25-5Symmetric peers modeFigure 25-4 Symmetric peers modeA device working in the symmetric active mode periodically sends clock synchronization messages,with the Mode field in the message set to 1 (symmetric active); the device that receives this messageautomatically enters the symmetric passive mode and sends a reply, with the Mode field in themessage set to 2 (symmetric passive). By exchanging messages, the symmetric peers mode isestablished between the two devices. Then, the two devices can synchronize, or be synchronized byeach other. If the clocks of both devices have been already synchronized, the device whose local clockhas a lower stratum level will synchronize the clock of the other device.Broadcast modeFigure 25-5 Broadcast modeNetworkClientServerAfter receiving the firstbroadcast message, theclient sends a requestClock synchronization messageexchange (Mode 3 and Mode 4)Periodically broadcasts clocksynchronization messages (Mode 5)Calculates the network delaybetween client and the serverand enters the broadcastclient modePeriodically broadcasts clocksynchronization messages (Mode 5) Receives broadcastmessages and synchronizesits local clockIn the broadcast mode, a server periodically sends clock synchronization messages to the broadcastaddress 255.255.255.255, with the Mode field in the messages set to 5 (broadcast mode). Clientslisten to the broadcast messages from servers. After a client receives the first broadcast message, theclient 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 thebroadcast client mode and continues listening to broadcast messages, and synchronizes its local clockbased on the received broadcast messages.
