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Video: Migrating to IP – Top Questions from Broadcasters

Posted on 28th August 2020 by Russell Trafford-Jones

Moving to IP can be difficult. For some, it’s about knowing where to even start. For others, it’s a matter of understanding some of the details which is the purpose of this talk from Leader US which looks at the top questions that Leader’s heard from its customer base:

How do we look at it?
How do we test it?
How is the data sent?
What is PTP?
How do we control it?
What is NMOS?
What are the standards involved?

These questions, and more, are covered in this webinar.

Steve Holmes from Lader Us details the IP relevant basics starting with the motivations: weight, cost, scale, density, and independent essences. We can then move on to the next questions covering RTP itself and how 2022-6 was built upon it. SMPTE ST 2022-6 splits up a regular SDI signal into sections and encapsulates them, uncompressed. This is one big difference from SMPTE ST 2110 where all essences are sent separately. For some, this is not a benefit, but for general broadcast workflows, it can sometimes be tricky getting them into alignment and some workflows are aimed at delivering an incoming bundle of PIDs so being able to separate them is a backward step.

With this groundwork laid, Steve explains how seamless redundancy works with SMPTE 2022-7 going on to then describe the difficulty of keeping jitter low and the importance of sender profiles in ST 2110. Steve finishes this section with a discussion of NMOS specifications such as IS-05 and IS-06. The session ends with a Q&A.

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Speaker

Steve Holmes
Freelance consultant

Video: SRT Protocol Overview

Posted on 14th August 2020 by Russell Trafford-Jones

SRT’s ability to make lossy networks seem like perfect video circuits is increasingly well known, testified to by the SRT Alliance having just surpassed 400 member companies. But this isn’t your average ‘overview’, it dispenses with the technology introductions and goes straight into the detail so is ideal for people who already know the basics and want some deeper knowledge plus a look at the new features to come.

For those wanting an introduction, this article What is SRT? is a good starter which also links to two other intro videos. But today we’re going to join Haivision’s Maxim Sharabayko to look below the surface of SRT.

Maxim starts by introducing the open-source Git repository and the open-source integrations available before heading into the feature matrix. This shows what is and isn’t in SRT. We see that on top of ARQ, it has FEC, encryption, stream multiplexing and, soon, connection bonding. Addressing the major feature areas one by one, we start with connectivity.

SRT has two modes to establish a connection which Maixm shows on handshake diagrams. We can see that establishment need only take 2x round trips so is quick to establish. This allows Maxim to show how firewall traversal is accomplished, though NAT traversal is not yet implemented.

Next on the list of topics is access control whereby we need to ensure that only authorised users can gain access. This is achieved using the Stream ID field within SRT control packets which can contain up to 512 characters meaning it can be used to transfer usernames, passwords (in the form of keys) and requests. Maxim then explains the AES PSK encryption function and discusses the potential implementation of TLS and DTLS.

Content delivery is next under the magnifying glass starting with the structure of SRT packets and the difference between the two types: Data and Control, the former being restricted to only containing payload or FEC data. Maxim covers the positive acknowledgement which is contained with SRT with the range of received packets being acknowledged every 10ms and, where 64 packets come in less than 10ms, a low-overhead acknowledgement being sent for each group of 64 data packets. But of course, it’s the NAK packets which are the most important part of the protocol. Maxim explains they are able to send back one sequence number or a range of lost packets and talks about when they are sent. We see how this then fits into the Timestamp Based Packet Delivery (TSBPD) mechanism which itself is a feature of SRT which delivers packets to the receiver with the same timing as they arrived at the sender. The last thing we look at in the section is a worked example of Too-Late Packet Drop which explains when and why packets are dropped.

ARQ isn’t the only recovery mechanism in SRT, it also provides FEC and, soon, channel bonding. FEC’s can be useful but do have downsides which should be understood. There is a permanent bandwidth overhead, even when the circuit is working well, and a further latency is needed in order to generate the necessary recovery packets. Bonding allows you to stream the same stream over more than one circuit and use data from circuit B to fill in any gaps in circuit A, this technique is used in SMPTE ST 2022-7. Connection bonding, though, can also be used with multiple connections at once and having dynamic balancing across them. Maxim sums up the pros and cons of the different techniques in the table below.

Pros and cons of different packet recovery techniques. Source: Haivision

The talk finishes with a look at stream multiplexing, congestion control and ways in which you can use the SRT statistics which are constantly updated to manage your connectivity.

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Speakers

Maxim Sharabayko
Senior Software Developer,
Havision

Video: ST 2110 Testing Fundamentals

Posted on 31st July 2020 by Russell Trafford-Jones

When you’ve chosen to go IP in your facility using ST 2110, you’ll need to know how to verify it’s working correctly, how to diagnose problems and have the right tools available. Vendors participate in several interop tests a year, so we can learn from how they set up their tests and the best practices they develop.

In this talk, Jean Lapierre explains what to test for and the types of things that typically go wrong in ST 2110 systems with PTP. Jean starts by talking about the parts of 2110 which are tested and the network and timing infrastructure which forms the basis of the testing. He then starts to go through problems to look for in deployments.

Jean talks about testing that IGMPv3 multicasts can be joined and then looks at checking the validity of SDP files which can be done by visual inspection and also SDPoker. A visual inspection is still important because whilst SDPoker checks the syntax, there can be basic issues in the content. 2022-7 testing is next. The simplest test is to turn one path off and check for disturbances, but this should be followed up by using a network emulator to deliver a variety of different types of errors of varying magnitudes to ensure there are no edge cases.

ST 2110 uses PTP for timing so, naturally, the timing system also needs to be tested. PTP is a bi-directional system for providing time to all parts of the network instead of a simple waterfall distribution of a centrally created time signal like black and burst. Whilst this system needs monitoring during normal operation, it’s important to check for proper grandmaster failover of your equipment.

PTP is also important when doing 2110 PCAPs in order to have accurate timing and to enable analysis with the EBU’s LIST project. Jean gives some guidelines on using and installing LIST and finishes his talk outlining some of the difficulties he has faced, providing tips on what to look out for.

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Speakers

Jean Lapierre
Senior Director of Engineering,
Matrox

Video: Case Study on a Large Scale Distributed ST 2110 Deployment

Posted on 20th July 2020 by Russell Trafford-Jones

We’re “past the early-adopter stage” of SMPTE 2110, notes Andy Rayner from Nevion as he introduces this case study of a multi-national broadcaster who’s created a 2110-based live production network spanning ten countries.

This isn’t the first IP project that Nevion have worked on, but it’s doubtless the biggest to date. And it’s in the context of these projects that Andy says he’s seen the maturing of the IP market in terms of how broadcasters want to use it and, to an extent, the solutions on the market.

Fully engaging with the benefits of IP drives the demand for scale as people are freer to define a workflow that works best for the business without the constraints of staying within one facility. Part of the point of this whole project is to centralise all the equipment in two, shared, facilities with everyone working remotely. This isn’t remote production of an individual show, this is remote production of whole buildings.

SMPTE ST-2110, famously, sends all essences separately so where an 1024×1024 SDI router might have carried 70% of the media between two locations, we’re now seeing tens of thousands of streams. In fact, the project as a whole is managing in the order of 100,000 connections.

With so many connections, many of which are linked, manual management isn’t practical. The only sensible way to manage them is through an abstraction layer. For instance, if you abstract the IP connections from the control, you can still have a panel for an engineer or operator which says ‘Playout Server O/P 3’ which allow you to route it with a button that says ‘Prod Mon 2’. Behind the scenes, that may have to make 18 connections across 5 separate switches.

This orchestration is possible using SDN – Software Defined Networking – where router decisions are actually taken away from the routers/switches. The problem is that if a switch has to decide how to send some traffic, all it can do is look at its small part of the network and do its best. SDN allows you to have a controller, or orchestrator, which understands the network as a whole and can make much more efficient decisions. For instance, it can make absolutely sure that ST 2022-7 traffic is routed separately by diverse paths. It can do bandwidth calculations to stop bandwidths from being oversubscribed.

Whilst the network is, indeed, based on SMPTE ST 2110, one of the key enablers is JPEG XS for international links. JPEG XS provides a similar compression level to JPEG 2000 but with much less latency. The encode itself requires less than 1ms of latency, unlike JPEG 2000’s 60ms. Whilst 60ms may seem small, when a video needs to move 4 or even 10 times as part of a production workflow, it soon adds up to a latency that humans can’t work with. JPEG XS promises to allow such international production to feel responsive and natural. Making this possible was the extension of SMPTE ST 2110, for the first time, to allow carriage of compressed video in ST 2110-22.

Andy finishes his overview of this uniquely large case study talking about conversion between types of audio, operating SDN with IGMP multicast islands, and NMOS Control. In fact, it’s NMOS which the answer to the final question asking what the biggest challenge is in putting this type of project together. Clearly, in a project of this magnitude, there are challenges around every corner, but problems due to quantity can be measured and managed. Andy points to NMOS adoption with manufacturers still needing to be pushed higher whilst he lays down the challenge to AMWA to develop NMOS further so that it’s extended to describe more aspects of the equipment – to date, there are not enough data points.

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Speakers