Kurt Van Hautegem

Scheduling in optical switching: Deploying shared wavelength converters more effectively

As internet traffic will further increase in coming years, the current network infrastructure will have to grow along in terms of capacity. To this end, optical packet/burst switching have been proposed, allowing more efficient use of the available fiber capacity. To resolve packet contention in the involved optical switches, Fiber Delay Lines (for delay assignment) and wavelength converters (for wavelength conversion) are used to reschedule the contending packets, by means of a scheduling algorithm. Existing algorithms are effective when employed with an infinite number of converters, but generally perform poorly when the number of wavelength converters is small, as is the case in most switch prototype architectures. In this paper, several parametric cost-based scheduling algorithms are proposed that take scarcity of both FDLs and converters into account. Results obtained by Monte Carlo simulation show that these algorithms not only enable improved performance (in terms of packet loss probability), but also reduce the usage of the wavelength converters, and thus, the switchs overall energy consumption.

OPS/OBS scheduling algorithms: Incorporating a wavelength conversion cost in the performance analysis

With ever-increasing demands for bandwidth optical packet/burst switching is used to utilise more of the available capacity of optical networks. In current prototypes of optical switches time and wavelength multiplexing are combined to resolve packet contentions by means of Fiber Delay Lines and wavelength converters in the switching elements. Although optical switches have lower energy consumption than their electronic counterparts, it remains substantial. Since wavelength converters contribute significantly to the switches overall energy consumption, they should be used sparingly, rather than continuously. Current scheduling algorithms however do not take the usage of wavelength converters (and the related energy consumption) into account. To this end, we developed and evaluated new cost-based scheduling algorithms, which take both gap and delay into account to schedule an incoming packet. The performance improvement of these algorithms over existing algorithms can be traded off for a significant reduction in up-time of the wavelength converters by introducing a conversion cost in the involved cost function. This is backed by Monte Carlo simulation results, in which the algorithms are applied both in a void-filling and non-void-filling setting. The algorithms are of the same implementation complexity as current algorithms, and thus of immediate value to switch designers.

Improving performance and energy consumption of shared wavelength converters in OPS/OBS

As Internet traffic will further increase in coming years, the current optical network infrastructure will have to grow along in terms of capacity. To this end, optical packet/burst switching have been proposed, allowing more efficient use of the available fibre capacity. To resolve packet contention in the involved optical switches, Fibre Delay Lines (for delay assignment) and wavelength converters (for wavelength conversion) are used to reschedule the contending packets, by means of a scheduling algorithm. Existing algorithms are effective in minimizing packet loss when employed with an infinite number of converters, but generally perform poorly when the number of wavelength converters is small, as is the case in most switch prototype architectures. In this paper, several parametric cost-based scheduling algorithms for a limited number of wavelength converters are proposed that take scarcity of both FDLs and converters into account. Results obtained by Monte Carlo simulation show that these algorithms not only enable improved performance (in terms of packet loss probability), but also reduce the usage of the wavelength converters, and thus, the switch?s overall energy consumption. The new algorithms are of the same implementation complexity as existing cost-based algorithms, and thus are of immediate value to switch designers.

Void-creating algorithm in OPS/OBS: mind the gap

In optical packet/burst switching, packet contention on a single wavelength is resolved effectively by means of Fiber Delay Lines. The involved scheduling algorithm is typically designed to minimize packet loss, by filling so-called voids, and trying to keep the so-called gaps small. We propose a new type of algorithm that selectively creates voids that are larger than strictly needed, only when these will likely be filled. Results obtained by Monte Carlo simulation show that selective void creation can significantly reduce packet loss.

Optical Switching for Variable Size Packets: Improved Void Filling through Selective Void Creation

With ever-increasing demand for bandwidth, both optical packet switching and optical burst switching are proposed as alternatives to increase the capacity of optical networks in the future. In these packet-based switching techniques, Fiber Delay Lines are used to avoid contention between packets on a single wavelength. The involved scheduling algorithms decide on which Fiber Delay Line each packet is scheduled in order to maximize performance. By selectively delaying packets longer than strictly necessary, we proposed a schedule called void-creation that outperforms existing void-filling algorithms by up to 50 % for a specific setting with fixed packet size. This contribution extends the concept of void-creation to the case of variable size packets. By conditioning the theoretical value of the packet size on the scheduling parameters, we are able to extend the applicability of the void-creating algorithm to a plurality of settings. We therefore developed a numerical procedure that assigns a theoretical value (or, equivalently, negative cost) to each void based on how likely the void will eventually be filled and thus proven useful. Results obtained by Monte Carlo simulation show that our void-values provide a solid and consistent basis to decide upon void creation, and this for a variety of packet size distributions.

Fill the Void: Improved Scheduling for Optical Switching

With ever-increasing demand for bandwidth, optical packet/burst switching is proposed to utilize more of the available capacity of optical networks in the future. In these packet-based switching techniques, packet contention on a single wavelength is resolved effectively by means of Fiber Delay Lines. The involved scheduling algorithms are typically designed to minimize packet loss and/or packet delay. By filling so-called voids, void-filling algorithms are known to outperform their non-void-filling counterparts. This however comes at a large computational cost as the void-filling algorithms have to keep track of beginnings and endings of all voids. This is opposed to the non-void-filling algorithms which only have to keep track of a single system state variable. We therefore propose a new type of algorithm that selectively creates voids that are larger than strictly needed, only when these will likely be filled. Results obtained by Monte Carlo simulation show that selective void creation can jointly reduce packet loss by 50% and packet delay by 18%, without imposing a high computational cost.

Analysis of VAS, WAS and XAS Scheduling Algorithms for Fiber-Loop Optical Buffers

In optical packet/burst switched networks fiber loops provide a viable and compact means of contention resolution. For fixed size packets it is known that a basic void-avoiding schedule (VAS) can vastly outperform a more classical pre-reservation algorithm as FCFS. In this contribution we propose two novel forward-looking algorithms, WAS and XAS, that outperform VAS in the setting of a uniform distributed packet size and a restricted buffer size. This paper presents results obtained by Monte Carlo simulation, showing that improvements of more than \(20\%\) in packet loss in specific settings are obtainable. In other settings and for other performance measures similar improvements are within reach.

Improving the energy efficiency of scheduling algorithms for OPS/OBS buffers

With ever-increasing demands for bandwidth, optical packet/burst switching is used to utilize more of the available capacity of optical networks. In existing prototypes of optical switches, packet contention is resolved by combining time and wavelength multiplexing by means of fiber delay lines and wavelength converters. Although optical switches dissipate less energy than their electronic counterparts, their consumption remains substantial. Since wavelength converters contribute significantly to the switches overall energy consumption, they should be powered only when needed. Existing scheduling algorithms, however, do not take the usage of wavelength converters (and the related energy consumption) into account. To this end, we developed and evaluated new cost-based scheduling algorithms, which take both gap and delay into account to schedule an incoming packet. The performance improvement of these algorithms over existing algorithms can be traded off for a significant reduction in up-time of the wavelength converters by introducing a conversion cost in the involved cost function. This is backed by Monte Carlo simulation results, in which the algorithms are applied both in a void-filling and non-void-filling setting. The algorithms are of the same implementation complexity as existing algorithms, and thus of immediate value to switch designers.