H3C S5600 SERIES Operation Manual page 226

Figure 1-1 A schematic diagram of designated bridges and designated ports
All the ports on the root bridge are designated ports.
4) Path cost
Path cost is a value used for measuring link capacity. By comparing the path costs of different links, STP
selects the most robust links and blocks the other links to prune the network into a tree.
How STP works
STP identifies the network topology by transmitting configuration BPDUs between network devices.
Configuration BPDUs contain sufficient information for network devices to complete the spanning tree
calculation. Important fields in a configuration BPDU include:
Root bridge ID, consisting of root bridge priority and MAC address.
Root path cost, the cost of the shortest path to the root bridge.
Designated bridge ID, designated bridge priority plus MAC address.
Designated port ID, designated port priority plus port name.
Message age: lifetime for the configuration BPDUs to be propagated within the network.
Max age, lifetime for the configuration BPDUs to be kept in a switch.
Hello time, configuration BPDU interval.
Forward delay, forward delay of the port.
1-3