Upgradable photonic slot routing networks to cope with increasing capacity demands

Recently, Photonic Slot Routing (PSR) has been proposed as a practical solution for achieving optically transparent communication in Wavelength Division Multiplexing (WDM) wide-area networks. PSR makes use of available and simple wavelength-non-sensitive optical devices to switch data ows at di erent wavelengths, but in the same time slot, as a single unit. It thereby trades switching node complexity for network performance. With continuing tra c growth, the need to increase the network performance will, however, inevitably arise. As optical device technology progresses, it will become feasible to implement more complex switching nodes that can perform Individual Switching of the Wavelengths within a time slot (IWS). While IWS nodes can be expected, at least in the beginning, to be more costly than PSR nodes, they o er increased switching exibility, thereby potentially improving the network performance. This paper presents a solution that supports a gradual migration from a PSR-based network to an IWS-based network, by replacing selected PSR nodes with IWS nodes. We show that with a controlled migration towards an IWS-based network it is possible to gradually increase the capacity of the network to cope with increasing tra c demands. An important property of the solution is that upgrading a PSR node to an IWS node does not require any changes to the other nodes, or the network layout. In addition, using the NSFNET backbone topology as a benchmark, the paper shows that with an 80% PSR and 20% IWS network almost 50% of the performance reduction incurred by slot routing can be recovered.