Nortel Networks OPTera Metro 3500 - Manual (Page 190)

2-152 Operation, administration, and maintenance (OAM) features
OPTera Metro 3500 Multiservice Platform NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
Figure 2-48
Hierarchical network synchronization
EX0130
Stratum 1
Stratum 2
2C 2A 2B
Stratum 1
3A 3B 3C
3D
4A 4B 4C
Stratum 3
Stratum 4
Legend
= Primary reference
= Secondary reference
Note: Each box represents an office using the building-integrated
timing supply (BITS) concept.