A new series of international standards are redefining the way audio and video equipment streams around the home. Paul Skelton reports.

It’s no secret that over the past decade, in particular the past two or three years, consumer electronics manufacturers have been developing new protocols to enhance the user experience. Some have succeeded, some haven’t.

Primarily, most of these efforts have been in relation to the streaming of audio and video from one device to another. But problems have ensued.

Several years ago, an effort was started within the Institute of Electrical and Electronics Engineers’ (IEEE’s) 802.3 and 802.1 working groups to define a ‘residential’ Ethernet, which would directly address the challenges of AV streaming.

The resultant Audio Video Bridging (AVB) Standards provide professional quality capabilities to networks for time-sensitive media streaming, to enable standards-based, networkattached audio systems to play audio in a synchronised fashion (i.e. no annoying stereo image shift or phasing).

Published in April 2011, the newly ratified IEEE 802.1AS, 1722 and 1733 Standards joined the already approved 802.1Qat and 802.1Qav Standards to redefine how 802-based AV networks are built.

“The core AVB standards are now complete!” AVB Task Group chair Michael Johas Teener stated at the time.

“Now it is possible to build a standards-based network with deterministic delays and precise synchronisation that supports professional quality AV streams while simultaneously carrying existing ‘best effort’ traffic.”

The core 802.1 AVB Standards bring new kinds of services to the network, which brings different kinds of improvements for media streaming applications. These new network services include accurate time synchronisation, making it possible for multiple devices to render audio and/ or video in-sync in a standard way; a reservation protocol which ensures that all devices in the path of a stream have agreed to allow the stream; and, a mechanism for ensuring that the requested latency and bandwidth of reserved streams is achieved (over links which do not significantly degrade).

There are four primary differences between the AVB architecture and existing 802 architectures:
1. Precise synchronisation;
2. Traffic shaping for media streams;
3. Admission controls; and,
4. Identification of non-participating devices.

In the past, there have been several attempts at solving the innate problems of 802 architectures, including:

Specialised pro AV technologies such as IEEE 1394/FireWire;
Various non-standard wireless digital audio distribution systems for home theatres;
Expensive and inflexible entertainment networks for automotive applications; and,
Adaptations of standard IT-type networks.

According to a white paper released by the AVnu Alliance – an industry forum dedicated to the advancement of AVB Standards through the creation of compliance test procedures and processes, and marketing to end users – “The specialised AV technologies for professional, home and automotive use were too specialised, in that they did not have any easy kind of interoperability with regular IT networks like Ethernet. This limited their market to those applications that needed those particular services, like video cameras or professional audio equipment.

“The adaptations of standard IT networks had the opposite problem: they were built from commodity equipment, but getting a professional level of service required very tight control over how the equipment was used and managed. The introduction of even one ‘unmanaged’ device could cause the whole network to fail.”

So what exactly is wrong with standard IT networks?

“Before that can be answered, the requirements for AV streaming must be understood. First, it must be possible to synchronise multiple streams so that they can be rendered correctly in time with respect to each other. Second, the worst case delay for a stream in the network, including buffering delays at the source and destination, must be low and deterministic. Finally, applications must be able to get a high level of confidence that the network resources needed are available and will remain available as long as the application needs it.

“Almost all current network equipment is based on IT requirements: move the data through the network as quickly as possible with minimum cost and minimal management. This is an excellent approach as long as there are no hard limits on delay or synchronisation requirements.

“IT-oriented networks do not always, however, meet the AV streaming requirements. Specifically, there is no concept of ‘time’ in an IT network; delays can be too high; and, the network itself does not prevent network congestion, so data can be lost if buffers are inadequate or link bandwidth is insufficient for offered traffic.

“The typical way these last two problems are handled today is with buffering, but excessive buffering can cause delays that are annoying in the consumer environment and completely unacceptable in a professional one.”

CERTFICATION

In July, the AVnu Alliance unveiled a certification mark for devices that have passed stringent interoperability testing to become an AVnu-certified AVB product. This certification process helps assure that once a product is certified, it will interoperate with other AVnu-certified AVB devices.

“AVnu-certified AVB devices offer manufacturers and their customers numerous practical advantages over legacy and proprietary solutions in streaming AV content,” marketing chair Lee Minich says.

“Only AVB products bearing the AVnu certification mark give end users the confidence that a device passed robust compliance and interoperability testing in a multi-vendor environment.

The AVnu Alliance currently has more than 45 member companies, including Dolby, Intel and Cisco, which support and promote AVB technology.

“The open AVB Standards provide a simple and reliable networking solution that overcomes the hurdles of AV network implementation,” Lee says.

“As the first non-proprietary Ethernet-based AV standards, AVB frees manufacturers and users of the royalty structures and long-term support issues associated with proprietary protocols. Further, the precision and reliability in AVB significantly improve AV transport for even the most rigorous applications such as live performance, studio, and gaming.

“A dedicated presentation time protocol within AVB synchronises audio and video data, a key feature in applications where synchronisation is critical, including cinema, post-production, broadcast. The data pathway from source to destination is guaranteed with AVB, providing a congestion-free system environment. And, since AVB is part of the new generation of the IEEE Ethernet standards, AVB retains compatibility with legacy Ethernet networks.”

Of course, one of the most attractive features of this Standard is that, considering it has been created by the IEEE, manufacturers who adopt the format won’t be liable for paying (and therefore passing on) exorbitant licensing fees.