<strong>Grid</strong> <strong>Job</strong> <strong>Routing</strong> <strong>Algorithms</strong>• 3R Regeneration (reamplification with reshaping and retiming): This includes signal amplification,reshaping and retiming that completely reset the effects of any impairment that the signal has experienced.By using optoelectronic regeneration we can assure that the signal can reach large distances, since whentransformation to the electrical domain also causes the signal to be cleaned and compensated for any noise,dispersion impairments and fiber nonlinearities. On the other hand the use of regeneration poses somelimitations. Most of the regenerators used nowadays are optoelectronic as their all-optical counterparts are notfeasible because of immature technology which imposes the use of bit rate and modulation format specificdevices. Also regenerators are expensive devices and operate on a wavelength per wavelength basis whichmeans that we require one regenerator for each wavelength on a link thus increasing thus the overall cost.Second generation networks obviate the need for conversion to the electronic domain by providing switchingand routing services at the optical layer. These networks are known as all-optical networks (transparentnetworks) and offer a reduction of unnecessary and expensive optoelectronic conversions, providing thus anability for high data rate, flexible switching, and support of multiple types of clients (different bit rates,modulation formats, protocols, etc.) In all-optical networks the signals are transported end-to-end optically,without being converted to the electrical domain along their path. This reduces complexity and overheads andoffers reduction of unnecessary and expensive optoelectronic conversions. However, due to the analoguenature of the optical networks as the optical signals propagate through the fibers, they experience severalimpairments degrading their performance. This has a direct impact on the dimensions that an all-opticalnetwork can support. Therefore when performing routing in all optical networks is of significant importance tocapture and take into account as much as possible all the impairments that affect and deteriorate the quality ofthe signal in order to improve the overall network performance.However, some optoelectronic conversion capability, at least to some limited extent and degree, may still bedesirable for several reasons. These reasons have to do mainly with wavelength conversion, protection,grooming, aggregation, demarcation, network monitoring, etc. Therefore, independent of transparencyrequirements it seems that some limited optoelectronic conversion may be unavoidable for purposes that arenot directly connected to the quality of the signal at the receiving nodes. For this reason islands of transparencywere recently proposed [Wagner00] as a compromise between all-optical and opaque networks. In thesenetworks selective regeneration is used at specific network locations as needed in order to maintain acceptablesignal quality from source to destination. This approach reduces the number of regenerators requiredcompared to the case of opaque networks, but requires more complicated monitoring of the signal quality andresource allocation schemes.3.2 <strong>Routing</strong> in Optical networksWith recent technology advances optical networks are evolving from simple point-to-point links into transparentarchitectures supporting switching using optical add/drop multiplexer (OADM) and optical cross-connect (OXC)nodes.Project:PHOSPHORUSDeliverable Number: D.5.3Date of Issue: 31/06/07EC Contract No.: 034115Document Code: <strong>Phosphorus</strong>-WP5-D5.316
<strong>Grid</strong> <strong>Job</strong> <strong>Routing</strong> <strong>Algorithms</strong>OADMs are elements that provide capability to add and drop traffic in the network (similar to SONET ADMs).They are located at sites supporting one or two (bi-directional) fibre pairs and enable a number of wavelengthchannels to be dropped and added reducing the number of unnecessary optoelectronic conversions, withoutaffecting the traffic that is transmitted transparently through the node (Figure 3.1).nλTx…1 mOADM…Tx1 mRxRxn>mnλFigure 3.1: Generic Optical Add/Drop Multiplexer (OADM) architectureOptical cross-connects (OXCs) are located at nodes cross-connecting a number of fibre pairs and alsosupport add and drop of local traffic providing the interface with the service layer. To support flexible pathprovisioning and network resilience, OXCs normally utilise a switch fabric to enable routing of any incomingchannels to the appropriate output port and access to the local client traffic. Various OXC architectures havebeen proposed and a common design is based on switches that are surrounded by wavelengthmultiplexers/demultiplexers as shown in Figure 3.2. Thus, an OXC can cross-connect the different wavelengthsfrom the input to the output, where the connection pattern of each wavelength is independent of the others. Byappropriately configuring the OXCs along the physical path, a logical connection may be established betweenany pair of edge nodes.Control Plane11.Opticalfabric.11nn11m..mnn……AddDropCh conditioning orλ conversion & ch conditioningFigure 3.2: Transparent optical cross-connect (OXC) technologiesProject:PHOSPHORUSDeliverable Number: D.5.3Date of Issue: 31/06/07EC Contract No.: 034115Document Code: <strong>Phosphorus</strong>-WP5-D5.317
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