Analysis of optical burst switched networks with edge-core joint nodes

Abstract

The evolution of high speed transmission technology is driven by the continuous growth of data-traffic. Third generation optical networks are envisioned as the most appropriate solution to meet future bandwidth and scalability demands by means of all-optical switching. Optical burst switching (OBS) is proposed as a switching paradigm that offers both, flexibility and efficiency, through exploiting statistical multiplexing in the optical domain. The OBS networks may be divided into edge nodes connecting the optical domain with the digital domain, and core nodes that switch optical bursts toward their destination. Incoming data packets are assembled into optical bursts at ingress nodes. These bursts are then transmitted hop-by-hop over wavelength division multiplexed (WDM) optical fiber links, commonly using an unacknowledged one-way reservation protocol. The transmission of many packets encapsulated in few bursts reduces the per-packet processing overhead, and the one way reservation scheme enables a latency considerably shorter than the latency required to reliably setup an optical circuit. For practical deployments the majority of OBS nodes will have to combine both functionalities, that of edge nodes and that of core nodes. This thesis focuses on the study of these combined nodes, hereinafter called edge-core joint nodes (ECJN). The major challenge in the design of an ECJN is that the locally assembled bursts and the transit bursts are switched to the same output channels. The first can be buffered, the latter not, which causes a hybrid queueing/loss system. In this PhD thesis, the performance of OBS networks composed of ECJN is evaluated through simulation studies. It is shown that the transit traffic volume affects the waiting time of locally assembled bursts, and vice versa, that a high ingress data-rate causes increased burst loss-rates for the transiting bursts.<br />The combination of bufferless core nodes with a one-way reservation strategy causes that sometimes a burst would require a currently occupied resource, and that in consequence it is dropped. Thus, assured transmission is out of the scope for any OBS network of this kind. To reduce this issue several contention resolution approaches have been proposed in the literature; fiber delay lines (FDLs) and deflection routing are the most generic among them.<br />Considering ECJN we recognize that these in principle have all the facilities required to electronically buffer and later re-insert a blocked transit burst. In the second part of this PhD thesis the option to buffer transit bursts is examined as contention resolution approach.<br />Because electronic buffering is opposing the OBS intention, we concentrate on restricted intermediate buffering (RIB) and show by simulation results that with limited buffering options the burst loss rate can be significantly reduced.<br />Finally, the PhD thesis emphasizes on adaptive burst routing techniques.<br />Strategies proposed for OBS in the literature are evaluated and compared by means of simulation studies. A smart route selection strategy is defined, one which is adaptable to different network topologies, and it is shown to perform better for all considered scenarios. Also for uniform as well as distance dependent traffic distribution it achieves reduced burst blocking probability and better network utilization.<br />