Nortel Communication Server 1000S Installation And Configuration Manual page 197

Figure 59
Hierarchical Synchronization
Stratum 1 nodes (clock derived directly from or controlled by Cesium clock)
Stratum 2 nodes (i.e. Toll Offices)
Stratum 3 nodes (i.e. Digital Central or End offices)
Stratum 4 nodes (i.e. Digital PBXs & Channel Banks)
Digital Transmission Facility
Primary Reference Source
Secondary Reference Source
Clock Controller description and installation
Primary
Reference Source
ISDN Primary Rate Interface
Page 197 of 394
553-7560.EPS
Installation and Configuration