Take it to the bridge


Will Strauss# TV-Bay Magazine
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by Will Strauss
Issue 91 - July 2014

Since the late 1980s, studios, facilities, OB trucks and many other professional broadcast set-ups have relied on digital video standards such as SDI (Serial Digital Interface) to move audio and video around.

Using SDI it has been possible to happily construct a reliable, error-free, plug-and-play, real-time operation capable of successfully getting a show to air.

But while it still works well, it is not perfect. SDI only allows for one-way, single-purpose and point-to-point infrastructures that are usually expensive, require highly skilled engineers and have limitations when it comes to higher resolutions, frame rates and other advances.

As a result, there are moves afoot that might eventually see SDI and other professional studio interfaces, signals and equipment replaced by generic IT technology and packetized networks using Ethernet.

Sounds great so far. The broadcast facility of the future will essentially be a data centre, with all the efficiencies that this brings.

But while sending full, finished TV programmes via Ethernet is childs play, streaming synchronous uncompressed HD video as a live source is much trickier. You need enough bandwidth and not too much latency, yes, but also a range of devices that obey a standard network protocol so that everything goes smoothly.

Audio Video Bridging (AVB) is potentially the answer. A trend for many years (talked about at least as far back as 2009) it has become fairly commonplace in audio, but only now is the technology being rolled out with video in mind.

What is it?

AVB is a manufacturer agnostic open standard based on the WAN and LAN standard IEEE 802.1 (and its sister standards). It is essentially a networking language for the connection of real-time media devices that is designed for bridging, carrying, routing, synchronizing and switching audio and video signals over standard Ethernet connections. Essentially, AVB makes a standard Ethernet network suitable for live television production.

The basis of AVB is a compliant switch aka the bridge that connects different types of equipment.

There is a whole industry association, the AVnu Alliance, dedicated to the development of AVB. Its job is to test and certify devices. Axon Digital Design, Calrec, Dolby, Harman, Avid, Barco, Riedel, Shure and Sennheiser are amongst the companies involved in this.

What are the benefits?

Using AVB has various benefits. For example, audio and video streams can be synchronized within a microsecond of each other, with low delay, and with minimal data loss. It also allows for: simplified remote production; fully bi-directional/duplex connections; multiple different signals to be multiplexed and transported on one cable; reduced cabling requirements.

This ability to have one connection that can carry multiple streams and work as both an input and output is what you might call game changing (if you worked in marketing).
Its not faultless though. AVB is what is referred to as a Layer-2 protocol. This makes it ideal for extremely low latency and tight synchronization but does mean its use is currently restricted to within a Local Area Network eg a facility or OB truck.

If you want to send broadcast signals down an Ethernet cable from, as an example, a sporting or music venue to a facility then a layer-3 protocol is required. An example is the BBC R&D developed Stagebox (but that is a subject for another article). While AVB does in theory have a Layer 3 derivative its availability is considered to be some distance away.

Who is currently using or adopting AVB?

US sports broadcaster ESPN is using AVB for audio signal distribution in its new $125m Digital Center 2 facility. Avids new S3L audio console is built on AVB. And proprietary deployments such as Audinates Dante audio networking technology, which is dominant in the live sound market, have AVB as their networking protocol.
Similarly, TSL unveiled PAM1 and PAM2 AVB Units at NAB 2014. These are versions of the established PAM precision audio monitoring systems that specifically address the needs of an Audio-over-IP AVB facility infrastructure.
Notice a theme there? They are all audio-related. Video is still some way behind. There are a couple of products available though. Axon launched Neuron last year, the first publicised device to use AVB for video. And Dutch broadcast facilities provider United is using that very technology in one of its OB vans.
That said, the first, and so far only, products to be certified by the AVnu Alliance are Extreme Networks Summit X440 stackable switches, which were handed their AVnu-certified stickers back in January and subsequently displayed by Axon at NAB. More are expected to follow.

Why the slow burn?

With so many potential advantages, and the ubiquity of IT networks within television, it is something of a surprise that products based on standards-based AVB have taken so long to come to market not least as there are lots of private systems already out there.

One argument is that AVB has been held back by its reliance on proprietary switches.
Another is that while the main standards components of AVB (Precise Time Synchronization, Stream Reservation Protocol and Traffic Shaping) were ratified some time ago, the final piece of the jigsaw, IEEE 1722.1-2013, the bit responsible for making AVB plug-and-play, is only a year old.

Or maybe it is simply because SDI with its familiar BNC connectors is still stable and widely used around the world. After all, not everyone likes change.

Either way, for those doubting the emergence of AVB, Apple already incorporates it into its products. That has to be a positive sign, even if this is a consumer development. The tipping point may come when big boys like Cisco or HP start implementing AVB in their switches.

Weve already seen strong interest from broadcasters who agree with us that AVB is a game-changing technology for the industry, argues Jans Eveleens, AVnu Alliance Pro Video Group chair and chief executive of Axon. The underlying standards and technology are already available. As part of the existing IEEE 802.1 suite, AVB makes a standard Ethernet network suitable for a full-blown production backbone.

Many will hope that he is right.


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Contributing Author Will Strauss#

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