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Browsing University of Manitoba Scholarship (login required) by Author "Alfa, AS"
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- ItemRestrictedAn analytical approach to providing controllable differentiated quality of service in Web servers(2005-11-30) Rashid, MM; Alfa, AS; Hossain, E; Maheswaran, MProvisioning quality of service (QoS) in Web servers has gained immense importance because Web servers are a major part of the Internet. To deliver the pledged QoS, Web service providers need control over the allocation of the resources in their Web servers. Control is also necessary for reaching the optimal resource allocation through proper service differentiation. In this paper, we propose and investigate an analytic approach that enables the service providers to deploy a differentiated service policy that offers this control. The proposed service policy is configurable by tunable control parameters. We devise the relationships between the performance measures and these parameters by adopting a unique queuing theoretic approach. Once these relationships are established, we describe how these parameters can be set to their most appropriate values depending on the objectives of the service providers. We illustrate the usefulness of our approach by conducting the analysis on a real Web trace.
- ItemRestrictedDelay statistics and throughput performance for multi-rate wireless networks under multiuser diversity(2006-11-30) Le, LB; Hossain, E; Alfa, ASAn analytical framework for radio link level performance evaluation under scheduling and automatic repeat request (ARQ)-based error, control in a multi-rate wireless network is presented. The multi-rate transmission is assumed to be achieved through adaptive modulation and coding (AMC) in a correlated fading channel. The analytical framework, which is developed based on a vacation queueing model, can be applied to any scheduling scheme as long as the evolution of the joint service/vacation and channel processes can be determined. The exact statistics of queue length, and delay are obtained and the radio link level throughput is calculated under both saturated and non-saturated buffer scenarios. As an example of using the general analytical model, we analyze the performance of max-rate (MR) scheduling scheme which exploits multiuser diversity and compare its performance with the round-robin (RR) scheduling scheme. Although the MR scheduling always results in higher throughput than the RR counterpart, we observe that the RR scheduling offers better delay performance than the MR scheme under light traffic load conditions. The usefulness of the presented analysis is highlighted by. illustrating its applications for cross-layer design and packet-level admission control under delay constraints. After all, this analytical framework would be very useful for comprehensive analysis of radio link level scheduling schemes and hence for design and engineering of radio link control protocols.
- ItemRestrictedEnd-to-end batch transmission in a multihop and multirate wireless network: Latency, reliability, and throughput analysis(2006-09-30) Issariyakul, T; Hossain, E; Alfa, ASThis paper presents a novel Markov-based model for analyzing the end-to-end transmission of a batch of packets in a multihop wireless network using multirate transmission. The end-to-end reliability of this transmission (in terms of the number of packets delivered to the destination node) is controlled through different types of Automatic Repeat reQuest (ARQ)-based error control mechanisms implemented at each node. For a batch of packets, we derive complete statistics (i.e., probability mass function) for end-to-end latency and the number of packets successfully delivered to the destination node. Typical numerical results obtained from the model are validated by means of simulation. These results reveal the trade-off between end-to-end latency and end-to-end reliability, which would be an important issue in designing and engineering multihop wireless networks. Also, we demonstrate the usefulness of the proposed analytical model in predicting the latency and the reliability performances of TCP (Transmission Control Protocol) in a multihop wireless scenario.
- ItemRestrictedQoS and energy trade off in distributed energy-limited mesh/relay networks: A queuing analysis(2006-06-30) Fallahi, A; Hossain, E; Alfa, ASIn a distributed multihop mesh/relay network (e.g., wireless ad hoc/sensor network, cellular multihop network), each node acts as a relay node to forward data packets from other nodes. These nodes are often energy-limited and also have limited buffer space. Therefore, efficient power saving mechanisms (e.g., sleeping mechanisms) are required so that the lifetime of these nodes can be extended while at the same time the quality of service (QoS) requirements (e.g., packet delay and packet loss rate) for the relayed packets can be satisfied. In this paper, we present a novel queueing analytical framework to study the tradeoff between the energy saving and the QoS at a relay node. Specifically, by modeling the bursty traffic arrival process as a MAP (Markovian Arrival Process) and the packet service process as having a phase-type (PH) distribution, we model each node as a MAP/PH/1 nonpreemptive priority queue. Here, the relayed packets and the node's own packets form two priority classes and the medium access control (MAC)/physical (PHY) layer protocol in the transmission protocol stack acts as the server process. Moreover, we use a phase-type vacation model for the energy-saving mechanism in a node when the MAC/PHY protocol refrains from transmitting in order to save battery power. Two different power saving mechanisms due to the standard exhaustive and the number-limited exhaustive vacation models (both in multiple vacation cases) are analyzed to study the tradeoff between the QoS performance of the relayed packets and the energy saving at a relay node. Also, an optimization formulation is presented to design an optimal wakeup strategy for the server process under QoS constraints. We use matrix-geometric method to obtain the stationary probability distribution for the system states from which the performance metrics are derived. Using phase-type distribution for both the service and the vacation processes and combining the priority queueing model with the vacation queueing model make the analysis very general and comprehensive.
- ItemRestrictedRadio link level performance evaluation in wireless networks using multi-rate transmission with ARQ-based error control(2006-10-31) Le, LB; Hossain, E; Alfa, ASThis letter presents an analytical framework for radio link level performance evaluation in a wireless network using adaptive modulation and coding (AMC) and automatic repeat request (ARQ)-based error control. Both the cases of finite and infinite buffer sizes at the radio link layer are considered when the packet arrival process is modeled by a batch Markovian arrival process (BMAP), which can capture correlation in the arrival process. Using the model, radio link level performance measures such as average delay, buffer overflow probability, packet loss rate, and average spectral efficiency can be obtained, and the impacts of channel Parameters on the performance measures can be determined. Using the queue length distributions for finite and infinite buffer cases, the buffer size can be designed such that the packet overflow probability remains below the desired level. Such a cross-layer analytical framework would be very useful for network designers.
- ItemRestrictedService differentiation in multirate wireless networks with weighted round-robin scheduling and ARQ-based error control(2006-02-28) Le, LB; Hossain, E; Alfa, ASThe radio link-level delay statistics in a wireless network using adaptive modulation and coding (AMC), weighted round-robin (WRR) scheduling, and automatic repeat request-based error control is analyzed in this letter. WRR scheduling can be used for service differentiation similar to that achievable by using the generalized processor sharing scheduling discipline. The analytical framework presented in this letter captures physical and radio link-level aspects of a multirate multiuser wireless network (e.g., general fading model, AMC, scheduling, error control) in a unified way. It can be used for admission control and cross-layer design under statistical delay constraints. The analytical results are validated by simulations. Typical numerical results are presented, and their useful implications on the system performance are discussed.