Optical memory architectures for fast routing address look-up (AL) table operation

Abstract

Today, the increasing demand for fast routing processes has turned the address look-up (AL) operation into one of the main critical performance operations in modern optical networks, since it conventionally relies on slow-performing AL tables. Specifically, AL memory tables are comprised of content addressable memories (CAMs) for storing a known route of the forwarding information base of the router, and random access memories (RAMs) for storing the respective output port for this route. They thus allow for a one-cycle search operation of a packet’s destination address, yet they typically operate at speeds well below 1 GHz, in contrast with the vastly increasing optical line rates. In this paper, we present our overall vision towards light-based optical AL memory functionalities that may facilitate faster router AL operations, as the means to replace slow-performing electronic counterparts. In order to achieve this, we report on the development of a novel optical RAM cell architecture that performs for the first time with a speed of up to 10 Gb s−1, as well as our latest works on multi-bit 10 Gb s−1 optical CAM cell architectures. Specifically, the proposed optical RAM cell exploits a semiconductor optical amplifier-Mach–Zehnder interferometer in a push-pull configuration and deep saturation regime, doubling the speed of prior optical RAM cell configurations. Error-free write/read operation is demonstrated with a peak power penalty of 6.2 dB and 0.4 dB, respectively. Next, we present the recent progress on optical CAM cell architectures, starting with an experimental demonstration of a 2-bit optical CAM match-line architecture that achieves an exact bitwise search operation of an incoming 2-bit destination address at 10 Gb s−1, while the analysis is also extended to a numerical evaluation of a multi-cell 4-bit CAM-based row architecture with wavelength division multiplexed outputs for fast parallel memory operations at speeds of up to 4 × 20 Gb s−1. Finally, we present a comparative study between electronic and optical RAMs and CAMs in terms of energy and speed and discuss the further challenges towards our vision.