eCall over IMS

This month an EU directive that seems to have been in the making for a decade will finally come into effect and require all new cars and trucks in the EU to embed an emergency call device that automatically calls an emergency call center when it senses a crash. Basically, the technology is based on stone age circuit switched voice telephony and consequently, crash information, location data and other stuff is sent in-band in the speech channel. For an introduction, have a look at this post I wrote two years ago.

To be prepared (perhaps in 10 years time <sarcasm off>) an IMS based eCall solution has now been specified in 3GPP Release 14 which will allow the migration towards something a bit more modern, at least from today’s point of view once circuit switched voice is no longer available in mobile networks.

MSD in the SIP Invite

The IMS based eCall solution basically establishes an IP based IMS Emergency (Voice) Call with a speech path and puts the MSD (Minimum Set of Data, i.e. the crash information, location etc.) into the SIP INVITE message. The PSAP (the emergency call center) is also connected via IMS/SIP to the mobile network, receives the data in the SIP Invite and confirms reception in the SIP response message. All very nice and straight forward, as it should be. For details see 3GPP TS 23.167 chapter 7.7.

IMS eCall Indication in SIB-1

For backwards compatibility reasons the LTE network indicates the availability of IMS eCall in SIB-1 in the eCallOverIMS-Support information element as per 3GPP TS 36.331. If this bit is not set the UE shall use a circuit switched cellular network for the eCall. If that is not possible, e.g. because no CS cellular network is available anymore or if the UE in the car itself is, for example, no longer 2G/3G capable, an IMS Emergency Call can be used instead and the MSD data is again sent in-band in the speech path.

eCall Module in EMM-Deregistered State

Another interesting reference I found which also applies to the CS eCall implementation is that the eCall module, if only used for this purpose, is always deregistered and only connects to the network for an eCall. In other words, no location/tracking area updates, privacy for the user and no signalling load in the network from millions of cars. For details see 3GPP TS 23.401 chapter In practice, however, I would assume that especially high end cars will have the eCall functionality implemented in their telemetry module so the joy of privacy is a short lived one.

Almost Nothing to do for the Network Operators

The good thing for network operators is that moving eCall from CS to IMS requires only very little work apart from making sure the MSD in the SIP invite properly makes it to the other end and setting a bit in the SIB-1 message. The PSAPs, however, must upgrade their connection to the mobile network from circuit switched to SIP and receive the digital emergency data in a different way than today. Certainly not rocket science, either. However, they’ve just upgraded their hardware and software to support eCall over CS so I assume that their thirst for yet another change is highly limited for the next decade.