Synchronization Mechanism - HPE FlexFabric 5700 Series Network Management And Monitoring Configuration Manual

2. The master node periodically sends announce messages to member nodes. If the member
nodes do not receive announce messages from the master node, they consider the master
node invalid and start to elect another GM.
Clock source type
A clock node of a device can use one of the following clock sources: local clock source and BITS
clock source (BITS1 and BITS2) that connects the device.
•
Local clock—38.88 MHz clock signals generated by a crystal oscillator inside the clock
monitoring module.
•
BITS clock—Clock signals generated by a BITS clock device. The signals are sent to the clock
monitoring module through a specific interface on the device and then sent to all member
devices by the clock monitoring module.
The clock node determines to use which type of clock source based on the specified algorithm.

Synchronization mechanism

Based on the exchanged synchronization messages, a member node calculates the round-trip delay
of the path to the master node. The one-way delay equals half of the round-trip delay (assume the
delays in both directions are the same). Then the member node synchronizes its clock with the
master clock according to the offset between the clocks.
PTP defines the following transmission delay measurement mechanisms:
•
Request_Response.
•
Peer Delay.
The basis of the two mechanisms is that the transmission delay from the master clock to the member
clock is the same as that from the member clock to the master clock.
Request_Response
Figure 19 Operation procedure of the Request_Response mechanism
Master clock
t1
t4
Figure 19 shows the operation procedure of the Request_Response mechanism, which applies only
to peer-to-peer delay measurement. It shows an example of the Request_Response mechanism in
two-step mode.
1. The master clock sends a Sync message to the member clock, and records the sending time t1.
Upon receiving the message, the member clock records the receiving time t2.
2. After sending the Sync message, the master clock immediately sends a Follow_Up message
carrying time t1.
Member clock
Timestamps
known by
member clock
t2 t2
t1, t2
t3 t1, t2, t3
t1, t2, t3, t4
49