Emergency Calls and Femtocells

Emergency Ambulance Would you benefit from owning a femtocell in case of a medical emergecny or if your house was burning down? How do femtocells handle emergency calls, and is this better or worse than existing mobile network operation? I’ve drawn some comparisons (and lessons learnt) from existing VoIP services.

 

 

Emergency calls have regulatory requirements

Laws in most countries require emergency calls made through the mobile network to be routed automatically to the correct local emergency call center. In the USA, these are called PSAPs (Public Safety Anwering Points). Other countries have more localised answer points, and some have different numbers for each emergency service (Police, Ambulance, Fire etc.). In North America, Enhanced 911 also determines the caller's location and presents this to the answering point in addition to the Caller ID.

There are many important aspects for handling the call

  • Emergency calls should take priority over other traffic. Cellsites will drop existing calls if there is no spare capacity to carry an emergency call, so you can always get through straightaway.
  • Emergency calls can be made over any network, not just your own. The network coverage in a given location differs for each operator. If you are out of coverage from your own network, an emergency call will seek out and automatically find another network to carry the traffic.
  • Emergency calls should be free of charge. In most countries, calls are free of charge and are not blocked when out of (prepaid) credit. Several US operators do impose a small monthly fee to permit the facility, but I’ve rarely come across this elsewhere.
  • Emergency calls should be routed to the correct local answering point. There’s not much point in someone answering the call at the other end of the country. The US has over 6,000 answering points nationwide.
  • Emergency calls should automatically report the location of the caller. Fixed phone lines generally have a fixed address associated with them, which can be stored and forwarded with the call. Caller ID can be used to lookup a database/address list. On a mobile network, the cellsite location can be reported but this can still cover quite a wide area, including several miles out to sea. In the US, the regulatory authorities mandated strict accuracy limits and a variety of technical solutions report the location. A benefit of a femtocell is that if it is registered at a known address, it can effectively report that much more accurately than other solutions. For example, if residing in a block of flats, then the precise apartment and floor can be identified.
  • Emergency calls should use a standard number well known in each country. Originally, the EU standardised 112 as the emergency number across Europe, and this was embodied into the GSM standard (and all GSM phones). Around 2000, largely due to pressure from North American operators, the standard was amended to include additional numbers specified by the home network operator held in the SIM card, such as 911. So I believe that Americans visiting the UK can call 911 on their own phones to access UK emergency services.

Surprisingly, at this stage not all PSAPs are yet able to receive and process information about the reported location. I recall some years ago that when calling the emergency number in the UK, the mobile operator call center answered the call, transferred it across to the regional emergency answering center and read out the Caller ID verbally. I’m sure things have progressed since then.

VoIP’s first E911 fatality (May 2008)

Several highly publicised cases have highlighted concerns about restrictions and inaccuracies with emergency calls from internet VoIP service operators, such as Vonage. The most widely publicised being the death of a baby which was partly attributed to the ambulance being despatched to the parents previous home - in a different state.

Fixed and Mobile Regulations extended to VoIP too

Here in the UK, new regulations came into force in September 2008. These place similar obligations on VoIP providers which are already mandated for fixed line and wireless operators. My own VoIP provider has recently asked me to confirm the address where I use the service for emergency reporting purposes. (Even though my VoIP provider is based in Germany). Of course, I can still use their service anywhere in the world, or on my mobile device (3G mobile or WiFi netbook), and that address would be incorrect. It would however, identify me and my home location.

The need for power

Another aspect relates to power supply. One of the original and remaining benefits of the familiar wireline telephone system (POTS or Plain Old Telephony System) is that it requires no power at the customer premises to work. Large banks of lead-acid batteries combined with backup diesel generators at the local telephone exchange (Central Office) ensure very high levels of availability and continued operation. But internet broadband services (including cable modems) require continuous power at the customer premises to work.

Relatively few domestic premises invest in UPS (Uninterruptible Power Supplies) to cater for this eventuality – we are all too complacent about the high availability of the telephone and mains power network. (At least in urban areas of most of the developed world).

Mobile and cordless phones also need to be charged up to be able to be used, but with much longer battery life this is now less of a problem.

Do femtocells comply with the principles above?

 

Feature Complies Comment

Priority

Yes

assuming the femtocell vendor complies with mandatory standards requirements

Multi-network

Yes

standards permit this, but operators/countries may decide not to implement

Free of charge

Yes

must be the case for SIM free emergency calls, but some US networks do charge

Routed to correct PSAP

Yes

based on registered location of femtocell

Report caller location

Yes

based on registered location of femtocell

Use home network

Yes

based on SIM card from home network operator

Works during power failure

No

Mobile phone will revert to outdoor mobile network coverage

A potential downside is where femtocells are moved by their owners to different locations (e.g. a holiday home or even abroad on a foreign trip). Some operators plan to block this using a “location lock” within the femtocell which detects that it has been moved and prevents it operating. A call to the network operator is required to report the new location and grant permission for use there.

Conclusion

Overall, femtocells should increase the quality of emergency call handling from mobiles. They will improve the call quality and the accuracy of location reporting with the familiarity of the mobile. They may be safer in some cases - for example, if you live in a block of flats the exact floor can be pinpointed or if you house is burning down you can go outside to make the call rather than staying indoors to use your fixed line phone. In both cases you will still be contactable by the emergency services should they need to, either via the femtocell or outdoor mobile network.

We’ll be explaining a bit more about location lock – the feature by which femtocells identify if they’ve been moved – in a separate article.

References:

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