On Mon, 2 May 2005, Simon Lyall wrote:
This speculation is fun but my question is how do people do this now? I would assume that many people on this list work for large companies with multiple sites and a single phone network spanning them all.
When somebody in the office picks up a phone and dials EXTERNAL-911 how do the emergancy services know they are in one building rather than another office across town?
Perhaps they don't. PBX's and nationwide tie-lines have been a problem for E911/ALI services since the beginning. PSAP call takers are trained to get/confirm the caller's location and the location of the emergency because people don't always call from the location of the emergency. And there has always been a problem some callers don't know, or are mistaken, about their current location. Or refer to their location by a different name, such as the Atlanta Olympic Park bombing where the caller and the pay phone records referred to a physical location which didn't exist in the police department's dispatching computers even though the physical location was on television every day of the Atlanta Olympics. The most common way people "solve" this today is by installing at least one ordinary POTS line in each building, and the PBX uses least-cost routing to route E911 calls to the local line. VOIP ATA's can do the same thing by including a POTS jack on the ATA and connecting 9-1-1 calls to the local POTS line. There are more advanced methods, but they all involve someone updating some database whenever a telephone is moved. They all have the exact same problem of assuming a person will keep the database with their current location up to date. People forget, or make mistakes, and its very difficult to discover the mistakes in advance. Life is complicated.