Lecture 3: Clocks

Terms you should know

Paul Krzyzanowski

February 17, 2021

Clock synchronization

  • Clock synchronization
  • Logical vs. physical clocks
  • Clock drift
  • Offset
  • Jitter
  • Drift compensation, linear compensation function
  • Time service
  • Synchronization delay (latency)
  • Cristian’s algorithm
  • Clock accuracy in Cristian’s algorithm
  • Berkeley algorithm
  • Fault-tolerant average
  • Network Time Protocol (NTP): goals
  • NTP synchronization subnet
  • Strata of clock servers
  • Use of UDP
  • Multicast, procedure call, and symmetric modes
  • Clock precision
  • Clock accuracy
  • Dispersion
  • Simple Network Time Protocol (SNTP) vs. NTP
  • Understand how to use the SNTP (NTP) forumula to find the offset
  • Precision time protocol
  • Best master clock
  • Master-initiated sync
  • PTP offset and delay

Logical clocks

  • Lamport’s happened-before relation
  • Logical clock timestamp
  • Causal events
  • Concurrent events
  • Lamport timestamps
  • Partial (causal) ordering
  • Lamport global logical timestamps (total ordering)
  • Deficiency of Lamport timestamps
  • Purpose of vector clock
  • Know how vector clocks get incremented
  • Identifying causal and concurrent events with vector clocks
  • Vector timestamps with process IDs
Last modified February 18, 2021.
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