42 CHAPTER 2: D IAL P LANAdding NewDial Plan TablesIf you are sharing the system with another company or group and wantto control calls differently at the two sites, you can add a fourth table.Example: You assign one extension range to Company A and a differentrange to Company B. The fourth table controls the extension range forCompany B, so that outbound calls from Company B’s extensions useonly their external telephone lines.You might also need a fourth table if a single company had two sites butonly one NBX system. In order to properly route emergency (911) calls,you use the fourth table to define which extensions use each dedicated911 telephone line.Example: Users at site A dial 911 and the system uses the Internal table(table ID 1) to make the emergency call on one external telephone line.Users at site B dial 911 and the system uses table ID 4 to make theemergency call on a different external telephone line. The emergencystaff know, based on the dialing number, which site has the emergency.Enhanced 911, E911, is available in some areas. This service enablesemergency staff to identify the specific location of the emergency. Forexample, in a campus of buildings, the emergency staff can identify thespecific building, floor, and location from which the emergency calloriginated. The NBX system supports E911 over ISDN. The administratormust define an outbound call pretranslator to provide the specificextension number from which the 911 call originated.Dial PlanPretranslatorsThe system uses pretranslators to modify digit sequences of incoming oroutgoing calls. On incoming calls, pretranslators can map the entiredialed number (including area code) to an internal extension number.For example, an external party dials 978-555-0101 to reach the personon extension 101. Pretranslators ensure that the proper digits aremapped to the correct extension number.For more information, see:■ Pretranslators for Incoming Calls on page 43■ Pretranslators for Certain Outgoing Calls on page 44A typical pretranslator function involves mapping incoming DDI/DIDtelephone calls to internal extension numbers.
