3Com Switch 4200G Configuration Guide

Introduction to NTP 293
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
4
-T
1
)-(T
3
-T
2
).
■ The time offset of LS_A with regard to LS_B: offset = ((T
2
-T
1
) + (T
3
-T
4
))/2.
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.
NTP Implementation
Mode
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
Peer mode
Figure 91 NTP implementation mode: peer mode
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
Client Server
Clock synchronization
request packet
Response packetFilter and select clocks
and synchronize its
ow n clock to that of
the selected server
Work as a server
automatically and
send response
packets
Netw ork
Client Server
Response packetFilter and select clocks
and synchronize its
ow n clock to that of
the selected server
Work as a server
automatically and
send response
packets
Netw ork
Client Server
Clock synchronization
request packet
Response packetFilter and select clocks
and synchronize its
ow n clock to that of
the selected server
Work as a server
automatically and
send response
packets
Netw ork
Client Server
Response packetFilter and select clocks
and synchronize its
ow n clock to that of
the selected server
Work as a server
automatically and
send response
packets
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
In peer mode, both
sides are synchronized
to the clock with
smaller stratum
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
Active peer Passive peer
Netw ork
Clock synchronization
request packet
Operates in the passive
peer mode automatically
Netw ork
Response packet
Synchronize
In peer mode, both
sides are synchronized
to the clock with
smaller stratum