What Changes
Power mode changes when the modem listens. It does not make the application magically reachable all day.
NB-IoT Power Saving Mode Animation
Animate NB-IoT PSM, eDRX paging windows, reachability, and battery-life trade-offs over a 24-hour day
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Interactive NB-IoT power-mode workbench showing T3324 active time, T3412 or scheduled wake intervals, eDRX paging windows, downlink delay, current draw, and battery-life estimates
Animation
NB-IoT power
12 min
NB-IoT PSM and eDRX Power Timeline
Animate a 24-hour NB-IoT device day. See when the device can receive commands, when it is only periodically reachable, and when Power Saving Mode makes it unreachable until the next wake.
PSM first
Active briefly, then deep sleep
2% reachable
Percent of the day the network can reach the device
0.8 mAh/day
Teaching estimate from state duration and current
10+ years
Before field derating and retry margin
Why It Matters
A meter that reports once per day can sleep deeply. A device that needs commands within minutes must pay for listening windows.
Try First
Use the delayed-command preset, then move the downlink attempt across the PSM region and watch the delay estimate change.
Common Mistake
Do not approve battery life from a sleep-current number alone. Include wake, transfer, retries, host current, and granted timers.
Scenario
PSM is lowest power but unreachable. eDRX adds paging windows.
6 h
This represents the application wake or the effective T3412/TAU rhythm used for the day model.
0.5 min
300 s
5 s
2 s
3.0 h
5000 mAh
PSM-first smart water meter
The device wakes on a schedule, sends a short uplink, stays reachable for a short T3324 active timer, then enters PSM where the network cannot page it.
Now: 0.0 h
24-Hour Reachability Timeline
Uplink TX
Active reachable
eDRX paging
PSM unreachable
Connected idle
00:00
06:00
12:00
18:00
24:00
Current Draw Model
Current state: uplink TX
The modem is spending high current to send or receive data.
Downlink: waits for next wake
A command sent during PSM cannot be delivered until the device becomes reachable again.
Timers: T3324 then sleep
The active timer controls the reachable period before PSM.
Evidence: network grants vary
The product must log the values granted by the operator and modem firmware.
Reachable for 0.6 h/day
Most of the day is PSM deep sleep in this scenario.
0.8 mAh/day
Teaching estimate based on typical state currents, not a production approval.
Model life: 10+ years
Real projects apply usable-capacity derating, weak coverage, retries, and host current.
Learning Support
Read The Timeline
Orange is expensive radio transfer. Green is reachable active time. Blue stripes mean eDRX paging opportunities. Navy is PSM, where downlink must wait.
Watch Reachability
Move the downlink marker. If it lands in PSM, the command waits until the next active or paging window.
Treat Values As Requests
Devices request timers, but networks can grant different values. A field pilot must confirm the behavior actually used.
Quick Reference
PSM
Registered but unreachable The device keeps cellular context but cannot receive downlink until it wakes.T3324
Active timer Controls how long the device remains reachable after activity before PSM starts.T3412
Periodic TAU rhythm Represents when the device wakes for tracking-area update or scheduled activity.eDRX
Periodic paging The device sleeps between paging windows, then listens during the PTW.PTW
Paging Time Window The short portion of an eDRX cycle when the network can page the device.Battery Model
current * duration Use measured whole-board current for each state, then add retries, updates, and derating.Guided Practice
1. Find The Blind Zone
Select delayed command. Move the downlink attempt into the navy region and note the command delay.
2. Pay For Reachability
Switch from PSM to eDRX. Reachability improves, but daily energy should increase.
3. Tune The Active Timer
Increase T3324. The device is easier to command after uplink, but idle listening costs battery.