scope:

This European Telecommunication Standard (ETS) outlines requirements for timing devices used in synchronizing network equipment that operates according to the principles governed by the Synchronous Digital Hierarchy (SDH). These requirements apply under the normal environmental conditions specified for SDH equipment. Typical SDH equipment contains a slave clock linked to a master, or a primary reference clock. The logical function of the SEC is described in figure 2 of ETS 300 462-2 [3]. In general for SDH Equipment Clock (SEC) will have multiple reference inputs.