GCCG Archives – The Broadcast Knowledge

Is SMPTE ST 2110 suitable for inter-site connectivity over the WAN? ST 2110 is putting the early adopter phase behind it with more and more installations and OB vans bringing 2110 into daily use yet most sites works independently. The market is already seeing a strong need to continue to derive cost and efficiency savings from the infrastructure in the larger broadcasters who have multiple facilities spread around one country or even in many. To do this, though there are a number of challenges still to be overcome and moving a large number of essence flows long distances and between PTP time domains is one of them.

Nevion’s Andy Rayner is chair of the VSF Activity Group looking into transporting SMPTE ST 2110 over WAN and is here to give an update on the achievements of the past two years. He underlines that the aim of the ST 2110 over WAN activity group is to detail how to securely share media and control between facilities. The key scenarios being considered are 1) special events/remote production/REMIs. 2) Facility sharing within a company. 3) Sharing facilities between companies. He also notes that there is a significant cross over in this work and that happening in the Ground-Cloud-Cloud-Ground (GCCG) activity group which is also co-chairs.

The group has produced drafts of two documents under TR-09. The first, TR-09-01 discusses the data plane and has been largely discussed previously. It defines data protection methods as the standard 2022-7 which uses multiple, identical, flows to deal with packet loss and also a constrained version of FEC standard ST 2022-5 which provides a low-latency FEC for the protection of individual data streams.

GRE trunking over RTP was previously announced as the recommended way to move traffic between sites, though Andy notes that no one aspect of the document is mandatory. The benefits of using a trunk are that all traffic is routed down the same path which helps keep the propagation delay for each essence identical, bitrate is kept high for efficient application of FEC, the workflow and IT requirements are simpler and finally, the trunk has now been specified so that it can transparently carry ethernet headers between locations.

Andy also introduces TR-09-02 which talks about sharing of control. The control plane in any facility is not specified and doesn’t have to be NMOS. However NMOS specifications such IS-04 and IS-05 are the basis chosen for control sharing. Andy describes the control as providing a constrained NMOS interface between autonomous locations and discusses how it makes available resources and metadata to the other location and how that location then has the choice of whether or not to consume the advertised media and control. This allows facilities to pick and choose what is shared.

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Speakers

Andy Rayner
Chief Technologist, Nevion,
Chair, WAN IP Activity Group, VSF

Timing is both everything and nothing. Although much fuss is made of timing, often it’s not important. But when it is important, it can be absolutely critical. Helping us navigate through the broadcast chains varying dependence on a central co-ordinated time source is Nevion’s Andy Rayner in this talk at the VSF’s VidTrans21. When it comes down to it, you need time for coordination. In the 1840s, the UK introduced ‘Railway time’ bringing each station’s clock into line with GMT to coordinate people and trains.

For broadcast, working with multiple signals in a low-latency workflow is the time we’re most likely to need synchronisation such as in a vision or audio mixer. Andy shows us some of the original television technology where the camera had to be directly synchronised to the display. This is the era timing came from, built on by analogue video and RF transmission systems which had components whose timing relied on those earlier in the chain. Andy brings us into the digital world reminding us of the ever-useful blanking areas of the video raster which we packed with non-video data. Now, as many people move to SMPTE’s ST 2110 there is still a timing legacy as we see that some devices are still generating data with gaps where the blanking of the video would be even though 2110 has no blanking. This means we have to have timing modes for linear and non-linear delivery of video.

In ST 2110 every packet is marked with a reduced resolution timestamp from PTP, the Precision Time Protocol (or See all our PTP articles). This allows highly accurate alignment of essences when bringing them together as even a slight offset between audios can create comb filters and destroy the sound. The idea of the PTP timestamp is to stamp the time the source was acquired. But Andy laments that in ST 2110 it’s hard to keep this timestamp since interim functions (e.g. graphics generators) may restamp the PTP breaking the association.

Taking a step back, though, there are delays now up to a minute later delivering content to the home. Which underlines that relative timing is what’s most important. A lesson learnt many years back when VR/AR was first being used in studios where whole sections of the gallery were running several frames delayed to the rest of the facility to account for the processing delay. Today this is more common as is remote production which takes this fixed time offset to the next level. Andy highlights NMOS IS-07 which allows you timestamp button presses and other tally info allowing this type of time-offset working to succeed.

The talk finishes by talking about the work of the GCCG Activity Group at the VSF of which Andy is the co-chair. This group is looking at how to get essences into and out of the cloud. Andy spends some time talking about the tests done to date and the fact that PTP doesn’t exist in the cloud (it may be available for select customers). In fact you may have live with NTP-derived time. Dealing with this is still a lively discussion in progress and Andy is welcoming participants.

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Speakers