8021AS

IEEE 802.1AS is a standard within the IEEE 802.1 family that defines clock synchronization for time-sensitive networking in Ethernet. It provides a profile for the Precision Time Protocol (PTP) defined by IEEE 1588, enabling networked devices to synchronize their local clocks to a common time reference with high precision. 802.1AS is designed for local area networks and is a foundational element of the broader Time-Sensitive Networking (TSN) suite.

Operation relies on a master clock, typically a grandmaster, and multiple slave clocks. The Best Master Clock Algorithm selects the grandmaster. Time information is distributed using a two-step PTP scheme: a Sync message followed by a Follow_Up, allowing slaves to compute the clock offset and path delay. To improve accuracy, 802.1AS supports optional delay measurement mechanisms and accommodates intermediate devices as boundary clocks or transparent clocks to correct for residence times.

The standard is intended to provide deterministic timing for traffic classes in TSN, enabling synchronized execution of time-critical applications such as professional audio and video, industrial automation, and control systems. 802.1AS interoperates with other TSN standards and conventional PTP implementations, ensuring cross-vendor compatibility within a TSN domain.

Since its introduction, 802.1AS has been revised to align with enhancements to IEEE 1588 and the evolving TSN landscape, maintaining compatibility with newer clock hardware and network topologies.