In the Internet-of-Things there are various classes of devices with various requirements. Among them there are devices that
1) need to survive very long time (months, years) on a single, regular-capacity battery and
2) do not need to be reachable from the network or application server side.
An environmental sensor hanging on a tree in a forest and sending a warning when smoke or fire is detected could be one example. An alarm device installed in some precious or dangerous cargo container reporting unauthorized opening of the container is another example, but not stationary in this case.
For devices with such requirements the Power Saving Mode (PSM) was introduced in 3GPP standards. In brief, a UE using PSM is initiating data connections, SMS transfer, or periodic updates when needed, but after the radio connection ends the UE is in a regular idle state only for a while (no more than approximately 3 hours) and then shuts down the radio communication module completely to save power. So no paging channel monitoring, no signal measurements, no cell reselections, no Routing Area or Tracking Area updates. The core network is aware of this state, so it will not initiate paging when downlink data or SMS arrives. The various connection contexts are kept in different network nodes when the device is ‘asleep’. In order to save even more power, the UICC card or chip in the device can be suspended or deactivated and periodic updates can be disabled or performed very, very seldom: maximum extended periodic timer value is 413 days! In the 5G system there is a very similar UE feature known as MICO mode (Mobile Initiated Connections Only).
Devices like this may present a new class of issues and problems in the mobile networks. One could imagine scenarios where some device is briefly active in a network to perform attach, possibly set up a data connection, then is ‘silent’ for a couple of months, and suddenly requests a connection to transmit data or SMS, possibly in a very different location, e.g. another country.
How can a mobile network operator ensure a fair use of roaming for devices like that? How long the connection data should be kept in different network elements? How long UE-related information should be kept in various monitoring probes and databases commonly used in mobile networks?
On the other hand, the described scenario may be a bit unrealistic: quite likely every couple of weeks or months devices will send some kind of a keep-alive signal to their application servers so the service provider is aware that the device is still functioning, and – for example – to detect cases when precious or dangerous cargo was taken away from the coverage area, opened and the alarm device destroyed. Or a tree with the fire sensor on it was cut down and became a nice wooden sofa. So all in all, cases with UEs attached, connected, but not communicating for five years should not be very common.
If you want to learn about IoT-specific issues and machine-related enhancements in 3GPP networks, we offer a couple of trainings on these topics.
Take me to Mobile IoT Training
Until next time,
The Apis IP-Solutions Team
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