Optical Networks - _8_5 Performance and Fault Management_98

Optical Networks - _8_5 Performance and Fault Management_98...

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8.5 Performance and Fault Management 481 equipment from a single vendor. For example, a subnet could simply be a WDM link with some intermediate add/drops. Therefore, a service provider could deploy vendor A’s equipment on one link and vendor B’s equipment on another link and have them interoperate through transponders. The interface between the transponders could be either SONET/SDH or OTN, which we will study in Section 8.5.7. In addition to accomplishing interoperability at the data level, we also need to have interoperability as far as the control and signaling protocols are concerned, particularly if we are using the distributed methods discussed in Section 8.6.2. 8.5 Performance and Fault Management As we stated earlier, the goal of performance management is to enable service providers to provide guaranteed quality of service to the users of their network. This usually requires monitoring of the performance parameters for all the connec- tions supported in the network and taking any actions necessary to ensure that the desired performance goals are met. Performance management is closely tied in to fault management. Fault management involves detecting problems in the network and alerting the management systems appropriately through alarms. If a certain pa- rameter is being monitored and its value falls outside its preset range, the network equipment generates an alarm. For example, we may monitor the power levels of an incoming signal and declare a loss-of-signal (LOS) alarm if we see the power level drop below a certain threshold. In other cases, alarms could be triggered by outright failures, such as the failure of a line card or other components in the system. Fault management also includes restoring service in the event of failures, a subject that we will cover in detail in Chapter 9. This function is considered an autonomous network control function because it is typically a distributed application without net- work managment intervention (except for configuring various protection parameters up front, reporting events, and performing maintenance operations). 8.5.1 The Impact of Transparency The lightpaths provided by the optical layer need to be managed just like SONET and SDH connections are managed. To a large extent, the amount of management that can be provided depends on the level of transparency provided by the optical layer. As we have seen in Chapter 1, different levels of transparency are possible, based on the range of signals, bit rates, and protocols that can be carried on a lightpath. In a purely transparent network, a lightpath will be capable of carrying ana- log and digital signals with arbitrary bit rates and protocol formats. This is the
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482 Control and Management utopian vision of optical networking and would allow service providers to offer a range of services without any constraints and provide future-proofing in case the service mix changes over time or when new services are added. However, such a network is very difficult to engineer and manage. It is difficult to engineer be-
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Optical Networks - _8_5 Performance and Fault Management_98...

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