Success Story

How does an internet phone find the closest emergency call centre?

More and more companies are using VoIP telephony. To enable emergency calls made with VoIP systems to function as effectively as with conventional telephones, modifications were required at various points in the telephony infrastructure.


Swisscom operates VoIP systems for a number of large companies operating across multiple sites and also uses VoIP in-house for its own 20,000 employees. Voice over IP (VoIP) uses Internet Protocol (IP) addresses, which are not firmly bound to a physical location. VoIP systems are therefore not always able to determine the location from which calls are made. This limits the ability of existing VoIP systems to route emergency calls – a particular issue for users who work from multiple sites.

This impedes emergency service interventions and increases the load on emergency call centres. In the absence of a technical or regulatory solution, Swisscom elected to develop its own comprehensive solution within the framework of a group-wide pilot project.


In a short-term subproject, Zuhlke engineers developed a new system that supplements the existing VoIP system by receiving all emergency calls, resolving the correct emergency call centre with the help of a Swisscom service and initiating call forwarding to that call centre in real time. To resolve the correct call centre, the system extracts location information that is either added to the emergency call by a specially modified VoIP server on the client’s network or provided by a DHCP server when the client logs in to the VoIP network. Because of the importance of its task, the new system features high availability and can handle a large number of emergency calls at the same time.

Client benefits

  • The individual solution developed by Zuhlke made implementation of the required functionality much faster and more cost-effective than waiting for product manufacturers to expand the existing VoIP system.
  • The short development period meant the overall project’s tight schedule could be met.
  • Close co-operation with Swisscom from the very beginning was key in developing an easy-to-operate application.