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007 Time Synchronization.rst

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SECoP Issue 7: Time Synchronization (closed)

As a SECoP server and a SECoP client might not run with a common clock, the SECoP client should be able to correct for time slips.

On the meetings in Berlin and Garching in 2017 it was proposed to put this into the standard, the exact wording has to be decided.

Agreement

The kind of SEC-node clock shall be noted as node property in the descriptive data.

Proposal

A SEC-node property called clock describes the kind of clock.

datatype: Enum(none=0, relative=1, absolute=2)

The default is none

Discussion

It might happen that for some parameters no timestamps are delivered while on others there are. What should the client do when none is specified, but a timestamp is delivered on a parameter? Is this a violation of the protocol, or should the client ignore the timestamp?

Decision

The ECS can easily detect if the clock is accurate enough by sending a ping command. If the timestamp delivered by the pong message lies between the time the ping message was sent and the pong message was received, then the timestamp can be trusted, else the ECS might record the time shift and decide to use relative times. (decision taken at the meeting 2018-02-13 in Grenoble)