Browsing by Author "Shih, J"

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A QoS packet/burst scheduler for broadband networks
(2002)
Yuang, MC
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Shih, J
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Tien, PL
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資訊工程學系
;
Department of Computer Science
Prevailing weight-based scheduling algorithms advocate static or coarse-grained simplification of timestamp computation, resulting in performance bottleneck and unnecessary downgrade under heavy and normal computation loads, respectively. Our goal is to design a scheduler that enables quantitative trade-off balance between performance and complexity. In this paper, we propose a Stepwise QoS Scheduler (SQS), enabling packet to burst scheduling under normal to heavy computation loads, based on a new notion of window. Window sizes of unity and greater than one correspond to packet and burst scheduling, respectively. SQS exerts simple FIFO service within the window and guarantees stepwise weight-proportional service at the window boundary. As a result, quantitative trade-off balance can be facilitated via the adjustment of the window size. We further formally specify the SQS service guarantee for a flow by a stepwise service curve, which is a function of W and theta(min) - the least-upper-bound delay incurred by the first packet of the busy period of the flow. Finally, we demonstrate through experimental results that, by applying a small window (W less than or equal to 10), SQS outperforms Weighted Fair Queueing (WFQ) and performs as superior as Worst-case Fair Weighted Fair Queueing (WF(2)Q) with respect to throughput fairness, mean delay, and worst-case delay fairness.
QoS contention control for optical coarse packet switched IP-over-WDM network
(2005)
Yuang, MC
;
Tien, PL
;
Shih, J
;
Lee, SSW
;
Lin, YM
In this paper, we first introduce an Optical Coarse Packet Switching (OCPS) paradigm. In principle, OCPS advocates the enforcement of traffic engineering and control to realize bandwidth-on-demand on sub-wavelength basis while circumventing optical packet switching limitations. Based on OCPS, we have constructed an experimental optical IP-over-WDM network testbed, referred to as OPSINET. In the paper, we present the architectural design of OPSINET and its Hybrid Contention Control (HCC) mechanism aiming to satisfy various classes of loss QoS guarantees. The mechanism preventively adopts appropriate burst sizes for different traffic classes during packet burstification at ingress routers. It also reactively performs prioritized contention resolution at OLSRs in the presence of contention. Experimental results show that HCC invariantly achieves low loss probability as a result of burstification-based traffic shaping. Moreover, it provides satisfied loss guarantees for high-priority classes while incurring minimal loss degradation for lower-priority classes.
QoS Scheduler/Shaper for optical coarse packet switching IP-over-WDM networks
(2004-11-01)
Yuang, MC
;
Tien, PL
;
Shih, J
;
Chen, A
;
資訊工程學系
For IP-over-WDM networks, optical coarse packet switching (OCPS) has been proposed to circumvent optical packet switching limitations by using in-band-controlled per-burst switching and advocating traffic control enforcement to achieve high bandwidth utilization and quality-of-service (QoS). In this paper, we first introduce the OCPS paradigm. Significantly, we present a QoS-enhanced traffic control scheme exerted during packet aggregation at ingress nodes, aiming at providing delay and loss class differentiations for OCPS networks. Serving a dual purpose, the scheme is called (psi, tau)-Scheduler/Shaper, where psi and tau are the maximum burst size and burst assembly time, respectively. To provide delay class differentiation, for IP packet flows designated with delay-associated weights, (psi, tau)-Scheduler performs packet scheduling and assembly into bursts based on their weights and a virtual window of size psi. The guaranteed delay bound for each delay class is quantified via the formal specification of a stepwise service curve. To provide loss class differentiation, (psi, tau)-Shaper facilitates traffic shaping with larger burst sizes assigned to higher loss priority classes. To examine the shaping effect on loss performance, we analytically derive the departure process of (psi, tau)-Shaper. The aggregate packet arrivals are modeled as a two-state Markov modulated Bernoulli process (MMBP) with batch arrivals. Analytical results delineate that (psi, tau)-Shaper yields substantial reduction, proportional to the burst size, in the coefficient of variation of the burst interdeparture time. Furthermore, we conduct extensive simulations on a 24-node ARPANET network to draw packet loss comparisons between OCPS and just-enough-time (JET)-based OBS. Simulation results demonstrate that, through burst size adjustment, (psi, tau)-Shaper effectively achieves differentiation of loss classes. Essentially, compared to JET-based OBS using out-of-band control and offset-time-based QoS strategy, OCPS is shown to achieve invariably superior packet loss probability for a high-priority class, facilitating better differentiation of loss traffic classes.