Video: PTP Over Wan

Work is ongoing in the IPMX project to reduce SMPTE ST 2110’s reliance on PTP, but the reality is that PTP is currently necessary for digital audio systems as well as for most ST 2110 workflows. There are certainly challenges in deploying PTP from an architectural standpoint with some established best practices, but these are only useful when you have the PTP signal itself. For the times when you don’t have a local PTP clock, delivery over a WAN may be your only solution. With PTP’s standards not written with a WAN in mind, can this be done and what are the problems?



Meinberg’s Daniel Boldt describes the work he’s been involved with in testing PTP delivery over Wide Area Networks (WANs) which are known for having higher, more variable latency than Local Area Networks (LANs) which are usually better managed with low latency which users can interrogate to understand exactly how traffic is moving and configure it to behave as needed. One aspect that Daniel focuses on today is Packet Delay Variation (PDV) which is a term that describes the difference in time between the packets which arrive the soonest and those that arrive last. For accurate timing, we would prefer overall latency to be very low and for each packet to take the same amount of time to arrive. In real networks, this isn’t what happens as there are queuing delays in network equipment depending on how busy the device is both in general and on the specific port being used for the traffic. These delays vary from second to second as well as throughout the day. Asymmetry can develop between send and receive paths meaning packets in one direction take half the time to arrive than those in the other. Finally, path switching can create sudden step changes in path latency.

Boundary Clocks and Transparent Clocks can resolve some of this as they take in to account the delays through switches. Over the internet, however, these just don’t exist so your options are to either build your own WAN using dark fibre or to deal with these problems at the remote site. If you are able to have a clock at the remote site, you could use the local GNSS-locked clock with the WAN as a backup feed to help when GNSS reception isn’t available. But when that’s not possible due to cost, space or inability to rack an antenna, something more clever is needed.

Lucky Packet Filter
Source: Meinberg

The ‘lucky packet filter’ is a way of cleaning up the timing packets. Typically, PTP timing packets will arrive between 8 and 16 times a second, each one stamped with the time it was sent. When received, its propagation time can be easily calculated and put in a buffer. The filter can look at the statistics then throw away any packets which took a long time to arrive. Effectively this helps select for those packets which had the least interference through the network. Packets which got held a long time are not useful for calculating the typical propagation time of packets so it makes sense to discard them. In a three-day-long test, Meinberg used a higher transmit rate of 64 packets per second saw the filter reduced jitter from 100 microseconds to an offset variation of 5 microseconds. When this was fed into a high-quality clock filter, the final jitter was only 300ns which was well within the 500ns requirement of ST 2059-2 used for SMPTE ST 2110.

Daniel concludes the video by showing the results of a test with WDR where a PTP Slave gateway device was fed with 16 packets a second from a master PTP switch over the WAN. The lucky packet filter produced a timing signal within 500ns and after going through an asymmetry step detection process in the clock produced a signal with an accuracy of no more than 100ns.

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Daniel Boldt Daniel Boldt

Video: Proper Network Designs and Considerations for SMPTE ST-2110

Networks from SMPTE ST 2110 systems can be fairly simple, but the simplicity achieved hides a whole heap of careful considerations. By asking the right questions at the outset, a flexible, scalable network can be built with relative ease.

“No two networks are the same” cautions Robert Welch from Arista as he introduces the questions he asks at the beginning of the designs for a network to carry professional media such as uncompressed audio and video. His thinking focusses on the network interfaces (NICs) of the devices: How many are there? Which receive PTP? Which are for management and how do you want out-of-band/ILO access managed? All of these answers then feed into the workflows that are needed influencing how the rest of the network is created. The philosophy is to work backwards from the end-nodes that receive the network traffic.

Robert then shows how these answers influence the different networks at play. For resilience, it’s common to have two separate networks at work sending the same media to each end node. Each node then uses ST 2022-7 to find the packets it needs from both networks. This isn’t always possible as there are some devices which only have one interface or simply don’t have -7 support. Sometimes equipment has two management interfaces, so that can feed into the network design.

PTP is an essential service for professional media networks, so Robert discusses some aspects of implementation. When you have two networks delivering the same media simultaneously, they will both need PTP. For resilience, a network should operate with at least two Grand Masters – and usually, two is the best number. Ideally, your two media networks will have no connection between them except for PTP whereby the amber network can benefit from the PTP from the blue network’s grandmaster. Robert explains how to make this link a pure PTP-only link, stopping it from leaking other information between networks.

Multicast is a vital technology for 2110 media production, so Robert looks at its incarnation at both layer 2 and layer 3. With layer 2, multicast is handled using multicast MAC addresses. It works well with snooping and a querier except when it comes to scaling up to a large network or when using a number of switches. Robert explains that this because all multicast traffic needs to be sent through the rendez-vous point. If you would like more detail on this, check out Arista’s Gerard Phillips’ talk on network architecture.

Looking at JT-NM TR-1001, the guidelines outlining the best practices for deploying 2110 and associated technologies, Robert explains that multicast routing at layer 3 works much increases stability, enables resiliency and scalability. He also takes a close look at the difference between ‘all source’ multicasting supported by IGMP version 2 and the ability to filter for only specific sources using IGMP version 3.

Finishing off, Robert talks about the difficulties in scaling PTP since all the replies/requests go into the same multicast group which means that as the network scales, so does the traffic on that multicast group. This can be a problem for lower-end gear which needs to process and reject a lot of traffic.

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Robert Welch Robert Welch
Technical Solutions Lead
Arista Networks

Video: Fibre Optics in the LAN and Data Centre

Fibres are the lifeblood of the major infrastructure broadcasters have today. But do you remember your SC from your LC connectors? Do you know which cable types are allowed in permenant installations? Did you know you can damage connectors by mating the wrong fibre endings? For some buildings, there’s only one fibre and connector type making patch cable selection all the easier. However there are always exceptions and when it comes to ordering more, do you know what to look out for to get exactly the right ones?

This video from Lowell Vanderpool takes a swift, but comprehensive, look at fibre types, connector types, light budget, ferrule types and SFPs. Delving straight in, Lowell quickly establishes the key differences between single-mode and multi-mode fibre with the latter using wider-diameter fibres. This keeps the costs down, but compared to single-mode fibre can’t transmit as far. Due to their cost, multi-mode fibres are common within the datacentre so Lowell takes us through the multimode cable types from the legacy OM1 to the latest OM5 cable.

OM1 cable was rated for 1GB, but the currently used OM3 and 4 fibre types can carry 10Gb up to 550m. Multimode fibres are typically colour-coded with OM3 an 4 being ‘aqua’. OM5 is the latest cable to standardised which can support Short Wavelength Division Multiplexing (SWDM) whereby 4 frequencies are sent down the same fibre giving an overall bandwidth of 10Gbx4 = 40GbE. For longer-distance, the yellow OS1 and, more recently, OS2 fibre types will achieve up to 10km distance.

Lowell explains that whilst 10km is far enough for many inter-building links, the distance quoted is a maximum which excludes the losses incurred as light leaves one fibre and enters another at connection points. Lowell has an excellent graphic which shows the overall light ‘budget’, how each connector represents a major drop in signal and how each interface will also reflect small amounts of the signal back up the fibre.

Having dealt with the inside of the cables, Lowell brings up the important topic of the outer jacket. All cables have different options for the outer jacket (for electrical cables, usually called insulation). These outer jackets allow for varying amounts of flexibility, water-tightness and armouring. Sometimes forgotten is that they have also got different properties in the event of fire. Depending on where a cable is, there are different rules on how flame retardant the cable can be. For instance, in the plenum of a room (false ceiling/wall) and a riser there are different requirements than patching between racks. Some areas keeping smoke low is important, in others ensuring fire doesn’t travel between areas is the aim so Lowell cautions us to check the local regulations.

The final part of the video covers connectors, ferrules and SFPs. Connectors come in many types, although as Lowell points out, LC is most popular in server rooms. LC connectors can come in pairs, locked together and called ‘duplex’ or individually, known as ‘simplex’. Lowell looks at pretty much every type of connector you might encounter from the legacy, metal bayonet & screw connectors (FC, ST) to the low-insertion loss, capped EC2000 connector for single mode cables and popular for telco applications. Lowell gives a close look at MPT and MPO connectors which combine 1×12 or 2×12 fibres into one connector making for a very high capacity connection. We also see how the fibres can be broken out individually at the other end into a breakout cassette.

The white, protruding end to a connector is called the ferrule and contains the fibre in the centre. The solid surround is shaped and polished to minimise gaps between the two fibre ends and to fully align the fibre ends themselves. Any errors will lead to loss of light due to it spilling out of the fibre or to excessive light bouncing back down the cable. Lowell highlights the existence of angled ferrules which will cause damage if mated with flat connectors.

The video finishes with a detailed talk through the make up of an SFP (Small Form-factor Pluggable) transceiver looking and what is going on inside. We see how the incoming data needs to be serialised, how heat dissipation and optical lanes are handled plus how that affects the cost.

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Lowell Vanderpool Lowell Vanderpool
Technical Trainger,
Lowell Vanderpool YouTube Channel

Video: IP Media Networks for Live Production

Building and controlling a network for SMPTE ST 2110 go hand in hand when it comes to planning an installation. As ST 2110 delivers all media essences separately, networks can easily end up carrying tens of thousands of flows emphasising the need for efficient network design and having a full understanding of the paths your media are using.

This video is co-presented by Nevion and Arista and starts by observing that the traditional difference between a LAN and WAN is being eroded leading as WANs get faster and better, we find that we can now deliver multi-location broadcast facilities which act similarly to if everything was co-located. Moreover, introduces Martin Walbum Media Function virtualisation which is enabled by network-connected equipment allowing for shared processing and shared control. For instance, it’s now possible to house all equipment in a datacentre and allow this to be used remotely maximising the utilisation of the equipment allowing a broadcaster to maximise the value of its purchases and minimise costs.

Arista’s Gerard Phillips takes a look at SDI systems to understand how we expect IP systems to behave and what we expect them to do. The system needs to deliver high throughput, instantaneous switching with low latency and no tolerance for failure. In order to do this, not only do we need to get the right software but to deliver the resilience we need, the network needs the correct architecture. Gerard takes us through the different options starting with a typical, flat, layer 2 networks and working up to leaf and spine along with a treatment of red, blue and purple networks.

Gerard recently did a deep dive on network design for live production for the IET. Take a look for much more detail on how to architect a network for uncompressed media.

Martin then looks at the need for orchestration. Broadcasters expect to deliver systems with, preferably, no downtime. As such, we’ve seen that network elements are typically duplicated as is the traffic which is delivered over two paths and SMPTE ST 2022-7. If you want to take something out of use for planned maintenance, it’s best to do that in a planned, ordered, way meaning you migrate flows away from it until it’s no longer in-circuit. Software-Defined Networks (SDNs), do exactly that. Martin walks us through the pros and cons of managing your network with IGMP and SDN. Gerard’s previous talk also looks at this in detail.

The video finishes with a look at which Arista switches can be used for media and a look at how Arista and Nevion implemented an ST 2110 network at Swiss broadcaster, tpc. This case study is presented in longer form in this video from the IP Showcase.

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Gerard Phillips Gerard Phillips
Systems Engineer,
Martin Walbum Martin Walbum
Senior Vice President of Solution Strategy,