Showing papers by "Mohsen Guizani published in 2004"

Routing framework for all-optical DWDM metro and long-haul transport networks with sparse wavelength conversion capabilities

Abstract: In this paper, we propose a novel routing framework for all-optical dense wavelength-division-multiplexing transport networks with sparse wavelength conversion capabilities. The routing framework includes an integer linear programming formulation to handle the static lightpath establishment problem and a novel open shortest path first protocol extension that advertises the availability of wavelength usage and wavelength conversion resources. Our routing framework addresses the limitations of the extensions presented in the literature because it also includes: 1) an efficient flooding protocol that is suitable for the dynamic nature of these networks and 2) an efficient route and wavelength computation engine that minimizes connection costs without hindering the blocking probability.

Execution of A Requirement Model in Software Development.

Abstract: Latest research results have shown that requirements errors have a prolonged impact on software development and that they are more expensive to fix during later stages than early stages in software development. Use case diagrams in UML are used to give requirements for a software system, but all descriptions for each use case are written in informal language. In this paper, we propose a new language HCL (High-Level Constraint Language) to which any requirement model given by use case diagrams can be mapped. Not only is the language HCL based on a formal language but also the requirement model written in HCL can be executed. Many errors occurring during requirements analysis and design can be detected by means of execution.

A cross-layer design for QoS support in the 3GPP2 wireless systems

Abstract: Due to the non-stationary wireless links and the rapid increase of new types of applications that require different levels of QoS parameters, the support for better QoS for the emerging 3GPP2 multimedia wireless applications is strongly needed. These parameters include: priority, delay, data loss, and data rate. Many possible combinations of system parameters have been specified in the current 1/spl times/EV-DV standard. However, there are no specifications about the dynamic resource allocations, i.e. the selection of optimal combination of system parameters such as the number of Walsh codes, the number of time slots, the modulation scheme, and the channel code rate. In this paper, a suite of cross-layer design modules for QoS support in the 1/spl times/EV-DV system is proposed. Our proposed design is composed of several modules build on top of each other. They include the priority admission control which admits users according to their QoS priority profiles, the resource allocation control module which is responsible for allocating the optimal combination of all system parameters, and the resource scheduling control module which aims at achieving a better overall throughput gain and guarantees the QoS requested by different users' service levels. The proposed dynamic resource allocation scheme is based on the effective capacity concept. Performance evaluation of the proposed cross-layer design has been carried out under a mix of traffic types.

Link-state update policies for all-optical DWDM transport networks

Abstract: It has been demonstrated that advertising the availability of wavelength and converter resources in all-optical DWDM transport networks with sparse wavelength conversion capabilities can drastically improve the blocking performance of these networks thus achieving better usage of the network resources. An important aspect with consequences in network performance is when to originate the wavelength-availability and converter-availability link state advertisements (LSAs). Frequent link-state advertisements could overwhelm the network control plane with many update messages that need to be processed. On the other hand, delaying these advertisements could result in inaccurate link-state information thus degrading the network blocking performance. In this paper, we propose two different link-state update policies to advertise the availability of wavelength and converter resource in all-optical DWDM transport networks with sparse wavelength conversion capabilities. The first one is very simple and serves as our base policy for comparison. The second policy, which is very efficient in handling the dynamic nature of all-optical DWDM networks with different degrees of wavelength conversion, reduces the number of LSAs considerably while maintaining the call blocking probability.

Performance Evaluation of TCP over Optical Channels and Heterogeneous Networks

Abstract: Next generation optical networks will soon provide users the capability to request and obtain end-to-end all optical 10 Gbps channels on demand. Individual users will use these channels to exchange large amounts of data and support applications for scientific collaborative work. These new applications, which expect steady transfer rates in the order of Gbps, will very likely use either TCP or a new transport layer protocol as the end-to-end communication protocol. In this paper, we investigate the performance of TCP and newer TCP versions over High Bandwidth Delay Product Channels (HBDPC), such as the on demand optical channels described above. In addition, we investigate the performance of these new TCP versions over wireless networks and according to old issues such as fairness. This is particularly important to make adoption decisions. Using simulations, we show that (1) the window-based mechanism of current TCP implementations is not suitable to achieve high link utilization and (2) congestion control mechanisms, such as the one utilized by TCP Vegas and Westwood are more appropriate and provide better performance. We also show that new TCP proposals, although perform better than current TCP versions, they still perform worse than TCP Vegas. In addition, we found that even though these newer versions improve TCP's performance over their original counterparts in HBDPC, they still have performance problems in wireless networks and present worse fairness problems than their old counterparts. We conclude that all these versions are still based on TCP's AIMD strategy or similar and therefore continue to be fairly blind in the way they increase and decrease their transmission rates. TCP will not be able to utilize the foreseen optical infrastructure adequately and support future applications if not redesigned to scale.

Performance evaluation of TCP over optical links

Abstract: Future applications will need steady transfer rates in the order of gigabits or even terabits per second in order to exchange exabytes of data in a reasonable amount of time and support collaborative scientific work. Although it is expected that next generation optical networks, computing and storage technologies will support this scenario, it has been shown that communications protocols, and in particular the widely used TCP protocol, will become the bottleneck. In this paper we present a performance evaluation of TCP Tahoe, Reno, New Reno, SACK, Vegas, Westwood and highspeed TCP over optical channels. We compared them in the same environment and found that the window-based mechanism of current TCP implementations is not suitable to achieve high link utilization, and that other congestion control mechanisms, such as the ones utilized by Vegas and Westwood, are more appropriate and provide better performance. In addition, we propose a simple modification to TCP Vegas that further improves its performance.