University:
University of Greenwich
Course:
COMP1560 | Computer Networks
Academic year:

2021
Views:

402

Pages:

2
Author:

J. Varghese

Computer Network Synchronization Time  Time Synchronization Basics    Computer clocks can drift and must be periodically synchronized over a network The happens-before relation states that events on one computer happen before news of those events reaches another computer   Servers send their current time in messages  Clients advance their clock if a received time is later than their clock Clocks are never set backwards to avoid violating happens-before Network time protocols like NTP and DTSS synchronize clocks accounting for network delays NTP goal is to synchronize clocks to within a few milliseconds of Coordinated Universal Time (UTC) Time Synchronization Protocols   Persistent: Always on  Preemptable: Demobilize if no response after timeout  Ephemeral: Create ondemand, demobilize after timeout Common modes:  Client/Server: Client polls stateless server  Symmetric: Peers sync each other  Broadcast: Single server syncs many clients Lamport's algorithm:    Three association modes: Protocols estimate client's time offset versus server clocks  Offset is estimated by client sending a request and measuring round-trip delay  Protocols operate over multiple stratum levels - servers at one level synchronize clients at the next level  Configuration management is needed to find servers and balance load Computer Clocks  Clocks based on quartz oscillators that tick at millisecond intervals  Clock error has systematic offset and random jitter components  NTP estimates both time offset and frequency offset terms  Sync protocols adjust clock to minimize offset  Small poll intervals (<15 min) needed for millisecond accuracy Processing Time Values  NTP uses engineered algorithms like cliques, clustering, combining to select good time values  Key NTP principle: Worst-case error reading remote clock is half the round-trip delay  NTP acts as a digital signal processor using techniques like filtering and feedback Highlights  Synchronizing computer clocks is critical for distributed systems  Protocols like NTP and DTSS synchronize clocks accounting for network delays  NTP uses advanced algorithms to filter noise and provide robust synchronization  Typical goal is to synchronize clocks to within a few milliseconds of UTC

Computer Network Time Synchronization

Related Documents

Recommended Documents

Description

Related Documents

Free up your schedule!

Take 5 seconds to unlock