Raisecom
ISCOM2600G-HI (A) Series Configuration Guide
Raisecom Proprietary and Confidential
Copyright © Raisecom Technology Co., Ltd.
NTP
Network Time Protocol (NTP) is a standard Internet protocol for time synchronization, used
to synchronize time between the distributed time servers and clients. NTP transmits data
based on UDP, using UDP port 123 and guaranteeing high precision (error around 10ms).
Figure 1-6 shows basic principles of NTP. Clock synchronization works as below:
Step 1 Switch A sends Switch B a NTP message which carries the timestamp of leaving Switch A.
The timestamp is 10:00:00am and recorded as t1.
Step 2 When the message reaches Switch B, it is added with the timestamp of reaching Switch B,
which is 11:00:01am and recorded as t2.
Step 3 When the message leaves Switch B, it is added with the timestamp of leaving Switch B,
which is 11:00:02am and recorded as t3.
Step 4 When switch A receives the response message, it adds a new timestamp, which is 11:00:03am
and recorded as t4.
At present, Switch A has enough information to calculate two important parameters:
Round-trip delay of the NTP message: delay = (t4 - t1) - ( t3 - t2)
Time offset between Switch A and Switch B: offset = ((t2 - t1) + (t3 - t4))/2
Switch A configures its clock based on previous two parameters to synchronize clock with
Switch B.
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