Live from SMPTE: Ethernet-based live production makes gains
The limitations and potential of IP-based live production were front and centre during the opening morning of SMPTE’s 2014 Annual Technical Conference and Exhibition in Hollywood, CA.
Ken Buttle, principle engineer/architect at Miranda Technologies and lead architect at Grass Valley, laid out the benefits of going IP. They include physical simplicity of the network, flexibility and extensibility of transport, the ability to leverage commoditised technologies, and scalability as a system can grow from 100 Gbps today to upwards of 400 Gbps in 2017.
But the drawbacks are still plentiful, including high latency. “A lot has to happen in order to allow for IT equipment and packet-switched networks to completely replace deterministic networks,” said Buttle.
What is needed for IP-based live production, however, are gateways between deterministic routing systems and those in the IT realm. SDI signal transport, for example, has timing that is accurate within one to seven pixels. Packet-based transport is not as deterministic as there is not only the media information but also a header that defines the packet and behavior as well as pre- and post-ambles that all needs to be processed before moving on to transporting the next packet.
“That generates a little more randomness to the timing,” he adds.
Toshiaki Kojima of Sony Japan laid out one solution to this challenge with a new concept: the AV Network Node. The system relies on the SMPTE 2022-6 standard for SDI-IP mapping; SMPTE 2022-7 for seamless switchover; a draft SMPTE standard, 2059-1 for AV signal alignment; and a second draft standard, SMPTE 2059-2 for PTP Profile.
The system, ultimately, allows for latency via Ethernet to be one frame so that it is easier to then correct any synchronisation errors.
Kojima added that there are some future developments, however, that will take the workflow to the next level. For example, the current 2022-6 system maps the entire SDI payload as a single package that includes video, audio, and metadata.
“Our proposal is for essence-independent mapping with video, audio, and metadata in separate packets,” he explained.
He also proposed that SMPTE 2022-5 can be enhanced by making the frame boundary aware of the forward error correction (FEC) block. “Replacement of SDI can be realized without changing the current production,” he said.
Ethernet advances
Jan Eveleens, CEO of Axon, laid out the benefits and future advances of Ethernet AVB for Audio Video Bridging, an emerging standard that extends Ethernet support to the streaming of audio and video signals.
“Ethernet has caught up to what we need in broadcast as for many years the needs of broadcast were faster than Ethernet, but 10 Gbps changed [this] and now 40 Gbps and even 100 Gbps Ethernet is commercially available,” he explained. “And the roadmap is very strong as we believe that within the next decade links will reach speeds on 1 Tbps.”
The advantages of Ethernet, he adds, are savings in the time and amount of cabling required to transport signals. The limitation, however, is the ability to move real-time video and audio properly, and that is one of the reasons IEEE created standards like IEEE 1588 that make sure Ethernet nodes are synchronized.
“Every link gets divided into two parts, one for carrying audio and video signals that can take up to 75% of the bandwith and then 25% of the link is for legacy traffic,” he explained. “That way there is no influence on each other so that legacy traffic cannot impact a file transfer while, likewise, an audio and video signal cannot impact control and monitoring.”
The key concept, he adds, is that devices like a camera would subscribe to the network to make sure that there is enough available bandwidth prior to moving data. For example, a 10 Gbps link can handle up to three cameras that are moving 2.5 Gbps each. A fourth camera would then be prohibited from transporting a signal as it would exceed the 75% limit.
Also important is FQTSS or Forward, Queuing, for Time-Sensitive Streams which allows for priority scheduling on outgoing links so that legacy data can be assigned lower priority.
“That way AVB nodes can avoid bursts on the links and prevent jumbo frames,” added Eveleens. “AVB can separate the traffic into priority lanes and offer a stop-and-go system.”
More importantly, it maintains low latency of 2 milliseconds so that complex networks can easily do 10 hops over a 10 Gbps network. And even lower latency is on the way as the new AVB Generation 2 standard promises to cut latencies to a few 100ths of a millisecond.
With respect to ongoing SMPTE work, IEEE 1722 is looking at how to move uncompressed audio and video, including audio signals up to 192 kHz and video up to 65,535×65,535 pixels so it is well future-proofed for resolutions well beyond 4K and 8K. Frame-rates of up to 85 Hz are supported as well as colour space up to 16 bits.
Eveleens said industry technologists should keep their eye on the AVnu Alliance that is looking to ensure that all AVB nodes can talk with other AVB nodes. Companies like Cisco, Harman, and even BMW are members of the Alliance.
It’s clear that SMPTE has plenty of activities focused on IP-based signal transport for a wide variety of production and distribution needs.