What Is Audio Video Bridging?
Audio Video Bridging (AVB) refers to a set of standards that enable low latency, time-synchronized streaming of audio and video content over Ethernet networks (https://en.wikipedia.org/wiki/Audio_Video_Bridging). The key benefits of AVB include improved quality of service, precise synchronization between audio and video streams, and guaranteed bandwidth for time-sensitive media traffic.
The primary purpose of AVB is to provide reliable delivery of media streams with microsecond accuracy for professional audio video applications. By reserving dedicated network capacity, AVB ensures media streams are not disrupted by other network traffic. This deterministic delivery allows AVB to be used for applications like live events, television broadcast, and automotive infotainment.
In summary, AVB is an Ethernet extension optimized for media streaming that provides low latency transport, precise timing, and guaranteed quality of service over standard Ethernet networks (https://www.electronicdesign.com/technologies/communications/article/21799089/understanding-audio-video-bridging). Its key benefits make it well-suited for professional media applications requiring robust, synchronized streaming.
AVB Standards
The Audio Video Bridging standards were developed by the IEEE 802.1 Audio Video Bridging Task Group established in 2005. The foundation of AVB is based on the following standards:
802.1AS – This provides precise timing through a Time Synchronization Protocol developed for AVB devices. It allows all the nodes in an AVB network to be synchronized to a common clock reference with nanosecond accuracy. This is critical for supporting consistent low-latency transmission of audio and video streams (Audio Video Bridging).
802.1Qav – This is known as the Forwarding and Queuing Enhancements for Time-Sensitive Streams standard. It provides procedures for bridge prioritization of time-sensitive AVB traffic streams. This ensures reliable real-time transport of AVB streams by limiting the transmission delays (802.1BA – Audio Video Bridging (AVB) Systems).
802.1BA – The Audio Video Bridging Systems standard unifies the preceding work done in 802.1AS and 802.1Qav. It details the full architecture for AVB networks including system-wide concepts, protocols, procedures, and managed objects (Understanding Audio Video Bridging).
How AVB Works
AVB provides quality of service by reserving bandwidth for audio and video traffic. It does this by using the IEEE 802.1Qat Stream Reservation Protocol (SRP) and the IEEE 802.1Qav Forwarding and Queuing Enhancements for Time-Sensitive Streams (FQTSS).
SRP allows endpoints to reserve bandwidth across a network by establishing a ‘talker advertise’ stream. This reserves the required bandwidth along the switches between the talker and listener(s). The switches use FQTSS to then prioritize the reserved streams and provide low latency transfer of the time-sensitive audio and video streams.
By reserving a percentage of the overall available bandwidth for AVB traffic, the switches can provide predictable latency for the reserved streams. Latency is kept consistently low (on the order of hundreds of microseconds), avoiding jitter and drops in the audio or video. The percentage used for reservations is configurable but typically defaults to 75% of total bandwidth, leaving 25% for non-AVB traffic.
AVB uses IEEE 802.1AS time synchronization to ensure coordinated reservations and playback. AVB capable devices have a synchronized sense of time using 802.1AS time sync, allowing the talker and listener(s) to maintain reservations across the network. Overall this provides low latency transport of time-sensitive media over an Ethernet network.1
1 https://en.wikipedia.org/wiki/Audio_Video_Bridging
AVB vs Ethernet
AVB differs from standard Ethernet in several key ways. AVB provides guarantees on network bandwidth and latency for time-sensitive streams like audio and video, whereas standard Ethernet networks do not make any quality of service guarantees. AVB reserves a portion of the network bandwidth for AV traffic using a credit-based shaper technology, which prevents AV data streams from being disrupted by other non-AVB data on the network.
AVB is capable of achieving less than 1ms latency and jitter between AVB-enabled devices, allowing for reliable delivery of high quality streams. This compares to standard Ethernet networks where latency and jitter will vary depending on overall network traffic. AVB also provides a mechanism for time synchronization via the IEEE 802.1AS standard allowing tight coordination between devices on the network.
AVB requires AVB-enabled Ethernet switches whereas standard Ethernet can use commodity switches. AVB certified devices embed AVB functionality at the MAC layer, providing out-of-the-box compatibility on AVB networks. Overall, AVB provides the quality of service necessary for professional, time-sensitive AV applications which standard Ethernet cannot reliably provide.
For more details, see: https://en.wikipedia.org/wiki/Audio_Video_Bridging
AVB Devices
AVB requires support from endpoint devices as well as the networking equipment. Devices like professional audio and video equipment, automotive infotainment systems, industrial control systems, and consumer electronics can become AVB-enabled with the addition of AVB functionality.
Most AVB-enabled endpoints contain an AVB interface with the required time synchronization and QoS mechanisms. This allows the devices to connect to an AVB network and benefit from the guaranteed bandwidth and low latency. Microchip, Analog Devices, Xilinx, and other semiconductor companies offer AVB IP cores and chips to allow manufacturers to build AVB functionality into their products.
In addition to endpoints, AVB relies on enabled Ethernet switches and network interface cards (NICs). Major switch vendors like Extreme Networks, Cisco, and Arista Networks offer AVB-compliant models. Intel, Marvell, and others produce AVB-enabled NICs. The switches provide features like credit-based shaper support, while the NICs handle time synchronization. Both are critical for delivering the QoS assurances over an AVB network.
AVB in Professional Audio
Audio Video Bridging has become increasingly popular for professional audio applications due to its ability to provide precision timing and synchronization over Ethernet networks 1. This allows professional audio devices like mixing consoles, IO devices, and DAWs to connect over a common Ethernet network and achieve sample-accurate playback and recording across multiple devices simultaneously.
Some key use cases for AVB in professional audio production include:
- Building networked studio setups with multiple AVB-enabled audio interfaces connected to a DAW. This allows flexible routing of audio signals between rooms while maintaining tight sync.
- Linking digital mixing consoles and stageboxes. Using AVB, the stageboxes can be located remotely while still receiving near instant console control data.
- Connecting digital consoles to PA systems. Eliminates analog snake cables by allowing consoles to output audio directly to amplified speakers over the network.
- Live sound reinforcement. AVB’s low latency allows front-of-house and monitor console signals to be networked and routed with negligible delay.
Major pro audio companies like Avid, Yamaha, Allen & Heath, and others now offer AVB-compatible products. The technology provides an open-standard networked audio solution without requiring proprietary hardware like other audio over Ethernet protocols.
AVB in Automotive Networks
Audio Video Bridging (AVB) is seeing increased usage in automotive networks, especially for in-vehicle infotainment systems. AVB provides guaranteed quality of service (QoS) for streaming time-sensitive audio and video data in vehicles. This allows automakers to consolidate multiple networks into a single Ethernet-based system.
AVB is well-suited for transferring high quality audio from infotainment systems to amplifiers and speakers throughout the vehicle. It ensures latency and jitter are kept very low, providing the level of performance needed for CD-quality audio playback. AVB also facilitates easy clock synchronization between audio sources, enabling glitch-free handoff as audio is routed to different zones in the car.
Major automotive suppliers like Harman, Bosch, and Continental are developing AVB-enabled components and full infotainment platforms. As cited from Wikipedia, leading automotive OEMs such as BMW and Hyundai are already using AVB in their in-vehicle networks. Adoption is expected to grow as infotainment systems add more audio channels and video streams. The guaranteed QoS of AVB makes it an ideal technology for future vehicle designs.
AVB and Time Sync
One of the key benefits of AVB is its ability to provide precise time synchronization across the network. This is critical for time-sensitive applications like professional audio and video, where even small timing errors can cause unacceptable defects like lip sync issues.
AVB utilizes the IEEE 802.1AS protocol and a feature called the Precision Time Protocol (PTP) to achieve tight synchronization. PTP allows all the devices on an AVB network to precisely synchronize their clocks to a common time source or grandmaster clock. This grandmaster sends out timing messages that allow the AVB devices to adjust and match their clocks down to the microsecond.
This kind of precise timing control significantly improves the streaming quality on an AVB network. It ensures low latency audio and video streams from multiple sources arrive exactly when they should for seamless playback. Errors and defects from timing mismatch and jitter are eliminated.
AVB’s synchronization capabilities go far beyond what is possible on a standard Ethernet network. As mentioned in the Wikipedia article, “AVB allows for reserving network paths with accurate bandwidth and latency control” (1). This makes AVB an ideal choice for professional media networks that require sample-accurate timing.
The Future of AVB
AVB adoption is expected to grow as more industries recognize the benefits it provides. The automotive industry in particular is poised to be a major adopter of AVB technology. As vehicles become more connected and automated, AVB provides the reliable, low latency networking critical for things like advanced driver assistance systems and infotainment. Major automotive suppliers like Bosch already utilize AVB for in-vehicle network applications.
AVB is also gaining traction in professional audio, where its synchronization and QoS capabilities allow for easier configuration of complex, multi-device setups. Leading pro audio companies like Avid, Meyer Sound, and others already incorporate AVB in their products. As more live event production moves towards network-based audio, AVB will likely become the standard.
Future AVB standards will focus on enhancements like improved redundancy protocols to ensure zero downtime. With IEEE 802.1ASbt, for example, AVB networks will support seamless switching between master clocks. There will also be efforts to expand AVB into new markets like industrial automation. The AVnu Alliance industrial segment is working to define an interoperable ecosystem for AVB in intensive real-time control applications.
Thanks to its technical strengths and support from major industry players, AVB is positioned to remain the leading networked A/V standard well into the future across both media and automotive environments.
Conclusion
In summary, Audio Video Bridging provides several key benefits for real-time audio and video streaming over Ethernet networks. By providing predictable network timing, low latency, and guaranteed quality of service, AVB enables reliable transport of time-sensitive media streams. Some of the key advantages of AVB include:
- Time synchronization – AVB allows all devices on the network to have a common clock reference, preventing jitter or skew issues.
- Low latency – By prioritizing media traffic, AVB can achieve less than 2ms of latency across even multiple network hops.
- Guaranteed bandwidth – AVB uses a reservation system to guarantee up to 75% of network bandwidth for media streams.
- Scalability – AVB networks can easily scale to support thousands of audio channels.
- Interoperability – AVB standards ensure interoperability between devices from different manufacturers.
- Compatibility – AVB runs over standard Ethernet networks, coexisting gracefully with non-AVB traffic.
Overall, AVB provides the reliability and performance needed for professional media networking applications like live sound, studio recording, and automotive infotainment systems. As Ethernet continues to proliferate, AVB will play an increasingly important role in real-time media transport and unified networking.
