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Quality of Service in Optical Burst-Switched Networks
Optical burst switching (OBS) is an all-optical data transport technique. In OBS networks, packets with the same destination address are aggregated in bursts by edge nodes. Then, before the burst transmission, the aggregating edge node sends a control packet to establish an all-optical path in an out-of-band signaling channel. The network resources are only held for the burst switching and transmission time and core nodes do not need buffers to store and process bursts. The quality-of-service (QoS) support is essential in OBS networks. Despite the bandwidth availability, the best-effort service is not able to guarantee the QoS required by new applications. The main problem is that only a few tens of wavelengths are available per optical link nowadays. Once a burst occupies one wavelength, or a fraction of it, during the transmission, some bursts will be blocked depending on the load offered to the network. In addition, the existing QoS mechanisms are proposed for packet switched networks and, at most, are based on management of electronic buffers. To employ these mechanisms in OBS networks, it is necessary to convert the optical signal to the electronic domain at each edge node, which limits the data transport rate. Such factors lead to development of OBS-specific QoS mechanisms. We proposed an admission control mechanism for providing service differentiation in OBS networks. The idea behind the Load-Level-based Admission Control Mechanism (LLAC) is to reserve a different amount of wavelengths in a link for each service class. The number of wavelengths that a class can occupy in a link is defined by a parameter called load level. Thus, LLAC differentiates the blocking probability experienced by a given class, admitting bursts according to the network load and the load level associated to this class. Selected Publications
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