AVB Demystified #2: How AVB Works & Key Features

by Read Wineland, CTS

Regional Director, Eastern No. America, Biamp Systems

The Editors: As this week's Feature, we've chosen to include Read Wineland's blog, AVB Demystified #2: How AVB Works & 10 Key Features of It. The second in a series of five from the Biamp Systems executive, this blog explains how AVB works and the AVB features that will mean the most to pro AV integrators. You can find the rest of the blogs at the link below his article.

AVB is a collection of IEEE 802.1 standards that ensure a single network can transmit audio, video, and other forms of data via "smart" switches -- without compromising network integrity.

How AVB Works

The commonly referenced network clock in every AVB-enabled device on a network ensures that every device will have a very close representation of what the precise time is in any given instance. After the devices communicate with each other, one AVB device is selected as the best master clock and communications proceed from talker endpoint to listener endpoint.

When an AVB talker endpoint device transmits one or more media streams to the network, an AVB listener endpoint device receives one or more of those streams from the network. The AVB Bridge/Switch acts as a conduit between the two. Both the talker and listener endpoints request stream reservations and the bridge between them fulfills those reservations, regulating the data streams between both endpoints so they are receiving the correct data streams.

Step 1: Talker endpoint advertises and Listener endpoint receives the advertisement.

Step 2: Talker endpoint is ready to send data and Listener endpoint is read to receive it.

Step 3: Talker endpoint sends stream and Listener endpoint receives it.

The AVB Bridge/Switch guarantees time-sensitive, loss-sensitive real-time AV data transmission while allowing audio and video data to seamlessly share the same network. The switches will only allow up to 75% of each network port to be used for AVB traffic, preventing other forms of data from being delayed or lost.

Key Features of AVB

1. Transports media data faster and simultaneously by referencing a network master clock. AVB devices periodically exchange timing information that allows both ends of the link to synchronize their time base reference clock very precisely across an AVB-aware LAN. This precise synchronization has two purposes: 1) To allow accurate synchronization of multiple streams and 2) To provide a common time base for sampling/receiving data streams at a source device and presenting those streams at the destination device with the same relative timing.
2. Guarantees bounded, low and constant media latency. Low latency is important in live situations where the receipt of audio needs to arrive within milliseconds of the original transmission. Bounded/constant latency prevents the timing from changingby guaranteeing a specific, known latency between endpoints. The latency of AVB provides 2ms over 7 switch hops in a 100Mbit Ethernet network. With one gigabit hops, 1ms latency becomes possible.



3. AVB provides higher channel count capabilities of 420 x 420.
4. Works over existing Ethernet infrastructure with proper switches.
5. Stream reservation protocol (SRP) defends bandwidth against oversubscription and ensures quality of service (QoS) through the use of admission control and traffic shaping. It also prevents information from being lost in cases of oversubscription.
6. Queuing and forwarding rules that ensure AV streams pass through the network with the delay specified.
7. Allowing synchronization of multiple flows of media/streams from different places, and arrive at their end point simultaneously. AVB allows you to not only transfer data at the same time from point-to-point, but also from point-to-many different points.
8. AVB devices can identify and communicate with non-AVB devices using standard 802 frames, but cannot send AVB data streams through non-AVB switches.

   

9. As an IEEE open network standard, AVB provides market stability and consistency for end-users, integrators, and manufacturers alike.
10. Modularity allows for the creation of different system configurations between centralized, hybrid and distributed systems. The system designs can be easily expanded and reconfigured to meet the facility's needs without having to install a completely new system.

In the next AVB Demystified post, we'll discuss why an AVB network could be beneficial for your customers. The short answer: Because AVB means end-to-end digital networks that are simple to design and easy to manage.

Author: Read Wineland is the Regional Director Eastern North America for Biamp Systems and has been with the company since 1995. Previously he was an independent representative for Biamp and several other professional audio product lines, based in Ohio.

Read started his audio career in 1973 with White House Communications while in the US Air Force, serving Presidents Nixon and Ford. Following his military career he worked for Hollywood Sound Systems in Los Angeles working on projects such as House PA for NBC's Saturday Night Live, The Academy Awards and The Emmy Awards. Read installed the original wireless microphone systems for the NFL, which the referees continue to use today.

Read holds a CTS (Certified Technology Specialist) certification awarded by InfoComm, the AV Industry's governing body, and is a member of the Audio Engineering Society.