YD/T 900-1997
Technical requirement for SDH equipment - clock (English Version)

Standard No.

YD/T 900-1997

Language

Chinese, Available in English version

Release Date

1997

Published By

Professional Standard - Post and Telecommunication

Latest

YD/T 900-1997

Scope

This standard outlines the timing requirements for synchronous network equipment operating on Synchronous Digital Hierarchy (SDH) principles. These requirements apply to the general environmental conditions specified for SDH equipment. Normally operating SDH equipment contains a slave clock that tracks the master reference clock. Usually the SDH Equipment Clock (SEC) has several reference clocks. When all links between the master clock and the slave clock fail, the SDH equipment should be able to maintain operation within the specified performance limits (i.e., holdover mode). SEC is part of the SDH equipment. As a synchronization equipment timing source (SETS), its function is specified in ITU-T recommendation G.783. Slave clocks used for SDH equipment must meet specific requirements in order to comply with network jitter requirements for quasi-synchronous tributaries. This standard specifies the minimum requirements for clocks in SDH network units (SDH network elements), however some SDH network elements may have higher quality clocks. This standard allows a SEC (that meets this standard) to be clocked by another SEC (that also meets this standard) in a normal operating network, or by a higher quality IT clock. It is recommended that SDH networks adopt hierarchical timing distribution. Timing should not be passed from a free-running or hold-mode SEC to a higher quality clock because the higher quality clock should not track the signal of an SEC operating under defective conditions.

YD/T 900-1997 history

• 1997 YD/T 900-1997 Technical requirement for SDH equipment - clock