Synchronization

"Synchrony" redirects here. For linguistic synchrony, see Synchronic analysis. For the X-Files episode, see Synchrony (The X-Files).

For similarly named concepts, see Synchronicity (disambiguation).

Not to be confused with data synchronization or file synchronization.

Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time.

Systems operating with all their parts in synchrony are said to be synchronous or in sync.

Firefighters marching in a parade

Some systems may be only approximately synchronized, or plesiochronous. For some applications relative offsets between events need to be determined, for others only the order of the event is important.

Today, synchronization can occur on a global basis due to GPS-enabled timekeeping systems.

Transport

Apart from its use for navigation (see John Harrison), synchronization was not important in transportation until the nineteenth century, when the coming of the railways made travel fast enough for the differences in local time between adjacent towns to be noticeable (see [1]).

In some territories, sharing of single railroad tracks was controlled by the timetable. Thus strict timekeeping was a safety requirement. To this day, railroads can communicate and signal along their tracks, independently of other systems for safety.

Communication

The lessons of timekeeping are part of engineering technology. In electrical engineering terms, for digital logic and data transfer, a synchronous object requires a clock signal. Timekeeping technologies such as the GPS satellites and Network time protocol (NTP) provide real-time access to a close approximation to the UTC timescale, and are used for many terrestrial synchronization applications.

Synchronization is an important concept in the following fields:

• Computer science (In computer science, especially parallel computing, synchronization refers to the coordination of simultaneous threads or processes to complete a task; in order to obtain correct runtime order and avoid unexpected race conditions.)
• Cryptography
• Multimedia
• Music (Rhythm)
• Neuroscience
• Photography
• Physics (The idea of simultaneity has many difficulties, both in practice and theory.)
• Synthesizers
• Telecommunication

Synchronization has several subtly distinct sub-concepts:

• Phase synchronization
• Rate synchronization
• Time offset synchronization
• Time order synchronization

Some uses of synchronization

• Film synchronization of image and sound in sound film.
• Synchronization is important in fields such as digital telephony, video and digital audio where streams of sampled data are manipulated.
• In electric power systems, alternator synchronization is required when mulitple generators are connected to an electrical grid.
• Arbiters are needed in digital electronic systems such as microprocessors to deal with asynchronous inputs. There are also electronic digital circuits called synchronizers that attempt to perform arbitration in one clock cycle. Synchronizers, unlike arbiters, are prone to failure. (See metastability in electronics).
• Encryption systems usually require some synchronization mechanism to ensure that the receiving cipher is decoding the right bits at the right time,,
• Automotive transmissions contain synchronizers which allow the toothed rotating parts (gears and splined shaft) to be brought to the same rotational velocity before engaging the teeth.
• Time codes are often used as a means of synchronization in film, video, and audio applications.
• Flash photography, see Flash synchronization

See also

Time portal

• Asynchrony
• Atomic clock
• Clock synchronization
• Double-ended synchronization
• Einstein synchronization
• Entrainment
• Flywheel
• Homochronous
• Kuramoto model
• Mutual exclusion
• Neural synchronization
• Phase-locked loops
• Reciprocal socialization
• Synchronism
• Synchronization (alternating current)
• Synchronization in telecommunications
• Synchronization of chaos
• Synchronizer
• Synchronous conferencing
• Time
• Timing Synchronization Function (TSF)
• Time transfer
• Timecode
• Tuning fork

In the field of video and audio engineering:

• Genlock
• Jam sync
• Word sync

In the field of aircraft gun engineering:

• Interrupter gear

Order synchronization and related topics:

• Rendezvous problem
• Interlocking
• Race condition
• Concurrency control
• Room synchronization
• Transient blocking synchronization
• Comparison of synchronous and asynchronous signalling

Compare with:

• Synchronicity, a mystical notion due to Carl Jung.

Notes