Ivan Andonovic

Buffering in optical packet switches

This paper consists of a categorization of optical buffering strategies for optical packet switches, and a comparison of the performance of these strategies both with respect to packet loss/delay and bit error rate (BER) performance. Issues surrounding optical buffer implementation are discussed, and representative architectures are introduced under different categories. Conclusions are drawn about packet loss and BER performance, and about the characteristics an architecture should have to be practical. It is shown that there is a strong case for the use of optical regeneration for successful cascading of these architectures.

Transparent optical packet switching: the European ACTS KEOPS project approach

This paper reviews the work carried out under the European ACTS KEOPS (KEys to Optical Packet Switching) project, centering on the definition, development and assessment of optical packet switching and routing networks capable of providing transparency to the payload bit rate. The adopted approach uses optical packets of fixed duration with low bit rate headers to facilitate processing at the network/node interfaces. The paper concentrates on the networking concepts developed in the KEOPS project through a description of the implementation issues pertinent to optical packet switching nodes and network/node interfacing blocks, and consideration of the network functionalities provided within the optical packet layer. The implementation, from necessity, relies on advanced optoelectronic components specifically developed within the project, which are also briefly described.

Transparent optical packet switching: network architecture and demonstrators in the KEOPS project

This paper reviews the work carried out in the ACTS KEOPS (Keys to Optical Packet Switching) project, describing the results obtained to date. The main objective of the project is the definition, development, and assessment of optical packet switching and routing networks, capable of providing transparency to the payload bit rate, using optical packets of fixed duration and low bit rate headers in order to enable easier processing at the network/node interfaces. The feasibility of the KEOPS concept is assessed by modeling, laboratory experiments, and testbed implementation of optical packet switching nodes and network/node interfacing blocks, including a fully equipped demonstrator. The demonstration relies on advanced optoelectronic components, developed within the project, which are described.

Approaches to optical Internet packet switching

Wavelength-division multiplexing is currently being deployed in telecommunications networks in order to satisfy the increased demand for capacity brought about by the explosion in Internet use. The most widely accepted network evolution prediction is via an extension of these initial predominantly point-to-point deployments, with limited system functionalities, into highly interconnected networks supporting circuit-switched paths. While current applications of WDM focus on relatively static usage of individual wavelength channels, optical switching technologies enable fast dynamic allocation of WDM channels. The challenge involves combining the advantages of these relatively coarse-grained WDM techniques with emerging optical switching capabilities to yield a high-throughput optical platform directly underpinning next-generation networks. One alternative longer-term strategy for network evolution employs optical packet switching, providing greater flexibility, functionality, and granularity. This article reviews progress on the definition of optical packet switching and routing networks capable of providing end-to-end optical paths and/or connectionless transport. To date the approaches proposed predominantly use fixed-duration optical packets with lower-bit-rate headers to facilitate processing at the network-node interfaces. Thus, the major advances toward the goal of developing an extensive optical packet-switched layer employing fixed-length packets are summarized, but initial concepts on the support of variable-length IP-like optical packets are also introduced. Particular strategies implementing the crucial optical buffering function at the switching nodes are described, motivated by the network functionalities required within the optical packet layer.

SLOB: a switch with large optical buffers for packet switching

Recently, optical packet switch architectures, composed of devices such as optical switches, fiber delay lines, and passive couplers, have been proposed to overcome the electromagnetic interference (EMI), pinout and interconnection problems that would be encountered in future large electronic switch cores. However, attaining the buffer size (buffer depth) in optical packet switches required in practice is a major problem; in this paper, a new solution is presented. An architectural concept is discussed and justified mathematically that relies on cascading many small switches to form a bigger switch with a larger buffer depth. The number of cascaded switches is proportional to the logarithm of the buffer depth, providing an economical and feasible hardware solution. Packet loss performance, control and buffer dimensioning are considered. The optical performance is also modeled, demonstrating the feasibility of buffer depths of several thousand, as required for bursty traffic.

Packet loss and delay performance of feedback and feed-forward arrayed-waveguide gratings-based optical packet switches with WDM inputs-outputs

This paper analyzes the packet loss and delay performance of an arrayed-waveguide-grating-based (AWG) optical packet switch developed within the EPSRC-funded project WASPNET (wavelength switched packet network). Two node designs are proposed based on feedback and feed-forward strategies, using sharing among multiple wavelengths to assist in contention resolution. The feedback configuration allows packet priority routing at the expense of using a larger AWG. An analytical framework has been established to compute the packet loss probability and delay under Bernoulli traffic, justified by simulation. A packet loss probability of less than 10/sup -9/ was obtained with a buffer depth per wavelength of 10 for a switch size of 16 inputs-outputs, four wavelengths per input at a uniform Bernoulli traffic load of 0.8 per wavelength. The mean delay is less than 0.5 timeslots at the same buffer depth per wavelength.

Solution paths to limit interferometric noise induced performance degradation in ASK/direct detection lightwave networks

Interferometric noise, arising on the optical interference of the desired information signal and parasitic crosstalk waveforms at the photodetector, afflicts practically all lightwave communication networks, inducing unacceptable power penalties and bit error rate floors. In this paper, the induced performance degradation is quantified, both experimentally and analytically, and solution paths are identified. It is concluded that the total crosstalk level of noise generating parasitics in a generalized optical network must be held below -25 dB for a penalty of less than 1 dB-a further 2 to 4 dB may lead to network failure; otherwise, means of suppressing the noise by RF rejection at the receiver must be invoked. A number of approaches to achieving a reduction in the level of interferometric noise are presented and contrasted.

On the various time constants of wavelength changes of a DFB laser under direct modulation

The temporal behavior of the optical frequency emitted by several DFB lasers under direct square wave modulation was measured using an all-fiber implementation of a Mach-Zender interferometer with an imbalance of 30 ps. The impulse response of the optical frequency to injection current modulation was found to contain a time constant as short as 10-20 ns, together with a few longer ones. The existence of such a short time constant is consistent with a thermal analysis of a laser structure with finite thermal impedance of the active region and should be taken into consideration in various wide bandwidth applications of direct modulated semiconductor lasers.

Dynamic bandwidth allocation algorithm for differentiated sservices over WDM EPONs

A variety of passive optical network (PON) systems has been proposed to target the bottleneck problem in the local access. The medium access controls (MACs) of the PON systems are either based on cyclic rotation or polling mechanism. However, these MACs have inherited a potential problem; the cycle time (or polling cycle in the polling MACs) increases linearly as the number of attached ONUs scale up, which can be caused by increasing customer numbers. The longer cycle time means that the ONUs have to wait longer before the next transmission window arrives thus contributing to longer packet delays and poorer QoS. In this paper, a new WDM PON system is proposed where multiple wavelength channels are established in both upstream and downstream directions. The MAC applied is based on an adaptive polling mechanism, and can be used as an upgrade solution for PON systems

2/spl times/2 buffered switch fabrics for traffic routing, merging, and shaping in photonic cell networks

An approach to optical packet switching is discussed, which uses small, simplified optical elements for traffic routing, merging, and shaping. The elements are constructed from 2/spl times/2 switches and optical delay lines, and may be implemented in a variety of technologies. They are designed for use with deflection routing, and even when using only six switches in a module, a deflection probability of 2.8/spl times/10/sup -7/ is possible with a load of 0.8. The modules may also be used as 2/spl times/1 mergers where a deflection probability of 10/sup -12/ is possible with six switches and a total load of 0.8. The BER performance of the modules is simulated with respect to crosstalk, with even relatively poor switch devices of -18.5 dB isolation yielding a power penalty of less than 1 dB. A networking strategy radically different from todays is discussed, driven by the need to reduce hardware, software and operating costs.