How do emergency calls work via a Business SIP Trunk in Austria?

A major advantage of Voice-over-IP (VoIP) is that the connection can also be used worldwide independently of the actual connection address. However, special care is therefore required if emergency calls are to be made via the VoIP connection.

Have you ever wondered how the delivery of an emergency call actually works and what data is transmitted in the process? With every VoIP call, a Network Provided Number (NPN) is sent as additional information. This has two important functions for emergency calls:

  • Determining responsibility.
    The NPN is used to determine to which local rescue center the emergency call will be delivered.
  • Determining the location.
    The NPN can be used to determine the geo location of the call. This can save lives if the caller is no longer able to provide information about their location (“roach call”).

Ensure emergency call functions

With this in mind, there are a few things you should bear in mind when setting up the SIP trunk and making emergency calls.

  • Although theoretically possible, telephone numbers should generally only be used at the associated line address.
  • The line address of the main number should correspond to the address of the office/branch.
  • Please ensure that you always inform us of the current line address.
  • When making emergency calls via a VoIP connection, take particular care to provide your actual location data.
  • If you are working from home, use your mobile phone number for the emergency call.
  • If you are working from home, use your private landline or mobile phone number and not the office number for an emergency call.

Special features when bundling several phone numbers

But what if several phone numbers with different connection addresses are managed in a SIP trunk? What if the number is displayed via CLIP no screening or is completely suppressed (CLIR)?

In this case, the emergency call center is selected according to the signaled number.

  • If this signaled number is identical to a trunk number, the emergency call center belonging to the line address of this number is called. This also applies to extensions of the respective telephone number.
  • However, if the signaled call number does not correspond to a call number of the trunk, the main call number of the SIP trunk is transmitted as NPN. This means that the emergency call center closest to the main number’s connection address is called.
    When setting up the SIP trunk, make absolutely sure that you select a main number whose line address corresponds to the address at which the numbers are used!
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