Enhanced 911

A more common form of emergency service is referred to as Enhanced 911, or E911. The difference with E911 is that the caller’s address and phone number are automatically transmitted to the PSAP when the call is placed. This way, the emergency responders can assist the caller even if the caller is unable to provide contact information. The association of address to the call is based on information provided to the telephony provider when the circuit is installed or enabled. This is typically not the user’s DID, but a main line or billing phone number associated to an organization.

The disadvantage to using the regular call flow for E911 is that users roaming between offices or signed in via an Edge Server are now placing calls out a media gateway and trunk that are associated to a different physical address. Emergency services might end up responding to the incorrect location.

It’s advisable to not allow emergency services calls to happen the same way as other calls in Lync because of this scenario. Instead, rules for emergency services should be purposely excluded from the dial plan, and PSTN usages for those calls should be created, but not inserted in voice policies.