Find out what to do when the power returns to ensure that your PBX will be up and running quickly. Many systems are installed with redundancy of varying de- grees up to and including having a complete duplicate system standing by. Other types of backup may include two separate sets of out- side lines from two separate telephone company central offices (very costly) or two different long distance carriers. Some organizations use a service known as Switch Redirect available from some telecommunications service providers. In the event of a disaster causing you to vacate your premises, all or some of your direct dial telephone numbers can be rerouted to another location. The most important aspect of disaster recovery planning is to document it and let everyone know how the plan is to be carried out. Periodic testing is also important. It is often surprising to learn that the typical PBX has not changed as dramatically as one might have expected over the past 10-15 years, particularly in terms of how the desktop tele- phone operates. It is true that the inner workings of most PBXs have evolved towards more efficient use of space with higher density circuit boards and improvement in the methods by which signals are transmitted. However, other than perhaps having the Caller ID displayed, the purchaser of a new PBX will not benefit from any new capabilities. Even with the newer systems cur- rently under development, but not yet ready for prime-time, the 56 is The Telecom Handbook CHAPTER 2 benefits to the person using the telephone are minimal or in some cases, regressing. The chapter on Convergence introduces the concept of a softswitch along with some applications with which organizations are experimenting such as Unified Messaging whose usefulness is yet to be demonstrated on a large scale. The Telecom Handbook os 57 Taylor & Francis Taylor & Francis Group http://taylorandfrancis.com CHAPTER 3 Purchasing a PBX Identifying Your Organization's Requirements While identifying your organization's requirements may sound lik