Section: 6.36.1 Overview
Content: 5G systems rely on reference precision timing signals for network synchronization in order to operate. These synchronization references are generated by Primary reference Time Clocks that typically get the timing reference from GNSS receivers and in order to meet the relevant synchronization requirements also during failure conditions, the synchronization network designs typically include means to address potential degradation of the GNSS signal performance. Some deployment of 5G involve applications that themselves can be sensitive to any degradation of the timing signal. In such cases it is beneficial for the 5G system to be enhanced to act as a backup for loss of their GNSS references. In some implementations, timing resiliency enhancements to the 5G system can work in collaboration with different types of time sources (e.g., atomic clock, time service delivered over the fibre) to provide a robust time synchronization. 5G as a consumer of time synchronization benefits from timing resiliency which enables the support of many critical services within the 5G network even during the event of a loss or degradation of the primary GNSS reference timing. Additionally, for time critical services (e.g. financial sector or smart grid), the 5G system can operate in collaboration with or as backup to other timing solutions. A base of clock synchronization requirements when 5G is providing a time signal, if it is deployed in conjunction with an IEEE TSN network or if it is providing support for IEEE 1588 related protocols, is included in [21] clause 5.6. The enhancements in this clause build on this to add timing resiliency to the 5G system enabling its use as a replacement or backup for other timing sources.