What happens if an LTE device misses an RRC Connection Release message?
It can happen, in poor coverage or high interference areas because RRC Release is not acknowledged.
The result?
The network believes the device is now in Idle mode.
But the UE is still in RRC Connected state and is now un-pageable.
This mismatch can last until the device next sends uplink data which may take minutes or longer on IoT devices.
The solution: 3GPP Rel-14 MAC Data Inactivity Timer (DIT):
The DIT timer starts when the UE enters Connected state.
It is reset on each UL or DL MAC PDU.
If no MAC activity is seen for the configured period e.g. 10 seconds, the UE forces a local RRC release → returning to Idle → state is re-aligned.
Why this matters for IoT:
Missed RRC Release happens more often in battery-powered IoT, due to low data rates, weak coverage or marginal radio conditions.
Without DIT, devices can remain in Connected, un-pageable state, draining battery and losing availability.
With DIT, they self-recover, returning to Idle thus saving power and restoring normal operation.
In this example:
Normal RRC Inactivity Timer at the eNB triggers RRC Release after 5 seconds.
Release is missed, UE remains Connected, OUT OF SYNC with the eNB.
DIT e.g. 10 seconds continues counting → after expiry, UE performs Forced Local Release.
State is re-aligned → UE is pageable again → battery preserved.
A small but critical feature, especially valuable for real-world IoT deployments.
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