Fill the Void: Improved Scheduling for Optical Switching

Abstract

Abstract-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.

Selective void creation/filling for variable size packets and multiple wavelengths

“…As these void-filling algorithms keep track of all voids this improvement comes at the cost of an increased computational complexity. In [21,18] we therefore proposed a totally new type of algorithm for a single wavelength set-up(and thus without wavelength conversion), the void-creating algorithm, that selectively creates larger voids only when they will likely be filled in the future. This algorithm does not only fill the available voids, it also, based on the system conditions, controls the creation of the voids enabling better switch performance.…”

“…Fixed size packets on a single wavelength. To achieve a better performance without excessively increasing the computational cost we proposed the voidcreating algorithm in [21,18] for the setting of a single wavelength and a fixed packet size equal to the granularity (E[B] = B = D). In this setting a possible provisional schedule looks like Fig.…”

“…To improve the performance, the void-creating algorithm in [21,18] creates fillable voids by scheduling the packet on the second FDL (triangle) instead of the first FDL (dot) to the right of the horizon. This creates voids larger than the fixed packet size B (fillable voids) which, if favorably positioned, can be filled in the future.…”

“…Motivation and assumptions. Throughout the paper the same continuoustime setting as in [19,20,21,18,22] is supposed. Fig.…”

“…As in [19,20,21,18,22] an arbitrary single output port is analyzed, marked by the dashed-line box in Fig. 1.…”