Zap911 - VoIP-Emergency Calling client for developers


Emergency calls are an important feature of the public telephony network. Emergency calls are placed by an individual to avert threat to life or physical condition and to property by calling an authority, e.g. the police. In almost any emergency situation, the timely response of action forces is necessary. Therefore an emergency call has to be connected to the responsible emergency call centre (often referred to as Public Safety Answering Point PSAP). This also applies for emergency calls placed via the Internet, e.g. Voice over IP (VoIP). The improvement of the current emergency call system to be also able to effectively deal with new Internet based communication ways is called Next Generation Emergency Calling.

Zap Emergency Calling Client

In order to allow also VoIP user to place emergency calls without any difficulties and to meet the user’s expectations of trouble-free emergency calling, some precations have to be taken and a new emergency calling framework has to be deployed. The IETF’s new emergency calling framework takes the changes in the world of the communication into account. Since IPcom has gained experience while particaipating in emergency calling related IETF working groups and implementing prototypes for placing test emergency calls, IPcom is a competent partner for planning and specifying next generation emergency calling systems. The prototype client, which allows placing and receiving test emergency calls according to the new emergency calling framework for the Internet, is available for free download. All the necessary steps for a VoIP emergency call can be tested with this client. Contact us in case you need further information.

Zap with its emergency calling extension combines all the necessary features for VoIP emergency calling:

  • Location Determination

    • GPS

  • Location Configuration

  • Detect responsible PSAP

  • Detect Emergency Call

    • by the dial string (like 911 or 112, emergency dial strings automatically configured via LoST)

  • Location Conveyance

  • Routing

    • directly to the PSAP or via a SIP proxy of a VoIP provider

  • Displaying of incoming location information

The figure below shows an overview of the Zap emergency calling client in action:

Usage of Zap

The Zap emergency calling client already showed its abilities at several international events. For example at the Emergency Services Workshop in Vienna the Zap client placed a “real” emergency call to a PSAP in the US. Furthermore, Zap is also considered as a reference client for several implementation of various components of the emergency calling framework (e.g. at the first industry interoperability event of the National Emergency number Association NENA).

Documentation and Support

Further information on the topic of VoIP is available at the Zap project web page at If you encounter any problems or have any inqueries regarding Zap and VoIP emergency calling, do not hesitate to contact karlheinz.wolf (at) directly.


Zap is open source software licensed under the Mozilla Public License The original Zap version (without the emergency call extension) is available at


Since the Client Zap as well as the emergency call extensions are all open source, you may extend Zap further on your own. All necessary files are included in the download or available on Zap’s webpage.

If you need extensions to Zap but you do not want to implement it yourself, we offer you development based on time and material - please contact karlheinz.wolf (at) for more details. If you are interested in VoIP emergency calling, you may want to attend our trainings or contact us for a customised offer.