The vital communications were never lost. This brings in the first rule toward survivability. A network management center is a place of point failure. Here we mean that if the center is lost, probably nearly all means of reconfiguring the network are lost. To avoid such a situation, a second network man- agement center should be installed. This second center should be geographically separate from the principal center. It is advisable that the second center share the network manage- ment load and be planned and sized to be able to take the entire load with the loss of the principal center. There should be a communications orderwire between the two centers. Both centers should be provided with no-break power and backup diesel generators. One simple expedient for survivability is to back up circuits with an arrangement with the local telephone company. This means that there must be compatibility between the enterprise network and the PSTN as well as one or more points of interface. A major concern is the network clock. One easy solution is to have the enterprise network derive its clock from the digital PSTN. The local enterprise network should also be provided a backup clock in case effective timing is lost from the PSTN. NETWORK MANAGEMENT In the following chapter sections we will describe means to enhance survivability still further. 21.4.1 Survivability Enhancement - Rapid Troubleshooting An ideal network management system will advise the operator of one or more events,2 indicate where in the network they occurred, and provide other handy troubleshooting data. In fact, the network management system should, in most cases, warn the operator in advance of an impending fault/faults. This would be a boon to survivability. Oftentimes the "ideal" is unachievable or only partially achievable. Human intervention will be required. The troubleshooter should have available a number of units of test equipment, some more automated than others, to aid in the pinpointing the cause of an event. Steve Dauber's article, Finding Fa