Utilizing an Active Fiber Optic Communication Network for Accurate Time Distribution

To achieve a robust and accurate time scale at an arbitrary location in Sweden, we propose and demonstrate a system where an existing back-bone communication network carries the timing reference. Furthermore, when using the proposed technique the timing is extracted from the data packages already transmitted in the system, thus not taking up additional bandwidth. This is a unique feature of this time transfer technique, enabling an implementation through add-on modules to the existing network, and it is independent of the manufacturer of the router equipment. The feasibility and accuracy of the distributed time is experimentally verified in the Swedish University Network, SUNET, which connects university cities in Sweden. The long-haul transmission in this network is based on SDH STM-64, which is a synchronous transmission at 9.953 Gbit/s over optical fibers. However, the proposed time distribution technique is applicable in any packet based digital transmission.