hem. There are different possible schemes, and the algorithms avail- able vary by SP. How to detect or determine a failure of a SIP trunk might also be provider-specific. Determine Emergency Call Handling Many enterprises choose to maintain TDM interfaces for their emergency calls, at least initially. If you decide to place emergency calls on the SIP trunk along with normal busi- ness calls, make sure you understand the following: How calls are routed to the appropriate emergency responder location. (This is espe- cially important in centralized trunking architectures where the SIP trunk entry point might be geographically distant from the emergency responder location.) What location information is delivered for the call and where that information comes from (for instance, from your enterprise network or from the SP's information on your DIDs). Whether jurisdiction boundaries are crossed (such as country boundaries) between the SIP trunk location and the emergency site location. These boundaries might ren- der the emergency location information useless or illegal because different systems are in place in the different locations. Determine the Physical Delivery of the SIP Trunk With your provider, discuss whether the SIP trunk can be delivered on existing fiber or wiring that already exists to your location, or whether a new physical connection must be put in place. This determination can play a factor in: The timeframe for installing the SIP trunk The cost of installation The security policy or protections you might (or might not) have on this connection 252 SIP Trunking Exercise great caution in accepting services from a SIP trunk provider that does not also provide the physical delivery to your location. Only the provider who owns the physical medium has control over QoS settings. Determine Network Demarcation As with data networks, determine the exact equipment that provides the demarcation between your network and the SP's network. Most business-grade SIP trunk services come with a customer-premise equipment 