Clock Synchronization Algorithm Assignment Help
- Multiple machines using physical clocks. How can we keep them more or even less synchronized.
- Internal versus External synchronization
- Perfect synchronization difficult due to communication delays
- Even synchronization inside a bound cannot be assured along with guarantee due to unpredictability associated with communication delays.
How clocks work
- Computer clocks tend to be crystals which oscillate in a particular rate of frequency
- Every H oscillations, the actual timer chip interrupts once. Number associated with interrupts per second is usually 18.2, 50, 60, 100; could be greater, settable in some instances
- The interrupt handler increments the counter which retains track associated with number of ticks from a reference previously
- Knowing number associated with ticks for each second, we areable to determine year, month, day, time of day and so on.
- Unfortunately, period associated with crystal oscillation differs somewhat
- If this oscillates quicker, much more ticks per real second, therefore clock runs faster; comparable with regard to slower clocks
- For machine p, when correct reference time is t, let machine clock show time as C = Cp(t)
- Ideally, Cp(t) = t for all p, t
- In practice, 1 – ρ ≤ dC/dt ≤ 1 + ρ
- ρ = max. clock drift rate, usually around 10-5 for cheap oscillators
- Drift => Skew between clocks (difference in clock values of two machines)
- Periodic resynchronization required to offset skew
- If two clocks tend to be drifting within reverse directions, maximum skew following period capital t is actually 2 ρ t
- If application requires which clock skew < δ, after that resynchronization period r < δ /(2 ρ)
- Usually ρ and δ are known.
Important topics in Clock Synchronization