113
Figure 42
Clock nodes in a PTP domain
Besides the three basic types of clock nodes, PTP introduces some hybrid clock nodes. For example, a
TC+OC has multiple PTP ports in a PTP domain. One port is the OC type, and the others are the TC type.
A TC+OC forwards PTP messages through TC-type ports and performs delay corrections. In addition, it
synchronizes time through its OC-type port. TC+OCs include these types: E2ETC+OC and P2PTC+OC.
Master-member/subordinate relationship
The master-member/subordinate relationship is defined as follows:
•
Master/Member node
—A master node sends a synchronization message, and a member node
receives the synchronization message.
•
Master/Member clock
—The clock on a master node is a master clock. The clock on a member
node is a member clock.
•
Master/Subordinate port
—A master port sends a synchronization message, and a subordinate
port receives the synchronization message. The master and subordinate ports can be on a BC or an
OC. A port that neither receives nor sends synchronization messages is a passive port.
Grandmaster clock
In
, all clock nodes are organized into a master-member hierarchy, where the grandmaster
clock GM operates as the reference clock for the entire PTP domain. Time synchronization is implemented
through exchanging PTP messages.
A GM can be manually configured, or it can be elected through the Best Master Clock (BMC) algorithm
by following this procedure:
1.
The clock nodes in a PTP domain exchange announce messages and elect a GM by using the
following rules in descending order:
a.
Clock node with higher priority 1.
TC 1
BC 1
OC 1
OC 2
BC 2
BC 3
TC 3
TC 4
OC 3
OC 4
OC 5
OC 6
Grandmaster clock
PTP domain
Master port
Subordinate port
TC 2
Passive port
