LTE-M Timers | T3324 timer, T3412 timer

This page describes LTE-M Timers viz. T3324 and T3412.It mentions functions of T3324 and T3412 used in LTE-M technology.

Introduction:
LTE-M follows 3GPP specifications similar to LTE technology. LTE-M stands for Long Term Evolution for Machine-Type Communications. There are different categories of LTE-M devices viz. Cat-0, Cat-M1 and Cat-M2 as per different 3GPP releases. LTE-M Cat-0, Cat-M1 and Cat-M2 follow 3GPP TS 36 series of rel.12, rel.13 and rel.14 respectively. There are two power saving modes viz. PSM and eDRX. PSM has 2 timers viz. T3324 and T3412.

T3324 Timer

Time the User Entity (UE) (otherwise known as "IOT Module") stays in ACTIVE / IDLE mode following a wake-up to Periodic Tracking Area Update or initiate a Mobile Origination event (Mobile Origination means the User Entity sends data or SMS up to the network destined to a back-end Application Server). This timer has a trade-off between lower values and maximum values: Lower values save more battery life by allowing the UE to go into HIBERNATE state quicker, which is the remaining duration of T3412 Extended timer. Higher values of T3324 will allow a longer time for the application server (AS) to respond to UE/MO data (e.g. Acknowledgements, network initiated data). Customers are advised to test out this parameter to come to a value that best fits their Use Case.
It is recommended a Ratio of T3324 Active Timer to T3412 Extended Timer: (T3412 Extended Timer - T3324 Active Timer)/T3412 Ratio should be > 90% in order to achieve optimum battery savings by use of the PSM feature.
There is no network recommended value but the value cannot be below:
➨Minimum: 16 Seconds Minimum Allowed Value, calculated from: (2*DRX cycles (MNO LTE DRX cycle value (e.g. 2.56sec)) + 10 seconds (buffer time)) = 2*2.56sec + 10 seconds = 16 seconds.

T3412 Timer

Extended T3412 Timer is the value the device informs the network with Periodic Tracking Area Update (pTAU) that it is still registered. The duration after T3324 Timer expiry and the next pTAU instance is the HIBERNATE period.

Note: The UE/Device is not reachable by a Mobile Terminated message/SMS during the PSM/Hibernate state.

It is recommended the following value of 4 Hours for this setting: Minimum: 4 Hours.
➨Note: Max T3412 Extended = 413 days , as defined by 3GPP (TS 24.008)

Regarding attempts to deliver mobile terminated SMS / Data, it is recommended that the enterprise application implement a "pull" model for MT Data, such that the device initiates MO data transmission to the application server, and the application server responds to the device with the downlink payload.

➨Note: On Mobile Originations: An Application Processor running on a UE, that controls the UE Module / the Radio, can initiate a Mobile Origination at any time, even if the device is within a PSM state. Therefore, Mobile Originations are not governed by the use of PSM. Furthermore, T3412 resets after MO events.

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