Berkley Algorithm

1
Berkley Algorithm

• An Example

2
Review

• In the last lecture we looked at the two methods
  of clock synchronisation
• External Synchronisation
• Christian Algorithm
• Internal Synchronisation
• Berkley Algorithm

3
Berkley Algorithm

• In a set of hosts one is designated the master
  and the rest are slaves
• Master polls slaves who send back their time.
• Master allows for round trip delay and calculates
  time for each slave.
• Master averages out the times (including its own)
  to produce local time.
• Master returns error between local time and slave
  time to each slave.

4
Example

• The distributed system has a master time server
  which uses Berkley Algorithm. The result of
  polling its two slaves which shows time stamps
  and round trip delays are given below

5
Example

• Time for master Clock
• Masters current time
• slave 1 current time Slave1 (RTT)/2
• slave 2 current time Slave2 (RTT)/2
• / 3 ---n1 3
• 101533352 (101535140 0.012/2)
• (101537752
  0.020/2) / 3
• 101533352 101535146 101537762/3
• 101535420

6
Example

• Returned Value to Slaves
• Slave 1 101535140 - 101535420
• -000280 (i.e. advance clock)
• Slave 2 101537752 101535420
• 000332 (i.e. retard clock)