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

Mind the gap: void-creating algorithms 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

Using shared wavelength converters effectively in optical switching

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 switch’s overall energy consumption

Exact performance analysis of a single-wavelength optical buffer with correlated inter-arrival times

Providing a photonic alternative to the current electronic switching in the backbone, optical packet switching (OPS) and optical bursts witching (OBS) require optical buffering. Optical buffering exploits delays in long optical fibers; an optical buffer is implemented by routing packets through a set of fiber delay lines (FDLs). Previous studies pointed out that, in comparison with electronic buffers, optical buffering suffers from an additional performance degradation. This contribution builds on this observation by studying optical buffer performance under more general traffic assumptions. Features of the optical buffer model under consideration include a Markovian arrival process, general burst sizes and a finite set of fiber delay lines of arbitrary length. Our algorithmic approach yields instant analytic results for important performance measures such as the burst loss ratio and the mean delay

Stochastic decomposition in discrete-time queues with generalized vacations and applications

For several specific queueing models with a vacation policy, the stationary system occupancy at the beginning of a rantdom slot is distributed as the sum of two independent random variables. One of these variables is the stationary number of customers in an equivalent queueing system with no vacations. For models in continuous time with Poissonian arrivals, this result is well-known, and referred to as stochastic decomposition, with proof provided by Fuhrmann and Cooper. For models in discrete time, this result received less attention, with no proof available to date. In this paper, we first establish a proof of the decomposition result in discrete time. When compared to the proof in continuous time, conditions for the proof in discrete time are somewhat more general. Second, we explore four different examples: non-preemptive proirity systems, slot-bound priority systems, polling systems, and fiber delay line (FDL) buffer systems. The first two examples are known results from literature that are given here as an illustration. The third is a new example, and the last one (FDL buffer systems) shows new results. It is shown that in some cases the queueing analysis can be considerably simplified using this property