Specifications

Cisco ONS 15327 Product Overview
Timing
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Cisco ONS 15327 Product Overview, R3.3
June 2002
Timing
The XTC card performs all system-timing functions for each ONS 15327. The
XTC card selects a recovered clock, a BITS, or an internal Stratum 3 reference as
the system-timing reference. You can provision any of the clock inputs as a
primary or secondary timing source. If you identify two timing references, the
secondary reference provides protection. A slow-reference tracking loop allows
the XTC card to synchronize to the recovered clock, which provides holdover if
the reference is lost.
Timing Parameters
You must set the SONET timing parameters for each ONS 15327. ONS 15327
timing is set to one of two modes: external or line. An externally-timed node
derives its timing from a BITS source wired to the BITS input on the MIC. The
BITS source, in turn, derives its timing from a Primary Reference Source (PRS)
such as a Stratum 1 clock or GPS signal. A line-timed node derives its timing for
an incoming optical signal on one of the optical line cards.
Figure 22 shows an example of an ONS 15327 network-timing setup. Node 1 is
set to external timing. Two references are set to BITS, and the third reference is
set to internal. The BITS output pin on the MIC of Node 3 provides timing to
outside equipment, such as a digital access line access multiplexer.