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Experiment on Cristian’s and Berkeley Time Synchronization Algorithms
- Rahul Sehgal
12/6/2007
Experiment on Cristians and Berkeley Time Synchronization - - PowerPoint PPT Presentation
Experiment on Cristians and Berkeley Time Synchronization - - PowerPoint PPT Presentation
Experiment on Cristians and Berkeley Time Synchronization Algorithms - Rahul Sehgal 1 12/6/2007 Introduction: Centralized Algorithm: 1) Cristians algorithm. ( timeserver ) 2) Berkeley algorithm. ( coordinator ) 2 12/6/2007 Concept of
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Concept of Simulation Time
Time changes on the basis of state change. Time always advances Time doesn’t increases by the fix amount
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Cristian’s Algorithm
External clock synchronization method. A process is the time server in the system. External time source (Coordinated Universal Time) is
used as reference for synchronizing computer clocks with real time.
– UTC is an international standard. – Standard bodies which, disseminate UTC signal by radio,
telephone and satellite. One of the body is Geostationary Operational Environmental Satellites. (GEOS)
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Cristian’s Algorithm … contd
Other processes request for current time by
sending request message (req_message) to time server.
time server sends a reply by attaching
current time with each reply message.
Message suffers:
Transmission delay
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Apparatus for Cristian’s Algorithm :
time server maintains a message_queue for
arriving requests from other processes.
A delay value is generated at
message_queue, due to message queue delay (states for which request was in queue)
Other issues : clock skew and clock drift
clock skew : The difference in time values of two clocks. clock drift : The difference between speeds of two
clocks.
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Implementation for measuring performance….contd
In run() step,
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The messages are delivered in the increasing order of delay, to time server.
–
timeserver computes delay_at_rqst_queue ( states for which the message was in queue)
–
timeserver sends a reply message to requesting process.
–
Requesting process receives the message and updates its time as follows: current time = Tserver + (T1 – T0 ) / 2, Tserver = server time returned by time server. In simulation engine T1 – T0 = message_queue_delay
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Berkeley Algorithm:
coordinator polls other processes. Finds difference between its time and time of
selected processes
Then takes an average including its own time. Coordinator predicts time of other process with an
error.
Inform polled processes about correction (this
message has error included)
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Apparatus:
coordinator polls processes and sends them request
for there time
processes sends reply. processes differ in their times Coordinator predicts error for each process. coordinator puts an upper bound errors . Two test environments are:
–
with minimal (or no) errors
–
with errors
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Comparison between Cristian and Berkeley Algorithms
Comparision for 10 processes with no skew
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2 4 1 2 3 4 5 6 7 8 9 10 Global Time Difference of process time from Global Time Cristian Berkeley
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Comparison between Cristian and Berkeley Algorithms
Comparision on 50 nodes with no skew
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2 4 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 Global Time Difference of process time from Global Time Cristian Berkeley
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Comparison between Cristian and Berkeley Algorithms
Comparision on 100 nodes with no skew
0.5 1 1.5 2 2.5 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 Global Time Difference of process time from Global Time Cristian Berkeley
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Comparison between Cristian and Berkeley Algorithms
Comparision on 10 processes with error and unbound delay
0.5 1 1.5 2 2.5 1 2 3 4 5 6 7 8 9 10 Global Time Difference of process time from Global Time Cristisn Berkeley
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Comparison between Cristian and Berkeley Algorithms
Comparision on 50 processes with error and unbound delay
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0.5 1 1.5 2 2.5 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 Global time Difference of process time from Global Time Cristian Berkeley
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Comparison between Cristian and Berkeley Algorithms
comparision on 100 nodes with error and unbound delay
0.5 1 1.5 2 2.5 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 Global Time Difference of process time from Global Time Cristian Berkeley
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Future Work
Enhance design for fault tolerance in
distributed system.
Measure the performance of the system by
combining Cristian’s and Berkley time synchronization algorithms.
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References:
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References:
http://deneb.cs.kent.edu/~mikhail/classes/ao
s.f07/Materials/SinhaPhysClocks.pdf
http://deneb.cs.kent.edu/~mikhail/Research/T
R-KSU-CS-2007-04.pdf
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