 reduce the number of candidates for faulty regenerators. The OSS would automatically trigger a battery of tests or diagnostics on the candidates to determine exactly which is faulty and what is the fault. 2 Network Management OSS Overview OSS server from where access privileges are set Workstation Workstation for user access for user access Figure 2.14 Security management. 2.7 Security Security administration involves restricting the use of the OSS and other network management resources. Network administrators can specify security requirements using additional OSS features. We shall see some security administration features available in some OSS implementations mentioned in this book. Security is implemented as in any multi-user software package. Each user is assigned to a group, each of whose members has default access privileges. For situa- tions when the network is accessed simultaneously by staff at different locations, such as at the NOC via the OSS and at a workstation terminal at a local exchange, a locking mechanism is necessary to avoid conflicting instructions being given to network equipment. There must also be protection against interference from the embedded communication channel (ECC) of SDH. Data flowing in the ECC are part of the telecom network traffic. It must be separated out so that it does not have the effect of issuing unintended and unwanted commands to the OSS. 2.8 Network Planning Support The OSS can support the operator in the modification, extension or design of networks by evaluating capacity limits. Simulation helps in network planning and design. To determine the new or modified network capability, the OSS can simulate network behaviour in specific traffic situations. This is done to determine how the network will behave in such situations. The OSS might also be able to simulate how services will be impacted by a fault. Simulation can also find unused capacity in an existing network. It can be used to find design flaws in an existing network that are responsible for recurring per- f