This paper addresses the problem of controlling the performance of optical burst switching (OBS) networks in presence of non-stationary traffic demands. We propose a joint burst admission control and forwarding mechanism that operates in core nodes. This mechanism dynamically adapts its behaviour according to the feedback messages received from other nodes. By not forwarding certain bursts not complying with given requirements, an admission control is implicitly made. Moreover, by forwarding bursts to appropriately selected nodes, traffic balancing is achieved. The advantageous effects of the proposed mechanism can additionally be amplified by granting extra offset time to the burst. The benefits provided by this mechanism are supported by numerical results. Keywords: optical burst switching, adaptive routing, deflection routing, performance analysis.
INTRODUCTIONModern communication networks are intended to deal with highly varying traffic conditions. The demands they have to carry out often imply traffic intensities varying both in the short and long term. Since the data traffic is generally statistically multiplexed, the networks that are subject to the varying traffic conditions are always susceptible to congestion states, in particular, to transient congestion due to short term traffic fluctuations, and to semi-permanent congestion due to long term traffic variation. Several approaches have been considered in order to diminish the network congestion under varying traffic demands. One consists in delaying temporarily the data traffic by means of buffering, which allows postponing the transmission until the outgoing link is available. This approach is effective for solving transient congestions but not for semi-permanent ones. It is also possible, when applying proper routing, to take advantage of the whole network capacity rather than only the one available on a specific path. Thus, by distributing intelligently the traffic over the network, permanent congestion can be avoided. Transient congestions can also be alleviated if alternative (or deflection) paths toward destination are explored. Eventually, in critical cases, a Connection Admission Control (CAC) mechanism can limit the amount of traffic entering or travelling through the network. In this way, the traffic supposed to cause congestion anyway is dropped, prior to consume network resources.On the other hand, high-capacity communication networks make an extensive use of photonic technologies. Primarily reserved to point-to-point transmission, fibre optics progressively acquired new functionalities such as switching and routing. With the advent of Wavelength Dimension Multiplexing (WDM) and optical crossconnects (OXC), Optical Circuit Switched (OCS) networks have been deployed, with nodes able to route transparently an optical signal (lightpath) to the next hop. Moreover, two upcoming technologies, Optical Packet Switching (OPS) and Optical Burst Switching (OBS) have been proposed to achieve statistical multiplexing directly at the optical leve...