ServerTimestamp
In OPC UA, the ServerTimestamp in a DataValue is the time the OPC UA server received or last updated the value in its own address space. It is measured against the server's clock, so it captures transport and polling latency rather than process time, which makes it the wrong default for historising.
What it actually measures
ServerTimestamp is written by the server when the value enters its cache. For a server sitting directly on a device it is close to source time. For a gateway or aggregating server it includes the downstream poll interval, the network hop and any queueing, so it can lag SourceTimestamp by tens or hundreds of milliseconds and will jitter with load. Two clients reading the same node at the same instant get the same ServerTimestamp, which is exactly why it is useful for diagnosing the server rather than the process.
The legitimate uses
Use ServerTimestamp to measure end-to-end latency against SourceTimestamp, to detect a stalled driver where source time advances but server time does not, and to order events within one server when source clocks across devices are unsynchronised. It is also the only meaningful timestamp on nodes the server computes itself, such as diagnostic counters and ServerStatus variables. When a server has no source time at all, it commonly duplicates its own clock into SourceTimestamp, so the two fields become indistinguishable.
Bandwidth and configuration
TimestampsToReturn lets you ask for Source, Server, Both or Neither on Read and on CreateMonitoredItems. Requesting Both on a high-rate subscription costs eight bytes per notification more than requesting one, which matters on constrained links but is rarely the bottleneck. Requesting Neither is legal and some servers use it to reduce payload; do not do that on data you intend to store, because you then have no time reference except your own receive time.
Defined in: Part 4 - Services.
Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.