On Tues March 9, 2010 the Boston Section of the Audio Engineering Society featured guest speaker Guy Fedorkow who presented "IEEE Audio Video Bridging and Professional Audio: A Preview of What's Coming".
The presentation focused on the activity currently underway by the IEEE (Institute of Electrical and Electronic Engineers) called 802.1 AVB and how it will impact the world of audio and video. The intent of the standard is to eliminate the need for the miscellaneous cables and plugs we now use, and to achieve the goal of having the Ethernet connection do it all.
A broad range of standards come out of the IEEE. A sub-committee within 802.1AVB is responsible for enhancing the existing 802.1 suite of Ethernet standards to incorporate the bits and pieces to carry audio and video across Ethernet.
There are four elements which go into existing specifications;
IEEE 802.1AS — The Precision Time Synchronization Protocol (PTP) specifies how to get the clocks locked. In order to make sure the sound and picture and synchronized, you need to have synchronized clocks to compensate for variable network delay. Synchronization within 1 microsecond is the goal 802.1AS.
IEEE Qat — The Stream reservation Protocol (SRP) is used to reserve bandwidth for audio or video content.
IEEE Qav — Specifies forwarding/queuing procedures, and ensures that AV Packets don't get dropped once they have been let in. Qav ensures that the streaming bandwidth you said you need is actually available, and ensures that bursty traffic is evened out.
IEEE P1722 Transport — Encoding and transport of audio and video streams is done according to this special purpose transport protocol, which takes the media samples and bundles them into an Ethernet Frame. P1722 uses a header to identify the stream, then has a timestamp and the stream data.
Intended Usage for AVB: Professional AV, Automotive and Consumer . The current problem with audio and video over Ethernet, addressed by AVB, is making content delivery real-time and dependable in a LAN environment, where the two main challenges to address are synchronization and network congestion. The AVB focus is to make real-time audio and video work. For Consumer, the goal is to use the existing LAN to carry Real-time media within the home. At the other end of the spectrum: Live Sound applications can benefit from AVB to handle all of the audio and media sources in real-time. There are recording studio applications as well.
The intent of the AVB committee's work in the IEE is to provide the infrastructure so real-time streaming can work across a mixture of different kinds of Ethernet (e.g., 100 Mbit, Gigabit and 10 Gigabit), with a variety of options for channel counts and configuration. AVB follows the traditional IEEE approach of specifying the infrastructure, but leaving the use of that infrastructure flexible enough to foster innovation in the industry.
Guy C. Fedorkow has years of experience in computer networking at Bolt, Beranek and Newman, and at Cisco Systems, where he worked in both development of communications products and also networking standards. He's currently working for Adamson Systems Engineering as a consultant on development of AVB standards and equipment.
