3Com MSR 50 Series Configuration Manual page 2054

2054 C 111: NTP C
HAPTER ONFIGURATION
active); the device that receives this message automatically enters the symmetric
passive mode and sends a reply, with the Mode field in the message set to 2
(symmetric passive). By exchanging messages, the symmetric peers mode is
established between the two devices. Then, the two devices can synchronize, or
be synchronized by, each other. If the clocks of both devices have been already
synchronized, the device whose local clock has a lower stratum level will
synchronize the clock of the other device.
Broadcast mode
Figure 614 Broadcast mode
Server
Network
Periodically broadcasts clock
synchronization messages (Mode 5)
Clock synchronization message
exchange (Mode 3 and Mode 4)
Periodically broadcasts clock
synchronization messages (Mode 5)
In the broadcast mode, a server periodically sends clock synchronization messages
to the broadcast address 255.255.255.255, with the Mode field in the messages
set to 5 (broadcast mode). Clients listen to the broadcast messages from servers.
After a client receives the first broadcast message, the client and the server start to
exchange messages, with the Mode field set to 3 (client mode) and 4 (server
mode) to calculate the network delay between client and the server. Then, the
client enters the broadcast client mode and continues listening to broadcast
messages, and synchronizes its local clock based on the received broadcast
messages.
Multicast mode
Figure 615 Multicast mode
Server
Network
Periodically multicasts clock
synchronization messages (Mode 5)
Clock synchronization message
exchange (Mode 3 and Mode 4)
Periodically multicasts clock
synchronization messages (Mode 5)
In the multicast mode, a server periodically sends clock synchronization messages
to the user-configured multicast address, or, if no multicast address is configured,
Client
After receiving the first
broadcast message , the
client sends a request
Calculates the network delay
between client and the server
and enters the broadcast
client mode
Receives broadcast
messages and synchronizes
its local clock
Client
After receiving the first
multicast message , the
client sends a request
Calculates the network delay
between client and the server
and enters the multicast
client mode
Receives multicast
messages and synchronizes
its local clock