KB106 - Multi-Location Trunks


Background: What is a multi-location trunk (MLT)?

Whereas most customer phone systems only serve a single location, many enterprise and multi-site customers prefer to leverage the economies of oversubscription and the ease of management obtained by serving multiple locations from a single centrally-managed phone system. Whether the remote site has a phone system of their own that is trunked back to the main site or is simply a home office with an IP phone that is registered to a central PBX, any SIP trunk to a phone system that can originate calls from multiple physical locations is an MLT.

MLT Considerations

When a 911 call originates from a standard single-location trunk, Clearfly will overwrite the calling number of the call with the Directory Number (DN) of the trunk. This is a number that has been registered as an 911 endpoint with our E911 provider and associated with the physical address of the location at which the phone system is housed. The 911 dispatcher at the relevant public-safety answering point (PSAP) then sees this physical address on his or her display and is able to direct emergency services accordingly.

Since MLT calls can originate from multiple physical locations, how can we be sure that emergency services will be directed to the correct address in the event of a 911 call? Quite simply, we can’t. We can, however, register multiple endpoints (phone numbers) with our E911 provider and then rely on the customer’s phone system to originate 911 calls with the pre-arranged calling phone number for that physical location.

It is important to note that if, for any reason, the phone system originates a 911 call from a phone number that has not been registered as an E911 endpoint, the call will be routed to a national 911 operator for manual routing to the correct PSAP. For each manual 911 call Clearfly is charged a substantial non-recurring fee that is then passed through to the customer’s invoice.

Provisioning & Testing MLT 911 Service

While the testing and provisioning of the SIP trunks themselves follows the standard process, MLT status does add an additional step to the process before SIP trunks can be activated for billing. When an MLT trunk is provisioned, it is provisioned in E911 test mode. E911 test mode ensures that any calls to 911 are routed to an automated readback number instead of to the PSAP. If the number you are calling from has been provisioned as an E911 endpoint, the automated test number will read back the calling number and the physical address associated with number. Since the default 911 handling with MLT is to trust what the phone system sends, this provides a good way for partners and customers to fully validate the 911 configuration before billing is activated. When you have completed your testing, simply complete the activation procedure as outlined in KB105 and when the trunk is taken active E911 test mode will be toggled off.

If new physical locations are added after your trunks have been activated for billing (or if you’d simply like to test your existing E911 endpoints) you can enable and disable E911 test mode at any time from the real-time switch information page under your voice group in the Clearfly Portal. Please note that when a trunk is in test mode all calls to 911 are routed to the automated test number instead of the PSAP, so this is something that should be coordinated with or communicated to end users for the duration of your testing. If test mode is not disabled manually, production trunks will automatically revert from test mode to active mode after six hours.