How PTP helps mobile operators meet the timing demands of 5G

To find out more about what this means for operators and the services that support them, I talked with Daniel Wiberg, Network and Security Architect at 3. In this Q&A, we discuss the challenges of time synchronisation and how Precision Time Protocol (PTP) services help provide essential redundancy as we move into the era of 5G. 

What are the challenges for mobile operators when it comes to time synchronisation?
Mobile operators need to build resilient networks that can continue to operate under all circumstances. This means that when we’re looking at time synchronisation we need to ensure redundancy and resilience. This involves a lot of planning, implementation and testing especially with regards to how failover scenarios work. We need to be sure the network will continue to function if one source of time suddenly ceases to become available or loses its accuracy. 

Why is time synchronisation so important for mobile networks?
In the currently deployed mobile networks, time synchronisation enables us to use the frequency band at the mobile base stations more efficiently. This means we can maximise the amount of data that can be used in a given frequency range. With 5G, the requirement for accuracy is much more demanding. 

Why is high-precision time synchronisation so important for 5G?
5G uses higher frequencies, which travel over shorter distances. This means it requires many more, smaller cells each with a base station to transmit the signals. Dual connectivity will enable mobile users to connect to multiple stations enabling significant increases in available bandwidth and speed. However, for this to work the base stations have to be in perfect synchronisation to get the radio signals in the right order. This is one example of how new 5G features demand the highest possible level of time synchronisation. When we’re looking at 5G, initially the level of accuracy needed will be in the range of plus/minus 1.5 microseconds. We will probably be looking at much higher requirements for time synchronisation as 5G services develop. 

What time sources do mobile networks use?
Most operators use the Global Navigation Satellite System (GNSS)—which includes GPS, GLONASS, Galileo, and BDS—as their primary source of time. But to ensure resilience, it is very important to have at least two different time sources from different locations. Satellite based time sources are subject to disruption from natural events (such as solar storms) or malicious attack (such as jamming). Just recently [in July 2019], the European satellite system Galileo had a week of outage. A fibre based PTP service is a good choice for an alternate time source. 

What are the advantages of using PTP?
From our perspective, using a fibre-based PTP service is very important and significantly increases the security of our network. It gives us essential redundancy regarding our satellite-based time sources. As the transport latency is predictable, we don’t have to deal with any jitter. With consistent, transport latency we can account for the time it takes the synchronisation signal to travel between base stations and the core network. 

As we were already present at a location where Netnod offered its PTP service, that made it a good choice for us. Being as close as possible to your time source makes things inherently more reliable.

If you have any questions regarding PTP, don´t hesitate to contact us. You can read more about our PTP service here. Thank you Daniel for talking to us and answering our questions!

//Christan