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CHAPTER
10-1
Cisco ONS 15454 Reference Manual, R8.5.x
78-18106-01
10
Timing
This chapter provides information about Cisco ONS 15454 SONET timing. To provision timing, refer to
the Cisco ONS 15454 Procedure Guide.
Chapter topics include:
• 10.1 Timing Parameters, page 10-1
• 10.2 Network Timing, page 10-2
• 10.3 Synchronization Status Messaging, page 10-3
10.1 Timing Parameters
SONET timing parameters must be set for each ONS 15454. In addition, an SDH external timing source
can be selected so that a SONET shelf can be deployed in a network using SDH timing. SDH timing is
typically used when the SONET platform is deployed for AU3 SDH applications. Each ONS 15454
independently accepts its timing reference from one of the following sources:
• The building integrated timing supply (BITS) pins on the ONS 15454 backplane.
• An OC-N card installed in the ONS 15454. The card is connected to a node that receives timing
through a BITS source.
• The internal ST3 clock on the TCC2/TCC2P card.
You can set ONS 15454 timing to one of three modes: external, line, or mixed. If timing is coming from
the BITS pins, set ONS 15454 timing to external. If the timing comes from an OC-N card, set the timing
to line. In typical ONS 15454 networks:
• One node is set to external. 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.
• The other nodes are set to line. The line nodes derive timing from the externally timed node through
the OC-N trunk (span) cards.
You can set three timing references for each ONS 15454. The first two references are typically two
BITS-level sources, or two line-level sources optically connected to a node with a BITS source. The third
reference is usually assigned to the internal clock provided on every ONS 15454 TCC2/TCC2P card.
However, if you assign all three references to other timing sources, the internal clock is always available
as a backup timing reference. The internal clock is a Stratum 3 (ST3), so if an ONS 15454 node becomes
isolated, timing is maintained at the ST3 level.
The CTC Maintenance > Timing > Report tabs show current timing information for an ONS 15454,
including the timing mode, clock state and status, switch type, and reference data.