3Com 4200G 12-Port Configuration Manual page 307

NTP Implementation
Mode
At this time, LS_A has enough information to calculate the following two parameters:
The delay for an NTP packet to make a round trip between LS_A and LS_B: delay =
■
(T -T )-(T -T ).
4 1 3 2
The time offset of LS_A with regard to LS_B: offset = ((T
■
LS_A can then set its own clock according to the above information to synchronize its
clock to that of LS_B.
For the detailed information, refer to RFC1305.
To accommodate networks of different structures and switches in different network
positions, NTP can operate in multiple modes, as described in the following.
Client/Server mode
Figure 90 NTP implementation mode: client/Sever mode
Client Client Client Client
Filter and select clocks Filter and select clocks Filter and select clocks Filter and select clocks
and synchronize its and synchronize its and synchronize its and synchronize its
ow n clock to that of ow n clock to that of ow n clock to that of ow n clock to that of
the selected server the selected server the selected server the selected server
Peer mode
Figure 91 NTP implementation mode: peer mode
Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer Active peer
In peer mode, both In peer mode, both
sides are synchronized sides are synchronized
to the clock with to the clock with
smaller stratum smaller stratum
In peer mode, the active peer sends clock synchronization packets first, and its peer
works as a passive peer automatically.
If both of the peers have reference clocks, the one with smaller stratum is adopted.
Netw ork Netw ork Netw ork Netw ork
Clock synchronization Clock synchronization
request packet request packet
Response packet Response packet Response packet Response packet
Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork Netw ork
Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization Clock synchronization
request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet request packet
Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet Response packet
Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize Synchronize
Introduction to NTP 293
-T ) + (T -T ))/2.
2 1 3 4
Server Server Server Server
Work as a server Work as a server Work as a server Work as a server
automatically and automatically and automatically and automatically and
send response send response send response send response
packets packets packets packets
Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer Passive peer
Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive Operates in the passive
peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically peer mode automatically