Audio Video Bridging (AVB)

Audio Video Bridging (AVB) is a set of IEEE 802.1 standards that extends standard Ethernet to provide deterministic, low-latency transport for time-sensitive audio and video streams. It guarantees bounded latency (typically 2 ms end-to-end) and precise clock synchronization across an Ethernet network - capabilities that standard “best effort” Ethernet cannot provide.

The AVB standard family later evolved into the broader Time-Sensitive Networking (TSN) framework, which extends the same deterministic capabilities to industrial automation, automotive, and other domains.

Core Standards

AVB is a suite of interrelated IEEE standards, not a single document:

Standard	Full name	Function
IEEE 802.1AS	Timing and Synchronization (gPTP)	Distributes a common network clock with sub-microsecond accuracy
IEEE 802.1Qav	Credit-Based Shaper (CBS)	Reserves bandwidth and smooths traffic to prevent burst-induced latency
IEEE 802.1Qat	Stream Reservation Protocol (SRP)	Enables endpoints to reserve bandwidth for a stream end-to-end through the network
IEEE 802.1BA	AVB Systems	Defines system-level requirements combining the above three

All four standards were published by 2011. IEEE 802.1Qav and 802.1Qat were later folded into IEEE 802.1Q (the main Ethernet bridging standard) as clauses 34 and 35 respectively.¹

IEEE 802.1AS - Generalized Precision Time Protocol (gPTP)

AVB requires all devices to share a common clock. 802.1AS implements a profile of IEEE 1588 (Precision Time Protocol, PTP) designed for Ethernet networks. A grandmaster clock distributes timing to all AVB switches and endpoints. Devices synchronize to within approximately 1 microsecond of each other, enabling sample-accurate audio playout across the network.²

IEEE 802.1Qav - Credit-Based Shaper

Standard Ethernet switches transmit packets on a “best effort” basis. A large video frame can block a switch port, delaying a small audio packet. The Credit-Based Shaper (CBS) allocates bandwidth “credits” to time-sensitive traffic classes. An AVB stream spends credits to transmit, then waits to accumulate them - ensuring no single stream monopolizes bandwidth and bounding worst-case latency.

IEEE 802.1Qat - Stream Reservation Protocol

Before an AVB stream is established, the source endpoint uses SRP to signal bandwidth requirements through every switch along the path. Each switch either admits the reservation (if sufficient bandwidth is available) or rejects it. This prevents the network from becoming overcommitted - a stream is either reliably admitted or explicitly rejected.³

History

The AVB working group within IEEE 802.1 was formed in 2005. The first published AVB standard was 802.1AS in 2011, followed closely by 802.1Qav and 802.1Qat.

Early industry adoption was led by Apple, which included AVB hardware support in Mac Pro, Mac mini, and Thunderbolt interfaces starting in 2011-2012, positioning AVB for professional audio workstations and studios. However, AVB adoption in the broader professional AV market was slower than anticipated, partly due to the requirement for AVB-capable network switches (standard unmanaged switches do not support AVB).

In 2015, the Milan protocol was launched by the AVnu Alliance (the AVB industry certification body) and major audio networking vendors (AVID, Yamaha, L-Acoustics, others) to address interoperability gaps in the base AVB standard. Milan is a strict profile of AVB that mandates specific discovery, registration, and media clock requirements to ensure plug-and-play interoperability between different vendors’ AVB devices.⁴

AVB vs Competing Protocols

Protocol	Transport	Sync	Latency	Network requirement	Interop standard
AVB / Milan	IEEE 802.1 (Layer 2)	IEEE 802.1AS (gPTP)	≤2 ms (1 hop)	AVB-capable switches	IEEE 802.1BA / Milan spec
Dante	IP/UDP (Layer 3)	PTPv2 (IEEE 1588)	~1 ms (typical)	Managed or unmanaged Ethernet	AES67 compatible
RAVENNA	IP/RTP (Layer 3)	PTPv2	~1 ms	Standard IP network	AES67 native
AES67	IP/RTP	PTPv2	1 ms (min)	Standard IP network	Industry standard
Dante via AES67	IP/UDP bridged	PTPv2	~1 ms	Standard Ethernet	AES67 gateway

A key difference between AVB and IP-based protocols (Dante, RAVENNA, AES67): AVB streams are routed at Layer 2 (MAC address / VLAN), while IP protocols route at Layer 3. AVB cannot traverse standard IP routers; IP protocols can be routed across WAN links.

AV Industry Usage

AVB in its Milan profile is used by:

• L-Acoustics (P1 processor, LA Network Manager)
• d&b audiotechnik (DS100 Signal Engine)
• Yamaha (mixing consoles with EtherSound/AVB ports)
• Meyer Sound (Galileo GALAXY processors)

The AVnu Alliance operates a compliance testing program. Only certified devices carry the AVnu mark and are verified for interoperability.

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Footnotes

1. IEEE 802.1 Working Group. IEEE Std 802.1Q-2018: Bridges and Bridged Networks. IEEE Standards Association. 2018. doi:10.1109/IEEESTD.2018.8403927. (Clause 34: Credit-Based Shaper; Clause 35: Stream Reservation Protocol.) ↩

2. IEEE Standards Association. IEEE Std 802.1AS-2020: Timing and Synchronization for Time-Sensitive Applications. IEEE. 2020. doi:10.1109/IEEESTD.2020.9121845. ↩

3. IEEE Standards Association. IEEE Std 802.1Qat-2010: Stream Reservation Protocol. IEEE. 2010. doi:10.1109/IEEESTD.2010.5594708. ↩

4. AVnu Alliance. Milan Specification v1.2. AVnu Alliance. 2021. (Defines Milan as a strict profile of IEEE 802.1BA with mandatory discovery via AVDECC and fixed media clock requirements for interoperability.) ↩