Audio Video Bridging

Last updated

AVB
AVnu certification mark.jpg
AVnu certification mark
Manufacturer Info
Manufacturer IEEE, AVnu
Development dateSeptember 2011;12 years ago (September 2011)
Network Compatibility
Switchable Yes
Routable No
Ethernet data rates Agnostic
Audio Specifications
Minimum latency 2  ms (maximum) [1]
Maximum channels per link256
Maximum sampling rate 192 kHz [2]
Maximum bit depth 32-bit floating point [2] : clause 8.3 

Audio Video Bridging (AVB) is a common name for the set of technical standards which provide improved synchronization, low latency, and reliability for switched Ethernet networks. [3] AVB embodies the following technologies and standards:

Contents

IEEE 802.1Qat and 802.1Qav amendments have been incorporated to the base IEEE 802.1Q-2011 document, which specifies the operation of Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks.

AVB was initially developed by the Institute of Electrical and Electronics Engineers (IEEE) Audio Video Bridging task group of the IEEE 802.1 standards committee. In November 2012, Audio Video Bridging task group was renamed to Time-Sensitive Networking task group to reflect the expanded scope of its work, which is to "provide the specifications that will allow time-synchronized low latency streaming services through IEEE 802 networks". [5] Further standardization efforts are ongoing in IEEE 802.1 TSN task group.

To help ensure interoperability between devices that implement the AVB and TSN standards, the AVnu Alliance develops device certification for the automotive, consumer, and professional audio and video markets. [6]

Background

Analog audio video (AV) equipment historically used one-way, single-purpose, point-to-point connections. Even digital AV standards, such as S/PDIF for audio and the serial digital interface (SDI) for video, retain these properties. This connection model results in large masses of cables, especially in professional applications and high-end audio. [7]

Wiring of a patch bay of an outside broadcasting van StudioWiring.png
Wiring of a patch bay of an outside broadcasting van

Attempts to solve these problems were based on multi-point network topologies, such as IEEE 1394 (FireWire), and included adaptation of standard switched computer network technologies such as Audio over Ethernet and Audio over IP. Professional, home, and automotive AV solutions came to use specialized protocols that do not interoperate between each other or standard IT protocols, while standard computer networks did not provide tight quality of service with strict timing and predictable or bounded latency. [7]

To overcome these limitations, Audio Video Bridging networks transmit multiple audiovisual streams through standard Ethernet switches (i.e. MAC bridges) connected in a hierarchical tree topology. AVB includes layer 2 protocols to reserve connection bandwidth and prioritise network traffic, which guarantee precise sync clock and low transmission latency for each stream. [7]

Tight sync between multiple AV streams is needed for lip sync between video and related audio streams, to keep multiple digitally connected speakers in phase in a professional environment (which requires 1 μs precision), and to prevent audio or video packets from arriving late to the endpoint, resulting in a dropped frame of video and unwanted audio glitches such as a pop or silence. Worst-case delay, including source and destination buffering, is required to be low and deterministic: the user-interface delay shall be around 50 ms, so that the pressing of a button and the resulting action are perceived as happening instantly, and 2 ms for live performance or studio work. [7]

Summary

Figure 2 - AVB Connections AVB-Ethernet-connections.svg
Figure 2 - AVB Connections

Audio Video Bridging is implemented as a switched Ethernet network which works by reserving a fraction of the available Ethernet for AV traffic. There are three primary differences introduced by the AVB architecture:

The IEEE 802.1BA is an umbrella standard for these three principal technologies, which defines application-specific configurations and operation procedures for devices in switched audio video networks.

The new layer-2 configuration protocols work with backward-compatible extensions to the Ethernet 802.1 frame format; such minimal changes allow AVB devices to coexist and communicate in standard IT networks, however, only AVB-capable switches and endpoint can reserve network resources with admission control and synchronize local time to a master clock, which is required for low latency time-sensitive traffic.

AVB traffic is replicated in a multicast manner, with one talker (stream initiator) and multiple listeners. AVB packets are sent at regular intervals in the allocated time slots, preventing collisions for AV traffic. AVB guarantees a latency of 2 ms for Class A traffic and 50 ms for Class B traffic over a maximum of 7 hops, with a transmission period of 125 μs for Class A and 250 μs for Class B traffic.

An IEEE 802.1AS network timing domain includes all devices that communicate using the gPTP protocol. The grandmaster is a device chosen as the reference clock; the 802.1BA specification requires every talker and network bridge to be grandmaster capable.

802.3 link management and 802.1AS link delay measurement protocols calculate the round-trip delay to the AVB endpoint; this needs to be better than worst-case wire delay from the 802.1AS peer delay algorithm.

Higher-level protocols may use 802.1AS clock information to set the exact presentation time for each AV stream.

AV transport and configuration

IEEE 1722 AVTP

IEEE Std 1722-2011 [8] for a Layer 2 Audio Video Transport Protocol (AVTP) defines details for transmitting IEEE 1394/IEC 61883 streams and other AV formats, setting the presentation time for each AV stream, and manage latencies from worst case delay calculated by the gPTP protocol.

IEEE 1722.1 AVDECC

IEEE Std 1722.1-2013 [9] is a standard which allows AVB Discovery, Enumeration, Connection management and Control (AVDECC) of devices using IEEE Std 1722-2011. AVDECC defines operations to discover device addition and removal, retrieve device entity model, connect and disconnect streams, manage device and connection status, and remote control devices.

Interoperability

Higher layer services can improve synchronisation and latency of media transmission by mapping the AVB Stream ID to internal stream identifiers to and basing internal timestamps on gPTP master clock.

IEEE 1733

IEEE Std 1733-2011 [10] defines a Layer 3 protocol profile for Real-time Transport Protocol (RTP) applications with a RTCP payload format, which assigns the Stream ID from SRP to the RTP's Synchronization source identifier (SSRC), and correlates RTP timestamps for presentation time with 802.1AS gPTP master clock.

AES67

AES67 is based on standard RTP over UDP/IP and IEEE 1588 Precision Time Protocol (PTPv2) for timing; interoperability with AVB/TSN can be achieved by linking IEEE 802.1AS timing information to AES67 PTPv2 payload data. [11] [12] [13] [14]

AES67 implementation with AVB interoperability has been demoed at InfoComm 2016. [15] [16]

Milan

In 2018, the Avnu Alliance announced the Milan initiative to promote interoperability of AVB devices and provide product certification and testing. [17]

The specification requires media clocking based on the AVTP CRF (Clock Reference Format) and sample rate of 48 kHz (optionally 96 and 192 kHz); audio stream format is based on AVTP IEC 61883-6 32-bit Standard AAF Audio Format with 1 to 8 audio channels per stream (optionally, 24- and 32-bit High Capacity Format with 56 and 64 channels). Redundancy is provided with two independent logical networks for every endpoint and a seamless switchover mechanism. [17]

DetNet

The IETF Deterministic Networking (DetNet) Working Group is working to define deterministic data paths with bounds on latency, loss, and packet delay variation (jitter), and high reliability. DetNet shall operate over both Layer 2 bridged segments and Layer 3 routed segments, relying on interoperability with AVB/TSN switches when possible. [18]

One of the possible application of DetNet is professional audio/video, such as music and film production, broadcast, cinema, live sound, and large venue (stadiums, halls, conference centers, theme parks, airports, train terminals, etc.) systems for public addressing, media streaming and emergency announcement. The stated goal is to enable geographically distributed, campus- or enterprise-wide Intranet for content delivery with bounded low latency (10-15 ms). A single network shall handle both A/V and IT traffic, with Layer 3 routing on top of AVB QoS networks to enable sharing content between Layer 2 AVB segments, and provide IntServ and DiffServ integration with AVB where possible. Unused reserved bandwidth shall be released for best-effort traffic. The protocol stack shall have Plug-and-play capabilities from top to bottom to reduce manual setup and administration, allow quick changes of network devices and network topology. [19]

Large-scale AVB networks, like those employed by ESPN SportsCenter "Digital Center 2" broadcast facility which hosts multiple individual studios, are laid with a thousand miles of fiber and have ten Tbps of bandwidth for a hundred thousand signals transmitted simultaneously; in the absence of standards-based solution to interconnect individual AVB segments, a custom software-defined networking router is required. [20] [21]

Standardization

The work on A/V streaming started at the IEEE 802.3re 'Residential Ethernet' study group in July 2004. [22] In November 2005, it was moved to the IEEE 802.1 committee responsible for cross-network bridging standards. [23]

Audio Video Bridging standards suite
StandardTitleStatusPublication Date
Audio Video Bridging (AVB) specifications
IEEE 802.1BA-2011Audio Video Bridging (AVB) SystemsSuperseded by IEEE 802.1BA-202130 September 2011
IEEE 802.1Qav-2009Forwarding and Queuing Enhancements for Time-Sensitive Streams (FQTSS)Incorporated into IEEE 802.1Q-2011 Clause 345 January 2010
IEEE 802.1Qat-2010 Stream Reservation Protocol (SRP)Incorporated into IEEE 802.1Q-2011 Clause 3530 September 2010
IEEE 802.1Q-2011 Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks (incorporates IEEE 802.1Qav and 802.1Qat amendmends)Superseded by IEEE 802.1Q-2014/2018/202231 August 2011
IEEE 802.1AS-2011Timing and Synchronization for Time-Sensitive Applications in Bridged Local Area Networks (gPTP)Superseded by IEEE 802.1AS-202030 March 2011
Time-Sensitive Networking (TSN) specifications
IEEE 802.1AS-2020Timing and Synchronization for Time-Sensitive Applications (gPTP)Current, [24] [25] amended by 802.1AS-2020/Cor1-2021 [26] 30 January 2020
IEEE 802.1BA-2021TSN profile for Audio Video Bridging (AVB) SystemsCurrent [27] 12 December 2021
IEEE 802.1Q-2022Bridges and Bridged NetworksCurrent [28] 22 December 2022
Audio Video Transport Protocol (AVTP) and AVDECC specifications
IEEE 1733-2011Layer 3 Transport Protocol for Time-Sensitive Applications in Local Area Networks (RTP)Current25 April 2011
IEEE 1722-2011Layer 2 Transport Protocol for Time-Sensitive Applications in a Bridged Local Area Network (AVTP)Superseded by IEEE 1722-20166 May 2011
IEEE 1722-2016Layer 2 Transport Protocol for Time-Sensitive Applications in a Bridged Local Area Network (AVTP)Current16 December 2016
IEEE P1722bAVTP - Amendment: New and Extended Streaming Formatspreparation-
IEEE 1722.1-2013Device Discovery, Enumeration, Connection Management and Control Protocol (AVDECC)Current23 August 2013

Related Research Articles

A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer. In this context, virtual refers to a physical object recreated and altered by additional logic, within the local area network. VLANs work by applying tags to network frames and handling these tags in networking systems – creating the appearance and functionality of network traffic that is physically on a single network but acts as if it is split between separate networks. In this way, VLANs can keep network applications separate despite being connected to the same physical network, and without requiring multiple sets of cabling and networking devices to be deployed.

IEEE 802.1 is a working group of the IEEE 802 project of the IEEE Standards Association.

Clock synchronization is a topic in computer science and engineering that aims to coordinate otherwise independent clocks. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift, caused by clocks counting time at slightly different rates. There are several problems that occur as a result of clock rate differences and several solutions, some being more acceptable than others in certain contexts.

The Precision Time Protocol (PTP) is a protocol used to synchronize clocks throughout a computer network. On a local area network, it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems. PTP is employed to synchronize financial transactions, mobile phone tower transmissions, sub-sea acoustic arrays, and networks that require precise timing but lack access to satellite navigation signals.

<span class="mw-page-title-main">Network bridge</span> Device that creates a larger computer network from two smaller networks

A network bridge is a computer networking device that creates a single, aggregate network from multiple communication networks or network segments. This function is called network bridging. Bridging is distinct from routing. Routing allows multiple networks to communicate independently and yet remain separate, whereas bridging connects two separate networks as if they were a single network. In the OSI model, bridging is performed in the data link layer. If one or more segments of the bridged network are wireless, the device is known as a wireless bridge.

<span class="mw-page-title-main">Profinet</span> Computer network protocol

Profinet is an industry technical standard for data communication over Industrial Ethernet, designed for collecting data from, and controlling equipment in industrial systems, with a particular strength in delivering data under tight time constraints. The standard is maintained and supported by Profibus and Profinet International, an umbrella organization headquartered in Karlsruhe, Germany.

In audio and broadcast engineering, audio over Ethernet (AoE) is the use of an Ethernet-based network to distribute real-time digital audio. AoE replaces bulky snake cables or audio-specific installed low-voltage wiring with standard network structured cabling in a facility. AoE provides a reliable backbone for any audio application, such as for large-scale sound reinforcement in stadiums, airports and convention centers, multiple studios or stages.

Carrier Ethernet is a marketing term for extensions to Ethernet for communications service providers that utilize Ethernet technology in their networks.

Stream Reservation Protocol (SRP) is an enhancement to Ethernet that implements admission control. In September 2010 SRP was standardized as IEEE 802.1Qat which has subsequently been incorporated into IEEE 802.1Q-2011. SRP defines the concept of streams at layer 2 of the OSI model. Also provided is a mechanism for end-to-end management of the streams' resources, to guarantee quality of service (QoS).

The Time-Triggered Ethernet standard defines a fault-tolerant synchronization strategy for building and maintaining synchronized time in Ethernet networks, and outlines mechanisms required for synchronous time-triggered packet switching for critical integrated applications and integrated modular avionics (IMA) architectures. SAE International released SAE AS6802 in November 2011.

<span class="mw-page-title-main">HDBaseT</span> Point-to-point media connection over category cable

HDBaseT is a consumer electronic (CE) and commercial connectivity standard for transmission of uncompressed ultra-high-definition video, digital audio, DC power, Ethernet, USB 2.0, and other control communication over a single category cable up to 100 m (328 ft) in length, terminated using the same 8P8C modular connectors as used in Ethernet networks. HDBaseT technology is promoted and advanced by the HDBaseT Alliance.

Media-accelerated Global Information Carrier (MaGIC) is an audio over Ethernet protocol developed by Gibson Guitar Corporation in partnership with 3COM. It allows bidirectional transmission of multichannel audio data, control data, and instrument power.

Ravenna is a technology for real-time transport of audio and other media data over IP networks. Ravenna was introduced on September 10, 2010 at the International Broadcasting Convention in Amsterdam. Ravenna can operate on most existing network infrastructures using standard networking technology. Performance and capacity scale with network performance. Ravenna is designed to match broadcasters' requirements for low latency, full signal transparency and high reliability. Fields of application include in-house signal distribution for broadcasting houses and other fixed installations, flexible setups at venues and live events, outside broadcasting support, and inter-studio links across wide area network links and production facilities.

White Rabbit is the name of a collaborative project including CERN, GSI Helmholtz Centre for Heavy Ion Research and other partners from universities and industry to develop a fully deterministic Ethernet-based network for general purpose data transfer and sub-nanosecond accuracy time transfer. Its initial use was as a timing distribution network for control and data acquisition timing of the accelerator sites at CERN as well as in GSI's Facility for Antiproton and Ion Research (FAIR) project. The hardware designs as well as the source code are publicly available. The name of the project is a reference to the White Rabbit appearing in Lewis Carroll's novel Alice's Adventures in Wonderland.

RTP-MIDI is a protocol to transport MIDI messages within Real-time Transport Protocol (RTP) packets over Ethernet and WiFi networks. It is completely open and free, and is compatible both with LAN and WAN application fields. Compared to MIDI 1.0, RTP-MIDI includes new features like session management, device synchronization and detection of lost packets, with automatic regeneration of lost data. RTP-MIDI is compatible with real-time applications, and supports sample-accurate synchronization for each MIDI message.

Avnu Alliance is a consortium of member companies working together to create an interoperable ecosystem of low-latency, time-synchronized, highly reliable networking devices using the IEEE open standard, Time-Sensitive Networking (TSN) and its Pro AV networking protocol, Milan. Avnu Alliance creates comprehensive certification programs to ensure interoperability of network devices. In the Professional Audio Video (AV) industry, Alliance member companies worked together to develop Milan: a standards-based, user-driven deterministic network protocol for professional media, that through certification, assures devices will work together at new levels of convenience, reliability, and functionality. Milan™ is a standards-based deterministic network protocol for real time media. Avnu Members may use the Avnu-certified or Milan-certified logo on devices that pass the conformance tests from Avnu. Not every device based on AVB or TSN is submitted for certification to the Avnu Alliance. The lack of the Avnu logo does not necessarily imply a device is incompatible with other Avnu-certified devices. The Alliance, in conjunction with other complimentary standards bodies and alliances, provides a united network foundation for use in professional AV, automotive, industrial control and consumer segments.

AES67 is a technical standard for audio over IP and audio over Ethernet (AoE) interoperability. The standard was developed by the Audio Engineering Society and first published in September 2013. It is a layer 3 protocol suite based on existing standards and is designed to allow interoperability between various IP-based audio networking systems such as RAVENNA, Livewire, Q-LAN and Dante.

Time-Sensitive Networking (TSN) is a set of standards under development by the Time-Sensitive Networking task group of the IEEE 802.1 working group. The TSN task group was formed in November 2012 by renaming the existing Audio Video Bridging Task Group and continuing its work. The name changed as a result of the extension of the working area of the standardization group. The standards define mechanisms for the time-sensitive transmission of data over deterministic Ethernet networks.

The following is a comparison of audio over Ethernet and audio over IP audio network protocols and systems.

Deterministic Networking (DetNet) is an effort by the IETF DetNet Working Group to study implementation of deterministic data paths for real-time applications with extremely low data loss rates, packet delay variation (jitter), and bounded latency, such as audio and video streaming, industrial automation, and vehicle control.

References

  1. ↑ "An Introduction to AVB Networking". PreSonus . Retrieved December 2, 2020.
  2. 1 2 IEC 61883-6
  3. ↑ Kreifeldt, Rick (30 July 2009). "AVB for Professional A/V Use" (PDF). AVnu Alliance White Paper.
  4. ↑ "IEEE 802.1: 802.1BA - Audio Video Bridging (AVB) Systems". www.ieee802.org. Retrieved 2019-10-21.
  5. ↑ "IEEE 802.1 AV Bridging Task Group". ieee802.org. Retrieved 2019-10-21.
  6. ↑ "AVnu Alliance". Official website. Retrieved September 27, 2011.
  7. 1 2 3 4 Michael Johas Teener; et al. "No-excuses Audio/Video Networking: the Technology Behind AVnu" (PDF). Avnu Alliance. Archived from the original (PDF) on 2014-04-05.
  8. ↑ "IEEE 1722-2011 - IEEE Standard for Layer 2 Transport Protocol for Time-Sensitive Applications in a Bridged Local Area Network". standards.ieee.org. Retrieved 2019-10-21.
  9. ↑ "IEEE 1722.1-2013 - IEEE Standard for Device Discovery, Connection Management, and Control Protocol for IEEE 1722(TM) Based Devices". standards.ieee.org. Retrieved 2019-10-21.
  10. ↑ "IEEE 1733-2011 - IEEE Standard for Layer 3 Transport Protocol for Time-Sensitive Applications in Local Area Networks". standards.ieee.org. Retrieved 2019-10-21.
  11. ↑ AES67-2018 – Annex D (Informative) – Interfacing to IEEE 802.1AS clock domains
  12. ↑ AES67-2018 – Annex C (Informative) – AVB network transport
  13. ↑ Geoffrey M. Garner, Michel Ouellette and Michael Johas Teener (2012-09-27). "Using an IEEE 802.1AS Network as a Distributed IEEE 1588 Boundary, Ordinary, or Transparent Clock". 2010 International IEEE Symposium on Precision Clock Synchronization for Measurement Control and Communication (ISPCS) (IEEE)
  14. ↑ Amaya, Nestor (March 2016). "AES67 FOR AUDIO PRODUCTION: BACKGROUND, APPLICATIONS AND CHALLENGES" (PDF). smpte.org. Retrieved 2019-10-21.
  15. ↑ Joao Martins (2016-06-16). "AVB/TSN Momentum and AES67/AVB Harmony at InfoComm 2016" . Retrieved 2016-12-08.
  16. ↑ "BACH ST2110 AES67 Audio Networking Modules, Chips, and Software | OEM Developer Solutions". Ross Video. Retrieved 2019-10-21.
  17. 1 2 "Milan | A User-Driven Network Protocol for Professional Media". avnu.org. Retrieved 2019-10-21.
  18. ↑ "Deterministic Networking (detnet) - Documents". datatracker.ietf.org. Retrieved 2019-10-21.
  19. ↑ Grossman, Ethan (November 11, 2018). "DetNet Use Cases Overview" (PDF). ieee802.org. Retrieved 2019-10-21.
  20. ↑ "ESPN Digital Center Ethernet AVB Case Study: Part 1". Digital Design Corporation. 2017-11-10. Retrieved 2019-10-21.
  21. ↑ Daley, Dan (10 June 2014). "ESPN's DC2 Scales AVB Large". Sports Video Group. Retrieved 2019-10-21.
  22. ↑ Richard Brand; et al. (July 14, 2004). "Residential Ethernet: IEEE 802.3 Call for Interest" (PDF). IEEE 802.3 standards committee. Retrieved September 27, 2011.
  23. ↑ "IEEE 802.3 Residential Ethernet Study Group". Official web site. IEEE 802.3 standards committee. January 10, 2006. Retrieved September 27, 2011.
  24. ↑ IEEE 802.1AS-2020 - IEEE Standard for Local and Metropolitan Area Networks--Timing and Synchronization for Time-Sensitive Applications, IEEE , retrieved 2021-01-26
  25. ↑ "P802.1AS-2020 – Timing and Synchronization for Time-Sensitive Applications". 1.ieee802.org. Retrieved 2019-10-21.
  26. ↑ "IEEE 802.1AS-2020 Local and Metropolitan Area Networks - Timing and Synchronization for Time-Sensitive Applications - Corrigendum 1: Technical and Editorial Correction". standards.ieee.org. IEEE.
  27. ↑ "IEEE 802.1BA-2021 - IEEE Standard for Local and Metropolitan Area Networks--Audio Video Bridging (AVB) Systems".
  28. ↑ IEEE 802.1Q-2022 - IEEE Standard for Local and Metropolitan Area Networks—Bridges and Bridged Networks, IEEE , retrieved 2021-01-26
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.