytical results, all results have been verified by simulations.

Performance modelling of energy efficient wireless nodes

In this paper, an extended Markov chain method is used to analyze the performance of energy efficient wireless nodes. A queueing system with multiple vacations and g-limited service is used to model a wireless node. For the analysis, Markov chains for the system state, flow process, active period and vacation period are introduced, from which performance measures and the power saving factor of a node can be calculated. In order to prove accuracy of the proposed model, all results are verified by simulations.

Performance model for an OBS node utilizing a shared-wavelength-converter-pool per node for contention resolution

To avoid optical buffering, wavelength conversion has been widely investigated to handle potential burst collisions in the optical domain. The objective of this study is to analyze an optical burst switched node that uses wavelength conversion for contention resolution. In an OBS node, wavelength converters may be available to each channel, may be shared per link, or shared per node, according to the node architecture. Due to the cost of wavelength converters, sharing is commonly preferred. With shared converters all except one of the contending burst switching demands are assigned to available converters from the pool to change their outgoing wavelength, solving contention. We propose a performance model for symmetric traffic case for a node employing shared converter pool per node (SPN), which is considered to be most cost saving architecture. The model is validated with simulations to prove that it effectively provides a tool for dimensioning of an OBS switch.