精确时间协议PTP介绍

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linux下的ptp协议介绍
Ken ICHIKAWA
FUJITSU LIMITED.
LinuxCon Japan 2014
Precision Time Protocol on Linux
~ Introduction to linuxptp
Copyright 2014 FUJITSU LIMITED
Agenda
Background
Overview of Precision Time Protocol (PTP)
About PTP on Linux
Tips
For easy trial or development
3
Copyright 2014 FUJITSU LIMITED
Background
Event ordering is very important
for incident analysis, performance analysis and so on
Event ordering is based on timestamps
Timestamps are collected from multiple servers
⇒Clock synchronization is important
If precision and accuracy of clock
synchronization are bad, event ordering can
reverse against actual time
4
Copyright 2014 FUJITSU LIMITED
Server A
Server B
Event 1
Event 2
Event 3
NTP is not enough
NTP provides millisecond level synchronization
Maybe enough for remote machines, but not enough for
locally cooperating machines
Many events occur in a millisecond in multiple servers
⇒Event ordering will frequently reverse
Need another protocol
Higher precision and accuracy
Not need to synchronize large area, but local servers
and devices
5
Copyright 2014 FUJITSU LIMITED
Example of wrong event ordering
6
Copyright 2014 FUJITSU LIMITED
Actual Time
Server A
diff:-1
Server B
diff:+3
Event 1
Event 2
Event 3
2
3 4 5 6 7 8
1
2 3 4 5 6 7
5
6 7 8 9 10 11
Time
Event
3
Event 1
5
Event 2
7
Event
3
Time
Event
2
Event 1
6
Event 3
8
Event
2
Event Ordering based on Actual Time Event Ordering based on Timestamp
reverse!
time

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