Dell PowerSwitch S5212F-ON EMC SmartFabric OS10 User Guide Release 10.5.1 - Page 168

○ Sync-Master sends a Sync message to distribute the time of the day. ○ Delay_Req-Slave sends a Delay_Req message to the master for end-to-end delay measurement, the request- response delay mechanism. ○ Pdelay_Req-Link node A sends a Pdelay_Req message to measure peer-to-peer delay. ○ Pdelay_Resp-Link node B sends a Pdelay_Resp message to measure peer-to-peer delay. ● General messages: Do not require accurate timestamps. ○ Follow_Up-In a two-step clock, the master sends a Follow_Up message after sending the Sync message. ○ Delay_Resp-Master sends a Delay_Resp message to measure the end-to-end delay. ○ Pdelay_Resp_FollowUp-Link node B sends a Pdelay_Resp_FollowUp message to measure peer-to-peer delay. ○ Announce-Master sends an Announce message to establish a synchronization hierarchy. The BMCA uses the Announce message to define a clock hierarchy and to select the grandmaster clock. ○ Signaling-Clock A sends a Signaling message to clock B for unicast negotiation and so on. Time synchronization Master and slave clock devices exchange PTP timing messages to achieve time synchronization. Slave clock devices adjust their time to synchronize with their master clock devices. For time synchronization and to determine the slave offset with the master, PTP accounts for the following: ● Communication delay between two PTP nodes ● End-to-end delay measured using the delay request message from the slave and delay response message from the master The following is the sequence of PTP messages during time synchronization: 1. Master sends a Sync message and makes note of the time t1 when the message was sent. 2. Slave receives the Sync message and makes note of the time t2 when the message was sent. 3. Master embeds the timestamp t1 in the Sync message. 4. Slave sends a Delay_request message to the master and makes note of the time t3 when the message was sent. 5. Master receives the Delay_request message and makes note of the time t4 when the message was sent. 6. Master conveys the timestamp t4 in a Delay_response message. 7. Slave uses these timestamps to adjust its local clock to synchronize with the master: ● Offset = [(t2 - t1) - (t4 - t3)] / 2 ● Delay = [(t2 - t1) + (t4 - t3)] / 2 168 System management