Linux PTP原理.pdf

发布时间：2022-06-23 发布人：admin 分类：说明书资料大小：1.44M 资料格式：pdf 举报版权申诉

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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 Event 2 Event 1 Event 3 Server A Server B 4 Copyright 2014 FUJITSU LIMITED

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 Actual Time 2 3 4 5 6 7 8 Server A diff:-1 1 Server B diff:+3 5 2 3 4 5 6 7 Event 1 Event 2 Event 3 6 7 8 9 10 11 time Event Ordering based on Actual Time Event Ordering based on Timestamp Time Event Time Event 3 5 7 Event 1 Event 2 Event 3 2 6 8 Event 1 Event 3 Event 2 reverse! 6 Copyright 2014 FUJITSU LIMITED

Example of correct event ordering based on better clock synchronization Actual Time 2 3 4 5 6 7 8 Server A diff:-0.001 1.999 Server B diff:+0.003 2.003 2.999 3.999 4.999 5.999 6.999 7.999 Event 1 Event 2 Event 3 3.003 4.003 5.003 6.003 7.003 8.003 time Event Ordering based on Actual Time Event Ordering based on Timestamp Time Event 3 5 7 Event 1 Event 2 Event 3 Time 2.999 5.003 6.999 Event Event 1 Event 2 Event 3 correct! 7 Copyright 2014 FUJITSU LIMITED

Agenda  Background  Overview of Precision Time Protocol (PTP)  What’s PTP  Term explanation  About packet timestamp  About PTP on Linux  Tips  For easy trial or development 8 Copyright 2014 FUJITSU LIMITED

Precision Time Protocol (PTP)  Standardized protocol, IEEE1588  Synchronize the clocks in local computing systems and devices  Microsecond to sub-microsecond accuracy and precision  Administration free  Capability to autonomously decide time server(master) • called Best Master Clock Algorithm (BMCA) 9 Copyright 2014 FUJITSU LIMITED

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