By: Brian Rosen
Date: April 17, 2016
In late 2004, members of the Session Initiation Protocol (SIP) working group (WG) gathered to discuss how SIP-based devices could place emergency calls (e.g., 1-1-2, 9-1-1). Around the same time, SIP-based phones started making such calls. In the case of North America, the calls were received with concern at public safety answering points (PSAPs, the call centers where emergency calls are answered). The concern stemmed from the fact that neither the devices nor the back-end systems that supported them were capable of adequately placing the calls or sending the information needed to correctly route them. North American PSAPs had recently settled a related issue with mobile operators: while no one anticipated that mobile phones would be used for emergency calls, users found their mobile phones were perfect for them. And because mobile phones and their systems were unprepared to handle such calls, when they were made problems ensued. Ultimately, regulation prompted the ability of mobile phones to support emergency calls. The SIP members realized that handling emergency calls properly would be a critical step in order for SIP to succeed as a multimedia session-initiation protocol.
Many of the standards that governed how emergency calls are handled in the United States and Canada come from the North American Emergency Number Association (NENA). In spring 2005, the SIP members met with NENA’s technical people to discuss how the existing emergency call system worked. They were surprised to learn that in addition to seeking a way to correctly handle VoIP calls in the current E9-1-1 system, NENA sought a redesign of the entire emergency call system based on modern IP protocols and mechanisms. The result of that meeting was a three-pronged plan:
- NENA would document several ad hoc mechanisms that VoIP providers had implemented, and detail the strengths and weaknesses of the ideas.
- NENA would standardize a method for SIP-based VoIP phones to place emergency calls using the current telephone network-based system. The IETF would assist with any needed SIP standards.
- The IETF would work with NENA to create a new IP-based emergency calling system for North America with IETF standards as the base and NENA standards built on top of the IETF standards.
Their efforts have been largely successful. NENA i2 standards now largely govern VoIP emergency calls on the existing E9-1-1 network. No significant work in the IETF was required to achieve this goal. NENA i3 standards, based on several IETF standards in the now concluded GEOPRIV WG and the still active ECRIT WG, form the technical base for the Next Generation 9-1-1. And the European Union Emergency Number Association (EENA) has developed its standards based on NENA and IETF standards for new pan- European Union 1-1-2 IP-based emergency calling.
One of the core standards that underpin these developments is RFC 5222, the “Location to Service Translation (LoST)” protocol. LoST accepts location information typically extracted from a Presence Information Data Format-Location Object (PIDF-LO), RFC 4119, which may be a civic (street) address or a latitude/longitude/altitude. LoST then maps that location information into a route the emergency call should take towards a PSAP. LoST is also used to validate a civic location prior to it being loaded into a Location Information Server (LIS). In this way, if an emergency call is subsequently placed by a SIP-based phone using the location associated with the phone stored in the LIS, that location will be recognized by emergency authorities, the call will route correctly, and responders can be directed to the location of the caller.
The entire NG9-1-1 system is based on emergency calls being routed by LoST and calls accepted by the PSAP being SIP-signaled. Calls that originate in legacy wireline or wireless networks are passed through a Legacy Network Gateway to translate the legacy signaling and routing information to SIP signaling and LoST-based routing.
The framework for how multimedia emergency calls are handled on the Internet is described in RFC 4883. RFC 6881 describes the best current practice for originating devices and networks to obtain the location of a caller, access a LoST server to get a route, and send a call using SIP signaling towards the PSAP.
Next Generation 9-1-1 is being deployed, albeit slowly. In a small number of U.S. states, emergency calls are being routed by LoST. The protocol is an unheralded IETF success—there are dozens of interoperable implementations, it’s deployed, and thousands of emergency calls are routed every day using the LoST protocol.
Emergency authorities, organizations like NENA and EENA, and callers who need help rely on IETF protocols, frameworks, and data structures to save lives. And we can trace the entire effort to a single meeting between a dedicated cohort of IETF members and NENA participants, who had a vision of what could be done and then did it.