The IEEE 1588-2008 supports peer-to-peer PTP (Pdelay) message in addition to the SYNC, Delay Request, Follow-up, and Delay Response messages.
The IEEE 1588-2008 supports peer-to-peer PTP
(Pdelay) message in addition to the SYNC, Delay Request, Follow-up, and Delay
Response messages. Figure 43-11 shows the
method to calculate the propagation delay in clocks supporting peer-to-peer path
correction.
- Port 1 issues a Pdelay_Req message and generates a timestamp (t1) for the Pdelay_Req message.
- Port 2 receives the Pdelay_Req message and generates a timestamp (t2) for this message.
- Port 2 returns a Pdelay_Resp message and generates a timestamp (t3) for this message. To minimize errors because of any frequency offset between the two ports, Port 2 returns the Pdelay_Resp message as quickly as possible after the receipt of the Pdelay_Req message. Port 2 returns any one of the following:
- Difference between the timestamps t2 and t3 in the Pdelay_Resp message
- Difference between the timestamps t2 and t3 in the Pdelay_Resp_Follow_Up message
- Timestamps t2 and t3 in the Pdelay_Resp and Pdelay_Resp_Follow_Up messages, respectively
- Port 1 generates a timestamp (t4) on receiving the Pdelay_Resp message.
- Port 1 uses all four timestamps to compute the mean link delay.