chapter10 - Introduction Clocks,events and process states...

Info iconThis preview shows pages 1–20. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Introduction Clocks,events and process states Synchronizing physical clocks Logical time and logical clocks Global states Distributed debugging Summary Chapter 10: Time and Global States Need to measure accurately E.g. auditing in e-commerce Algorithms depending on E.g. consistency, make Time is an important issue in DS Physicists view Newtons notation: absolute physical time Einsteins Relativity Theory Peoples approaches dealing with time Approximately synchronize Logical clocks There is no universe physical clock Introduction Clocks,events and process states Synchronizing physical clocks Logical time and logical clocks Global states Distributed debugging Summary Chapter 10: Time and Global States Model of a distributed system e Event: occurrence of a single action Model of a distributed system A device that count oscillations occurring in a crystal at a definite frequency Clock in computer Clock drift Crystal oscillate at different rate Clock drift can not be avoided Clock skew The instantaneous difference between the readings of any two clocks Clock skew and clock drift Network Rotation of earth on its axis and about the Sun Days, Years, etc Second is 1/86400 astronomical time Standard second Atomic oscillator Astronomical Time &International Atomic Time shift between astronomical time and atomic time The period of the Earths rotation about its axis is gradually getting longer Tidal friction, atmospheric effects, etc Leap second Atomic time which is inserted a leap second occasionally to keep in step with astronomical time Broadcast UTC to the World E.g., by GPS or WWV Coordinated Universal Time (UTC) Introduction Clocks,events and process states Synchronizing physical clocks Logical time and logical clocks Global states Distributed debugging Summary Chapter 10: Time and Global States External & Internal synchronization Internal synchronization For a synchronization bound D > 0, | C i (t)- C j (t) | < D for i , j =1,2, N , and for all real times t in I External & Internal synchronization (2) Correctness of a hardware clock H General synchronization issues <= ( 1 + ) H ( t ) - H ( t ) ( t - t ) ( 1 - ) <= Clock failures Crash failure: stop ticking Arbitrary failure, e.g. Y2K bug General synchronization issues (2) Protocol Sender: send M ( t ) Synchronization in a synchronous system Clock skew between sender and receiver (max min ) / 2 Synchronization in a synchronous system(2) t t +max t + T trans t + min Applying circumstance C/S Round-trip time is short compared with the required accuracy Protocol Cristians method of synchronizing clocks m r m t p Time server,S Accuracy analysis If the minimum delay of a message transmission is...
View Full Document

This note was uploaded on 06/12/2011 for the course CS 551 taught by Professor Staff during the Summer '08 term at Colorado State.

Page1 / 76

chapter10 - Introduction Clocks,events and process states...

This preview shows document pages 1 - 20. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online