Comms In Hybrid SDI - IP - Cloud Systems - Part 1

We examine the demands placed on hybrid, distributed comms systems and the practical requirements for connectivity, transport and functionality.


This article was first published as part of Essential Guide: Comms In Hybrid SDI - IP - Cloud Systems - download the complete Essential Guide HERE.

The Silent Partner

Intercoms are the silent partner in every broadcast environment, quietly keeping every single person on a production in the loop.

Production personnel on a live broadcast can be anywhere. From the director in the heart of the control room, to talent on the studio floor, camera operators, runners and floor managers, so efficient and reliable communication is essential. It is the comms that ensures everyone hears exactly what they need to hear, when they need to hear it, wherever they are.

Today, with more productions split across multiple sites and reporters operating in remote locations, and with all of them embracing different connectivity formats, the comms system provides the fabric to manage the entire signal flow. Whether it’s the interruptible foldback in the talent’s earpiece or the instructions to camera four to switch to a wider shot, the comms system delivers the connectivity for anyone to talk to anyone else across panels, belt-packs and radios.

But intercom systems are not just about guaranteeing a quality of service for all these signals; they are also about how they are managed and controlled, who has access to them and how everything hangs together.

Geography has always been an important consideration in broadcast communications, but changes in the way broadcasters work have had a massive impact on how intercoms are delivered and moves towards IP-infrastructures are demanding step-changes in how these networks are managed and where they might go next.

Meanwhile, the decoupling of audio from video is encouraging the adoption of scalable cloud-based workflows.

Nothing is the same as it was. And that’s a good thing.

The Big Shift

Analog comms systems have always provided reliable one- and two-way communication between selected people, or Partylines between multiple people at the same time. And they still do, but VoIP, Dante, AES67 and SMPTE 2110 networks are changing the game. Established IP protocols are not only simplifying connectivity, but they are making it more efficient by carrying more signals of asynchronous audio down fewer cables.

This is nothing new. In fact, non-synchronous broadcast audio transport dates back to the 1990s when the telecoms industry first used fixed data packets to transfer audio over long distances. As a point-to-point infrastructure it was not as flexible as modern IP networks, but it proved the use case of using packets for transferring real-time data.

Today, IP infrastructure promotes much greater flexibility at lower latencies, it is an enabler for cloud workflows, and it is hugely scalable. It enables companies to provide remote support, and it does all this using cost-efficient COTS equipment.

The reason that broadcasters have been able to take advantage is that they are all on the same roadmap. Thank goodness for standards.

We Have Standards

Since its introduction in 2016, the SMPTE 2110 (ST2110) standard has governed all broadcast IP infrastructures and covers how video and audio media streams are packetized on a network. But while the audio element (ST2110-30) is based around the AES67 standard, it doesn’t mean that all AES67 devices are compliant with ST2110.

Despite differences, which include support for IGMPv3 which enables multiple devices to receive the same stream, they both share the same approaches to important shared components, such as adherence to the RTP (Real-time Transport Protocol) and time alignment with PTPv2 (Precision Time Protocol), both of which we will cover later.

It’s not to say other IP codecs don’t exist either; they do, and proprietary protocols like Dante and Ravenna are no strangers to broadcast infrastructures, although all are compatible with ST2110 streams. 

Power & Control

Adherence to the ST2110 standard helps create cross-vendor support and eases the transition from more traditional SDI networks to IP networks, but it is only part of the story. ST2110 only covers encoding, transport and synchronization of broadcast media streams.

To be truly effective, the discovery and management of devices on a network should also adhere to interoperable standards. As a consortium made up of the Advanced Media Workflow Association (AMWA), SMPTE, the EBU, and Video Services Forum (VSF), the Joint Task Force on Networked Media (JT-NM) provides a series of recommendations with guidance on how to approach these aspects.

NMOS IS-04 and IS-05 both have wide support from audio for broadcast manufacturers. IS-04 provides a way for devices to advertise what media streams they are outputting, and once advertised NMOS IS-05 forms connections between them. IP networks require these as an absolute minimum, while recommendations like IS-07 (which provides the potential to stream status and control data with GPIO-style switching) and IS-08 (which gives IP networks the ability to do audio channel mapping), continue to add value.

Building Bridges

These are all important considerations for broadcasters, but more crucially for broadcast vendors; without interoperability, IP has few benefits to leverage. 

Keeping up to date with evolving standards is one of the biggest challenges for technology suppliers. Unhelpfully, they don’t develop at the same rate, and interoperability is compromised further because vendors don’t implement changes at the same rate as each other.

Large IP infrastructures are constructed using a combination of technologies made up of islands of IP, and bridges which connect these islands together. These bridges, or gateways, provide the glue which allow IP networks to operate, and are the reason why most broadcast IP networks are hybrid SDI/IP systems.  They work by embedding and de-embedding multiplexed audio between SDI/MADI and ST2110, and often incorporate additional codecs like Dante.

Launched in 2006, Audinate’s Dante is well-liked by audio folks because it already does everything they need; it discovers, routes, and manages signals under the hood, and is well established in many broadcast infrastructures. But if the main transport is over ST2110, it needs bridging.

No Such Thing As A Standard IP Network

Although the industry seems to currently have settled on ST2110 and NMOS for transport and management, every single IP network is constructed using different combinations of equipment, and network designers have to approach each project on its own merit.

In addition, unless an IP infrastructure is a greenfield build, switching to IP from a traditional baseband network is not easy; particularly if the broadcaster is still on air at the time.

And we haven’t even mentioned the cloud yet (but, inevitably, we will).

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