Digital audio routing, switching and
control have grown dramatically in broadcast facilities. TDM-based
(time-division multiplex) systems were the first to appear in the 1990s. But in
recent years, audio-over-IP, or AoIP, systems have gained widespread
Unfortunately, all these systems use unique
protocol features and proprietary components, making interoperability among the
different platforms and brands difficult, if not impossible. As Radio World
reported in its Aug. 1 issue, the Audio Engineering Society is stepping up to
tackle the challenge of standardization so that interoperability might be
The AES Standards Committee has
initiated a project called AES-X192, with the goal of developing a
high-performance streaming audio-over-IP interoperability standard. The issues
involved are reminiscent of when AES became involved in the serial digital
audio standards setting process that eventually produced AES3 (AES/EBU) in
AES-X192 was conceived two years ago and
is being led by Kevin Gross, a media network consultant with AVA Networks,
which developed the CobraNet standard. About 100 members including most of the
major console and router manufacturers are taking part in this project.
Radio World Technical Advisor Tom
McGinley interviewed Gross via email to glean more background and how the
effort is progressing.
Kevin, you’ve been interested in this
topic for a number of years and now have the AES involved pushing for a formal
new AES industry standard for interoperability. Tell us about your background
and current work as a media consultant, and how X192 got started.
I’ve been working in audio networking since the
mid-1990s when we came up with CobraNet at Peak Audio. CobraNet is
now owned by Cirrus Logic, and I’m no longer involved with it. I have
continued as an independent consultant helping end users, system designers and
equipment manufacturers with media and networking technology.
In this role, I keep abreast of the IT
industry in general and media networking specifically.
From that position, I noticed two
things. First, the IT industry has been rallying around the Internet Protocol
(IP) as a framework for all things networking. Second, there has been an
emergence of a new generation of media networking protocols. Unlike previous
generations, the protocols in this new generation use similar technical
concepts and standards. Like previous generations, these new protocols do not
I recognized an interoperability opportunity between
these technically similar protocols and approached the AES with the idea of
developing an interoperability standard.
Describe how the AES Standards Committee approaches and
conducts the standards setting process.
Standards development at the AES is
conducted in a very open manner. Membership in task groups that develop
standards is open to any “materially affected individual.” This basically means
that standards are developed by individuals, not companies, and the
participants have a stake in the outcome. The task groups are given
great autonomy in how they choose to organize themselves and conduct
business. This autonomy and openness has allowed for quick progress
What is the proposed schedule for meetings of the X192 group
and when do you estimate that a new standard could likely be finalized and
emerge for the pro audio and broadcast industry?
We have a draft standard and have been
holding teleconferences twice a month to edit that to everyone’s satisfaction.
We are nearing the end of that process and are working to have a final draft
approved by the task group later this year. There are
several further AES approval steps beyond that before it is published
as a standard. “X192” is the AES designation for the project. The X192 work
product will be published as an AES standard named AESxx, where xx is some
number to be determined.
Telos/Axia got the AoIP ball rolling
first for console and routing systems. Other manufacturers like Wheatstone and
Logitek are now offering their own AoIP solutions. Briefly explain the major
similarities and the differences within the various AoIP platforms.
Here’s a summary at right of AoIP
protocols from the Objectives and Benefits document you can download from
www.x192.org [find the direct URL at radioworld.com/links]. The
similarities are use of User Datagram Protocol or Real-time Transport Protocol
for transport and IEEE 1588 for synchronization. But it is possible for two
systems to use the same protocol in different, non-interoperable ways. The
other differences are in management protocols used for discovering other
devices on a network and setting up a connection.
|| Date Introduced
|| ALC NetworX
|| In development
|| IEEE 1588-2008
|| IEEE, AVnu
|| IEEE 1588-2008 advanced profile (IEEE 802.1AS)
|| Ethernet, RTP
|| QSC Audio
|| IEEE 1588-2002
|| Data packet arrival times
|| IEEE 1588-2002
Table 1: Summary of AoIP Protocols
U.S. broadcasters are familiar with Telos/Axia and
Wheatstone, but the others listed on your chart are less familiar to many of
us. Can you tell us a little more about those?
Ravenna is most well known in
the broadcast industry in Europe. It is a technology
developed by one of the Lawo companies, but available to other
manufacturers for a reasonable fee.
AVB is a set of IEEE standards jointly
developed by the pro audio and networking industries. The automotive industry
is now also contributing to development. Special AVB network equipment is
required to make this work.
Q-LAN is the networking piece of QSC’s integrated
Q-Sys signal processing and distribution system. This is currently used mostly
in commercial audio systems though there are some prominent broadcast
applications (e.g., U.S.
Senate recording studio)
Dante was developed by a network startup
in Australia. The technology is licensed to audio equipment manufacturers.
Dante is most commonly found in commercial and live applications.
To what extent will details of the proprietary features have
to be revealed for AES to be successful in crafting a new standard with
One of the ground
rules we’ve used in X192 development is to reference existing
standards wherever possible, rather than invent new techniques
and protocols. I believe this approach reduces exposure to
intellectual property issues. You never eliminate the risk entirely, however.
Broadcast engineers have hoped that generic, off-the-shelf
Ethernet switches could be employed in AoIP systems. However the switches now
being used have to be qualified, managed switches and how they are configured
is critical. Why is this issue of switch implementation so fussy and confusing?
An important piece of
a successful AoIP system is network quality of service features. QoS
standards and technology have existed in the network world for years but have
not, until now, been given a real workout. Network vendors are learning
from fussiness experienced by their customers and the situation is
rapidly improving. Anyone building an AVB switch has to explicitly deal with
these issues, for instance.
I was involved
in the development of early systems for recording direct to hard disks.
That was also initially quite fussy. Media networking feels like it is on a
similar technology curve. We’re not going to remember any of this in a few
In some cases, only a specific manufacturer’s switch is
compatible. Won’t there need to be some kind of standardization of switch
architecture, firmware and programming established as part of any X192
One of the stated goals of X192 is to
work with standard IP network equipment. I have tested a fair amount of network
equipment for QSC, and my general findings are that some of the equipment (even
otherwise high-performance equipment) does not give the real-time performance
or offer some of the QoS features required by real-time media networking. As I
say, this situation is improving quickly.
Is it realistic to expect that after an AES-X192 standard is
established, engineers might eventually be able to buy a generic $50 switch
from Best Buy and run a multi-studio broadcast facility through it?
If you’re going to build a small
audio-only network, we’re already there. Surprisingly, the cheap switches
often have the best raw performance. That’s because everything is done on one
IC. Things have to slow down to go between ICs in the larger and more
complicated equipment. If you want to mix audio with other IT functions, you
will need QoS and that generally requires a managed switch. Fortunately,
almost all gigabit switches you can buy today are managed and have the QoS
features. They’re not exactly $50, but the Cisco Small Business switches, for
instance, get the job done for less than $1,000.
Most of the U.S.-based AoIP systems use the same Cisco or HP
Ethernet managed switch models. What other switches are being used?
Just about anyone who builds a gigabit
Ethernet switch has a switch that has the required QoS feature set. Examples
can be found from all these manufacturers:Dell, Cisco Small Business (formerly Linksys) Extreme Networks, Juniper,
Brocade, Netgear, 3Com, Alaxala, Allied Telesys, Avaya, Moxa and Hirshmann.
Beyond the IP network itself, the other major hardware
link of any AoIP system is how source devices get connected to the network. To
what extent will X192 set any protocols or rules for these components in the
X192 describes how audio data is
formatted into network packets and how everything is
synchronized. Additionally, X192 specifies protocols that allow devices to
find one another on the network and then exchange commands to set up the
aforementioned audio transmissions across the network.
Other aspects of configuring these boxes
such as preamp gain settings, logic inputs and contact closure outputs are
outside the scope of X192.
I don’t know whether X192 makes these
network interface products commodity items. I don’t think it is a
question of great import because where I see the real value of interoperability
is where, instead of using a second piece of gear to interface a
product to the network, the network interface is built into audio products such
as automation equipment, processors, consoles, amplifiers, microphones,
speakers and transmitters.
Synchronization is a vital element within AoIP. Some systems
are using the IEEE 1588-2002/8 standard while others are proprietary. Will X192
likely specify the IEEE standard?
Standards development rules of
participation discourage me from confirming or denying this to the press, but,
yes, it is very likely. :)
Aside from the hardware, what other factors and
considerations within an AoIP system complicate the goal of forging an
I think business issues are really the
important complicating factors. There are business models out there that
rely on proprietary systems. I think many of these would work better for
everyone if opened up, but that can be a scary transition to make.
Axia/Livewire is collaborating with Lawo/Ravenna from Germany
and appears to be leading the effort to leverage an open standards approach for
AoIP interoperability. Axia’s Mike Dosch has even said that he would expect any
AES-X192 standard to look very much like “the new Livewire.” What is your
position on this development and how might it affect the X192 process?
Axia and ALC (Lawo/Ravenna) have been
very active in the development of X192. It is clear to me that open
interoperability is a business priority for both of them. With X192 we’re going
to make interoperability available to the industry. Anyone who sees the value
in it can pick it up and run with it. We appear to have a game going with Axia
and ALC even before the standard has been finished. To me, that’s a good sign
that X192 will achieve the critical mass of acceptance required to make real
and useful interoperability.
Compared to the AES3 standard setting process and result,
what similarities and differences do you see with the X192 process as it
AES3 was first published in 1985, so I
can’t make a first-hand comparison. I have encountered some sour attitudes
about the standards process and results. What is important to understand about
AES standards is that there’s a lot of autonomy given to the individual groups
developing standards, and so there’s no single process. Because of the
generosity of my sponsors, Axia and QSC, I’m able to devote a significant
amount of my time leading the effort, researching basic technology, drafting
the standard and interfacing with related standards bodies.
I believe this level of attention has helped move things forward
full interoperability of the major systems and protocols would be an ideal goal
of X192 as a new AES standard, in the end it may come up short of establishing
or requiring that for all participating systems and specific protocols. Expand
on that as a possible outcome.
I think what you’re getting at is described here [see comic below]. I’m not
going to claim that I have a surefire way around this pitfall, but we are not
trying to solve everyone’s problems with X192. Full interoperability is
not the goal. We’re trying to define a fairly basic
interoperability mode. We expect manufacturers to go beyond that and
develop their own extensions. If X192 is successful, maybe we’ll
have the opportunity go back and standardize some of those extensions.
What major players have not yet stepped up to be part of the
There are over 100 individual members of
the task group. Members come from networking, silicon, broadcast, live sound,
commercial audio, music production and other fields. End users, system
designers, integrators and equipment manufacturers are represented. X192 is a
technical effort, but there has not been a lot of publicity yet (publicity
doesn’t usually help get technical work done), so I’m sure there are some that
are simply not aware of the initiative.
Is there the expectation that similar to AES serial, there
will be two standards developed … one high-performance interface for pro audio
and a cheaper one for consumer systems?
We’re including in the standard several
options in terms of latency, bit resolution and sample rate. It is not feasible
to require all devices to implement all modes so I expect AoIP products will
self-classify themselves in the market based on the capabilities they
implement. Because of the protocols we’re using, X192 will have a certain
amount of intrinsic interoperability with VoIP systems. A VoIP device could be
dialed up to minimally support X192.
Tom McGinley is technical advisor and
longtime contributor to Radio World.
Comment on this or any article. Write to
attention Letter to the Editor.