This document discusses clock synchronization in distributed systems and proposes a solution called Servo-Clock. It notes that nodes in a distributed system have their own clocks that tend to diverge over time due to local drift. The proposed Servo-Clock solution involves a master node sending a reference clock signal to slave nodes. The slaves then estimate network delay and follow the master clock signal by continuously correcting their rate and offset based on error measurements to synchronize with the master clock. Experimental results show that Servo-Clock enables faster convergence and compensation for offset errors compared to slower, smoother correction approaches.

1. Clock synchronization using servo-clock
This work was developed within the scope of the Distributed Systems of MIEEC
André Costa Lima
Hugo Marques

2. Clock sync – importance
Medium access control Synchronized sampling
TDM

3. Clock sync – problem & solution
Network nodes have their own clock
• Clocks evolve at their own pace
• There is no coherent notion of time
• Clocks tend to diverge due to local drift
Possible solution
• Master node sends reference clock to slaves
• Not perfect !!
• Upon reception the reference is late
• Network induced delay
• Overheads

4. Estimating the network delay
Measuring Round-Trip delay
(RTD)

5. Following the clock reference
rate offset

6. Clock correction with Servo-Clock
Rate correction
Slave clock at time instant t
error

7. Base experimental parameters
Client-Server approach
• Implementation in Java
• TCP sockets
• Clock server – master
• Client – slave
• Periodic clock reference request
Clock generator
Java Virtual Machine (JVM) high-resolution timer
• System.nanoTime()

8. Slower and smoother correction

9. Unstable behavior

10. Faster convergence compensating offset errors

11. Conclusions