White Paper - Emergency Call Handling in VoIP Networks
Introduction
Emergency Call Handling (ECH) is an essential feature of today's public telephone networks, and if Voice over IP based PSTN replacement is to become a reality, the new technology will have to deliver reliable handling of emergency calls. The needs of ECH have been extended as a result of recent national emergencies, such as floods and terrorist atrocities. These have focused Governments' attention on the need to secure the lines of communication for key workers and facilities, as well as support for emergency calls.
SIP is now the accepted technology for next generation IP based PSTN and mobile networks, underpinned by standards bodies such as ETSI TISPAN, PacketCable, 3GPP and 3GPP2.
There are two main issues relating to the implementation of ECH for VoIP:
- Locating the caller
- Prioritising emergency call and privileged user traffic.
Locating the Caller
One of the great advantages of a VoIP service is that it can be accessed from virtually anywhere; subscribers simply log on with their chosen device and their calls come to them. This potential for mobility is at the core of the problem of delivering accurate positional information to the Emergency Call Handling Centre.
Although each subscriber device may be allocated a unique IP address and port number, this, by itself, is not sufficient to physically locate a caller. IP addresses do not have the same geographic significance of fixed line telephones, nor are they supported by the purpose built network such as a mobile service provider's infrastructure.
So a new capability is required to enable emergency services to be sent to the right place. This does not just apply to callers roaming within national boundaries, but perhaps on a global scale. Despite copious warnings that VoIP services should not be used to call 911 or 999, fatalities have occurred because the caller was actually in a different country to where the called ECH centre was located.
In the US the FCC has mandated that Interconnected VoIP providers must provide emergency operators with the call back number and location information of their customers where the emergency operator is capable of receiving it. The onus is on the customer to provide the location information, but the VoIP provider must provide the customer with a means of updating this information. This move offers the prospect of greater security for the subscriber, but for the most nomadic users, the overhead of constantly having to update location information will be an onerous task. In fact, some VoIP service providers require between 5 and 10 days notice to update the registered location of the service. Therefore, we need to supplement the manual updating of information with automatic device and network based solutions.
Due to the broad range of terminals that can support VoIP and equally broad range of technologies need to be employed to assist in providing location information. For limited types of terminals GPS may be the answer; however even this technology may only work in outdoor locations. New location technologies are being investigated such as using TV and radio station transmissions to triangulate the client device; however these techniques are currently only experimental and in any case may be of limited applicability. However, locating callers effectively with any degree of accuracy using the IP network itself will require a new level of openness on the part of service providers.
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IPsec and VoIP
