050 REPORT


TAKE IT TO THE BRIDGE...


Tim Goodyer looks at the emerging Audio Video Bridging standard, and its claim to be ready to dramatically simplify audiovisual networking...


The air is thick with discussion of Audio Video Bridging. So thick, that it’s more confusing than enlightening to those not directly involved - and to some who are. Whether you’re walking a tradeshow floor or surfing the industry’s social media groups, AVB can be as hard to escape as it is to understand. Crucially, AVB recognises the growing difficulties that manufacturers, systems integrators and operators face. These appear at every turn - when equipment is be- ing designed, when it is specified and installed, when it is configured and when it is in use. There is no escaping the complication that comes with the sophistication of present (and future) audio and audiovisual systems, but AVB reckons to intervene in a way that will reduce the difficulties of their use. This starts to make sense when you consider the background AVB – the legacy of competing and contrasting audiovisual communication and integration protocols is a minefield of alternative and mismatched ‘standards’ that fills manufacturers and systems integrators with equal levels of trepidation. An indication of this was given by Kevin Gross on LinkedIn’s AVB Group recently, with his hope that ‘AVB can be disruptive enough to tip us towards sanity’. And Kevin Gross invented CobraNet. If it is successful in its uptake, AVB will see Ethernet technologies such as Co- braNet, Dante and EtherSound pulled together under a much larger umbrella, as well as stepping across the pro-consumer border into domestic AV installations. The first firm steps toward this goal came in January 2010, with the publication of the (ratified) IEEE 802.1Qav specification, the first of the ‘core’ Audio Video Bridg- ing standards. This ‘defines forwarding and queueing for time-sensitive streams’ and is part of a suite of standards developed by an Institute of Electrical and Elec- tronics Engineers (IEEE) task group.


The alliance of science


If we are to make any useful sense of AVB we need to take a step back. Several steps back, in fact. Let’s begin with the present cast of key players. These work with the broader IEEE 802 standards family that addresses local area networks (LAN) and metropolitan area networks (MAN). This covers a range of ‘bridging’ considerations for Ethernet, Token Ring, Wireless LAN, Bridging and Virtual Bridged LANs - with IEEE 802.1 concerned specifically with Audio Video Bridging.


While the IEEE 802.1 AVB Task Group is the body behind the defining document, another group called the AVnu Alliance has organised itself to help oversee the smooth and successful uptake of AVB in audiovisual circles, including compliance with the standards. In its own words, this is ‘an industry forum dedicated to the advancement of professional quality audio / video by promoting the adoption of the IEEE 802.1 Audio / Video Bridging (AVB), and the related IEEE 1722 and IEEE 1733 (which extends Real-time Transport Protocol for use on AVB) standards over


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various networking link-layers’, and aims to promote the AVB networking standards across a broad range of markets including automotive and consumer electronics. Its founding members include Cisco Systems, Harman International, Intel, Samsung Electronics and Xilinx, with further support coming from Analog Devices, Audinate, Avid Technology, Barco, Biamp Systems, Lab X Technologies, Marvell, Meyer Sound, Sennheiser and Shure, among others. London’s PLASA Show saw a panel of representatives drawn from AVnu present the case for AVB. With AVnu Alliance panellists John McMahon (Audinate), David Gibbons (Avid), Adam Holladay (Harman Systems Development Integration Group), Lee Minich (Lab X Technologies), Jerry Placken (Meyer Sound) and Ed Clarke (XMOS) in the line-up, it gave a good indication of the weight behind AVB and was a compelling and convincing session.


In opening, the panellists quickly outlined the mission - ‘to address the jumble of present options’, in John McMahon’s words. The picture painted by AVB offers an audio-video network presenting less than 2ms audio latency, through seven switching hubs (worst case) at 100MB speeds (sig- nificantly lower over increasingly common Gigabit Ethernet), while retaining sample sync by using a distributed clock. It also guarantees operating bandwidth while co-existing with other devices. On top of this technical dexterity, AVB aims to make life considerably easier for systems integrators and managers by being self configuring - avoiding conflict with connections and the need to key in IP addresses in order to identify equipment on a network. And it will be invisible to users. The standard does not set out to define every possible remote control option over the internet, but – like the Midi control standard in the eighties – promises a frame- work that leaves options open to manufacturers. In this way, there is no requirement to wait for agreement on lots of specific comms protocols before new developments and equipment can be brought to market. It worked for Midi... “With IEEE 802.1Qav published and two additional standards nearing completion, AVnu has the confidence to move quickly in developing our AVB compliance and interoperability programmes, which are vital for widespread commercial adoption,” said Rick Kreifeldt, AVnu Alliance Chairman and President, on the publication of the initial IEEE paper. “This is the first time the core technology of Ethernet switches and network bridges has specific methods defined for traffic shaping,” added Michael Johas Teener, Chair of the IEEE AVB Task Group. This allows an IEEE 802 network to provide assured (and low) delays for streaming data with minimal lost packets. When combined with the almost-finished 802.1Qat Stream Reservation Protocol, IEEE 802.1Qav will be the fundamental toolkit to provide the kind of virtual plumbing needed for professional-quality audio-video networking.


Although not on the PLASA panel, Harman Professional CEO Blake Augsburger is


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