PRISM MPI2-25 and MPX2-25 Media Analysis Platform User Manual
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The five basic PTP timing messages
This section describes the five basic timing messages in a PTP system. Other
messages are present in some instances. For example, grant requests and
responses appear in unicast systems, and Type Length Value (TLV) management
messages appear in SMPTE ST2059 profile systems.
Announce message
The Announce message is sent by the master to advertise its capability. This
message contains the clock quality and priority settings needed for the BMCA to
evaluate which device is the best master.
Sync message
The Sync message is sent by the master and is used to measure the propagation
delay from the master to slave. The sync message may contain the timestamp
indicating when it was sent, or that time may be in the Follow-up message. The
receiver must timestamp the sync message upon receipt. These two timestamps
are usually called t1 and t2 and provide the first delay measurement.
Follow-up message
The Follow-up message is sent only in cases where the PTP network hardware is
not capable of inserting the timestamp or corrections into the Sync message.
(See
One-step and two-step operation.)
Delay request message
The Delay request is sent by the slave. The time it is sent is noted by the slave but
is not included in the message. This time is usually called t3. When the delay
request is received by the master, the master timestamps the receive time. This
timestamp is usually called t4.
Delay response message
The delay response is sent from the master to the slave. The response contains
the t4 time stamp from when the master received the delay request. After the
slave receives the delay response, it has the second pair of timestamps needed to
calculate the second delay measurement of the slave to master delay.
