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Opinion – Frank Sheehan, Visual Acuity

test 27 October 2009

IEEE 802.1 audio-video bridging (AVB) is a draft standard for streaming high-definition audio/video data over Ethernet to networked music or video display systems. In an exclusive interview, Visual Acuity’s director of technology gives an insight into this major development

What types of applications will AVB be used for?
I believe that initially AVB will be used predominantly for networked audio. Research has shown that for video applications the adoption of AVB has not been so brisk. AVB technically is still in its infancy and needs to earn its stars as far as video is concerned.
At the moment, Harman seems to have the biggest buy-in to the new standard with its BSS networked audio products. Part of the Harman group has worked with the IEEE task group along with Broadcom and Netgear to develop the technology.

Also, Meyer Sound Lab’s D-Mitri Gigabit network-based digital audio processing and distribution system is AVB compliant.

Historically, as network technology has matured over the years to enable it to host such things as high-resolution video, with the addition of further layers it has moved from half-duplex to full duplex. These bridging technologies evolved further to VLAN (Virtually Bridged LAN) technology. Also one needs to consider technologies such as H.264, which have come into circulation to get us over the heavy network traffic conundrum.

How significant is it?
Potentially AVB is very significant. High-quality multimedia applications could be provided over the network more reliably if the network is carefully designed (inclusive of endpoints, switch gear and bridges). Within the domestic consumer market many interactive multimedia applications used within homes could also be enabled if the delay and jitter through a legacy network were kept low.

Multimedia applications such as streaming require high bandwidth, so there is a constraint on timeliness attached to audio/video streams. Another requirement for multimedia traffic is that occasional data loss is acceptable provided that timely delivery is guaranteed most of the time, in other words the system’s Quality of Service (QoS) is good.

Some interactive multimedia applications over a LAN, such as recording an HD session, require extremely low delays, of the order of 2ms or less. Providing only a standard layer of service to multimedia traffic doesn’t guarantee any limits on point-to-point delay and jitter, which AVB will address. The video traffic could still be delayed if high-quality multichannel audio streams are being played.

Interaction with TCP (Transmission Control Protocol) traffic, which is in itself extremely transient in nature, could still quite easily lead to unacceptable user quality, such as with disc back-ups and large file FTP. This is because this traffic could introduce excessive jitter in audio and video streams if the same network is shared.

A point to be considered here would be that standard class of service could also lead to bundling and bunching of data packets caused by different priority-level traffic, thus creating jitter. Over-provisioning and VLANs have worked in the past for such cases; however, having the ability to support three or more HDTV streams (60Mbps net) over a low-cost 100Mbps network would enable wide customer acceptance purely because of its price point.

How will it affect the industry? Which technologies will it be improving or replacing?
This is an interesting question and one that I believe only time will answer, as AVB is technically still in its infancy. There will be early adopters who will welcome it with open arms and of course others who, metaphorically speaking, are quite comfortable in the shoes that they already wear and see no need to change at present – they get by quite nicely without adding another layer, particularly in these challenging economic times. The real beneficiaries of AVB are those interested in uncompressed video transmission over a low-cost small LAN. In other words, these are users without the benefits of fibre.

Who will welcome it?
Although AVB was designed for the pro-AV market, in my opinion principally it will be welcomed by the consumer market and in particular CI integrators such as Netgear and Broadcom, which are mainstream network switch gear manufacturers/providers found generally in high-street stores and internet-based retail outlets. Also as a matter of importance one needs to consider users that require the following:

  • Low-latency high channel count audio streams, up to 200 channels
  • Streaming video requiring frame synchronized video with excellent QoS
  • Precise timing to support low-jitter media clocks and accurate synchronisation of multiple streams
  • A simple reservation protocol that allows an endpoint device to notify the various network elements in a path so that they can reserve the resources necessary to support a particular stream
  • Queuing and forwarding rules that ensure that such a stream will pass through the network within the delay specified by the reservation.

Will any sectors be less enthusiastic?
Large corporate ICT managers/executives and specialist AV consulting in various vertical markets may not welcome AVB.

At Visual Acuity, it is always interesting when, on a project, we approach those responsible for the ICT infrastructure within the organisation. Although these people have an acute awareness of AV on networks there is a clear reluctance to allow it to share ‘their’ network; in fact they insist that AV is another department and so should have its own network. Then they inform you that the parent company has a framework agreement with a provider such as Cisco or Alcatel for a particular switch that may not be AVB compliant at present.

Here’s another reason: I was told recently was that anything attached to the main ICT network has to have anti-virus and firewall software installed. How do you install that into a Crown amplifier, for instance? Fortunately for the client I was there to help them through all this, but I’m sure you see my point regarding dealing with a large powerful IT department.

How long before AVB becomes mainstream?
This depends upon what you classify as ‘mainstream’. If you mean the consumer market rather than the pro-AV market, then it could happen relatively quickly, although I doubt it.

However, a recent statement by Netgear regarding its joint AVB switch with BSS, called BSS Audio|NETGEAR, said it "will provide the professional community with plug & play standardization coupled with great sound and video". The statement continued: "Working with Harman Professional enables Netgear to prove this remarkably high-performance and rugged technology in the most demanding professional-grade applications before migrating it to other markets." Will it become mainstream quickly? The jury is still out on that one!

What are the opportunities it offers to integrators, especially in the early stages?
I believe in the early stages it offers more to the design consultant than the integrator in ensuring that it is part of the building network infrastructure.

More often than not, at Visual Acuity we employ forward thinking to ensure that a client’s system and infrastructure has scalability built in and not future upgrades or growth designed out. Obviously, in the end integrators will become part of that process – well, the forward-thinking ones will anyway.

  • Note: It is important to note that, although AVB sounds like it is what everyone has been waiting for, it does have its challenges and requires careful planning. These are:
  • All switch gear within the LAN or even WAN has to be AVB compliant. If is not, then the endpoints connected to that hop will not benefit from AVB
  • AVB is limited to maximum of seven hops – a big issue if you are multicasting throughout a whole large network, such as large corporate environments or even a large museum where everything network-centric is routed via a telecomms room or telecomms closet. These technical areas can have many hops in some instances.


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