336 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 9, NO. 3, MARCH 1997 Reliability Analysis of an Optical ATM Switch Based on Wavelength Routing Lena Wosinska and Lars Thylen Abstract—Reliability studies of a demonstrated asynchronous transfer mode (ATM) switch with all-optical packet routing are presented. Calculations are based on available reliability data for commercial components. An additional inherent redundancy is shown to improve switch availability. Our calculation results further show that a proposed multiplane switch satisfies the general reliability requirement for switching systems. Index Terms—Asynchronous transfer mode, optical fiber com- munications, photonic switching, reliability estimations. I. INTRODUCTION A SYNCHRONOUS transfer mode (ATM) has been iden- tified as a standard switching technique for future broad- band networks. For this reason, several optical ATM-switching architectures have been proposed [1]–[3]. Telecommunications consumers demand a high degree of availability of service. Therefore, one of the system character- istics that must be analyzed before the system can be used in telecommunication applications is the system reliability. For that purpose, this paper presents reliability studies of a proposed and partially implemented optical ATM-switch, named OASIS [1], to investigate if OASIS satisfies the general requirement for switching systems (i.e. average downtime below 3 min/year [4]). OASIS is a photonic switch based on the wavelength-routing scheme, adopting the ATM technique, developed within the European RACE II project ATMOS (ATM Optical Switching). II. SYSTEM DESCRIPTION OASIS is described in detail in [1]. Here, we describe it briefly for better understanding the reliability model and reliability performance evaluation presented in the following sections. A switch module, shown in Fig. 1 [1], is a single-plane space-time switching matrix based on wavelength routing. In our calculations, we assumed as pro- posed in [1]. Each input provides ATM-cells at 2.5 Gb/s. For higher switch capacity, one has to build multistage switching structures (e.g., Clos-network) based on the 16 16 modules. Synchronization at the inputs, as well as header processing, is achieved in the electrical domain. The E/O converters before Manuscript received July 12, 1996; revised October 28, 1996. L. Wosinska is with the Royal Institute of Technology (KTH), School of Applied Engineering, Electrum 213, S-164 40 Kista, Sweden. L. Thylen is with the Royal Institute of Technology (KTH), Laboratory of Photonics and Microwave Engineering, Electrum 213, S-164 40 Kista, Sweden. Publisher Item Identifier S 1041-1135(97)01919-8. Fig. 1. ATM-switch schematic diagram [1]. each input (not indicated in the figure) are included in our reliability calculations. The switching module has an internally nonblocking struc- ture. An output buffer in the form of fiber delay lines is provided to avoid output blocking. If the buffer size is limited to 16 queue places (assuming that it is not practical to implement more than 16 fiber delay lines for each output), a four-plane structure is proposed in order to keep load at each input low enough to achieve cell loss probability less than 10 satisfying ATM service requirements [5]. Each output of the switching matrix is defined by a specific wavelength. Incoming cells to the switching matrix arrive in phase at the 16 inputs with their associated tags (5 b) and are wavelength-encoded by wavelength converters. It means that at the output of each converter the cells are at wavelengths appropriate to their destination outputs. To avoid collisions between synchronous cells with identical wavelengths, the time-switching block is provided, which is an optical partially shared buffer. The output of each wavelength encoder is connected to all the 16 fiber delay lines via 1 : 16 splitter and a set of 16 laser amplifier gates. Each fiber delay line is shared by up to 16 cells at different wavelengths which are assigned to the same queue place, since each fiber can support up to 16 cells at 16 different wavelengths in the same time slot. For this purpose, cells from every input are collected by a 16 : 1 combiner before they enter appropriate delay line. Then, the cells from all delay fibers are combined by 16 : 1 combiner, amplified by fiber amplifier (not indicated in Fig. 1) to compensate for power loss and wavelength demultiplexed. Wavelength encoding can, for example, be based on one of three devices listed below: 1) tunable DFB laser and semiconductor laser amplifier [6]; 1041–1135/97$10.00  1997 IEEE