In spite of its long term promise, all-optical switching is still plagued by high cost, low efficiency when handling bursty data traffic, immature management and protection and poor output port contention resolution leading to heavy loss. Given the current situation, hybrid approaches that keep the best features of optics, reverting to the electrical plane when expedient, constitute sensible interim steps that can offer cost-effective solutions along the road to an eventual all-optical core. Two such approaches developed in the framework of the European IP project NOBEL are presented in this work. The first is a quite mature solution that extends present day concepts to achieve multiplexing gain while keeping all the management and restoration benefits of SDH. The other mimics early LANs in executing a distributed switching via its electrical control plane using two-way reservations, thus restricting its applicability to smaller domains. Combining the two leads to a system fulfilling most of today's requirements for Tb/s core networks.
IP based traffic is seen as the convergence protocol for all future services and is already dominating today's networks. From the current situation with circuit switched SDH/SONET and packet switched IP backbones, an evolution is described towards long term optical transport network architectures featuring multi-layer transport with a novel Layer 2 transport service based on optical and opto-electronic burst/packet techniques as convergence layer providing the flexibility, scalability, reliability and Quality-of-Service to support all future higher layer services optimizing both CAPEX and OPEX. The operation of such a network will be mostly automatic supported by an integrated Control Plane on the basis of GMPLS protocols covering Layer 1, Layer 2 and Layer 3 (vertical integration of WDM, SDH, Ethernet, Bursts, IP etc.) and providing end-to-end control over various administrative and vendor domains (horizontal integration). The introduction of a new L2 transport service and its integration into a multi-layer Control Plane will be a long term evolutionary process also involving the necessary steps in the evolution of current standards. A few examples of network architectures and solutions are described together with dimensioning and control aspects and their relation to a roadmap for the introduction of optical burst/packet networks.
With the high interest of network operators and manufacturers for wavelength division multiplexing (WDM) networking technology, the need for management systems adapted to this new technology keeps increasing. We investigated this topic and produced outputs through the specification of the functional architecture, network layered model, and through the development of new, TMN- based, information models for the management of optical networks and network elements. Based on these first outputs, defects in each layer together with parameters for performance management/monitoring have been identified for each type of optical network element, and each atomic function describing the element, including functions for both the transport of payload signals and of overhead information. The list of probable causes has been established for the identified defects. A second aspect consists in the definition of network-level parameters, if such photonic technology-related parameters are to be considered at this level. It is our conviction that some parameters can be taken into account at the network level for performance management, based on physical measurements within the network. Some parameters could possibly be used as criteria for configuration management, in the route calculation processes, including protection. The outputs of these specification activities are taken into account in the development of a manageable WDM network prototype which will be used as a test platform to demonstrate configuration, fault, protection and performance management in a real network, in the scope of the ACTS-MEPHISTO project. This network prototype will also be used in a larger size experiment in the context of the ACTS-PELICAN field trial (Pan-European Lightwave Core and Access Network).
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