AT&T DS1/DMi/ISDN-PRI manual Internal Reference Selection Rules

SYNCHRONIZATION OF DIGITAL FACILITIES 5-19

DIGITAL SERVING OFFICE

EXTERNALLY REFERENCED NODES

SYSTEM 85 OR 75

INTERNALLY REFERENCED NODES

SYSTEM 85 OR 75

DIGITAL TRANSMISSION FACILITY

PRIMARY FREQUENCY REFERENCE

Figure 5-11.External and Internal Reference Levels

For externally referenced nodes, the operating company personnel will specify what the source of timing is on those links. If the network does not receive timing from the public network at any of its nodes, the master-slave relationships in the network will then be determined by those persons responsible for engineering the synchronization of the network.

This internal and external referencing concept permits constraints in synchronization network layout to be expressed in terms of network layout rules. The rules constitute a procedure to select the nodes used as primary and secondary references. Two sets of reference selection rules are available: one set for internally referenced networks and the other for externally referenced networks.

Internal Reference Selection Rules

The seven rules used to select internal synchronization references are described next.

RULE 1:

Select the node with the lowest stratum clock as the network reference clock master and have the rest of the nodes derive slave timing from it.