Broadcast Beat Magazine September, 2015 - Page 76

IP AMBITIONS: AUDIO OVER IP by Pieter Schillebeeckx

Audio Over IP has been in existence for quite some time, so it's difficult to call it a new or emerging technology. Axia Audio's LiveWire system was launched in 2003, for example. For that, you have to take your hat off to them; they designed and implemented their own Precision Time Protocol (PTP) before most people had heard of such a thing.

For some reason though it's taken this long for IP to catch the imagination of many broadcasters, and now the debate is heating up.

Ambitions for Audio Over IP (AoIP) in the broadcast community are set high. Some see it as a technology of ultra-convenience, or as a magic bullet for the bloated capital budgets that come with infrastructure and capacity upgrade - a high channel count transport system that can use existing IT provision. In practice, however, these might be false headlines – distractions from an even brighter future where infrastructure flexibility with software-driven routing of audio, video and metadata, complete with all-encompassing synchronization, is actually the main prize.

Take a typical US broadcast truck set-up. MADI is still king here, not just for linking trucks and stageboxes, but for providing feeds at every production position via audio monitoring units where personnel can create their own mix.

To provide this they typically use a large video router expanded with MADI routing capability, sending out one MADI stream for eight positions, another one for the next eight, and so on. It's a little inefficient - you could pick off feeds from a single MADI loop, for example, but the central control is an important factor.

If you replace that with an AoIP network - AES 67, for example - you no longer need the 20U router; you can use a virtual patch panel on a simple App and the workflow stays the same. Reliability improves too - using multiple switches and distributor logic means that if one switch goes down, you might lose what's connected to that switch, but everything else will continue to work. If that central router goes down, you lose everything.

If you scale these gains up from a truck to a regional or national broadcast centre, then this kind of flexibility, control, and reliability, surely becomes the main incentive for making the move?

To get there though, we must be realistic about the hurdles to practical implementation of AoIP and VoIP in the broadcast environment.

First, it is most likely that a broadcaster's IP transport will require a separate, managed network, which itself has a cost. Dispensing with the central router is a goal worth striving for, but we shouldn't dismiss the network as a simple trip to the local computer store for some Cat5 and a few off-the-shelf switches. A network built and managed to tight parameters, with high enough bandwidth for audio and video, and capable of clean switching is certainly not trivial. Every point where you might have a camera really needs to have a 10Gb switch. A busy area on a network might be the video mixer on a live production, which would certainly require a 40Gb or even a 100Gb switch. This is neither commonplace nor inexpensive technology.

Audio-only is a different matter and its bandwidth requirements are tiny in comparison. A high-spec, nicely managed existing IT infrastructure with well managed Quality Of Service, VLAN, priority rules, and so on can cope with high numbers of audio channels with good reliability via 1Gb switching.

AoIP and VoIP are correctly termed layer 3 technologies, but maybe the requirement for specific network hardware and management challenges this in spirit and brings it into the realm of a layer 2 protocol like AVB?

This leads to the second hurdle; all of this comes with the training and knowledge requirement that up until now has not been prevalent in the broadcast department. Staff will have to become fluent in IT, and comfortable with IT infrastructure. Some are already there, but many are not. (continued on next page)


IBC Issue September 2015