Timing in Global Optical Networks

This paper presents an overview of timing in the Optical Transport Network (OTN). The OTN is a new layer network (more precisely, a set of layers) for global optical networking; a series of standards for the OTN are being developed by the ITU-T. The paper presents the timing and jitter requirements for the OTN, emphasizing the technical basis and consistency of related requirements. The key differences between OTN and SDH/SONET timing requirements are emphasized, namely: (1) the OTN is not required to be synchronized nor transport synchronization via its physical layer; rather, synchronization is transported via SDH clients; and (2) there is a single set of OTN timing and jitter requirements that are applicable globally (unlike SDH, which has two Options). The paper includes discussion of background material on timing, synchronization, and jitter in digital networks; an overview of OTN rates, formats, and interfaces; and a roadmap of ITU-T recommendations covering timing, synchronization, and jitter.