About SMPTE

SMPTE creates and manages many standards that we also need when building a broadcast production infrastructure. Other organizations such as AMWA look after NMOS which supplements ST 2110. Precise timing is based on work by the IEEE, and ISO contributes MPEG and JPEG based video coding tools. Additional help comes from the EBU, IETF and W3C.

Membership of the AES is recommended as good value for money when acquiring their standards. SMPTE is equally valuable given that a very modest annual membership fee gives access to all of their published standards as well.

What Is ST 2110?

ST 2110 facilitates the transport of live streams of media content around a broadcast production environment as a replacement for SDI cabling and to enable entirely new production workflows.

ST 2110 is targeted at that part of a broadcast production architecture that needs to send and receive live video feeds. These often come from external sources such as sports, entertainment or news events. Outgoing feeds from playout systems are delivered to distribution outlets. The quality of the content is paramount. Available network bandwidth should not be a limiting factor. Streaming services operate under a different regime where video quality may be compressed to a lower quality so it can work within a limited network capacity.

There Are Lots Of Moving Parts

Whilst all of the ST 2110 specifications are published by SMPTE, some of the documents are ST standards, one is an OV overview and a few are RP recommended practices which are important but not canonical as they are not ratified as ST documents. If you only search the ST collection, you won’t see the complete picture.

The individual parts of the ST 2110 standards are organized into these categories:

• ST 2110-1x – Systems layer.
• ST 2110-2x – Video content.
• ST 2110-3x – Audio content.
• ST 2110-4x – Ancillary data, metadata and synchronized text.

SMPTE standards are generally free of any patent encumbrance. That is not to say there are no patents involved, but they are very rare compared with ISO and MPEG standards for example.

The SMPTE standards documents have a common structure with a glossary of terms followed by textual conventions and notation before the main body.

The main standards are prefixed with ST and are what is most often quoted. The recommended practices usually go unnoticed. They are numbered consistently with the ST documents but have an RP prefix. Draft standards are occasionally published first as an RP document and then promoted to ST status when they are ratified.

OV 2110-0 – Overview Document

Before reading anything else, consult the OV 2110 overview document to see the ST 2110 architectural design. It describes the provenance of the standards you need to use:

• ST 2110 parts.
• Other SMPTE standards.
• Standards from other organizations.

The latest version was released in 2018 and needs to be revised to cover the new parts.

A search for information about ST 2110 reveals many articles that were published immediately after it was introduced in 2017. That early material focuses on the original four core parts of the standard. This was a starting point and some observers suggested the standard was incomplete at that time. From the perspective of 2017, that may be a fair comment because they could not predict how things would evolve over the next seven years with the addition of new parts and the introduction of AMWA NMOS.

None of the standards we routinely use exist in isolation. No single standard on its own can ever be complete or cover every possible eventuality. You need to see the entire panoply of standards working collaboratively together to build your architectural designs. Combining standards from different organizations is frequently necessary. Deeming a single standard to be incomplete is due to a misunderstanding of their relationships to each other.

This is evident when you read the ST 2110 overview document (OV 2110-0). Standards are constantly evolving as their working groups discover shortcomings. These are then addressed and the standards are republished with enhancements.

Taken as a whole there are only a few gaps here and there and they are being addressed by current work to create new standards. ST 2138 addresses the control plane for example.

The situation is quite different now with many additional ST 2110 parts and supporting standards from other organizations now available.

SDI In The Context Of ST 2110

It is no surprise that ST 2110 is closely related to the Serial Digital Interface (SDI) standard since both were developed by SMPTE. SDI is described in ST 259. The vertical and horizontal ancillary data in an SDI stream is specified by ST 291.

ST 2110 dismantles the SDI media streams and ancillary data into component parts and manages them separately:

Separated Elementary Streams

The ST 2110 standard mandates that all the elementary streams are de-embedded and delivered individually. This is useful within a production environment but it is contrary to previous approaches. This led to some criticism in the early days but the PTP synchronization keeps it all under control. There are some workflow advantages to having each essence stream delivered separately.

The essence content of each stream is assembled into RTP packets that are time-stamped and synchronized to a precise system-wide clock.

Each stream is delivered to a different IP address. Arguably, this is very wasteful of IP addresses which may be at a premium depending on your sub-net class. They might also need to be mapped to the same physical destination hardware device which may be awkward when using DNS.

By default, the RTP protocol can use any IP port number between 16384 and 32767.

Technical details for IP port number configuration in an ST 2110 context are hard to find. If streams can use different ports as inlets, it would avoid using up the more valuable IP address real-estate. This is something that the working groups could address at some point. This is an example of why it is important to create multi-disciplinary teams comprising some skilled broadcasting engineers with some experienced IT professionals and networking architects.

Transport Protocol

ST 2110 networking uses the IETF Real Time Transport Protocol (RTP) with the packets delivered via UDP. The UDP protocol reduces latency because there is no buffering. TCP would be unsuitable in this context. There is no handshake protocol with UDP, so dropped or out of sequence packets might be lost but they will arrive as quickly as possible.

ST 2110 manages this potential UDP packet loss with Forward Error Correction (FEC). This sends additional data as a small overhead which is sufficient to fix minor errors in the UDP packet sequence on arrival. The ST2022-7 document describes the FEC technique in more detail.

The FEC support handles errors in a predictive fashion whereas TCP uses buffering and handshaking to deal with the problem in a reactive way. FEC works better because it may never be needed to repair missing data but is always available. TCP would make the stream behave in an asynchronous manner while it pauses to retransmit a missing packet. Timing and synchronization would be all over the place as a result!

There are significant network bandwidth challenges to overcome with the ST 2110 approach. It is conceptually similar to the historical hardware-based solution and relies on being tightly synchronized in real-time. Achieving real-time low latency performance is the major technical challenge to overcome with ST 2110 architectures.

Relevant SMPTE Standards

Here is a list of the SMPTE standards released as individual parts of ST 2110 and the other related SMPTE ST documents that support them. Refer to the SMPE document repository for a complete list of all their standards:

Relevant Standards From Other Organizations

ST 2110 depends on standards from other organizations to complete the specification for a broadcast architecture.

The Networked Media Open Specifications (NMOS) published by AMWA add discoverability, registering of devices, connection and metadata management within the ST 2110 network.

The video and audio formats are not hardwired. Different image sizes and frame-rates including HD and UHD can be supported.

ST 2110 Part 22 describes how to use other video codecs to compress the media. Part 31 supports arbitrary compressed audio formats carried as AES-3 data payloads.

You may also deploy non-SMPTE standards such as AES, MPEG and others in your workflow architectural design. These non-SMPTE standards should be consulted to provide supporting knowledge:

Deploying ST 2110

It is important to keep an open mind and use the standards pragmatically where they are best suited to your architectural design. You don’t need to implement all of ST 2110, nor should you exclude standards from other organizations.

You should be able to cherry-pick the best solutions. In 2018, BBC R&D engineers suggested that a hybrid approach was called for when you need to interoperate with cloud-based systems.

Media identification, timing and synchronization data needs to be preserved when content is moved outside of an ST 2110 environment and reliably restored when it is brought back in. This is no different to any other integration scenario where information loss is undesirable.

Although there is a lot of helpful information on the Internet, be wary of taking everything at face value. A lot of ST 2110 coverage was written when it was first introduced and less complete than it is now. Always refer back to the latest editions of the original source standards documents as an authoritative source. Wikipedia can also be reliable but it depends on industry experts to bring it up to date. Their time is precious and updates can take a little while before they are edited in. Try and check your research against several sources. That often reveals the missing information that is not present in the others.

Obtaining the SMPTE standards has become much easier lately. The standards documents can be downloaded free of charge if you are a member. Joining is very simple and the cost of membership is equivalent to purchasing several standards as a non-member. Obtain all the SMPTE standards you need for the price of a single year’s membership.

These Appendix articles contain additional information you may find useful: