We analyze the throughput of fixed-length, variable-capacity (FL-VC) packet technology in OPS MANs with lengths up to several tens of kilometers. Compared to conventional OPS networks using fixed-bit-rate packets, FL-VC often offers throughput increases of ≃50% to TCP flows, and of ≃100% to UDP flows, under realistic traffic patterns. Throughput also increases with respect to equivalent topologies where switches have random-access buffers.

Due to lack of optical RAM buffers in fast optical switches (FOS), statistical multiplexing technologies using FOS like Optical Burst Switching (OBS) or Optical Packet Switching (OPS) are expected to have higher data losses than conventional electronic networks. Consequently, applications transferring data by means of TCP can suffer from a lower throughput. In this paper, we show that this low-throughput problem is mainly an artifact caused by the conventional TCP congestion control algorithms, and can be remedied by using a simple yet effective stop-and-wait congestion control algorithm instead, as long as the propagation delay between TCP source and TCP destination is small compared to the transmission time of an optical packet. We show that such a condition holds for a wide range of scenarios, including fat-tree-based data center networks. We also show that the throughput achieved in a FOS network using stop-and-wait can be the same as, or higher than that in an equivalent, conventional electronic network.

In this paper, we propose probabilistic splitting of a packet stream at the edge routers as the basic method to provide end-to-end proportional QoS to packet flows carried through an OBS network, in terms of loss probability. We argue that the only requirement that the optical transport infrastructure has to satisfy is the support for two internal burst classes with wide separation between their respective service levels. Under this condition, we show how quantifiable end-to-end per-flow guarantees can be attained without diminishing network resource usage. The scheme is analyzed theoretically and evaluated through numerical simulations, both in regular topologies (ring networks) and in a mesh network. Our results suggest that a layered approach to the problem of end-to-end QoS provisioning can be very effective when a proportional service model is offered, and that the research on sophisticated scheduling algorithms at the optical switches could be too narrow-focused for that purpose.

This paper addresses the provision of proportional differentiated services to an arbitrary number of traffic classes in terms of the class packet loss probability measured between the ingress node and the egress node of an OBS network. Our solution relies on a key idea: OBS networks consist of bufferless nodes and can therefore be regarded as a whole like a one-hop bufferless subnetwork characterized by a collection of loss probabilities computable with simple, approximate circuit switching models. Consequently, we believe it is possible to attain packet loss proportionality merely using a simple stochastic algorithm to assemble two classes of bursts, provided there exists some form of internal relative differentiation such that one of the burst classes has a much lower loss probability than the other. In order to evaluate the algorithm accuracy in attaining the proportionality, we present an analytical study of two idealized scenarios (a single link and a multi-node symmetrical network), including the effect caused by the flow dynamics of the traffic received at the ingress nodes. Our results show that, despite its simplicity, this approach is able to provide the desired proportionality over a wide range of operating conditions.