AVB Presents An Open, Digitally-Networked Future For Local-Area Media Distribution
Just as there is no doubt that digital systems represent the present and future of audio/video processing, interconnect, and storage, there is no doubt that distribution of audio and video will increasingly be accomplished through digital networking. To be sure, there are many media network technologies available, each filling a niche in the diverse requirements for distribution systems.
Let’s look out a little further. Because interoperability is a strong motivator, evolution in networking tends to favor open technologies over proprietary ones. Barring any disruptive developments, cost and momentum considerations favor improvements to existing technology over new invention. It is therefore a safe bet to expect continued advancement of established network technologies such as ethernet and WiFi. Over time, these improvements should help ethernet work its way into the spaces occupied by today’s proprietary media distribution systems. In this context, an open network standards initiative called Audio/Video Bridging (AVB) may figure prominently in the future of media networking.AVB BEGINNINGS
The AVB initiative began as early as 2005 when Gibson, looking to develop a follow-on to its MaGIC audio network, approached the IEEE 802 standards committee with early ideas for a gigabit media network.
While the ideas have since evolved away from those original Gibson proposals, involving the IEEE in the initiative garnered crucial interest from the larger data communications and consumer electronics communities. In fact, in the formative months in 2005-06, the initiative was dubbed “residential ethernet” and targeted the “wired home” and “digital living room.”
Today’s participants in the AVB effort include Cisco, Intel, Samsung, Apple, and Harman, along with companies such as Marvell, Broadcom, Xilinx, and Freescale that design and manufacture the chips that make modern networks and network applications possible.
AVB participants share a common belief that media applications strain existing data communication networks, but with improvements, ethernet is up to the challenge. Participants are eager to invest towards the goal of extending the capabilities of ethernet (and thereby extending their own market opportunities).
The IEEE 802 standards committee is responsible for originating, maintaining and extending a number of communications standards most notably wired ethernet and wireless ethernet (a.k.a. 802.11, WiFi). The AVB work is being treated as an extension of ethernet’s basic capabilities.
Current estimates from the AVB task group indicate that work on the standard may be completed in 2009 with final ratification possible in 2010.NETWORK SERVICES
AVB is a set of services running on an ethernet or ethernet-like network. The scope of AVB includes both wired and wireless ethernet and also contemplates networks such as Power Line Carrier (PLC) and Multimedia over Coax Alliance (MoCA) networking. Among these, wired ethernet has so far received the most attention from the AVB task group though concerted efforts are being made to work through the considerable challenges of AVB on wireless ethernet.
The core media services offered by an AVB network are as follows (see sidebar for details):
- Synchronization: distribution of accurate time information.
- Delivery: timely delivery of media data packets to intended recipients.
- Admissions Control: a mechanism to prevent overloading of the network.
The core AVB network services are necessary but not sufficient to build a media network. The services say nothing about how audio and video data is to be formatted into individual network packets. Without these definitions, media cannot be generated and decoded by end stations. This piece of the puzzle is being handled as separate projects named IEEE P1722 and P1733. When complete, these standards will give specific recommendations for the use of existing media protocols in an interoperable way on an AVB network. P1722 is working with a FireWire standard known as IEC 61883 and P1733 uses Real Time Protocol (RTP) from the IETF, the engineers that brought you venerable internet protocols including TCP/IP.
The AVB services do not include a means to discover other media-capable end stations on the network and make connections between transmitters and receivers. Existing network protocols such as Domain Name System (DNS) offer this capability but guidelines need to be developed before these can be used in an interoperable manner.
Finally, the existence of a standard does not magically bring into existence standards-compliant equipment. The fact that significant network vendors are contributing to the initiative is encouraging as is participation from our commercial audio world, principally Harman International at this point.FIRST PRODUCTS
Since AVB is based on existing standards, IEEE 1588, 802.1p, IEC 61883 etc., the technical information is available such that pre-standards implementation and even commercialization is feasible.
Harman, Apple, and Broadcom demonstrated AVB-based technology at a 125th AES convention tutorial in October 2008. Pre-standards release of AVB product in 2009 seems to be a definite possibility.
Arguably, product is already available. Audinate’s Dante network could be considered “AVB ready” as it uses IEEE 1588 for clock distribution and existing network QoS schemes to help it play nicely with other network applications.
Platforms capable of supporting basic AVB requirements are already available from silicon vendors such as Intel, Freescale, and Xilinx. In some sense, implementing AVB on these platforms is a simple matter of programming. Let’s get started!Kevin Gross (firstname.lastname@example.org) is the inventor of CobraNet and is now an independent media-network consultant.