scope:

This standard addresses the interconnection between the Timing Signal Generator (TSG) and Network Elements (NE) in an intra-Central-Office environment. The principal focus of this standard is the physical layer connectivity for enabling Ethernet-based timing distribution. The primary facets addressed are the connectorization, cabling, and shielding requirements for delivering a timing reference from the Office TSG to the NE.

The Ethernet signals considered here belong to the Fast Ethernet and Gigabit Ethernet categories. Both electrical (i.e., utilizing twisted-pair cabling) and optical (i.e., utilizing fiber-optic cabling) signals are considered. The relevant forms of Fast Ethernet included are 100Base-TX, 100Base-FX, 100Base-SX, and 100Base-BX. The relevant forms of Gigabit Ethernet included are 1000Base-T, 1000Base-LX, 1000Base- SX, and 1000Base-BX10.

Higher layer protocols, formats, and methods that make the Ethernet signal suitable for timing are not within the scope of this standard, but indicated in Appendix I for information. These include Precision Time Protocol (PTP), Network Time Protocol (NTP) and Synchronous Ethernet. The standard does not preclude the development of enhancements or additional protocols provided the physical layer connectivity comply with the requirements provided herein.

Protection (e.g. lightning) is out of the scope of this document.

The standard does not render timing distribution methods based on prevailing twisted-pair cabling (e.g. DS1, composite-clock or CC) obsolete or irrelevant.