ST-2110: Introduction & History

Since its introduction, the ST-2110 standard has been presented as a true technological revolution. After several years of being prominently featured at IBC booths and in marketing brochures, ST-2110 is finally emerging from labs to enter production at well-equipped broadcasters, and its adoption is accelerating.

As broadcast solutions providers, we’ve naturally followed this standard’s evolution since its release, integrating it into our products… But we must admit, our perspective on this standard is far more nuanced than the superlative articles found online. In this series, we’ll dive deep into the standards to support our viewpoint, hoping you’ll share yours with us.

We’ve divided our analysis into 6 parts:

1 - History	The technologies that preceded the ST-2110 standard.
2 - Overview	The fundamental advantages and limitations of ST-2110.
3 - Codecs and infrastructure	Impact on networks and format selection.
4 - Transport and signaling	Transmission protocols, limitations and improvement paths.
5 - NMOS	The essential building block for ST-2110 production.
6 - Conclusion	Should you invest in coaxial cable recycling companies?

Our technical expertise, particularly in audiovisual transmission protocols, gives us a precise view of implementation challenges. However, this technical focus combined with an unfortunate tendency toward pragmatism can sometimes cause us to miss broader strategic and political issues: we’re counting on you to enrich our thinking and share yours on our LinkedIn page.

History

It may seem strange and somewhat unnecessary to go back as far as analog when the subject we’re interested in is supposed to discuss revolutionary technology. However, we can only observe that successive evolutions in "baseband" video stream transport have systematically built upon the ancestor they’re meant to replace. While the absence of a clear technological break is reassuring, the legacy of the past still weighs quite heavily on standards efficiency.

Analog: A legacy still present today

The concept of "baseband" signals dates from this era. Blanking intervals are used to insert auxiliary data. Point-to-point, the signal is carried on 75-ohm coaxial cables.

Video

To understand the origin of SMPTE 2110, we must go back to analog signals. The PAL standard is a good example, with its CVBS (Composite Video Blanking and Sync) composite format.

A PAL composite video signal occupies a useful bandwidth of approximately 5 to 5.5 MHz in baseband. This signal includes luminance, chrominance (encoded on a quadrature subcarrier) as well as synchronization and blanking pulses.

Once demodulated, the video signal directly drives the cathode ray tube of our good old television: the electron beam sweeps the phosphors from left to right and top to bottom. At the end of each line and each frame, the beam must return to its starting position: during these return intervals, the video signal is still transmitted but the beam is turned off — these are the blanking intervals. These blanking intervals are still exploited by inserting auxiliary data, such as teletext or timecodes.

Audio

Audio, on its side, is completely decorrelated from the video signal. It actually transits through other media: RCA cables, dedicated connection on the SCART connector.

Transmission

In the professional world, video signals are transported point-to-point on a 75-ohm coaxial cable, equipped with BNC connectors.

In terrestrial broadcasting, the PAL composite signal modulates the video carrier in vestigial sideband AM (VSB), while audio is transmitted on a separate carrier, FM modulated and offset by a few megahertz above the video carrier.

Figure 1. Spectrum of a PAL-I transmission (Source Wikipedia)

SDI: Analog/digital bridge

A robust and reliable technology that brings audiovisual signals the reliability of digital transmission. Among other things, we find the coaxial cable, as well as blanking intervals inherited from analog.

Standardized by SMPTE, SDI is an almost direct digitization of the analog video signal. The signal is sampled then transported point-to-point on a serial link carried by a 75-ohm coaxial cable.

Like any serial link, the clock is not transmitted separately but recovered by the receiver directly from the stream, thus guaranteeing proper synchronization of both devices. If a device must process multiple streams from different sources, the ensemble must then be slaved to a common clock via a "genlock" port, to ensure frequency unity.

Regarding data, the video signal is transmitted almost identically to analog, including horizontal and vertical blanking intervals that continue to serve for transporting associated data. We still insert, for example, subtitles (encoded as teletext, OP-47 standard) or timecodes (LTC and VITC).

Unlike PAL broadcasting, the SDI standard also provides for audio channel integration. To this end, audio tracks are encapsulated… in the blanking intervals.

The main advantage of SDI over PAL comes from its digital transmission, much more robust to errors: when the signal passes correctly, its lossless reproduction is guaranteed, regardless of cable length or electromagnetic disturbances present on site.

The robustness of coaxial cable and the simplicity of the serial link have allowed this technology to follow evolutions: HD resolutions, then 4K, HDR, Dolby…

Even though technologically SDI is just a simple serial link carrying a digitized version of our analog signal, this standard covers everything expected in the broadcast industry:

Reliable and robust,
Easy to deploy and maintain,
Well integrated into the PC world thanks to manufacturers like DekTec, and therefore easily integrable into editing or broadcast applications,
Economically accessible — we now find 80x80 12G-SDI matrices for less than 10K€.

ST-2022-6: A first SDI to IP gateway

An SDI/IP gateway implemented according to state of the art, without additional value.

With the evolution of IP networks and the democratization of 10 Gbps then 25 Gbps links, transporting SDI signals over IP became possible without needing to think too much about it. ST-2022-6 is a "gateway" protocol between the SDI world and the IP universe: the signal is sent without any modification via an IP link: only the transport method varies.

To do this, ST-2022-6 is based on RTP, whose philosophy it perfectly respects. It adds a specific header in the payload that provides the clock information necessary for signal reconstruction as well as the description of the transmitted video format.

However, it doesn’t take much advantage of the possibilities offered by the medium change, particularly the fact of no longer being limited by a serial link, and its adoption has been quite marginal, insofar as — as is — it only replaces SDI matrices and coaxial cables with network equipment and optical fibers.

Standards outside SDI

ST-2110 is far from being the first standard addressing audiovisual stream transmission over IP, and the advantages as well as disadvantages it presents have already been addressed multiple times. Surprisingly, the proposed solutions already covered most of ST-2110’s advantages, often using the same technologies.

IETF standards

The IETF (Internet Engineering Task Force) has addressed audiovisual stream transport issues multiple times.

In 1996, it published an open standard: RFC 1890 Profile for Audio and Video Conferences with Minimal Control, which relies on RTP to transport audiovisual streams. Essence separation, profile definitions including "lossless" codecs like 16-bit PCM for audio, and simple codecs for video like H.261 or JPEG. It was revised and corrected in 2003 with the publication of RFC 3551. It is complemented by other standards, notably:

RFC 8860 Sending Multiple Types of Media in a Single RTP Session which allows multiplexing the transport of multiple essences on the same multicast stream.

RFC 4571: Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection-Oriented Transport, which proposes a method to encapsulate RTP streams in a TCP/IP link.

NDI - Network Device Interface

Still on the video transmission side, NewTek published the NDI standard in 2015, a protocol accompanied by a free SDK. This standard provides not only audiovisual stream transport but also integrates device discovery on the network, as well as mechanisms necessary for device control.

In its current state, it could potentially be criticized for being a proprietary standard, controlled by a single company and possibly for not integrating a truly lossless codec.

OMT - Open Media Transport

OMT is the open counterpart to NDI. Made public in early 2024, it shares most of the functionalities offered by NDI — including adoption of a visually lossless codec. Like NDI, a free SDK is provided, and an implementation is integrated into ffmpeg, which will enable extremely rapid and low-cost testing.

It’s interesting to note that this standard chose TCP/IP transport, which may seem counter-intuitive given the bitrates considered. Unlike UDP, TCP/IP ensures packet transmission: its use therefore effectively avoids programming an overlay to recover any lost packets. However, this implies several disadvantages, notably the obligation to have a return channel (in TCP/IP each packet is acknowledged), as well as jitter due to retransmissions. This isn’t necessarily a deal-breaker, but it places strong constraints on the underlying network.

Bibliography

[1] SMPTE ST 2022-6:2012. Transport of High Bit Rate Media Signals over IP Networks. Society of Motion Picture and Television Engineers, 2012.

[2] AES67-2018. AES standard for audio applications of networks - High-performance streaming audio-over-IP interoperability. Audio Engineering Society, 2018.

[3] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson. RTP Profile for Audio and Video Conferences with Minimal Control. RFC 3551, IETF, July 2003.

[4] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson. RTP Profile for Audio and Video Conferences with Minimal Control. RFC 1890, IETF, January 1996.

[5] M. Westerlund, C. Perkins, and J. Lennox. Sending Multiple Types of Media in a Single RTP Session. RFC 8860, IETF, January 2021.

[6] J. Rosenberg and H. Schulzrinne. Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection-Oriented Transport. RFC 4571, IETF, July 2006.

[7] NewTek. NDI (Network Device Interface) Technical Overview. NewTek, 2015.

[8] Open Media Transport Consortium. OMT Specification v1.0. 2024.