Precise Time as a critical national service | NetInsight

How Sweden leads the way in solutions for GNSS independence

People and businesses across the entire economy rely on the availability of mobile communications. With IoT and M2M, this is further amplified. Sweden has developed one of the world’s leading time services to ensure national robustness and remove the dependencies from foreign impact on this critical national service. 

In this article, we cover some of the key players involved in developing the framework and technical solution for Sweden’s time service: PTS, the Swedish telecom regulator; Netnod, the neutral organization working to develop core technical infrastructure in Sweden; and Net Insight, inventor of the Precision TimeNet technology for network-based time distribution using existing infrastructure, including over leased lines.

For more than ten years, the Swedish regulator, PTS, has worked with a range of organizations and operators, including Netnod and Net Insight, to discuss the best way to deal with the vulnerabilities related to time services dependent on GNSS. This resulted in a mandate issued by PTS in 2021 that all Swedish 5G operators had to have a redundant time sync solution independent from GNSS. 

PTS has been working with a large-scale public/private cooperation since 2014 to ensure that Sweden has a robust, secure, and neutral national time service that all 5G operators could use for their time synchronization. 

To distribute the time from the national time reference out to the 5G radio access networks without GNSS support can be a challenge, since network-based time synchronization solutions can be both costly and complex in a nationwide rollout. Several Swedish operators in 5G and critical networks have chosen a new GNSS-independent network-based synchronization solution called Precision TimeNet to reduce cost and accelerate rollouts. Standardization of this technology has started within ITU.

Background | Precise Time as a critical national service

The dangerous overreliance on the Global Navigation Satellite System (GNSS) for timing has become increasingly apparent in our daily lives. GNSS (which is a generic term for satellite systems such as the American system GPS), was initially developed for navigation purposes and has evolved to play a crucial role in providing highly accurate time synchronization for a range of critical national services such as telecommunications, financial transactions, power grids, national security, and blue-light services. Today, many critical systems and functions rely on accurate time for synchronization and coordination.

• Mobile networks, especially 5G and the emerging 6G depend on accurate timing for synchronization. GNSS is often used to provide a common time reference for different network elements and at the RAN (Radio Access Network)
• Power grids require precise timing for the synchronization of electricity generation and distribution. GNSS is used to ensure that different components of the grid operate in harmony. When moving to more renewable energy sources and digital power stations, the dependency on robust time synchronization will further increase.
• Blue light services, as well as military and national security, often use technology sharing with the 5G communication networks, and timing from GNSS is often integrated with the communication systems used.

In particular, 5G TDD and 5G advanced services have a hard requirement on precise time and frequency, which, so far, has often been supplied by GNSS. However, with the inherent vulnerabilities of GNSS to spoofing and jamming together with the shifting geopolitical situation, governments, regulators, and operators throughout the world are coming to see the overreliance on GNSS as a dangerous dependency. 

For example, during the Christmas period, parts of Poland, Lithuania, and southern Sweden experienced significant GNSS signal disruptions, affecting aviation and navigation systems. Experts suggest that these disruptions were intentional, stemming from geopolitical tensions. Such incidents not only pose immediate operational challenges but also raise long-term security concerns for all industries relying on GNSS for critical operations.

 
Source: https://gpsjam.org/ 

A recent report from the UK government estimates the economic impact of a large-scale GNSS attack or failure in the UK would be about GBP 7.5 billion in a seven-day outage or about GBP 1.4 billion in a 24-hour outage. The GNSS loss estimates in the UK study assume a reasonable worst-case scenario of seven days of GNSS outage. In reality, more plausible sources of disruptions are likely to be more limited in both scope and duration. The study clearly shows that smaller and highly likely disruptions of GNSS will heavily impact critical national services and cause significant economic and societal impact. 

A similar US government report estimated the cost in the US for a similar failure to be over USD 1 billion per day, where half of the impact is telecom-related. 

Today, the importance of time and synchronization as a critical national service is recognized globally, with countries planning actions and investments to address their national vulnerability when only reliant on GNSS.

The Swedish model | GNSS redundancy

The Swedish regulator, the Swedish Post and Telecom Authority (PTS ) has set the technical requirements for granting licenses for frequency bands that are internationally harmonized for mobile communications networks. The technical requirements are set to meet the very high-capacity requirements by allowing for the fifth generation of terrestrial systems (5G).

The PTS requirements are explicit that a GNSS-independent solution to transport synchronization is a mandatory requirement for operating the 5G network. This is written in the license conditions for the spectrum auctions: “Conditions for license to use radio transmitters in allocated frequency space within 3400–3720 MHz, Appendix A2”:

26. If the primary source of common time reference is the reception of signals from satellite (GNSS) or if the source is otherwise located outside Sweden, a redundant source located in Sweden must be functionally tested and ready to put into use when required at latest by January 1st, 2025.

To support the 5G licensed mobile operators and ensure they are all operating their 5G TDD networks using the same time reference source even if the GNSS signal is completely lost, PTS could rely on the work they had initiated to provide a distributed national time infrastructure with connections to atomic ePRTC clocks. These clocks, located throughout the country, operate independently of GNSS and are traceable to Swedish National Time UTC(SP). This is monitored by the organization responsible for UTC(SP), RISE, which is Sweden’s National Metrology Institute. The journey to such a well-developed national time service independent of GNSS provides an excellent example of public/private cooperation together with the long-term view of how to implement a platform that can meet evolving needs across a range of sectors. 

Sweden has been looking at GNSS redundancy for a long time. Netnod’s work with GNSS redundancy goes back to 1997 when Netnod offered their first-time service over fiber. Since then, Netnod has been involved in discussions with operators, the government, and the Swedish telecom authority on the best way to deal with the problems related to GNSS.

In 2014, the government commissioned Netnod to develop a national time distribution network without GNSS dependency. The first question was that of funding. Netnod was commissioned to develop a system that would be robust and available throughout the country but which also had to be affordable for all operators. The costs here are significant beyond what can be covered by the market alone. 

The funding model is, therefore, based on public/private cooperation, which works very well. This model enables Netnod to develop long-term plans for the time distribution service and ensures state-of-the-art time nodes in all parts of the country. 

Each of these nodes is redundant from the others and has all critical equipment doubled in a dual node setup to ensure local redundancy. The time nodes are housed in secure bunkers in 6 locations throughout Sweden. 

Netnod provides time traceable to Swedish national time and offers free and commercial services with different SLAs and accuracy. This includes Netnod Time Direct, delivering time to a customer at a Netnod Internet Exchange to within 30 microseconds, and a PTP service which delivers time over dedicated fiber to within 30 nanoseconds of Swedish national time. GNSS still plays an important role, so the Netnod time services not only ensure redundancy from GNSS but also help operators to monitor the accuracy of their other time services, like GNSS.

When it comes to operators and time, the landscape and requirements keep evolving. Netnod is in discussions with governments throughout Europe who want to know more about how Sweden has developed what Netnod considers the leading national time service in the world. 

Distributing the time nationwide

For 5G mobile operators, the PTS mandate presents both a challenge and an opportunity. The task is to distribute time (Time Transfer) from the national clock sources provided by Netnod to their 5G radio access networks efficiently, without GNSS or other satellite synchronization methods. This approach must be cost-effective and agile, ensuring the swift deployment of 5G services and their subsequent monetization.

Transfer of Time from the Netnod Time service to the 5G RAN over the operators’ networks

Traditionally, network-based synchronization solutions have required extensive infrastructure upgrades, resulting in increased costs and complexity in 5G rollouts. However, a breakthrough has been achieved with Net Insight’s Precision TimeNet solution. This innovative technology facilitates GNSS-independent time distribution using existing infrastructure, including over leased lines. The result is a significant reduction in costs and an acceleration of 5G deployment across both urban and rural areas. Important parts of this new synchronization technology are now also undergoing standardization work in ITU study group 15.

Precision TimeNet – How it works

Precision TimeNet disaggregates the synchronization function from the hardware. It thus creates a synchronization overlay across the existing IP infrastructure without requiring PTP IEEE1588 hardware support in intermediate nodes. This allows all operators to cost-effectively transfer precise time from the central time reference sites all the way out to the radio access networks (RANs). There are two main issues when sending accurate time over wide area networks, jitter (PDV) and link asymmetries. Network jitters are typically caused by traffic congestion in network switches and routers and will cause noise and diurnal wander in the time distribution, which results in dynamic time offsets at the receivers. Static asymmetries e.g., caused by different fiber lengths or static delays in switches are easily compensated, but dynamic asymmetries e.g., due to protection switches or change of wavelengths are troublesome to discover and compensate for. 

Precision TimeNet streams time stamps at a much higher rate to enable much more advanced filtering mechanisms and algorithms in combination with collaborative clock links to reduce the jitter noise and thus significantly enhance the time accuracy. In addition, Precision TimeNet technology is combining real time algorithms for asymmetry control with centralized intelligence to detect and compensate for dynamic asymmetries to remove constant time errors from the synchronization network.     

Precision TimeNet delivers PTP to 5G RAN sites across a IP network without PTP FTS in intermediate nodes

In Sweden, major 5G operators such as 3 Sweden and critical network operator Teracom, after thorough evaluation of various alternatives, have opted for Net Insight’s Precision TimeNet technology for their national time distribution. This decision reflects a strong endorsement of the technology’s capability to meet the strict requirements of new advanced 5G networks and services.

Summary – The Swedish Model

By supporting a national time distribution network free from GNSS dependency and mandating 5G operators to adopt network-based synchronization independent of satellite systems, PTS has ensured the creation of a secure, highly available 5G infrastructure. This infrastructure is not only equipped to support essential societal services but is also primed to enable new and critical advanced business services, key to the monetization of 5G technology.

The Swedish government and telecom authority have taken a pioneering decision that sets a global precedent. Working with a very successful public/private cooperation, Sweden has developed one of the world’s leading national time infrastructures and has pointed the way for how to secure critical national services from an over-dependence on GNSS.