OPN06-2: Performance of Scheduling Algorithms in Multi-Stage Optical Packet Switches with Sparse Wavelength Converters (original) (raw)
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Multi-stage optical packet switching fabric based on the broadcast-and-select principle is considered to implement the shared-per-node wavelength conversion scheme. This approach fairly allows to combine contention resolution in the wavelength and space domains. A scheduling algorithm is proposed to control optical packet forwarding in synchronous context. The results aim at showing how the sharing of wavelength converters impacts on node performance, the degree of sharing achieved with respect to the reference shared-per-node architecture, and at providing a meaningful support for cost-performance benchmarking studies. An important aspect dealt with in the paper is the complexity evaluation in terms of expensive optical components, tunable wavelength converters (TWCs) and semiconductor optical amplifiers (SOAs) used as optical gates. The multi-stage switching fabric is compared with the reference shared-per-node scheme in terms of complexity, thus showing the better scalability property of the proposed architecture, given the reduced number of optical gates employed.
Journal of Lightwave Technology, 2000
This paper describes an optical switch architecture based on the shared-per-wavelength strategy for contention resolution in the wavelength domain. This strategy impacts on wavelength converters requirements and switch organization, by allowing to obtain cost saving. The general sharing concept is first introduced and the related practical solution as a multistage switch architecture is presented and thoroughly analyzed in terms of performance, control and cost perspectives. Heuristic scheduling to manage packet forwarding in a synchronous context is developed and discussed in terms of computational complexity. A simple accurate analytical model is developed and validated against simulation to numerically evaluate packet loss performance of the shared-per-wavelength switch. The main achievement of the work is represented by the proposal of a feasible approach which leads to remarkable cost saving in terms of optical gates and wavelength converters under the conditions outlined.
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This paper describes a multistage switch based on the broadcast-and-select principle. It implements shared per node wavelength conversion for contention resolution in optical packetswitched networks. A novel scheduling algorithm is proposed to control packet forwarding in synchronous context. An analytical model is provided to calculate the packet loss probability related to the multistage configuration. Results show how the sharing of wavelength converters impacts on node performance, and provide a meaningful support for cost-performance benchmarking studies. 0-7803-9569-7/06/$20.00 c 2006 IEEE
Journal of Lightwave Technology, 2000
In all-optical packet switching, packets may arrive at an optical switch in an uncoordinated fashion. When contention occurs, fiber delay lines (FDLs) are needed to delay (buffer) the packets that have lost in the contention to some future timeslots for the desired output ports. There have been several optical-buffered switch architectures and FDL assignment algorithms proposed in the literature. However, most of them either have high implementation complexity or fail to schedule in advance departure time for the delayed packets. In this paper, we study the packet scheduling algorithms for the single-stage shared-FDL optical packet switch. We propose three new FDL assignment algorithms, namely sequential FDL assignment (SEFA), multi-cell FDL assignment (MUFA), and parallel iterative FDL assignment (PIFA) algorithms for the switch. Our algorithms can make FDL and output-port reservation so as to schedule departure time for packets. Owing to FDL and/or output-port conflicts, the packets that fail to be scheduled are discarded before entering the switch so that they do not occupy any FDL resources. We show by simulation that with these algorithms, the optical-buffered switch can achieve a loss rate of ~10 −7 even at the load of 0.9. These algorithms are extended to the three-stage Clos-network optical packet switches in our companion paper.
Complexity/performance trade-off in Optical Packet Switches
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Optical Burst Switching and Packet Switching require the adoption of suitable contention resolution mechanisms at the optical nodes due to multiple packets/bursts attempting to access the shared output channel at the same time. Contentions can be solved by exploiting the space, wavelength and time domain. The many alternatives possible call for suitable scheduling policy aiming at an optimal system performance. This paper provides an assessment of the role of key parameters for an optical packet/burst contention resolution scheme and the resulting node cost estimation in terms of CAPEX, footprint and power consumption. Feasibility tradeoffs due to limited optical buffering and wavelength conversion capability are also taken into account.
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An analytical approach based on a reduced Markov chain (RMC) model of an optical packet switch with partially shared output buffer has been presented and a combined scheme for the contention resolution in optical packet switches has been proposed. The proposed scheme takes the advantage of output buffering, shared buffering and wavelength conversion to enhance the switch performance. The performance evaluation of the switch architecture based on RMC modelling has been validated through extensive simulation. Moreover, for a self-similar input traffic, the switch performance has been shown to achieve further improvement if a traffic shaping mechanism is incorporated at the input end of the switch architecture.
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In this paper, we consider synchronous optical packet networks formed by switches equipped with a complete set of limited-range wavelength converters. On these networks, we dealt with scheduling algorithm that maximizes the switch throughput. So far, previous literature works have formalized this scheduling problem as the finding of a maximum bipartite matching (MBM) in a convex graph. The MBM formalization has collected various follow-ups, mainly focused on measuring switch-level performance. We revise the MBM formalization by measuring network-level performance. Surprisingly, we find out that when optical switches are cascaded, MBM formalization has two not negligible lacks: 1) a useless degradation of optical signal quality and 2) a tendency of shifting optical packets toward lower wavelengths, thus increasing the occurrence of wavelength contention.
A novel Optical Packet Switch architecture with reduced wavelength conversion complexity
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In this paper, a novel optical packet switch (OPS) architecture is proposed and its scheduling algorithm is implemented and analyzed. The proposed architecture makes use of shared wavelength exchange optical crossbars (WOCs) to reduce wavelength conversion complexity. Simulation results show that, under heavy traffic loads, the conversion cost of the proposed OPS architecture is only 25% of that of a typical OPS architecture. Moreover, under low traffic loads, the conversion cost of the proposed architecture can be reduced to half of that of typical OPS designs.
Performance evaluation of optical packet switches equipped with heterogeneous wavelength converters
Optics Express, 2009
An optical packet switch that shares both limited range and full range wavelength converters for contention resolution is proposed with the aim to guarantee a high conversion cost saving. To optimally dimension the number and the conversion range of the wavelength converters, an analytical model, validated by simulation, is introduced. Numerical results show that the proposed switch architecture allows for a conversion cost saving in the order of 90% with respect to a traditional architecture in which only shared full range wavelength converters are used.