Infinera : Solving End-to-End Sync Distribution

In the first two blogs in our series of addressing the critically important topic of synchronization distribution in 5G networks, we discussed the changing role of GNSS/GPS and the importance of understanding the impact of the DWDM layer within a synchronization distribution network. In this third installment, we'll address the topic of end-to-end multi-layer synchronization strategies and solutions.

Hitting the required synchronization performance within a network requires a combination of features/functionality and measurable performance characteristics, such as constant time error (cTE) and dynamic time error (dTE) of networking devices. The specifications enable the transport network to deliver a suitable clock to the cell towers in the mobile network of the right quality to support the demanding features required in the 5G RAN. Meeting the basic synchronization performance levels enables network operators to fully utilize their most valuable asset, their spectrum. Lower synchronization performance can mean that frequency management within the RAN isn't tight enough and the spectrum can't be fully utilized or that advanced functionality such as carrier aggregation or MIMO antennas cannot be fully utilized or even activated at all. Overall, getting synchronization right is mandatory in mobile networks.

However, synchronization performance is not simply a pass/fail test. It is possible to exceed the synchronization specifications and have a higher-performance network. It is too early to see the impact of higher synchronization performance that exceeds the specifications in full 5G standalone (SA) networks yet, although we can be sure this certainly will not be a negative factor. But we can look back at 4G networks to see how above-standard synchronization helped network operators improve network efficiency and user experience. These performance improvements are hard to quantify in most cases - sometimes it is simply a case of network engineers being able to tell which backhaul network a cell tower is supported by just from looking at the performance metrics for the cell site - for example, one backhaul network with OK synchronization versus one with much better synchronization performance. In other cases, network operators have used before-and-after user experience data such as upload speed, download speed, and latency and seen over 40% improvement in all metrics once the backhaul network was upgraded to one with much better synchronization performance. In this instance, there was no increase in backhaul capacity to the cell site, just better synchronization over the backhaul network and the capacity for growth in the future.

Overall, delivering high-quality synchronization is a must for 5G networks, and it is not simply a case of meeting the minimum possible standard. Superior synchronization performance can bring improved network performance and user experience. It is always a balancing act over the economics of chasing ever-improving synchronization performance, but the goal should always be to get the best performance that meets or exceeds the required level for 5G without breaking the bank.

In order to meet the complex transport requirements in 5G mobile networks, Infinera has developed a complete end-to-end mobile transport solution. This includes synchronization delivery for all aspects of the optical network from the mobile core to the cell tower and comprises of a number of major building blocks. These building blocks can be deployed in a standalone manner for a particular segment, layered in the 5G transport network, or deployed together as a complete solution.

Infinera has a full portfolio of DWDM, Layer 2/2.5 packet optical and IP products that are widely deployed across fixed and mobile networks around the globe. The synchronization distribution solution outlined in this blog focuses on the products within the portfolio that are most commonly positioned today for new mobile network deployments where synchronization is a critical consideration. Within the DWDM and Layer 2 packet optical layers of the network, this comprises the XTM Series within the access and aggregation packet optical domains at the edge of the network and the OTC2.0 solution deeper in the network across regional and long-haul networks.

Figure 1: Infinera's end-to-end 5G transport solution

5G synchronization is a complex topic with many moving parts that all need to come together harmoniously across all aspects of the transport network to provide the right quality synchronization to the cell tower without overengineering the network and driving up cost. Infinera's toolbox of high-performance synchronization capabilities is enabling both mobile network operators and wholesale carriers who provide mobile transport services to deliver network-based synchronization with industry-leading performance. In some cases, this Infinera solution simply supports high-quality synchronization within a particular network layer or geographic domain, and in others, operators are able to combine the solutions to create end-to-end synchronization strategies to meet their 5G performance demands now and in the future.

We won't dive into the detailed product specifications and synchronization performance within this blog, but it should be stressed that the solution is optimized to address the network asymmetry challenges within the DWDM layer that we outlined in the second blog in the series.

Figure 2: Infinera's synchronization options in DWDM transport networks

GNSS has a critical role to play in synchronization distribution, but as we outlined in the first blog in this series, operators are moving away from 'GNSS-everywhere' strategies to those that utilize resilient GNSS at key network locations and network-based synchronization distribution. This approach provides better holdover performance and removes the risk of GNSS jamming and interference at cell sites. It also removes the challenges of providing GNSS signals into hard-to-reach cell sites planned for 5G, such as those deep inside buildings or in underground metro railway stations.

The benefits that Infinera's solution brings to those operators who are building network-based synchronization strategies over alternative approaches include:

• Better overall synchronization performance, leading to potentially better RAN performance and spectrum utilization
• Better overall network economics with optimized solutions for in-band synchronization delivery for metro access and aggregation networks, OTC2.0 for long-haul/core/legacy networks, and the ability to blend the two solutions within the same network
• More resilient synchronization distribution
• More stable synchronization environments requiring less ongoing maintenance and support

This blog series has focused on synchronization in mobile networks as this is currently a large focus area within the telecom industry. But the benefits of high-performance synchronization are not limited to mobile networks. Network operators are also benefiting from Infinera's high-quality synchronization in a broad range of applications such as power utility networks, financial trading networks, TDM circuit emulation, and video/DAB distribution networks, and we'll discuss these additional applications soon in the last blog post in this series.

For those readers who want to dive into this topic in more detail, our new Synchronization Distribution in 5G Transport Networks e-book provides a detailed overview of synchronization distribution challenges and standardization along with an end-to-end synchronization distribution strategy that meets the demanding requirements that 5G is driving into optical networks.