Mobile operators and regulators are showing interest in mandating non GNSS-based solutions to implement timing synch across their networks, according to Net Insight, one provider of timing and synch technology that does not rely on satellite clocks.
Net Insight, of course, could be expected to take that view, but it is certainly clear that relying on GPS and GNSSS has become more risky of late.
Financial Times analysis, reported this week, found that there has been an increase in military jamming and spoofing of GNSS services, mainly to target drone and other military navigation systems. The report said, “Almost 40 million people lived in areas with unreliable GPS signals for at least half of the past six months, according to Financial Times analysis of data from the tracking service Flightradar24. This includes Turkey’s capital Ankara, where its armed forces are based, stretches of the Black Sea coastline, Egypt’s Sinai peninsula, several of Iraq’s biggest cities and war-torn Myanmar’s borders. Strong interference — causing issues for at least a quarter of the time — has also affected areas with a combined population of 110mn, including cities with military facilities such as St Petersburg in Russia, Lahore in Pakistan and Beirut, Lebanon.”
Much of the FT article concentrated on the impact of this on commercial airlines, but if GNSS is to become viewed as unreliable or too vulnerable to mailcious actions, then that will also have a major impact on how timing is sychronised across mobile networks.
When Turk Telecom was rolling out its 5G network, it too had a problem. Its ability to provide time synch, so crucial in 5G TDD networks, was threatened by the fact that there was a lot of GPS interference, driven by the Syrian war, affecting its territories. It approached Net Insight for a solution and in 2022 said it was the first operator to roll out a network based on Net Insight’s non-GNSS overlay solution.
Most operators can put PTP in the core, where they have lots of fibre. In the RAN for 5G, fronthaul switches have PTP and are very well suited for any local or regional setting. The problem typically lies in the aggregation layer
Net Insight Group CTO Per Lindgren said, “With Turk Telecom they said 30% of their infrastructure was PTP enabled and all the others they would need to replace, which was about 100,000 line cards. They said that would be too complex and that our solution would be much better. So we did it using our media orientated products and it works really well. in fact they had a number of outages where it became their primary synch for all their mobile services.”
There is a very well established grouping of Ethernet and computing standards known as Precision Time Protocol – IEEE 1588 – that has protocols specifically to provide varieties of non-GNSS synch in telecom networks. This is the protocol that Grandmaster clock providers such as OscilloQuartz and Microchip provide to the market. But Net Insight’s argument is that this approach relies on expensive or complex hardware upgrades for all elements that sit within the timing path. By acting as a virtual overlay between timing nodes on the network, Net Insight’s solution takes away the need for every intermediate node to support PTP. And it can also support providers who are leasing capacity.
Net Insight’s Zyntai TimeNode receives synchronisation from a source in the network, typically a PTP signal (Precision Time Protocol, G.8275.1 Full Timing Support). The TimeNode processes and converts the sync signal, enabling its distribution across network areas and multiple hops. As the signal is distributed through the network, another TimeNode located farther out to the edge receives the signal and converts it back to e.g. PTP for distribution to various endpoints, such as radio sites.
Lindgren told TMN, “Most operators can put PTP in the core, where they have lots of fibre. In the RAN for 5G, fronthaul switches have PTP and are very well suited for any local or regional setting. The problem typically lies in the aggregation layer, because that’s were there is a lot of equipment from different vendors and it becomes complex to make this fully PTP-enabled. You need hardware support in every line card to achieve the accuracy requirements – end to end it’s 1.5 micro seconds.”
“What we do is set up a virtual channel and send time as a service, like an IP service, instead of having to reply on hardware support. Typically operators will put a Grandmaster for a region, then put a GPS receiver on the aggregation site, and in this way you get lots of local islands with PTP. The problem is if GPS goes down, then you will lose performance. With our solution you can still keep the Grandmaster if you want, but we provide a backup over non-PTP enabled infrastructure so you can have a GPS independent nationwide infrastructure.”
Lindgren said the main challenge of this architecture is to allow for jitter and congestion on the IP connection.
“If you are limited to 64 or 128 packets per second, sending that over a congested network you will start to get delay and bad statistics. What we do is since we are not constrained on hardware, set up an MPLS channel for 1 or 10 or 20Mbps, meaning that we can send thousands instead a of hundred packets and that gives much better stats, combining that with smart filtering and asymmetry detection algorithms.
“We also use some smart routing. PTP only looks at the shortest path, but that does not mean that is the best path from a synch perspective. We measure quality between our time nodes, and are able to use all available links, getting better stats and more resilience.”
As well as Turk Telecom, Net Insight counts Three Sweden (which has a lot of leased capacity) as a customer, along with “large” operators in Canada and the USA that it cannot name. In Sweden the regulator has said all 5G TDD spectrum operators need a GNSS independent backup solution, and Net Insight is obviously interested in encouraging other regulators to look at the Swedish model.
Another fertile area could be critical and Government networks and services, where resilience and GNSS independence are both important.
“Right now.” Lindgren said, “We are still very much evangelists; operators don’t know it’s possible to do this – delivering PTP in a way that enables or overcomes non-PTP infrastructure or capacity.”
