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PTP Operational Overview
One-step and Two-step Operation
PRISM MPI-MPX User Manual
298
One-step and Two-step Operation
Some PTP messages have a time stamp associated with them. This time stamp
indicates the time of the local clock when the message was sent or received. In some
cases, the hardware is capable of embedding the time stamp in the message as it is
sent. This is known as “one-step” mode because the message and its associated time
are sent together.
In other cases, the hardware is not capable of inserting the time into the message, so
instead it is sent in a second follow-up message. This is called “two-step” mode because
there are two messages.
It is interesting to note that in End-to-End mode, only the Sync message is affected by
the one-step and two-step setting since it is the only message that needs the transmit
time stamp inserted. In a similar fashion, Peer-to-Peer mode has some messages that
may require follow-up support.
The IEEE1588 standard specifies that all slaves are required to operate with either one-
step or two-step message types. One type of device which often requires two-step
operation is a Transparent Clock, since it has to calculate the residence time of a
message and insert that time into the message or the follow-up message.