Video: Keeping Time with PTP

The audio world has been using PTP for years, but now there is renewed interest thanks to its inclusion in SMPTE ST 2110. Replacing the black and burst timing signal (and for those that used it, TLS), PTP changes the way we distribute time. B&B was a waterfall distribution, PTP is a bi-directional conversation which, as a system, needs to be monitored and should be actively maintained.

Michael Waidson from Telestream (who now own Tektronix) brings us the foundational basics of PTP as well as tips and tricks to troubleshoot your PTP system. He starts by explaining. the types of messages which are exchanged between the clock and the device as well as why all these different messages are necessary. We see that we can set the frequency at which the announce, sync and follow-up messages. The sync and follow-up messages actually contain the time. When a device receives one of these messages, it needs to respond with a ‘delay request’ in order to work out how much of a delay there is between it and the grand master clock. This will result in it receiving a delay response. On top of these basic messages, there is a periodic management message which can contain further information such as daylight savings time or drop-frame information.

Michael moves on to looking at troubleshooting highlighting the four main numbers to check: The domain value, grandmaster ID, message rates and the communication mode. PTP is a global standard used in many industries. To make PTP most useful to the broadcast industry, SMPTE ST 2059 defines values to use for message repetition (4 per second for announce messages, 8 for sync, delay request and delay response). ST 2059 also defines how devices can determine the phase of any broadcast signal for any given time which is the fundamental link needed to ensure all devices keep synchronicity.

Another good tip from Michael is if you see the grandmaster MAC changing between the grandmasters on the system, this indicates it’s no receiving any announce messages so is initiating the Best Master Clock Algorithm (BMCA) and trying the next grandmaster. Some PTP monitoring equipment including from Meinberg and from Telestream can show the phase lag of the PTP timing as well as the delay between the primary and secondary grandmaster – the lower the better.

A talk on PTP can’t avoid mentioning boundary clocks and transparent switches. Boundary clocks take on much of the two-way traffic in PTP protecting the grandmasters from having to speak directly to all the, potentially, thousands of devices. Transparent switches, simply update the time announcements with the delay for the message to move through the switch. Whilst this is useful in keeping the timing accurate, it provides no protection for the grandmasters. He finishes video ends with a look at how to check PTP messages on the switch.

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Speakers

Michael Waidson Michael Waidson
Application Engineer
Telestream (formerly Tektronix)

Video: Monolithic and Spine-Leaf Architectures

It’s hard to talk about SMPTE 2110 system design without hearing the term ‘spine and leaf’. It’s a fundamental decision that needs to be made early on in the project; how many switches will you use and how will they be interconnected? Deciding is not without accepting compromises, so what needs to be considered?

Chris Lapp from Diversified shares his experience in designing such systems. Monolithic design has a single switch at the centre of the network with everything connected directly to it. For redundancy, this is normally complemented by a separate, identical switch providing a second network. For networks which are likely to need to scale, monolithic designs can add a hurdle to expansion once they get full. Also, if there are many ‘low bandwidth’ devices, it may not be cost-effective to attach them. For instance, if your central switch has many 40Gbps ports, it’s a waste to use many to connect to 1Gbps devices such as audio endpoints.

The answer to these problems is spine and leaf. Chris explains that this is more resilient to failure and allows easy scaling whilst retaining a non-blocking network. These improvements come at a price, naturally. Firstly, it does cost more and secondly, there is. added complexity. In a large facility with endpoints spread out, spine and leaf may be the only sensible option. However, Chris explores a cheaper version of spine and leaf often called ‘hub and spoke’ or ‘hybrid’.

If you are interested in this topic, listen to last week’s video from Arista’s Gerard Philips which talked in more detail about network design covering the pros and cons of spine and leaf, control using IGMP and SDN, PTP design amongst other topics. Read more here.

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Speakers

Chris Lapp Chris Lapp
Project Engineer, SME Routing
Diversified
Wes Simpson Wes Simpson
President, Telcom Product Consulting
Owner, LearnIPVideo.com

Video: Case Study FIS Ski World Championship

There’s a lot to learn when it comes to implementing video over IP, so it’s healthy to stand back from the details and see a working system in use to understand how the theory becomes reality. There’s been a clear change in the tone of conversation at the IP Showcase over the years as we’ve shifted from ‘trust us, this could work’ to ‘this is what it looks like!’ That’s not to say there’s not plenty to be done, but this talk about an uncompressed 2110 remote production workflow is great example of how the benefits of IP are being realised by broadcasters.
Robert Erickson is with Grass Valley specialising in sports such as the FIS Alpine World Ski Championships which were in the city of Åre in Sweden some 600km from Stockholm where Sweden’s public broadcaster SVT is based. With 80 cameras at the championships to be remotely controlled over an uncompressed network, this was no small project. Robert explains the two locations were linked by a backbone of two 100Gbps circuits.

The principle behind SVT’s project was to implement a system which could be redeployed, wouldn’t alter the viewers’ experience and would reduce staff and equipment on site. Interestingly the director wanted to be on-site meaning that the production was then split between much of the staff being in Stockholm, which of course was where most of the equipment was, and Åre. The cameras were natively IP, so no converters were needed in the field.

Centralisation was the name of the game, based in Stockholm, producing an end-to-end IP chain. Network switching was provided by Arista which aggregated the feeds of the cameras and brought them to Stockholm where the CCUs were located. Robert highlights the benefits of this approach which include the use of COTS switches, scalability and indifference as to the circuits in use. We then have a look inside the DirectIP connection which is a 10gig ‘pipe’ carrying 2022-6 camera and return feeds along with control and talkback, replicating the functionality of a SMPTE fibre in IP.

To finish up, Robert talks about the return visions, including multivewers, which were sent back to Åre. A Nimbra setup was used to take advantage of a lower-bandwidth circuit using JPEG 2000 to send the vision back. In addition, it carried the data to connect the vision mixer/switcher at Åre with the switch at Stockholm. This was the only point at which noticeable latency was introduced to the tune of around 4 frames.

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Download the presentation
Speakers

Robert Erickson Robert Erickson
Strategic Account Manager Sports and Venues,
Grass Valley