This paper reviews recent work on photonic packet switching. Di#erent approaches to photonic packet switching and key design issues are discussed.

Photonic slot routing has been proposed as an approach to implement an all-optical packet-switched network in a manner which is scalable and not overly complex. In photonic slot routing, packets are transmitted within a basic transport unit referred to as a photonic slot. The photonic slot is fixed in length and spans multiple wavelengths. Each photonic slot is routed through the network as a single entity; thus, individual wavelengths do not need to be multiplexed or demultiplexed at intermediate nodes through which the photonic slot is traversing. When implementing photonic slot routing in a mesh environment, a number of significant issues must be addressed. Two such issues are fairness and contention resolution. In this study, we propose a novel approach for allocating capacity on each link in a fair manner, and we investigate various approaches, such as buffering and deflection, for handling contention. We develop an analytical model to evaluate the performance of such networks, and validate the analysis through simulation. It is shown that the proposed capacity allocation approach can significantly reduce contention in the network and provide a fair allocation of bandwidth to each source-destination pair. 1

For the future development of residential broadband telecommunication services the present access infrastructure must be upgraded. Fiber-To-The-Home (FTTH) optical networks, though still expensive today, appear to be a future-proof solution. FTTH networks based on passive optical Remote Nodes (RN) and supporting ATM switching (ATM-PONs) have been demonstrated and are going to be standardized. In these networks the optical hardware in the RN is very simple, but a multiple access protocol is needed for upstream traffic control. In most protocols proposed in literature the control is performed electronically in a centralized wayby the Central Office (CO). In this paper we study multiple access schemes for FTTH networks which perform upstream traffic control in a distributed way with the intervention of the user Optical Network Terminations (ONTs) and of the RN only.We will also consider the case, based on recent research in photonic packet switching, in which the RN is able to perform alloptical ATM-multiplexing. We will employ ONT-RN signalling to make the relatively expensive RN optical buffer co-operate with the electronic buffers located in the ONTs. The different solutions presented will be compared by simulating the network behavior under various traffic conditions. In conclusion, in this work we evaluate performance advantages achievable in FTTH networks by increasing the optical complexity of the RN and by introducing control schemes which allow a distributed upstream traffic management and, in the case of an RN able to perform all-optical ATM-multiplexing, the co-operation of the RN buffer with the ONT buffers.

Dense wavelength-division multiplexing (DWDM) technology has provided tremendous transmission capacity in optical fiber communications. However, switching and routing capacity is still far behind transmission capacity. This is because most of today's packet switches and routers are implemented using electronic technologies. Optical packet switches are the potential candidate to boost switching capacity to be comparable with transmission capacity. In this paper, we present a photonic asynchronous transfer mode (ATM) front-end processor that has been implemented and is to be used in an optically transparent WDM ATM Multicast (3M) switch. We have successfully demonstrate the front-end processor in two different experiments. One performs cell delineation based on ITU standards and overwrites VCI/VPI optically at 2.5 Gb/s. The other performs cell synchronization, where cells from different input ports running at 2.5 Gb/s are phase-aligned in the optical domain before they are routed in the switch fabric. The resolution of alignment is achieved to the extent of 100 ps (or 1/4 bit). An integrated 1 2 Y-junction semiconductor optical amplifier (SOA) switch has been developed to facilitate the cell synchronizer.