Optical burst switching (OBS) is a promising technique for wavelength division multiplexing (WDM) networks. In practice, wavelength converters (WCs) are either absent or only sparsely deployed in WDM networks due to economic and technical limitations. Thus, wavelength assignment is expected to be an important component of OBS networks. In this paper, an offline wavelength assignment scheme in OBS networks without wavelength conversion capability is proposed. The key idea of the scheme is to decide the wavelength searching order of each traffic connection at edge nodes according to the wavelength priorities determined by the calculated burst loss probabilities on different wavelengths. Simulation results indicate that the proposed scheme can reduce the network-wide burst loss probability significantly compared with other schemes. It is also illustrated that the performance of the proposed scheme can be further enhanced by a larger number of wavelengths per link and a reasonable delay bound at edge nodes.

In order to meet the requirements of real-time applications, Optical Burst Switched backbone networks need to provide quantitative edge-to-edge loss guarantees to traffic flows. For this purpose, there have been several proposals based on the relative differentiation quality of service (QoS) model. However, this model has an inherent difficulty in communicating information about internal network states to the edge in a timely manner for making admission control decisions. In this paper, we propose an absolute QoS framework to overcome this difficulty. The key idea is to offer quantitative loss guarantees at each hop using a differentiation mechanism and an admission control mechanism. The edge-to-edge loss requirement is then translated into a series of small per-node loss probabilities that are allocated to the intermediate core nodes. The framework includes a preemptive differentiation scheme, a node-based admission control scheme and an edge-to-edge reservation scheme. The schemes are analyzed and evaluated through simulation. It is shown that the framework can effectively offer quantitative edge-to-edge loss guarantees under various traffic conditions.

In this paper, we describe and study a phenomenon unique to bufferless optical burst switched (OBS) networks called the streamline effect. This is the phenomenon wherein bursts within an input stream to a core node only contend with those from other input streams but not among themselves. It causes the burst loss probability at a link to depend strongly on the number of input streams to the link and their relative burst rates. We analyse the streamline effect and provide a burst loss probability formula that is more accurate than the traditionally used Erlang B formula. The formula is then used in a load balancing scheme for reservation-based quality of service (QoS) traffic to give a better link cost function. Through extensive simulation experiments for different traffic scenarios, we show that the proposed load balancing scheme utilising the streamline effect performs better than the shortest path routing scheme and the load balancing scheme without considering the streamline effect.

Recently, some absolute QoS schemes have been proposed to offer quantitative loss guarantees at core nodes in OBS networks. By moving the admission control process to core nodes, which have the most updated information about their own traffic conditions, these schemes can provide reliable and robust per-link loss guarantees. However, the issue of how to provide edge-to-edge guarantees for burst flows over the entire edge-to-edge paths have not been investigated in any of the proposals. In this paper, we propose a signalling and reservation scheme to coordinate the reservation and teardown process over the edge-to-edge path in the absolute QoS model. The key idea is to judiciously divide the edge-to-edge loss requirement into a series of small loss probabilities that are allocated to the intermediate links. The performance of the scheme is evaluated through simulation.