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In December 2023, it was announced that ITU has started a working item to begin the standardization of a new synchronization technology, building on Net Insight’s Precision TimeNet (PTN) technology. We asked Magnus Danielson, our Senior Sync Technologist, what this means.
The problem is around synchronization of mobile networks, or actually, it could also be a power grid network, but let’s assume here a mobile network. In order for a network to function, it needs proper synchronization all the way out to the base stations at the radio sites. The normal way to get a sync is to take it down to radio sites from a GNSS signal, like GPS. There are however issues with GNSS. Because the signal is coming from space, it’s very weak and can easily be interrupted by interference, or even jammed or spoofed by someone. Some radio sites may also have problems receiving a GNSS signal. For these reasons it’s good to have a network-based synchronization, either instead of GNSS or as a backup solution in case GNSS goes down. This solution traditionally uses a protocol called IEEE 1588 Precision Time Protocol, or PTP, where the sync is sent through the network. However, PTP comes with its own problems, and that is what we will now address in the new standardization group.
Well, there is nothing wrong with PTP, it’s just that it was never designed for wide area networks. If we look at one of the PTP profiles, FTS or Full Timing Support, also known as ITU-T G.8275.1, it requires time support in every node it passes through, and it will not work over leased capacity, which is being used by a majority of mobile operators today. This is not the case with the other PTP profile PTS, Partial Timing Support, or ITU-T G.8275.2, which doesn’t require hardware support everywhere and works also over leased capacity. On the downside though, it’s not as precise as FTS. It was good enough for 3G and 4G, but in 5G the requirements are more stringent, and PTS will not be sufficient. Or, it may work well in a lab environment, but not in a real network environment. One would therefore be required to use FTS which again, doesn’t work if there is leased capacity, and it will require FTS hardware support throughout the whole network.
In this standardization, the aim is to have an enhanced technology that enables sync transmission on top of the existing network without hardware requirements and even if it’s leased capacity, while still being adequate for 5G. Basically, you can say it should be PTS with the performance of FTS. It may sound straight-forward, but there are challenges like packet delay variation and asymmetries that need to be managed well in order for this to work. When it does work though, it’s a game changer for how sync is distributed.
Transmitting time sync over wide area networks is a challenge experienced by many industries, and therefore it’s important that ITU takes this up to apply a universal solution. For mobile operators, there are benefits of using a standardized technology since it guarantees interoperability. For Net Insight, who already use Precision TimeNet that this technology will build on, it would mean we can send our sync directly into a base station or maybe even directly to a user device, like a professional camera, over the 5G air interface. Now we need to convert the sync at the end-point to traditional PTP and then transmit into a base station. So standardizing, I would say, is one of those cases where everyone wins in the end.
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