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avelength-division multiplexing (WDM) is currently being deployed in telecommunications networks in order to satisfy the increased demand for capacity brought about by both narrowband services and new broadband services such as high-speed Internet. While it is thought that WDM will ultimately evolve to interconnected rings or perhaps a mesh network, the objective of the Wavelength Switched Packet Network (WASPNET) project is to gain a more long-term understanding of how optical networks will develop. WASPNET is a WDM transport network that uses optical packet switching, resulting in greater flexibility, functionality, and granularity than possible with the current generation of WDM networks. These optical packets may be used to carry asynchronous transfer mode (ATM) or IP, for example, and the network is also designed to support synchronous digital hierarchy/synchronous optical network (SDH/SONET) traffic, thus permitting a smooth upgrade path. Optical packet switches [1-3] have attracted considerable research interest internationally due to their potential for overcoming projected difficulties with very large electronic switching cores, such as connection, pinout, and electromagnetic interference (EMI) problems. A key problem when designing packet switches of any kind is contention resolution, since multiple packets may arrive asynchronously at the same time to go to the same output. Buffering is often employed to solve this problem, but since optical random access memory (RAM) does not exist, delay lines (usually made of optical fiber) must be used to store optical packets and implement buffering. Various solutions to optical packet switching have been proposed, dictated by the buffering strategy [1]. Implement Medium to Large Buffers-The switches implemented by this technique may be cascaded to implement very large buffers, suitable for bursty traffic. Use No Buffers in the Switch Nodes, but Employ Deflection Routing-When multiple packets arrive destined for a given output, all but one are "deflected" to other outputs, to find their way to the destination by another route through the network. This not only provides fast and flexible routing, but also allows nodes to have no buffering. However, each packet transmitted from a node may be routed across a different path to the same destination. Some packets may wander within the network and waste bandwidth. Consequently, each packet will experience different propagation delays, and the traffic may not arrive at the destination node in sequence. Compromise by Using a Small Amount of Buffering with Deflection Routing-There are various such 2 x 2 buffered switches consisting of a chain of 2 x 2 switch devices and delay lines.

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 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.

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Communication networks are undergoing dramatic changes due to increasing demands from a diversity of users. Consumers, scientists, business users all have there own specific requirements on the network in terms of bandwidth, quality of service, network resources (storage and processing). Optical technology has a key role to play in enabling networks that can support these demands, and this tutorial looks at how optics will increasingly penetrate the network. The tutorial will review the current status of networking, the role of optics in future networks (including current roadmap visions of the switching technologies to be used), major recent programmes [on optical networking] in regions of the world such as USA, Japan and EU are described.

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