Soracom Air for Cellular
eDRX and PSM Timer Configuration
For battery-powered IoT devices, managing power consumption is critical to maximizing operational lifetime. Extended Discontinuous Reception (eDRX) and Power Saving Mode (PSM) are cellular network features that help these devices conserve battery power by controlling how often they wake up to communicate with the network.
When a device connects to a cellular network, it establishes a session that requires time and power to negotiate. Normally, a device would detach from the network to save power, but then must reattach and renegotiate the session when it wakes up. eDRX and PSM allow the device to sleep while maintaining the network session, so when the device wakes up, it can resume communication immediately without the overhead of reattaching. This reduces both power consumption and connection latency for devices that communicate intermittently.
If your devices are not battery powered, eDRX and PSM configurations may not be necessary for your use case.
Standard DRX (Discontinuous Reception) in 4G/LTE networks allows devices to briefly turn off their receiver to conserve battery power, but has a maximum cycle length of only 1.28 or 2.56 seconds. With LTE Cat-M1 (LTE-M) and NB-IoT networks, eDRX and PSM extend these intervals significantly:
- eDRX extends the interval between when a device checks for incoming network data, up to 44 minutes (LTE-M) or 175 minutes (NB-IoT)
- PSM allows a device to enter a deep sleep state where it cannot receive data from the network, but uses minimal power for periods up to about 310 hours
These timers can be configured either on the device itself or, with Soracom's network-side configuration feature, managed centrally through the Soracom platform. Normally, eDRX and PSM parameters should be configured directly on your device using AT commands (typically AT+CEDRXS for eDRX and AT+CPSMS for PSM), and the parameters will be sent from the device to the local network as part of the network attach process.
Network Compatibility
eDRX and PSM support is carrier-dependent and not guaranteed on all networks. See Soracom LPWAN Coverage for carrier-specific information about eDRX and PSM availability.
Note that local networks may override requested timer values. For example, if your device requests a 44-minute eDRX cycle but the network only supports 22 minutes, the device will operate with the 22-minute value. Devices should query the network's accepted values after attaching to confirm the active timer settings rather than assuming the requested values were accepted.
Soracom provides multi-carrier coverage in most countries. For example, in the United States, coverage is available across AT&T, T-Mobile, Verizon, and US Cellular. Since each carrier network may have different eDRX and PSM compatibility, the active timer settings can vary if your device switches between local networks, even when using the same configured values. See the Supported Carriers page for network availability by country.
PSM Calculation Tool
Soracom provides an online PSM calculation tool to help you generate the correct AT command parameters for configuring PSM timers on your device.
The tool allows you to:
- Adjust your desired Active Timer (T3324) and Periodic TAU Timer (T3412) values using sliders
- Automatically generate the binary-encoded timer values (T3324 and T3412 in binary format) required for the AT+CPSMS command
- Copy the complete AT command ready to send to your device
This is particularly useful because PSM timer values must be encoded in a specific binary format that can be difficult to calculate manually. The tool handles this conversion for you, ensuring your device receives the correct timer configuration.
Configuring Timers on Your Device
Configuring eDRX and PSM directly on your device gives you full control over timer settings at the device level and works with any carrier that supports these features. However, changing these settings requires modifying device firmware or configuration, and each device must be configured individually.
eDRX Configuration
To configure eDRX on your device, use the AT+CEDRXS command:
AT+CEDRXS=<mode>,<AcT-type>,<Requested_eDRX_value>For example, to enable eDRX for LTE-M with a cycle length of 20.48 seconds:
AT+CEDRXS=2,4,"0011"mode:2to enable eDRXAcT-type:4for LTE-M,5for NB-IoTRequested_eDRX_value: Binary-encoded string representing the cycle length
PSM Configuration
To configure PSM on your device, use the AT+CPSMS command:
AT+CPSMS=<mode>,[<Requested_Periodic-RAU>],[<Requested_GPRS-READY-timer>],[<Requested_Periodic-TAU>],[<Requested_Active-Time>]For example, to enable PSM with a 24-hour periodic TAU and 10-second active time:
AT+CPSMS=1,,,"01000011","00000101"mode:1to enable PSMRequested_Periodic-TAU(T3412): Time between TAU updates (binary-encoded)Requested_Active-Time(T3324): How long the device stays active after sending data (binary-encoded)
Use the PSM calculation tool to generate the correct binary-encoded values for your desired timer settings.
Configuring Timers from Soracom
Soracom provides a feature that allows you to set the eDRX and PSM timer parameters within a group. When a Soracom IoT SIM belonging to the group attaches to a network, the eDRX and PSM timer parameters will be sent from Soracom to the local network, allowing these parameters to be configured and managed on the network-side without the need to modify device firmware or configuration directly.
This approach offers centralized management without requiring device firmware changes, making it easy to adjust settings remotely for all devices in a group. To use this feature, contact Soracom Support in order to request access.