Philip Dumortier

Guidelines for scalable optical telecommunication networks

Optical networks based on wavelength division multiplexing (WDM) hold some promising features for application as future worldwide telecommunication transport network. Besides the obvious advantage of increased transmission capacity, optical routing of wavelengths by means of optical crossconnect nodes, allows to overcome the routing bottlenecks of electrical nodes, and enables the transport of high bandwidths at once over long distances. This paves the way to simpler and less-hierarchical networks, an important property to keep future networks manageable. In any case, not all WDM-based architectures can be simply extrapolated to a worldwide scale. Some seemingly scalable elements of these architectures saturate at some point along network expansion. This paper analyses scalability issues related to the core network.

IP multicast shortcut over ATM: a winner combination

The philosophy of full IP control over ATM equipment has been advocated by the Multi-Protocol Label Switching (MPLS) working group of the Internet Engineering Task Force (IETF), as a fairly simple but promising approach to boost Internet throughput. Existing IP routing protocols run on ATM switches to do topology discovery and route calculation, but packet forwarding is done by switching encapsulated IP packets directly in ATM, i.e. by shortcutting the IP forwarding engine. This paper evaluates the potential of applying this model to IP multicast, based on the experience gained from a lab prototype that demonstrates the concept of IP multicast shortcut over ATM.

Dual-mode routing in IP over ATM networks

The purpose of this paper is to investigate how to design an integrated routing architecture for IP and ATM meeting the requirements for a large scale Internet based on IP and ATM. Integration of IP and ATM at the routing level leads us to consider two separate aspects: using a common routing architecture for IP and ATM on one hand (layer integration) and, on the other hand, integrating best-effort and QoS traffic support in the same routing architecture (service integration). The first level of integration is, for obvious reasons, highly recommended. In contrast, we show that the second level of integration is not desirable because best- effort and QoS traffic flows have, in terms of routing contradictory requirements. To conduct this analysis, we feel that, because of the inherent complexity of the problem, confronting the existing proposals is too restrictive. Instead, we propose to go one step back in the design process and identify the basic design options to be considered when designing a routing architecture. We identify three options, namely, route updating vs. route pinning, hop by hop vs. explicit routing and pre-computed routes vs. on-demand route computation. A fourth option is whether or not to integrate in the routing architecture the capability to compute shortcut paths, that is, bypassing layer 3 (L3) nodes and using only layer 2 (L2) devices. Using this framework, we conclude that best-effort traffic flows are well served by a combination of route updating, hop by hop routing and pre-computed routes while QoS flow routing is built on route pinning, explicit routing and on-demand route computation. We also observe that the capability to compute L2 shortcuts in an L2/L3 integrated routing architecture is an added value simplifying the overall network design and optimizing the efficiency of the forwarding path.

Optical network architecture for future global telecommunications

The introduction of Wavelength Division Multiplexing techniques into fiber networks opens perspectives for a global transport optical telecommunication backbone. By using signal transparent optical crossconnects, based on space and wavelength routing, a rearrangeable network topology can be achieved. Local exchanges could, in principle, be connected directly to each other through end-to-end transparent optical paths. Nevertheless, to attain a full- meshed interconnection, a relatively large number of wavelength channels is required between two nodes, growing rapidly to unrealistic numbers. Therefore, in order to achieve a more scalable network architecture, it is necessary to improve the routing granularity, without compromising too much the optical transparency and network simplicity. The architecture proposed introduces the required granularity by dividing the network in overlapping partitions, accessing the time domain at partition boundaries. The result is a scalable, flexible and simple high-capacity network architecture, ready to cope with future telecommunication demands well into the next century.