Your carrier can provide you E911 DID's for specific locations, or you can use ones you already have, but I would call the carrier and let them know what you want and why. In general I find they are willing to work with customers on this. Depending on your needs you may want an E911 number for each floor of a building. I've even heard of cases where people are as specific as building/floor/area.
You can have default E911 numbers on the controller, but then each line can have it's own too, if it's at a remote building for instance.
Your CESID is the Caller ID that is displayed when the call goes out an ARS Route marked as "Emergency." To go out a specific trunk you'll need to to use ARS routing for where the call goes when a user dials 911.
