It’s open season with these AES67 audio-over-Ip experts who are all the questions put to them on working with AES67. Not only was AES67 baked in to SMPTE ST 2110-30, it’s also a standard that brings compatability between Dante and RAVENNA as well as other AoIP technologies.
After a quick summary of what AES66 is, this talk quickly moves into answering these, and other questions:
How much bandwidth does stereo AES67 require?
Can multicast be used within Ravenna
Will there be a slipless switching/2022-7 style function?
Should receivers automatically adjust to original stream
Is it possible to avoid using PTP in an audio-only system?
Cost of PTP-capable switches
What’s the difference between Boundary Clocks and Transparent Clocks
Can AES67 go over the internet?
Tools for spotting problems
IPMX for Pro-AV update (See this talk)
Is NMOS ‘the answer’ for discovery and configuration?
Uncompressed audio has been in the IP game a lot longer than uncompressed video. Because of its long history, it’s had chance to create a fair number of formats ahead of the current standard AES67. Since many people were trying to achieve the same thing, we find that some formats are compatible with AES67 – in part, whilst we that others are not compatible.
To navigate this difficult world of compatibility, Axon CTO Peter Schut continues the Broadcast 101 webinar series with this video recorded this month.
Peter starts by explaining the different audio formats available today including Dante, RAVENNA and others and outlines the ways in which they do and don’t interoperate. After spending a couple of minutes summarising each format individually, including the two SMPTE audio formats -30 and -31, he shows a helpful table comparing the,
Timing is next on the list discussing PTP and the way that SMPTE ST 2059 is used then packet time is covered explaining how the RTP payload fits into the equation. This payload directly affects the duration of audio you can fit into a packet. The duration is important in terms of keeping a low latency and is restricted to either 1ms or 125 microseconds by SMPTE ST 2110-30.
Peter finishes up this webinar talking about some further details about the interoperability problems between the formats.
It’s being closely watched throughout the industry, a long-in-the-making project to deploy SMPTE ST 2110 throughout a fully green-field development. Its failure would be a big setback for the push to a completely network-based broadcast workflow.
The BBC Cardiff Central Square project is nearing completion now and is a great example of the early-adopter approach to bringing cutting-edge, complex, large-scale projects to market. They chose a single principle vendor so that they could work closely in partnership at a time when the market for ST 2110 was very sparse. This gave them leverage over the product roadmap and allowed to the for the tight integration which would be required to bring this project to market.
Nowadays, the market for ST 2110 products continues to mature and whilst it has still quite a way to go, it has also come a long way in the past four years. Companies embarking similar projects now have a better choice of products and some may now feel they can start to pick ‘best of breed’ rather than taking the BBC approach. Whichever approach is taken there is still a lot to be gained by following and learning from the mistakes and successes of others. Fortunately, Mark Patrick, Lead Architect on the project is here to provide an update on the project.
Mark starts by giving and overview of the project, its scale and its aims. He presents the opportunities and challenges it presents and the key achievements and milestones passed to date.
Live IP has benefits and risks. Mark takes some time to explain the benefits of the flexibility and increasingly lower cost of the infrastructure and weighs them agains the the risks which include the continually developing standards and skills challenges
The progress overview names Grass Vally as the main vendor, control via BNCS having being designed and virtualised, ST 2110 network topology deployed and now the final commissioning and acceptance testing is in progress.
The media topology for the system uses an principal of an A and a B network plus a separate control network. It’s fundamentally a leaf and spine network and Mark shows how this links in to both the Grass Valley equipment but also the audio equipment via Dante and AES67. Mark takes some time to discuss the separate networks they’ve deployed for the audio part of the project, driven by compatibility issues but also within the constraints of this project, it was better to separate the networks rather than address the changes necessary to force them together.
PTP timing is discussed with a nod to the fact that PTP design can be difficult and that it can be expensive too. NMOS issues are also actively being worked on and remains an outstanding issue in terms of getting enough vendors to support it, but also having compatible systems once an implementation is deployed. This has driven the BBC to use NMOS in a more limited way than desired and creating fall-back systems.
From this we can deduce, if it wasn’t already understood, that interoperability testing is a vital aspect of the project, but Mark explains that formalised testing (i.e. IT-style automated) is really important in creating a uniform way of ensuring problems have been fully addressed and there are no regressions. ST 2110 systems are complex and fault finding can be similarly complex and time consuming.
Mark leaves us by explaining what keeps him awake at night which includes items such as lack of available test equipment, lack of single-stream UHD support and NMOS which leads him to a few comments on ST 2110 readiness such as the need for vendors to put much more effort into configuration and management tools.
Anyone with an interest in IP in broadcast will be very grateful at Mark’s, and the BBC’s, willingness to share the project’s successes and challenges in such a constructive way.
AES67 is a method of sending audio over IP which was standardised by the Audio Engineering Society as a way of sending uncompressed video over networks between equipment. It’s become widespread and is part of SMPTE’s professional essences-over-IP standards suite, ST 2110.
Here, Conrad Bebbington gives us an introduction to AES67 explaining why AES67 exists and what it tries to achieve. Conrad then goes on to look at interoperability with other competing standards like Dante. After going into some implementation details, importantly, the video then looks the ‘Session Description Protocol’, SDP, and ‘Session Initialisation Protocol’, SIP which are important parts of how AES67 works.
Other topics covered are:
Packetisation – how much audio is in a packet, number of channels etc.
Synchronisation – using PTP
What are SDP and SIP and how are they used
Use of IGMP multicast
Implementation availability in open source software
For a more in-depth look at AES67, watch this video
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