This section describes the PTP message sequences that occur during synchronization. The PTP clocks configured for End-to-End delay mechanism use the following PTP messages:

  • Syncz
  • Follow_Up
  • Delay_Req
  • Delay_Resp

These messages are sent in the following sequence:

  1. The Grand Master Clock sends a Sync message to the Slave Clocks and registers the transmit time stemp (t1)
  2. Each Slave Clock receives the Sync message and registers the receive time stamp (t2).
  3. The Slave Clocks receive a Follow_Up message from the Grand Master Clock with time stamp (t1).
  4. Each Slave Clock sends a Delay_Req message to the Grand Master Clock and registers the time stamp (t3) when the packet was sent.
  5. The Grand Master Clock receives the Delay_Req message from a Slave Clock and registers the receive time stamp (t4).
  6. The Grand Master Clock conveys to the given Slave clock the time stamp t4 by embedding the time stamp into a Delay_Resp message.

ptp message sequences

The Slave Clock receives a Delay_Resp message from the Grand Master Clock with time stamp (t4). After this sequence, a Slave Clock possesses all four time stamps that can be used to compute the offset of the Slave Clock relative to the master, and the propagation time between the two clocks. The offset calculation is based on the assumption that the uplink and downlink propagation times are the same.