What TimeSynchronization Is
TimeSynchronization is a remote-device-management service in BACnet, defined in Clause 16.7 of ANSI/ASHRAE 135-2024. A time master uses it to tell devices the correct current local time so their internal clocks stay aligned. It is an unconfirmed service and is usually broadcast, though it can be multicast or sent to a single device.
Aligned clocks matter across a site: schedules fire at the right moment, trend samples carry consistent timestamps, and alarm times line up when an operator correlates events across devices.
How It Works
A single device is designated the time master. It periodically sends TimeSynchronization carrying the current date and time, and receiving devices set their clocks from it. The message conveys local time directly; devices that need to reason about time zones or daylight saving use the UTCTimeSynchronization variant instead, which carries UTC plus offset information. A device typically supports one or the other based on how its clock model works.
Where You’ll See It
- Keeping schedules honest. A time master broadcasting local time so every controller’s Schedule fires on the same clock.
- Consistent trend timestamps. Time sync keeps Trend Log records comparable across devices.
- Correlating alarms. Event timestamps that line up depend on synchronized clocks.
TimeSynchronization Error Codes
TimeSynchronization is an unconfirmed, usually broadcast service, so it has no acknowledgment and returns no application-layer error. If clocks drift despite a time master, the causes are operational rather than protocol errors:
- Devices are listening for UTCTimeSynchronization instead of the local-time service, or vice versa.
- The broadcast does not reach devices on other subnets without a BACnet BBMD path.
- No device is configured as the time master, so no synchronization is sent at all.
Profiles That Require It
Accepting TimeSynchronization comes from DM-TS-B. The controller profiles that must keep an accurate clock, B-BC and B-AAC and the advanced life-safety, access-control, and elevator controllers, require either DM-TS-B or the UTC equivalent DM-UTC-B, not both. Sending time synchronization is the behavior of a time master, typically an operator workstation or supervisory controller.
What Chipkin Provides
The CAS BACnet Stack accepts TimeSynchronization to set the device clock, and can act as a time master in the test tooling. Talk to us about adding BACnet server support to your device.