Power Saving Mode (PSM) Part II

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Hi Guys, today we learn more about PSM in Nb-IoT. if you are new at my blog please go through my Power Saving Mode (PSM) Part I for more details.

How does PSM actually work?

·        A UE is PSM enabled only when it sends T3324 timer in Attach/TAU request. 
·        Power Saving Mode configured by providing T3324 active and T3412 extended timers or by configuring "UE requested" timer values.
·        Network provides two options: accept UE requested values or MME configured values for these timers.
·        When PSM configuration is enabled in the Network, the MME accepts the use of PSM and a UE requested value of T3324 timer is received in Attach/TAU request.
·        When PSM is enabled and the Network is configured to accept UE requested values of timers, if T3412 extended timer is not received from the UE along with T3324 in Attach/TAU request, then MME uses the value of T3412 timer available in MME service configuration.
·        If the network includes the T3324 value IE in the Attach/TAU Accept message, and if the UE is not attached for emergency bearer services and has no PDN connection for emergency bearer services, the MME sets the active timer value equal to the value of T3324 timer.
·        The T3324 active timer is an integer value ranging from 0 to 11160 seconds.
·        The T3412 extended timer is an integer value ranging from 0 to 35712000 seconds.

What are the benefits when DUT (device) in PSM?

When DUT is in PSM that time power consumption is significantly reduced with longer dormant periods, networking layer signaling overhead is reduced, radio resource signaling is reduced.

Does emergency bearer is supported by NB-IoT device?

Emergency bearer service is not supported by NB-IoT RAT type. Hence MME don't support emergency bearer service during attach as well as TAU with devices having NB-IOT RAT type.

PSM is active in the DUT (UE). If PSM is active, the DUT can deactivate PSM at any time by activating the AS layer, when the DUT needs to send mobile originated signaling or user data. Otherwise, the DUT shall not initiate any EMM procedure except for cell and PLMN reselection.

1)3GPP TS 24.301 Release 13.5.0
2)3GPP TS 23.401 Release 13.5.0
3)3GPP TS 29.274 Release 13.5.0


  1. Hi there,
    a have a question regarding the connection reestablishment after PSM. Does the NB-IoT UE have to acquire SIB1-NB again after PSM? This would lead to an increased latency and energy consumption for the UE...


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