Abstract
Electronic Content Addressable Memories (CAM) implement Address Look-Up (AL) table functionalities of network routers; however, they typically operate in the MHz regime, turning AL into a critical network bottleneck. In this communication, we demonstrate the first steps towards developing optical CAM alternatives to enable a re-engineering of AL memories. Firstly, we report on the photonic integration of Semiconductor Optical Amplifier-Mach Zehnder Interferometer (SOA-MZI)-based optical Flip-Flop and Random Access Memories on a monolithic InP platform, capable of storing the binary prefix-address data-bits and the outgoing port information for next hop routing, respectively. Subsequently the first optical Binary CAM cell (B-CAM) is experimentally demonstrated, comprising an InP Flip-Flop and a SOA-MZI Exclusive OR (XOR) gate for fast search operations through an XOR-based bit comparison, yielding an error-free 10 Gb/s operation. This is later extended via physical layer simulations in an optical Ternary-CAM (T-CAM) cell and a 4-bit Matchline (ML) configuration, supporting a third state of the “logical X” value towards wildcard bits of network subnet masks. The proposed functional CAM and Random Access Memories (RAM) sub-circuits may facilitate light-based Address Look-Up tables supporting search operations at 10 Gb/s and beyond, paving the way towards minimizing the disparity with the frantic optical transmission linerates, and fast re-configurability through multiple simultaneous Wavelength Division Multiplexed (WDM) memory access requests.
Highlights
The last decades have been marked by the widespread use of bandwidth-hungry internet applications by multiple wireless users and cloud-network devices always connected online
T-Content Addressable Memories (CAM) cell within a row, all four of the T-CAM cell outputs can be combined at the row output by using an Arrayed Waveguide Grating (AWG) multiplexer, as presented at the right side of Figure 7; λa through λd are used for the different cell outputs, while λe, λf, and the wavelengths used for the Set/Reset signals are employed in all T-CAM cells
An ML signal of a logical value “0” indicates a completely using an AWG multiplexer, as presented at the right side of Figure 7; λa through λd are used for the different cell outputs, while λe, λf, and the wavelengths used for the Set/Reset signals are employed in all T-CAM cells
Summary
The last decades have been marked by the widespread use of bandwidth-hungry internet applications by multiple wireless users and cloud-network devices always connected online. Address Selectors [45,46] and optical Tag Comparators [47], the first designs of a complete optical cache memory architecture for high-performance computers revealed a 16 GHz operation via physical layer simulations [48] All of these have increased the maturity of optical memories towards penetrating the computing domain, where the use of electronics is so far undisputable, whereas in optical networks, optical FFs have been suggested for contention resolution [49]. Following the paradigm of optical RAMs, optical alternatives of CAM architectures may facilitate similar advances and speed enhancements towards ultra-fast router AL memories in the high-end router domain In this regime, some preliminary first steps, stemming from our group, have managed to develop the first photonic alternative CAM-based elements [50,51], which is the main focus of this paper. We present a discussion on the future challenges that need to be addressed for migrating towards optical AL table architectures, bearing promises to directly resolve the AL in the optical domain that can significantly speed-up AL-speeds in high-end router architectures
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