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SUMMARYOptical burst switching (OBS) provides a future-proof alternative to the current electronic switching in the backbone, but has buffering implemented with a set of fiber delay lines (FDLs). The resulting buffering system fundamentally differs from a classic one, in that the set of possible waiting times is not a continuum (like in the classic case) but rather a denumerable set, each value corresponding to the length of a delay line. As a result, arriving bursts in general have to wait longer than they would in a classic buffer, since their waiting time has to be in that denumerable set. The additional delay results in overall longer waiting times, when compared to a classic infinite buffer system with a continuous waiting room. While previous work already focused on the performance evaluation of finite optical buffers, the stability problem of the infinite system received only little attention. This contribution is the first to present a complete proof of sufficient stability conditions in the case of a general infinite FDL set, general arrival process and general service times. The key elements of analysis is the exploiting of the regenerative property of the waiting-time process and a characterisation of the limiting forward renewal time process. The given bound on the traffic load guarantees stability for a wide class of GI/G/1 optical buffers, and poses no restriction on the FDL lengths.

We investigate the behaviour of an asynchronous optical buffer by means of a continuous-time queueing model. Through a limit procedure, previously obtained results for a discrete-time queueing model are translated to a continuous-time setting. We also show that the same results can be obtained by a direct analysis using Laplace transforms. Closed-form expressions are obtained for the cases of exponentially distributed burst sizes, deterministic burst sizes and mixtures of deterministic burst sizes.The performance of asynchronous optical buffers shows the same characteristics as that of synchronous optical buffers: a reduction in throughput due to the creation of voids on the outgoing channel and a burst loss probability that is strongly influenced by the choice of fiber delay line granularity. The optimal value of the latter depends on the burst size distribution and the offered load.

Abstract. Optical Burst Switching proposes a future-proof alternative to the current electronic switching in the backbone. The involved optical buffers are implemented with a set of Fiber Delay Lines, and suffer serious performance loss, when compared to RAM. Various existing models trace this loss, but either lack generality, accuracy, or effectiveness. The optical buffer model we constructed is valid for general line lengths and burst sizes. An effective approach allowed to strongly reduce the solution's complexity, while remaining exact. This document presents the key formulas and performance graphs. The obtained model serves as a basic optimization tool, yielding results fast.

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