t. Many support functions seek to provide NEs with accurate input data and to maintain the OSS inventory database. This picture of input data and equipment is used by the OSS in calculations that are made when traffic is rerouted or when leased lines or other telecom traffic-carrying capacity are installed. When equipment is installed in the network, the OSS database is updated with an indication of service status, which says whether or not the equipment is free or blocked. The database can be synchronised with the current equipment status, either using incoming SDH or PDH signals or using a clock. When a leased line is to be installed, the operator specifies the termination points, which are called the "A end" and "B end" in the terminology of some OSS systems. 2 Network Management OSS Overview Figure 2.11 Path between specified endpoints. cable fault traffic routed around fault Figure 2.12 Traffic routed around cable fault. In calculating the path, the OSS uses an algorithm and all available network data - including factors such as obtainable resources and network quality - to calculate the optimal path between nodes. The operator can specify a cost parameter for any given path and this will be taken into account by the OSS in suggesting an optimal route. In Figure 2.11, we see that the route suggested is not necessarily the most direct route. This might be because the more direct route has already been provi- sioned for a higher paying customer, or because some links on the more direct route are already operating at a high percentage of their capacity. The OSS suggests a path and, if the operator accepts it, then the OSS sends the rel- evant commands to the NEs concerned making the line ready to use. Using time-related rerouting, the operator can specify that one path be used dur- ing certain times of the day, week or month while another path be used at all other times. More complicated time-related routing specifications could also be defined. Most configurations include network protection options to enable t