Authors: Chaporkar, Prasanna | Kuri, Joy

Article Type: Research Article

Abstract: Many real‐time applications demand delay guarantees from the network. A network architecture designed to support these applications should be robust and scalable. The IntServ architecture provides per‐flow QoS at the cost of robustness and scalability. The DiffServ architecture is robust and scalable but can provide QoS at a class level and not at a flow level. In this paper, our aim is to design architectures that are scalable and robust like DiffServ and at the same time able to provide per‐flow QoS like IntServ. We propose a non work‐conserving and a work‐conserving architecture to achieve this goal. The guaranteeable …delay regions of these architectures are the same as those of GPS based policies with rate proportional resource allocation. We also propose a scheme to provide meaningful throughput and responsiveness to best effort traffic even in the presence of heavy QoS load. Show more

Keywords: QoS, differentiated services, scalable core, delay guarantee, schedulability

Citation: Journal of High Speed Networks, vol. 12, no. 3-4, pp. 87-109, 2002

Authors: Veeravalli, Bharadwaj

Article Type: Research Article

Abstract: We investigate the performance of a network system on the World‐Wide Web employing proxies that interact with a pool of servers to service a pool of client requests. We focus on modelling the interaction of a proxy with the server system and its performance in maximizing the number of requests that can be served. We formulate the problem using a discrete time Markov chain model capturing the state of the client (equivalently the state of the proxy) and quantify the performance in terms of number of requests that are successfully processed by the server system. We derive a closed‐form solution …to determine the percentage of requests that can be admitted by the servers, referred to as admission control factor, which is our performance metric of interest. We conduct a systematic and rigorous simulation study to demonstrate the behavior of our performance metric with respect to the number of client requests and the number of available servers in the system. We also study the effect of server response time and propose three different strategies that a proxy may adopt to tune the performance of the system. The behavior of the three strategies – Conservative, Greedy, and Incremental Tuning, with respect to our performance metric is rigorously studied under a variety of system dependent parameters, with respect to the probability of a client request, and the probability of a new request arrival. Further, we perform an asymptotic analysis to quantify the ultimate performance limits of the admission control factor with respect to the number of client requests than can be supported by the system and the number of servers in the system. In the study with respect to the number of servers, we derive an exact bound on the behavior of our performance metric and testify this finding with our rigorous simulation experiments. Several interesting features are highlighted and the model is conclusively shown to be robust and elegant in capturing the behavior of the system. Show more

Keywords: Web Proxy, discrete time Markov chain, admission control, Web‐servers, Web‐client, response time

Citation: Journal of High Speed Networks, vol. 12, no. 3-4, pp. 111-131, 2002

Authors: Freire, Mário M. | da Silva, Henrique J.A.

Article Type: Research Article

Abstract: In this paper, we present a comparison of the blocking performance in unidirectional and bi‐directional wavelength routed ring networks. This performance comparison reveals that, for the same load per node and equal number of wavelengths per link, the performance of a unidirectional ring with N nodes is very close to the performance of a bi‐directional ring with 4N nodes. This comparison also suggests that, for the same number of nodes and equal number of wavelengths per link, the performance of a unidirectional ring network with a load per node of ρ is similar to the performance of a bi‐directional ring …network with a load per node of 4ρ. An explanation is presented for this four‐fold capacity increase of bi‐directional rings over unidirectional rings, regarding number of nodes or loads per node. Show more

Citation: Journal of High Speed Networks, vol. 12, no. 3-4, pp. 133-140, 2002

Authors: Sreenath, N. | Siva Ram Murthy, C.

Article Type: Research Article

Abstract: Wavelength‐division multiplexed (WDM) networks employing wavelength‐routing are considered to be potential candidates for the next generation wide‐area backbone networks. In these networks, messages are carried in all‐optical form using lightpaths. In a WDM network, the set of semi‐permanent lightpaths which are set up in the network may be viewed as a virtual topology by higher layers such as SONET, ATM, and IP. The virtual topology is designed with an aim of minimizing certain objective function value. The underlying virtual topology may need to be changed in response to the changing traffic patterns in the higher layer. This process of changing …the virtual topology to meet the traffic requirement is called as reconfiguration. The reconfiguration can be performed either on‐line or off‐line. We view the reconfiguration as an on‐line process and it provides a trade‐off between the objective function value and the number of changes to the virtual topology. The objective function value decides how best the topology is suited for the given traffic demand. The number of changes decides the extent of disruption of traffic in the network while making a transition to the new virtual topology. As the reconfiguration problem is computationally intractable, we propose four heuristic algorithms for reconfiguration of virtual topology, namely, Phase1, Phase2‐Single, Phase2‐Multi, and Two‐Phase. These heuristic algorithms reconfigure the current virtual topology if traffic pattern changes from the existing one. The performance of these heuristic algorithms are compared in terms of objective function value of reconfigured topology, number of changes performed to get the reconfigured topology, and the amount of time taken by these algorithms to compute changes in the existing virtual topology. Show more

Keywords: WDM optical networks, wavelength routing, virtual topology, virtual topology reconfiguration, traffic changes

Citation: Journal of High Speed Networks, vol. 12, no. 3-4, pp. 141-169, 2002

Article Type: Other

Citation: Journal of High Speed Networks, vol. 12, no. 3-4, pp. 171-171, 2002