displayed graphically or as raw numerical data. Apart from traffic monitoring, OMC functions include: data registering creating and maintaining logs of network events issuing trouble reports. These functions simplify routine tasks in an OMC. Data registers are helpful as staff can look up exchange data, find out which software versions a specific exchange is loaded with and figure out the configuration of that software. Work carried out in an OMC is logged for general audit purposes, so that there is a record of who made which changes and when. The OSS can also support the staff by simplifying the handling of trouble reports. Even without further automation, simply by having text-based fields in software, mundane administrative tasks such as form-filling can be simplified using cut and paste. 2.3.2 Network Management at the NOC OSS which present the network at various levels of abstraction are becoming more common. These are known as hierarchical OSS, and the NOC is typically installed at a higher level of abstraction than the OMCs (see Figure 2.5). The NOC has different functions from an OMC and has some network management advantages over the OMC. Having a NOC means that OMCs need only be staffed during normal busi- ness hours, to avoid paying higher wage rates for unusual working hours. When the 2 Network Management OSS Overview link 1 Exchange 1 link 2 link 4 Cloud link 5 link 3 Exchange 3 Exchange 2 link 6 cable problem Exchange 4 OSS at NOC Figure 2.7 Fault detected by OSS at NOC. OMCs are not staffed, urgent alarms from exchanges managed by an OMC are directed to the NOC. Since the NOC is connected to all OMCs, the NOC has indirect access to all man- aged NEs. Thus, staff at the NOC are given an overall view of the telecommunications network, which generally comprises several bearer networks. Because of the depend- ency of a large number of circuits on bearer networks, a fault in the transport net- work can affect a large number of services. The main NOC functions are: traffic management, including traffic 