3Com 4500 PWR 26-Port Configuration Manual page 648

Server/client mode
Figure 54-2 Server/client mode
Symmetric peer mode
Figure 54-3 Symmetric peer mode
In the symmetric peer mode, the local S4500 Ethernet switch serves as the symmetric-active peer and
sends clock synchronization request first, while the remote server serves as the symmetric-passive
peer automatically.
If both of the peers have reference clocks, the one with a smaller stratum number is adopted.
Broadcast mode
Figure 54-4 Broadcast mode
54-4