Optically assisted internet routing using arrays of novel dynamically reconfigurable FBG-based correlators

Abstract

As routing tables in core Internet routers grow to exceed 100 000 entries, it is becoming essential to develop methods to reduce the lookup time required to forward packets toward their destinations. In this paper, we employ a bank of novel thermally tuned fiber-Bragg-grating-based optical correlators to construct an "optical bypass" to accelerate conventional electronic Internet routers. The correlators are configured as a routing table cache that can quickly determine the destination port for a fraction of the incoming traffic by examining only a subset of the bits in an IP packet's 32-bit destination address.We also demonstrate a novel multiwavelength correlator based on fiber Bragg grating that can simultaneously recognize the header bits on multiple wavelengths for use in wavelength-division-multiplexed (WDM) systems. Using the optical bypass, routing table lookup times are reduced by an order of magnitude from microseconds to nanoseconds and are limited only by the speed of the optical switch. Index Terms-Optical communications, optical correlators, optical signal processing, wavelength-division-multiplexed (WDM) networks. I. INTRODUCTION I N present-day fiber-optic networks, data packets are converted to electrical form at each node to process their headers and make routing decisions, as shown in Fig. 1(a). As routing tables grow in size, more memory accesses are required to determine the next-hop address and appropriate output port to which to forward each packet. The associated increase in routing-table lookup times is becoming a significant source of latency in the network core. To make matters worse, the transmission capacity of optical fibers is rapidly increasing, forcing the routers to accommodate more packets, more often. Since routing tables will Manuscript

A Design for an Internet Router with a Digital Optical Data Plane

“…This process is sometimes simplified in modern routers, so that the forwarding table uses only fixed-length entries, replicating entries where necessary to represent shorter patterns. As a result, longest-prefix matching can be implemented as fixed-length pattern match, which itself can be implemented optically by a set of correlators (Figure 3, left) [13]. The number and length of the correlators can be managed by compressing the forwarding table to represent the most frequently used entries, in which several hundred thousand entries often can be sufficiently represented by approximately 100 entries (Figure 3, right) [14].…”

Components developed for all-optical Internet router

“…Our filter and address matching systems use pairs of complementary optical correlators that check for zeroes and ones in the pattern separately. 3 Our decrementer mechanism uses a single latch and comparator. 4 Our Internet checksum mechanism uses a single, two-input full adder.…”

Optical performance monitoring in optical packet-switched networks

“…But this solution is disadvantageous in cost and packaging losses (input/output coupling losses). A simpler, easily manufactured, and manageable correlator may be constructed by writing a series of fiber Bragg grating mirrors into a single length of fiber [Pet01,Hau03]. Indeed, in order to validate the OSNR monitoring technique a FBG-based correlator is designed and characterized by simulations.…”

“…In order to reduce this effect, the proposed correlator is designed with unequal grating spacing, i.e. with different time intervals, which is a novelty with respect to other correlators present in the literature [Hau03]. By means of simulations, a study of the correlator output as function of the pattern is carried out in order to decide which one provided better performance and less overhead.…”

“…To overcome Bragg wavelength detuning, the FBG should be written with the same index modulation depth and the reflectivity can be adjusted by varying the FBG physical length as it is explained in [Fsa06b]. According to this requirement, the index modulation used in the correlator is set to A FBG-based optical correlator is commonly constructed by using thermally controlled FBGs as tunable-reflectivity mirrors [Hau03]. The thermal control consists of a series of thin-film microheaters onto the surface of a single uniform grating which cause a shift in the grating spectrum towards longer wavelengths in response to the rise in temperature.…”