8021Qbv

IEEE 802.1Qbv, part of the Time-Sensitive Networking (TSN) suite, is an amendment to IEEE 802.1Q that specifies the Time-Aware Shaper (TAS). The TAS provides deterministic Ethernet by shaping traffic with a global time reference, using a cycle-based schedule to control when frames may be transmitted.

Key concepts include a cycle time C and a Gate Control List (GCL). Within each cycle, gates associated with traffic classes can be opened or closed at defined times, determining when frames from those queues can be transmitted. Time synchronization across devices, typically using IEEE 802.1AS (Precision Time Protocol), is required for consistent scheduling.

Operation yields bounded latency and reduced jitter for scheduled traffic, since high-priority streams transmit only in their designated windows. Best-effort traffic is delayed when gates are closed to ensure deterministic behavior for critical streams. TAS can be used alongside other TSN mechanisms such as time-based shaping and filtering.

Deployment considerations: devices must support hardware TAS, configuration of GCLs, and clocks that stay synchronized. It is commonly used in industrial automation, automotive networks, and professional media networks that require deterministic timing, though full end-to-end TSN requires coordination across multiple vendors and standards.

History and status: 802.1Qbv was published in 2015 as an amendment to 802.1Q, under the TSN umbrella. It has influenced subsequent scheduling standards and remains a core element of deterministic Ethernet approaches.