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. Errorfree 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. entries, even causing the depletion of the remaining IPv4 address space and leading to the advent of an IPv6 protocol with a quadrupled need for address look-up (AL) requirements [5]. This increasing need for faster routing functionalities, including AL, which also requires fast hardware memories to perform fast look-up of the packet's destination address immediately upon its arrival and across the forwarding information base (FIB) of the router.On the path to speeding up hardware memory and lower latency times when fetching data, state-of-the-art highly performing electronic static random access memory (RAM) cell technology has managed to achieve operation up to 5 GHz [6][7][8]. However, RAMs are inherently limited in fast AL as, owing to the address-based fetching of data, they would require multiple sequential random access to the memory and consecutive searches of the desired content. As a re...