C H A P T E R
6-1
Cisco ONS 15600 SDH Reference Manual, Release 9.0
78-18400-01
6
Timing
This chapter provides information about Cisco ONS 15600 SDH timing. To provision timing, refer to
the
Cisco ONS 15600 SDH Procedure Guide
.
Chapter topics include:
•
6.1 Timing Parameters, page 6-1
•
•
6.3 Synchronization Status Messaging, page 6-3
6.1 Timing Parameters
SDH timing parameters must be set for each ONS 15600 SDH node. Each ONS 15600 SDH
independently accepts its timing reference from one of three sources:
•
The building integrated timing supply(BITS) pins on the Customer Access Panel (CAP/CAP2).
•
A port on an STM-N card installed in the ONS 15600 SDH. The timing is traceable to a node that
receives timing through a BITS source.
•
The internal Stratum 3E clock (ST3E) on the TSC card.
You can set ONS 15600 SDH timing to one of three modes: external, line, or mixed. If the timing comes
from BITS, set ONS 15600 SDH timing to external. If the timing comes from an STM-N port, set the
timing to line. If the timing comes from both BITS and STM-N port, set ONS 15600 SDH timing to
mixed. In typical ONS 15600 SDH networks:
•
One node is set to external timing. The external node derives its timing from a BITS source wired
to the BITS backplane pins. The BITS source, in turn, derives its timing from a Primary Reference
Source (PRS), such as a Stratum 1 clock or global positioning satellite (GPS) signal.
•
Other nodes are set to line timing. The line nodes derive timing from the externally timed node
through the STM-N trunk cards.
You can set three timing references for each ONS 15600 SDH. The first two references are typically two
BITS-level sources, or two line-level sources optically traceable to a node with a BITS source. The third
reference is the internal ST3E clock provided on every ONS 15600 SDH TSC card. If an
ONS 15600 SDH becomes isolated, the TSC maintains timing at the ST3E level.
