 Excess capacity, of course, can accom- modate short-term growth. Therefore, performance/growth management supplies vital information on network utilization. Such data provide the groundwork for future planning. 21.3.4 Security Management Security management controls access to and protects both the network and the network management subsystem against intentional or accidental abuse, unauthorized access, and communication loss. It involves link encryption, changes in encryption keys, user authen- tication, passwords, firewalls, and unauthorized usage of telecommunication resources. 21.3.5 Accounting Management Accounting management processes and records service and utilization information. It generates customer billing reports for services rendered. It identifies costs and establishes charges for the use of services and resources in the network. It may also be a repository for plant-in-place investment for telecommunications plant and provides reports to upper management on return on that investment. 21.4 SURVIVABILITY - WHERE NETWORK MANAGEMENT REALLY PAYS The network management center is the front-line command post for the battle for network survivability. We can model numerous catastrophic events affecting a telecommunications network, whether the PSTN or a private/enterprise network. Among such events are fires, earthquakes, floods, hurricanes, terrorism, and public disorder. Telecommunications have brought revolutionary efficiencies to the way we do business and is SO very necessary even for life itself. Loss of these facilities could destroy a business, even possibly destroy a nation. A properly designed network management system could mitigate losses, even save a network almost in its entirety. Cite the World Trade Center explosion (first attack) in New York City. The entire PABX telephone system survived, less the extensions in the immediate area of the bomb, simply because the PABX was mounted on the 6th floor. All offices in the building had communications within the building and with the outside world. 