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Technical Approach
METON is studying the potential of exploiting an optical WDM network in the metropolitan area from several perspectives: network demands, dimensioning/cost issues, network/system functionality and architectures, manageability, transmission capability, technology choice. These issues are approached with theoretical studies of general cases, combined with experiences gained from practical system and component development towards a field demonstrator.
Network demands are identified by working out scenarios that are stressing present network technology. Different network scenarios and architectures can then be evaluated with the cost/dimensioning DIAMOND tool (Dimensioning Application for Multi-wavelength Optical Network Design) that has been developed in the project. Transmission modelling is also performed to identify scaleability limitations caused by interferometric cross-talk and noise.
A functional specification of a WDM network with respect to configuration, fault, and performance management has been produced, and in particular a fault and performance monitoring scheme that complies with the ITU-T G.otn architecture. Mapping of these functions into a management system requires an information model, which has been developed for those optical network elements that will be used, i.e., the OADM and OXC. The management system architecture conforms to the TMN architecture, which was confirmed in an optical network by RACE project MWTN. However, in METON new technologies are exploited, e.g., CORBA interfaces and a web based Graphical User Interface (GUI).
To enable exchange of management information between network elements an optical control channel is used, i.e. a dedicated wavelength channel, forming a new communication profile to the TMN Data Communication Network (DCN). A different channel, which is implemented as a modulated pilot tone superimposed on the SDH signal, provides for supervision along the path of individual optical channels.
The METON demonstrator will be upgraded continuously as new sub-systems are completed, tested and delivered, or when new software is developed. All new developments are focused on the optical transport layer and its functionality. For the purpose of this demonstration the wavelength allocation has been specified to a 400 GHz frequency scheme, where four channels have been selected: 193.5, 193.1, 192.7, and 192.3 THz.
The WDM-based optical layer in METON will consist of an optical cross connect (OXC) and five optical add/drop multiplexers (OADM). The OXC fabric will be based on the RACE MWTN architecture, in a more compact realisation and with enhanced functionality.
Each of the five OADM nodes will be constructed for evaluation of different wavelength selection technologies: bulk grating-, Fabry-Perot-, acousto-optic-, phased array-, multi-layer interference-, fibre Bragg-, grating assisted coupler-, planar Bragg-, multi-mode interference (MMI) technologies. To give an example, a prototype of an MMI-MZI device that demonstrates a tuneable 4-channel WDM has been realised in InP. OEICs represent another promising technology, that is under development for applications such as a 4-channel receiver and a non-linear O/E/O pulse reshaper. The goal of testing these technologies in the OADM nodes is to make a critical evaluation of different technical approaches under identical conditions encountered in the demonstrator.
To guarantee the optical signal quality in terms of frequency deviation, signal level, signal to noise ratio, and to detect any ambiguities in the network, supervision within the optical layer is necessary. Appropriate monitoring points are implemented to provide sufficient supervisory information for the management system.
An Optical Control Channel (OCC) enables transfer of management information and control signals over the network through the optical medium. Thus, remote optical nodes can be connected through an integrated control path.
Management Functional Architecture:
Network Manager (M), Sub-network Agent (SA) with intelligence, Agents (A).
Summary of Trial
The demonstration will be staged in the Stockholm Gigabit Network which is divided into a service/application layer, an ATM/SDH layer, and an optical transport layer. The network topology consists of two rings connected to each other through a centralised node. Five sites, distributed over the network as remote units, will have ATM multiplexers that provide user access to the network. An OXC, co-located with the ATM switch, performs the desired routing of the different optical channels over the network, whereas OADMs select and drop dedicated optical channels at each ATM multiplexer.
The first OADM node, based on a tuneable Fabry-Perot filter, is in operation in SGN with a CORBA management interface.
Key Issues
Demonstrator outline. To be demonstrated in Stockholm Gigabit Network
Achievements
Contact:
Patrik Evaldsson Ericsson Telecom AB S-126 25 Stockholm Sweden Tel: +46 8719 8592 Fax: +46 8719 6677 E-mail: etxpaev@kk.ericsson.se
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Photonics Domain
Network Interworking Chains
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