New ITU clock concept for more resilient synchronization networks
Global navigation satellite systems (GNSS) provide precise timing for synchronization networks that are critical to mobile telecoms and data centres, power supply and smart grids, railway and road transport, and security and public safety.
Long disruptions to GNSS could be catastrophic without solutions to maintain precise timing. These solutions are provided by ITU standards, assuring network operators and regulators that precise time will keep ticking.
Common causes of GNSS disruptions:
- GNSS segment errors
- Adjacent-band transmitters
- GNSS spoofing
- Environmental interference
- GNSS jamming
The ITU standard G.8272.1 defines the enhanced Primary Reference Time Clock (ePRTC), the primary source of time synchronization worldwide.
The GNSS signal is typically used as time reference for this clock. The latest version of this international standard provides for the delivery of timing with accuracy better than 100 nanoseconds, for up to 40 days after a GNSS loss.
Network-wide timekeeping
Introducing a new architectural concept, the new ITU standard G.8272.2 provides a coherent network reference clock (cnPRTC) that ensures highly accurate, resilient, and robust timekeeping throughout a telecom network.
The cnPRTC architecture involves interconnected clocks cooperating at the highest network level.
This allows stable, network-wide ePRTC time accuracy, even during periods of regional or network-wide GNSS unavailability or other failures and interruptions.
cnPRTC architecture at the core network level:
Comparative measurements between the clocks are another important component of the new architecture. Each clock’s performance is continuously monitored.
The whole group of clocks – connected by fibre or satellite systems such as GNSS common view – are combined under a “timescale algorithm.”
National time labs, GNSS control segments, and the UTC (coordinated universal time) established at the BIPM (international bureau of weights and measures) all rely on such algorithms to generate the time.
The revised G.8272.1 and new G.8272.2 standards are products of the working group on network synchronization and time distribution performance (Q13/15) in the ITU standardization study group for transport, access and home (ITU-T Study Group 15).
The OFC conference in San Diego (US) will feature an ITU booth (#5226), expert talks on “Tight Sync in Precision Time Protocol” on 26 March, and more hot topics at a “Standards Updates” session by the study group on 27 March.
The recent World Radiocommunication Conference (WRC-23), considering relevant ITU studies, endorsed the BIPM decision to adopt continuous UTC as the de facto time standard by 2035, with the possibility to extend the deadline to 2040 in cases where existing equipment cannot be replaced earlier.
