Technology: SMPTE ST 2110 AV-over-IP interoperability and standards
Technology: SMPTE ST 2110 AV-over-IP interoperability and standards
For several years, audio and video signals have been transitioning to IP networks. Jed Deame, Antoine Hermans and Rob Green examine the flexibility added with an AV-over-IP network and the ST 2110 standards
When it comes to AV, be it at a house of worship or elsewhere, there is an ever-present demand for better quality and connectivity. As camera and display technologies improve, the images they capture and present get closer to ‘real-life’ viewing. Pro AV is spearheading much of this demand, as user interaction with displays from short distances, such as the magnification of video images provided by large format displays in digital signage and LED walls, becomes more common. As video frame sizes and frame rates increase from HD to 4K and 8K and from 60fps to 120fps, connectivity bandwidth between video sources and displays needs to keep up. For example, uncompressed 4Kp60 video over HDMI 2.0 uses an aggregate bitrate of up to 18Gbps, severely limiting cable distances.
In the past, and depending on the protocol used, supporting higher resolutions and frame rates would require either the use of compression, multiple video links, or a new standard and cabling specification altogether. However, AV-over-IP is emerging as the preferred way to support higher bandwidths, extend the reach of point-to-point connections, reduce infrastructure costs and enable more flexibility in using equipment on the network.
As with any emerging technology, early suppliers will look to standardise their proprietary techniques. This can essentially impose limitations and compromises on the rest of the industry and, while it can be very successful when the technology works well and interoperability is less of a concern, professional AV systems really need something that’s scalable, that works independently of resolution and network speed, and that isn’t tied to a single vendor’s product. As an example, the table below compares the scalability of the Society of Motion Picture and Television Engineers’ open SMPTE ST 2110 with the proprietary SDVoE and Dante AV.
SMPTE ST 2110
The SMPTE ST 2110 suite of standards was developed by a group of key figures in the pro AV industry to ensure system flexibility and scalability for years to come. As a result of its collaborative formation, there are many sub-standards as part of ST 2110, including ST 2110-10, which covers system timing, -20 for uncompressed video and -22 for compressed video. There are also sub-standards for traffic shaping, splitting one stream over multiple Ethernet links, uncompressed audio, AES audio and ancillary data.
These sub-standards are mixed and matched to meet the needs of particular applications. While television broadcasters may be content with uncompressed video, for example, a house of worship might have more of a need for compressed video (ST 2110-22), which enables the use of more cost-effective solutions, such as a 1Gbps Cat-5 cable. In addition, multiple links can be aggregated using RP 2110-23 (single video essence transport over multiple ST 2110-20 streams).
Another important factor is timing and latency. Synchronisation of network nodes is necessary to realise low latency and ST 2110-10 specifies that nodes need to be synchronised according to the ST 2059 standard, which consists of two sub-standards: ST 2059-1 (generation and alignment of interface signals) and ST 2059-2 (SMPTE profile for the use of the IEEE-1588 precision time protocol).
These specify the use of the precision time protocol – or PTP – standard (IEEE 1588v2) and the generation of alignment pulses from the PTP time to align media (video frames, for example). Synchronisation over Ethernet is a different animal to synchronisation via Genlock (also known as generator locking, a technique whereby the video output of one source is used to synchronise other picture sources together), although the end result is similar. This is because Ethernet is packet based and the time it takes for a packet to reach its destination over the network is not fixed. PTP is designed to solve this issue. For best timing results, PTP-aware switches (such as transparent clocks or boundary clocks) should be used, but smaller systems won’t necessarily need them. In addition to ensuring lips are in sync, PTP synchronisation also enables ultra-low latency for video displays and digital signage.
Control and management
The Advanced Media Workflow Association (AMWA) developed the Networked Media Open Specifications (NMOS) to provide a control and management layer for use in IP-based infrastructures, in addition to the transport layer delivered by SMPTE ST 2110.
Its goal is to offer a means for straightforward interoperability between products, therefore allowing systems to be built using components from multiple manufacturers. The NMOS specifications are mandated by the European Broadcasters Union (EBU) as part of its Minimum User Requirements to Build and Manage an IP-based Media Facility document. There are several NMOS specifications available, but the three key components are IS-04, IS-05 and IS-08.
IS-04 allows for ST 2110 devices to be discovered and registered on an IP network and their abilities published. A Registration and Discovery Server (RDS) is found automatically using MDNS or DNS service discovery for simple plug-and-play capabilities. Meanwhile, IS-05 facilitates the configuration of ST 2110 devices and allows them to be switched by any broadcast controller, such as an HDMI router-like button panel or soft control panel via an HTTP API. Audio channel mapping is introduced by IS-08, a key feature that lets users re-map audio channels at the transmitter or receiver. The IS-08 API also allows the routing of multiple diverse audio streams to any receiver.
ST 2110 was designed from the ground up for seamless interoperability. This has been the key to its accelerating adoption rate. End users, including houses of worship, don’t want to be locked in with the ability to only use equipment from a single manufacturer.
In order to facilitate interoperability between products, the EBU and IRT broadcast technology institute, in conjunction with the Joint Taskforce on Networked Media (JT-NM), established the JT-NM Tested programme, in which ST 2110 product manufacturers are invited to a huge ‘plug-fest’ where the JT-NM hosts compatibility testing for both the electrical transport of packets and the NMOS control system. The results are posted on the JT-NM website to provide potential users with the confidence that purchased systems will carry interoperability with other systems that they own.
With emerging technologies such as AV-over-IP and ST 2110, it’s important to remain adaptable to changes. While there are many devices specifically designed for IP-based use in 2020, many equipment designers prefer to adopt programmable platforms such as standalone FPGAs (field-programmable gate arrays) or, more frequently, SoCs (system on a chip) combining FPGA fabric with embedded ARM processors. This provides an ideal link between software and AV domains as well as Ethernet and IP traffic, combining interfaces with video, audio and software processing functions in the same device. The programmable nature of these devices means they are adaptable to new and changing video formats and codecs, with the scalability and flexibility required to support multichannel AV and the software stacks to enable reliable network transport.