Tarek S. El-Bawab

Optical packet switching in core networks: between vision and reality

The research on optical packet switching (OPS) has witnessed considerable progress in the 1990s. We examine the future potential of OPS in the core network by discussing this switching approach and the current status of a number of its enabling technologies. Many of these technologies are still in the stage of research and experimentation. We see that optical packet switching may be deployed in the long-term future subject to satisfaction of three main conditions/developments. First, additional technological developments have to take place to overcome remaining implementation challenges while making OPS cost-effective to deploy. Second, a rational migration scenario of the network toward gradual deployment of packet-based optical switching approaches should exist. Finally, carriers have to become more interested in packet-based optical switching solutions.

A preemptive scheduling technique for OBS networks with service differentiation

Existing burst scheduling techniques could be improved in terms of bandwidth utilization and QoS support. In this paper, we introduced a new partially preemptive scheduling technique with QoS support. The technique is capable of handling data bursts in parts and may use preemption due to the priorities of data bursts in a multi-service OBS network environment. Simulation studies suggest that more than 50% reduction in dropping probability and approximately 40% improvement in channel utilization is reachable at 0.8 load. The studies also reveal that the new scheduling technique has the ability to predict and control service performance differentiation among defined service classes.

Group-scheduling for optical burst switched (OBS) networks

To date, all of the proposals for burst-scheduling techniques have considered scheduling individual bursts. We introduce a new scheme called OBS group scheduling. In this approach, a burst is represented by an interval of time. The process of scheduling a number of bursts, thus, turns to be a process of fitting a set of the corresponding time intervals on a channel time line that represents a channel-time resource. By doing so, we can formulate the scheduling process as a combinatorial optimization problem. Then, graph theory is applied to schedule as many non-overlapping intervals as possible onto the channel time line. The underlying concept of the group scheduling is that of briefly delaying the scheduling of a burst so that a much better decision can be made about a number of bursts all-together. This scheme is shown, through simulations, to improve performance in terms of burst loss probability and channel utilization over existing schemes.

Medium access control protocols for robust wavelength division multiplexed local area networks

The wavelength-division-multiplexing (WDM) network architectures, in general, are based on transmitters and/or receivers that can be precisely, and speedily, tuned to predetermined, fixed wavelengths. These requirements are not easy to meet in practice. Robust WDM networks do not rely on fixed wavelength channels. Any node that requires a connection with another node dynamically selects a currently unused wavelength in the spectrum. Two medium access control protocols for robust WDM networks are presented and evaluated.

Operation and maintenance issues in optical burst-switched networks

We discuss a number of operation and maintenance (OAM) issues in optical burst-switched (OBS) networks and propose an OAM framework in this respect. Four OBS functions are identified as bases for the proposed framework. These are the burst termination function, the burst transmission function, the switching function, and the routing and switching control function. The study focuses on the unique aspects of OBS networks and how they can be addressed from an OAM point of view. We propose an OAM architecture and investigate the functional, network, and node aspects of it. Novel OAM-capable structures for core and edge OBS nodes are introduced for the first time.

Robust wavelength division multiplexed local area networks

Abstract The wavelength division multiplexing (WDM) network architectures, in general, are based on transmitters and/or receivers that can be precisely and speedily tuned to predetermined, fixed wavelengths. These requirements are not easy to meet in practice. Robust WDM, the subject of this paper, has been introduced as a technique to implement WDM in the local area. The strength of this novel approach is that it does not rely on wavelength-sensitive devices that are required to perform with extreme stability. This paper describes the basis of this approach and presents two types of medium access control (MAC) protocols that are suitable for Robust WDM local area networks (LANs). The performance of networks based on these protocols is discussed in detail. It is shown that the new approach has considerable promise for WDM networks in the local area.

Comparative Account of Bandwidth Efficiency in Optical Burst Switching and Optical Circuit Switching Networks

The performance of Optical Burst Switched (OBS) networks is compared to that of Optical Circuit Switched (OCS) networks in terms of bandwidth efficiency. Two traffic flow models are employed to investigate the effects of traffic grooming, packetization, buffering and burst assembly on bandwidth efficiency and utilization. Traffic is represented by fluid-flow continuous bit streams in the first model and by packet-based discrete flows in the second model. It is shown that the parameters of traffic characteristics and burst assembly have significant impact on the relative bandwidth savings of OBS. The bandwidth efficiency of OBS compared to OCS should not be taken for granted and has to be examined carefully on a case by case basis.

Procedures and functions for operation and maintenance in optical burst-switching networks

Very little work has been carried out so far in the area of operation and maintenance (OAM) schemes for optical bursts switched (OBS) networks. We continue to discuss OAM issues for OBS networks. The spectral and temporal de-coupling of data and control in an OBS network calls for special OAM attention. In this paper, OAM procedures, functions and sessions based on specific network and node architectures are discussed. An OAM information model, encompassing OAM-specific packet/burst formats is also presented.

Modeling and performance analysis of a symmetric fast-circuit switched robust-WDM LAN with the AR/LTP protocol

Robust wavelength division multiplexing (WDM) is a technique to implement WDM local area networks (LANs) in the presence of laser wavelength drifts. A medium access control (MAC) protocol is used in conjunction with a wavelength-tracking receiver to tolerate the variations of transmission wavelengths. Among the proposed medium access schemes, the aperiodic reservation (AR) scheme with token-passing based control channel gives the best performance. An AR protocol with a lenient token passing policy (AR/LTP) is thus presented. An analytical model is developed to design Robust-WDM AR/LTP LANs and predict their performance characteristics. The model can be used to evaluate the variation of waiting time and throughput for load and network parameters such as the arrival rate, number of nodes, number of channels and timing parameters. It also addresses the issues related to traffic loss, channel-blocking, token rotation time, network span, and the effect of device parameters.

A European multiwavelength optical network

A number of research issues are considered in the study of an European multiwavelength optical network. The main part of the study is the design of an all-optical network to overlay the European national networks and link major centers therein. We survey most of the issues considered in this respect within the frame of two projects funded by the European Commission. Another part of the study focuses on the underlying European national networks and their possible development to interface with the proposed overlay. The main aim of this paper is to put together these two parts and oversee the prospect of an European ultra-high capacity multiwavelength optical infrastructure.