Video: PTP in Virtualized Media Environment

How do we reconcile the tension between the continual move towards virtualisation, microservices and docker-like deployments and the requirements of SMPTE 2110 to have highly precise timing so it can synchronise the video, audio and other essence streams? Virtualisation adds fluidity in to computing so it can share a single set of resources amongst many virtual computers yet PTP, the Precision Time Protocol a successor to NTP, requires close to nano-second precision in its timestamps.

Alex Vainman from Mellanox explains how to make PTP work in these cases and brings along a case study to boot. Starting with a little overview and a glossary, Alex explains the parts of the virtual machine and the environment in which it sits. There’s the physical layer, the hypervisor as well as the virtual machines themselves – each virtual machine being it’s own self-contained computer sitting on a shared computer. Hardware must be shared between, often, many different computers. However some devices aren’t intended to be shared. Take, for instance, a dongle that contains a licence for software. This should clearly be only owned by one computer therefore there is a ‘direct’ mode which means that it is only seen by one computer. Alex goes on to explain the different virtualisation I/O modes which allow devices which can be shared, a printer, storage or CPU for instance need to have access computers may need to wait until they have access to the device to enable sharing. Waiting, of course, is not good for a precision time protocol.

In order to understand the impact that virtualisation might have, Alex details the accuracy and other requirements necessary to have PTP working well enough to support SMPTE 2110 workflows. Although PTP is an IEEE standard, this is just a standard to define how to establish accurate time. It doesn’t help us understand how to phase and bring together media signals without SMPTE ST 2059-1 and -2 which provide the standard of the incoming PTP signal and the way by which we can compare timing and media signals (more info here.) All important is to understand how PTP can actually determine the accurate time given that we know every single message has an unknown propagation delay. By exchanging messages, Alex shows, it is quite practical to measure the delays involved and bring them into the time calculation.

We now have enough information to see why the increased jitter of VM-based systems is going to cause a problem as there are non-deterministic factors such as contention and traffic load to consider as well as factors such as software overhead. Alex takes us through the different options of getting PTP well synchronised in a variety of different VM architectures. The first takes the host clock and ensures that is synchronised to PTP. Using a dedicated PTP library within the VM, this then speaks to the host clock and synchronises the VM OS clock providing very accurate timing. Another, where hardware support in the VM’s hardware for PTP isn’t present, is to have NICs with dedicated PTP support which can directly support the VM OSes maintaining their own PTP clock. The major downside here is that each OS will have to make their own PTP calls creating more load on the PTP system as opposed to the previous architecture whereby the host clock of the VM was the only clock synchronising to the system PTP and therefore there was only ever one set of PTP messages no matter how many VMs were being supported.

To finish off, Alex explains how Windows VMs can be supported – for now through third-party software – and summarises the ways in which we can, in fact, create PTP ecosystems that incorporate virtual machines.

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Alex Vainman Alex Vainman
Senior Staff Engineer,
Mellanox Technologies

Video: Timing Tails & Buffers

Timing and synchronisation have always been a fundamental aspect of TV and as we move to IP, we see that timing is just as important. Whilst there are digital workflows that don’t need to be synchronised against each other, many do such as studio productions. However, as we see in this talk from The Broadcast Bridge’s Tony Orme, IP networks make timing all the more variable and accounting for this is key to success.

To start with Tony looks at the way the OBs, also known as REMIs, are moving to IP and need a timing plane across all of the different parts of production. We see how traditionally synchronisation is needed and the effect of timing problems not only in missed data but also with all essences being sent separately synchronisation problems between them can easily creep in.

When it comes to IP timing itself, Tony explains how PTP is used to record the capture time of the media/essences and distribute through the system. Looking at the data on the wire and the interval between that and the last will show a distribution of, hopefully, a few microseconds variation. This variation gives rise to jitter which is a varying delay in data arrival. The larger the spread, the more difficult it will be to recover data. To examine this more closely, Tony looks at the reasons for and the impacts of congestion, jitter, reordering of data.

Bursting, to make one of these as an example, is a much overlooked issue on networks. While it can occur in many scenarios without any undue problems, microbusting can be a major issue and one that you need to look for to find. This surrounds the issue of how you decide that a data flow is, say, 500Mbps. If you had an encoder which sent data at 1Gbps for 5 minutes and no data for 5 minutes, then over the 10 minute window, the average bitrate would have been 500Mbps. This clearly isn’t a 500Mbps encoder, but how narrow do you need to have your measurement window to be happy it is, indeed, 500Mbps by all reasonable definitions? Do you need to measure it over 1 second, 1 millisecond? Behind microbursting is the tendency of computers to send whatever data they have as quickly as possible; if a computer has a 10Gbe NIC, then it will send at 10Gbps. What video receivers actually need is well spaced packets which always come a set time apart.

Buffers a necessary for IP transmission, in fact within a computer there are many buffers. So using and understanding buffers is very important. Tony takes us through the thought process of considering what buffers are and why we need them. With this groundwork laid, understanding their use and potential problems is easier and well illustrated in this talk. For instance, since there are buffers in many parts of the chain to send data from an application to a NIC and have it arrive at the destination, the best way to maximise the chances of having a deterministic delay in the Tx path is to insert PTP information almost at the point of egress in the NIC rather than in the application itself.

The talk concludes by looking at buffer fill models and the problems that come with streaming using TCP/IP rather then UDP/IP (or RTP). The latter being the most common.

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Tony Orme Tony Orme
The Broadcast Bridge

Video: NMOS and ST 2110 Pro AV Roadmap

ProAV and Broadcast should be best buddies, but only a relatively few companies sell into both. This is because there are legitimate differences in what we need. That being said, interoperability is a helpful end goal for any industry. Whilst proprietary solutions can help kickstart new technologies and be a positive disruptive force, standardisation is almost always beneficial to the industry in the medium to long term.

Whilst broadcast is happy to live with 4:2:2 colour subsampling in much of its workflow, then deliver in 4:2:0, this is often not an option for ProAV who need to take full 4:4:4 4K at 60fps and throw it on a monitor. Whilst 4:4:4 has, technically been possible over SDI for a while, adoption even in the broadcast market has been small.

There are many opportunities for both industries to learn from each other, but it’s hard to overstate the difference in approach of the SMPTE 2110 and NMOS approach to the problem of media over IP compared to the SDVoE model. The former relies on detailed documentation published publicly for anyone who is willing to buy the standard to implement in any way they see fit be that in software or hardware. The latter specifies a chip which has a documented API that does all of the heavy lifting with no option for self-implementation. The fact that the same chip is used everywhere provides the guarantee of interoperability.

One technology which has bridged the gap between ProAV and broadcast is NDI from Vizrt’s Newtek which uses the same binary software application wherever it’s implemented thus providing, like in SDVoE, the interoperability required. The same is true for SRT although they have just released their first draft for IETF standardisation.

In this talk, PESA CTO Scott Barella examines the many existing standards within ProAV and examines their needs such as HDCP. Whilst HDCP, the High-bandwidth Digital Content Protection mechanism, has often been grappled with by broadcasters, it is at least a standard. And it’s a standard that any vendor will have to deal with if they want their equipment to be widely used in the industry. Similarly the requirement for full-frame rate, full-colour UHD is not simply done within many boxes.

The use of PTP within SMPTE’s ST 2110 suite works perfectly in the studio, is arguably not necessary in much of ‘the cloud’ and is widely considered too complex for a ProAV environment. Scott explains that he has thoughts on how to simplify it to make it more practical and taking into account the different use cases.

Secondary interfaces are crucial in much ProAV whereby USB, RS 232 serial and GPI/GPO need to be transported along with the media. And whilst security and encryption are increasingly important for the broadcast industry as it comes to grips with the fact that all broadcasters are vulnerable to hacking attempts, their requirements are not as stringent as the military’s which drives a notable part of the ProAV market. All of these aspects are being considered as part of the ongoing work the Scott is involved with.

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Scott Barella Scott Barella
AIMS co-chair.

Video: Live Closed Captioning and Subtitling in SMPTE 2110 (update)

The SMPTE ST 2110-40 standard specifies the real-time, RTP transport of SMPTE ST 291-1 Ancillary Data packets. It allows creation of IP essence flows carrying the VANC data familiar to us from SDI (like AFD, closed captions or ad triggering), complementing the existing video and audio portions of the SMPTE ST 2110 suite.

This presentation, by Bill McLaughlin from EEG, is an updated tutorial on subtitling, closed captioning, and other ancillary data workflows using the ST 2110-40 standard. Topics include synchronization, merging of data from different sources and standards conversion.

Building on Bill’s previous presentation at the IP Showcase), this talk at NAB 2019 demonstrates a big increase in the number of vendors supporting ST 2110-40 standard. Previously a generic packet analyser like Wireshark with dissector was recommended for troubleshooting IP ancillary data. But now most leading multiviewer / analyser products can display captioning, subtitling and timecode from 2110-40 streams. At the recent “JT-NM Tested Program” event 29 products passed 2110-40 Reception Validation. Moreover, 27 products passed 2110-40 Transmitter Validation which mean that their output can be reconstructed into SDI video signals with appropriate timing and then decoded correctly.

Bill points out that ST 2110-40 is not really a new standard at this point, it only defines how to carry ancillary data from the traditional payloads over IP. Special care needs to be taken when different VANC data packets are concatenated in the IP domain. A lot of existing devices are simple ST 2110-40 receivers which would require a kind of VANC funnel to create a combined stream of all the relevant ancillary data, making sure that line numbers and packet types don’t conflict, especially when signals need to be converted back to SDI.

There is a new ST 2110-41 standard being developed for additional ancilary data which do not match up with ancillary data standardised in ST 291-1. Another idea discussed is to move away from SDI VANC data format and use a TTML track (Timed Text Markup Language – textual information associated with timing information) to carry ancillary information.

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Bill McLaughlin Bill McLaughlin
VP of Product Development