UBM Tech
UBM Tech

Networking and interoperability in AVB-capable devices

-September 04, 2012

Technologies are always evolving in the fast-paced world of networking.  Network bridging has come a long way since its inception and continues to become more complex as time goes on.  With new complexities come emerging challenges in how to manage the increase of various types of network traffic.  AVnu networks continue to advance the functionality of these devices, while managing to provide a much needed service to the networking community. As a result, this will impact almost every consumer of such devices as modern audio visual (A/V) electronics and automobiles.  To understand how the underlying technology works, it is important to first understand the basics of what the AVnu Alliance is and the audio video bridging (AVB) technology upon which the technology is based.

AVnu and You

    AVB allows for bandwidth reservation, syncing, and pacing of audio and video traffic over a network and ensures that all AVB-capable devices are behaving in the scope of the standards.  The concept of AVB involves a broad spectrum of different IEEE standards synthesized into one common goal: providing interoperability between devices of differing layer-2 AVB-capable technologies.
     It is necessary to distinguish the difference between AVB and AVnu.  AVB refers to the technologies covered by the standards included in the IEEE 802.1 Audio/Video Bridging working group.  The AVnu Alliance is an organization which was founded by five major corporations: Broadcom, Cisco, Harman, Intel, and Xilinx.  Today the member’s list contains almost 50 members, including the UNH-IOL, and is a “who's-who” of companies involved in AVB technology. AVnu promotes AVB technology by creating and maintaining compliance test procedures and processes to ensure AVB interoperability of networked AVnu devices.  Creating an ecosystem of compatible devices is no small task, but the wide range of uses for the technology make the ends definitely worth the means.
    One of the major utilizations of these technologies is in the automotive industry where the primary focus of AVnu is to successfully deploy AVB technology for streaming of A/V in the automotive space for 'infotainment' purposes.  Once considered a luxury, navigation units and in-car A/V are becoming standard options in many new automobiles.  As A/V technologies become more commonplace, and continue to advance, the complexity of the networking system increases.  Currently, communication networking systems such as controller area network (CAN) or media oriented system transport (MOST) are used by automakers around the world.  There are many benefits of AVB in automobiles which include increased reliability and lowered weight from simpler cabling, low latency, high reliability and predictability, precise synchronization, scalable and versatile topologies, and diagnostics.  AVB also creates one standard technology for the auto industry, which promotes competition among businesses; when corporations compete, the consumer wins.
     AVB also provides unique opportunities in professional A/V, which has been hampered by high per-node cost, and the massive technical knowledge needed to deploy an A/V network.  AVB seeks to alleviate this by developing technologies that provide extremely dependable delivery of synchronized low-latency A/V.  Networking for pro-audio will no longer be kept to the networking experts; anyone will be able to set up an A/V network, even with little to no networking experience.   The major achievement of this technology is that these devices can be used to construct a low latency network that can stream synchronized, live A/V.  Since there are multiple suppliers for AVB technologies, the costs will stay low and the competition between manufacturers high.  This will allow these networks to be able to keep pace with improvements in network and Ethernet technologies by being highly adaptable and relatively inexpensive.  This last detail is also a major selling point for another focus of AVnu consumer electronics and home networking.
    In the past decade, home A/V networking has taken leaps and bounds to become a major facet in many people's homes. The main issues with the current infrastructure are the technical skills needed to set up an A/V network, as well as the reliability of the network.  AVB solves these issues by providing solutions that centering on three major focuses: home theater, whole-home audio with network-attached surround-sound speakers, and glitch-free media streaming over wired networks. Take for example a consumer watching a movie on the television, which is being streamed from the computer, while someone else is surfing the web on a second computer.  AVB's bandwidth reservation mechanisms will ensure that the person watching the movie is not interrupted by something the second computer does, such as a file download.  AVB technology in the home shares all the same benefits that it has in the auto industry.  The cost of the devices will stay reasonable while functionality will be increased. Again, this technology will allow almost anyone to set up an A/V network in the home without needing a vast technical knowledge of networking.
    AVB is a technology that will benefit anyone who uses A/V in the home, car, or for work.  Once the technology is implemented worldwide, A/V networks will become more common, meaning they will benefit everyone from consumer to manufacturer.  AVB technology is also able to support transport technologies other than Ethernet, such as Wi-Fi, MoCA, and EPON.
    The AVnu Alliance continues to support the advancement of AVnu networking in Professional A/V, Automotive and Consumer spaces, while looking into spaces such as Industrial Automation and Control, and Aeronautics/Aerospace.  While capabilities exist today for such needs, improvements for finer-grained bandwidth reservation and ultra lower latency are in the works through IEEE 802.1 and layer-3 transport via IEEE 1733 and ongoing work with the IETF.  New physical layer technologies are also being pursued, which enable 100Mbps and 1Gbps speeds on lighter-weight cabling, critical to automotive needs.

A Good Idea Requires a Functional Infrastructure
    The typical setup of an AVnu network is as follows: an A/V source, which is also called a talker, is connected to an AVB-capable bridge.  From here the stream could go to any number of AVB-capable bridges, which take care of bandwidth reservation and traffic pacing through credit-based shaping.  Lastly, the stream is forwarded from the bridge to a device referred to as a listener which identifies the stream and reserves the bandwidth and is connected to an A/V output device, such as speakers or a television.  This is illustrated below in a diagram of basic AVnu network topology.

    Packets for a reserved stream are distinct from other packets in more than one way.  There are two types of stream traffic which have each been assigned a stream reservation class (SR class) of either A or B, where SR class A always takes precedence over SR class B, thereby ensuring that SR class A traffic has a lower-latency (2ms max) than SR class B traffic (50ms max).  Since any lapse in a stream’s transmission would immediately be perceivable to the end user, stream packets must not be dropped.  At the same time legacy traffic (any traffic that is not stream traffic) must also get through, while not impacting the stream's bandwidth reservation.  This is why the SR classes were assigned, to ensure that each category of traffic could be handled separately and deliberately, controlling the latency and available remaining bandwidth.  The entire process of figuring out which traffic gets forwarded by a bridge and at what time is computed by the credit-based shaper algorithms.
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