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DeviceTimeReq is a payload-free LoRaWAN MAC command that asks the Network Server for the current network time. If the server responds, it sends DeviceTimeAns in a Class A downlink on RX1 or RX2. The answer carries GPS time—not a ready-to-use UTC timestamp—and is especially useful for helping a device acquire Class B beacons.
What DeviceTimeReq does
DeviceTimeReq is a request from an end-device to its Network Server for time. The request itself contains no payload. LoRaWAN L2 1.0.4 says end-devices and Network Servers shall implement the commands, but the request-and-response behavior is specified as optional; a device should not assume every request will receive an answer. See the LoRaWAN L2 1.0.4 specification, section 5.9.
The command is part of the LoRaWAN MAC layer. It gives a device a way to obtain network time without using the separate Application Layer Clock Synchronization package. The LoRa Alliance identifies DeviceTimeRequest as a new command for synchronizing a device real-time clock in its LoRaWAN Specification v1.0.3 page.
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What DeviceTimeAns contains
DeviceTimeAns is five octets long: a 32-bit unsigned seconds count followed by an 8-bit fractional-seconds value. Each fractional unit represents 1/256 of a second. The network time refers to the end of the uplink transmission that prompted the response.
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| Field | Size | Meaning |
|---|---|---|
| Seconds | 4 octets | Unsigned count of seconds since the GPS epoch. |
| Fractional seconds | 1 octet | Fraction in increments of 1/256 second. |
The specification requires the provided network time to have worst-case accuracy of ±100 ms. This is a protocol requirement for the time provided by the network, not a guarantee that an end-device’s clock will remain within that accuracy after it has drifted, missed updates, or applied its own clock-discipline logic.
Why the timestamp is GPS time, not UTC
The seconds count begins at the GPS epoch: January 6, 1980, at 00:00:00 UTC. It represents GPS-timescale seconds, which do not include leap seconds. To produce a UTC timestamp, software must account for the leap-second difference between GPS time and UTC; DeviceTimeAns is not itself a ready-made UTC date and time.
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- Support Arduino Development Environment: Support ESP32 + LoRaWAN protocol Arduino library, this is a standard LoRaWAN protocol that can communicate with any LoRa gateway running the LoRaWAN protocol
- Highly Integrated: Integrated WiFi, LoRa, Bluetooth three network connections, onboard WiFi, Bluetooth dedicated 2.4GHz metal spring antenna, reserved IPEX (U.FL) interface for LoRa use. Integrated CP2102 USB to serial port chip, convenient for program downloading, debugging information printing
- Power Supply Method: Onboard SH1.25 battery interface, integrated lithium battery management system; you can also use the Type-C interface to power the development board
- Highly Interactive: Onboard 0.96-inch 128*64 dot matrix OLED display, which can be used to display debugging information, battery power and other information
- Widely Application: ESP32 LoRa V3 is now widely used in well-known long-range wireless open-source projects such as Meshtastic and Meshcore, serving applications in smart cities, smart farms, industrial control, and security systems
The specification gives an example of 1,139,322,288 seconds corresponding to February 12, 2016, at 14:24:31 UTC. It also says GPS time was 17 seconds ahead of UTC as of June 2017. That 17-second figure is historical, not a current offset; implementations need an appropriate leap-second table or other current conversion source.
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DeviceTimeAns is sent as a Class A downlink, using the end-device’s RX1 or RX2 receive window after an uplink. This means the exchange follows the device’s uplink and receive-window schedule; it is not a continuously available clock feed. Whether a request is answered depends on the network’s behavior and downlink availability, so applications should handle a missing response rather than treating it as a guaranteed transaction.
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How DeviceTimeReq helps Class B devices
Class B operation uses scheduled beacons, so a device must acquire beacon timing. LoRaWAN L2 1.0.4 explains that synchronizing the internal clock can speed beacon acquisition. It also says the older BeaconTimingReq and BeaconTimingAns commands have been deprecated since L2 1.0.3 and should be replaced by DeviceTimeReq and DeviceTimeAns.
DeviceTimeReq supplies a time reference; it does not replace the beacon as the time source for a Class B device once beacon operation is established. The LoRa Alliance’s clock-synchronization guidance says Class B end-devices should use network beacon time directly.
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Which time source should a device use?
| Device situation | Guidance |
|---|---|
| LoRaWAN 1.1 or later, with no other accurate clock source | The Alliance says the device should use DeviceTimeReq instead of the separate Application Layer Clock Synchronization package. |
| Class B device | Use network beacon time directly, according to the Alliance’s guidance. |
| Device with an accurate external clock, such as GPS | Use that external source instead. |
The guidance appears on the LoRa Alliance’s Application Layer Clock Synchronization Specification v1.0.0 page, published September 10, 2018. The page provides recommendations, not a measured comparison of accuracy or efficiency among these approaches.
Quick Recap
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- Support Arduino Development Environment: Support ESP32 + LoRaWAN protocol Arduino library, this is a standard LoRaWAN protocol that can communicate with any LoRa gateway running the LoRaWAN protocol
- Highly Integrated: Integrated WiFi, LoRa, Bluetooth three network connections, onboard WiFi, Bluetooth dedicated 2.4GHz metal spring antenna, reserved IPEX (U.FL) interface for LoRa use. Integrated CP2102 USB to serial port chip, convenient for program downloading, debugging information printing
- Power Supply Method: Onboard SH1.25 battery interface, integrated lithium battery management system; you can also use the Type-C interface to power the development board
- Highly Interactive: Onboard 0.96-inch 128*64 dot matrix OLED display, which can be used to display debugging information, battery power and other information
- Widely Application: ESP32 LoRa V3 is now widely used in well-known long-range wireless open-source projects such as Meshtastic and Meshcore, serving applications in smart cities, smart farms, industrial control, and security systems
What to check when implementing it
- Interpret the fields correctly. Parse the 32-bit seconds value and 8-bit fraction, then convert the GPS-timescale value to UTC only with an appropriate leap-second adjustment.
- Anchor the time correctly. The network time refers to the end of the uplink transmission, not the later moment when the answer is received.
- Respect the Class A exchange. Expect the answer, if provided, through RX1 or RX2 following the uplink.
- Plan for no answer. The standard does not guarantee that a particular Network Server will respond to every request, nor does it prescribe an application’s full clock-maintenance strategy.
- Check the applicable specification version and regional parameters. The detailed command description here is from TS001-1.0.4. The Alliance’s technical publications index lists later documents, including TS001-1.0.4, TS003-2.0.0, and RP002-1.0.5; implementation details should be checked against the versions applicable to the device and network.
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