AVB — Audio Video Bridging

Audio Video Bridging (AVB) is a suite of IEEE 802.1 and 802.1AS/1722 standards for transmitting time-sensitive AV streams over standard Ethernet with guaranteed bandwidth and bounded latency. Unlike best-effort networking where packets may be delayed by traffic congestion, AVB reserves bandwidth for streams before transmitting — guaranteeing that audio and video arrive within defined latency windows regardless of other network activity.

The AVB Standards Suite

AVB is not a single standard but a coordinated set:

All five components must be present for a compliant AVB system. The absence of any one — particularly SRP for bandwidth reservation or gPTP for synchronization — means devices cannot guarantee the latency and timing that AVB promises.

gPTP: Generalized Precision Time Protocol

IEEE 802.1AS defines gPTP, a profile of IEEE 1588 PTP optimized for bridged Ethernet networks. Key differences from standard PTP:

• Peer-to-peer delay measurement (rather than end-to-end), which works correctly through 802.1AS-aware bridges
• gPTP domains — AVB uses gPTP domain 0 by default
• Synchronization interval: 125 ms for gPTP (vs. 1 s default for standard PTP)
• Accuracy: Sub-microsecond across the network; sufficient for sample-accurate audio synchronization

gPTP requires that every switch in the path between two devices is an 802.1AS-aware bridge — meaning it measures and compensates for residence time (the time spent in the switch) and link propagation delay. A non-AVB switch in the path breaks gPTP synchronization.

This is the key practical distinction from AES67/Dante: every switch must be AVB-capable. In existing networks with a mixture of switch hardware, installing AVB requires either replacing all switches or carefully designing the AVB segment as a separate dedicated network.

Stream Reservation Protocol (SRP)

Before an AVB device sends a stream, it negotiates with the network to reserve bandwidth. The process:

1. Talker (source) advertises the stream: required bandwidth, latency class
2. Bridges (switches) along the path check if bandwidth is available and reserve it
3. Listener (destination) confirms registration
4. Stream flows only after reservation is confirmed end-to-end

If bandwidth is unavailable, the SRP reservation fails and the talker does not transmit — preventing congestion. This admission control is what makes AVB deterministic. A new stream that would overload any link in the path simply cannot start.

Latency classes: AVB defines two stream classes:

• Class A: 2 ms end-to-end latency (high priority, limited bandwidth per link)
• Class B: 50 ms end-to-end latency (more bandwidth available per class, more flexible)

Class A is used for live audio production; Class B suits video or less latency-critical data.

AVDECC: Device Discovery and Control

IEEE 1722.1 (AVDECC — AV Device Enumeration, Discovery, Connection Management, and Control) defines how AVB devices announce themselves and how connections are made:

• ADP (AVDECC Discovery Protocol) — devices multicast their presence on the network
• ACMP (AVDECC Connection Management Protocol) — establishes and tears down connections between talkers and listeners
• AECP (AVDECC Enumeration and Control Protocol) — reads device capabilities, sets parameters

AVDECC is the "routing matrix" for AVB — the equivalent of Dante Controller in the Dante ecosystem. It is implemented in software controllers from manufacturers and open-source tools.

Hive (by L-Acoustics) and AVBTools are common AVDECC controllers used in live production. Some AVB audio devices include embedded web UI for AVDECC management.

AVB-Compatible Hardware

AVB adoption is concentrated in specific market segments:

Professional audio consoles: MOTU (AVB ethernet on 1248, 16A, 8A), PreSonus (StudioLive RM mixers with AVB option), Meyer Sound (Galileo Galaxy processors), L-Acoustics (P1/Q-SYS plugin via AVB), Avid (MADI-based but increasingly AVB I/O)

Networked I/O: MOTU Ultralite AVB, MOTU 624, 8pre AVB; RME M-1610 Pro (via expansion)

Switches: Cisco IE 2000/3000 (with AVB support), Netgear M4300 (AVB model), Extreme Networks, Marvell-chipset switches. Note: standard Cisco Catalyst or Meraki switches typically do not support AVB.

The ecosystem is significantly smaller than Dante. AVB is strongest in theater, live touring, and broadcast where MOTU and L-Acoustics systems are common.

AVB vs. TSN: The Evolution

Time-Sensitive Networking (TSN) is the IEEE 802.1 working group's expansion of AVB concepts to a broader range of industries — automotive, industrial automation, video surveillance, and AV. TSN is essentially "AVB generalized":

TSN switches are increasingly available from Cisco, Belden, and Hirschmann, and are appearing in AV applications as the technology matures. SMPTE ST 2110 systems running at scale use TSN infrastructure for deterministic video delivery.

Practical Use in AV

For most corporate AV and conferencing installations, AVB is overkill and Dante is simpler. AVB's advantages materialize in:

• Large-scale live production with many synchronized audio zones
• Theater systems requiring sample-accurate audio routing across many racks
• Broadcast where the same infrastructure carries video, audio, and control
• Systems where open standards and multi-vendor flexibility are required over a single-vendor solution

If specifying AVB, engage an integrator with specific AVB experience. AVB commissioning requires understanding SRP reservation limits, gPTP sync verification, and AVDECC controller software — a steeper learning curve than Dante.

Common Pitfalls

• Non-AVB switch in the path — Any switch between two AVB endpoints that does not support 802.1AS breaks gPTP sync. The devices will lose synchronization and audio clicks, drifts, or fails entirely. Every switch must be AVB-capable.
• Exceeding reservation limits — SRP will reject streams that would overload a link. This manifests as streams that fail to connect with no obvious error. Check the switch's SRP reservation tables to identify the bottleneck link.
• AVDECC controller software gaps — Not all AVDECC controllers support all vendor extensions. A controller from vendor A may not expose all parameters of a device from vendor B. Test your specific controller+device combination before deployment.
• Limited ecosystem — If a particular DSP, amplifier, or microphone you need doesn't support AVB, you'll need a protocol bridge to Dante or analog I/O at that point. Check the entire signal chain for AVB compatibility before specifying.
• Class A bandwidth limits — Class A streams reserve 75% of link bandwidth, leaving 25% for Class B and best-effort. In dense systems, Class A reservation failures are common when too many streams are configured. Calculate reserved bandwidth before commissioning.