Cisco Cisco ONS 15454 SONET Multiservice Provisioning Platform (MSPP) Guía De Diseño
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this to SF if necessary. The default setting for BITS line coding reference is B8ZS, however this
can be changed to AMI if required. The default setting for BITS State is OOS (out of service).
For nodes using external timing or the external BITS Out, you must change this setting to IS (in-
service). The redundant architecture of the ONS 15454 provides two inputs for connection to
external BITS clocks – BITS1 and BITS2. If these inputs have been selected as the primary and
secondary synchronization sources, the active and standby TCC cards will monitor both inputs. If
the primary input fails, the secondary input will be selected. Failure switching is discussed in
more detail later. It is recommended, but not necessary, to have redundant BITS inputs.
However, if only a single BITS source is available, the secondary source can be set to Internal or
Line synchronization.
Note that DS-1s delivered over traffic links are not suitable BITS sources. The primary reason is
that SONET compensation for off-frequency DS-1s results in jitter since controlled slips are not
performed.
Table 2-15 provides a summary of the BITS input physical connections and signal formats for the
ONS 15454.
can be changed to AMI if required. The default setting for BITS State is OOS (out of service).
For nodes using external timing or the external BITS Out, you must change this setting to IS (in-
service). The redundant architecture of the ONS 15454 provides two inputs for connection to
external BITS clocks – BITS1 and BITS2. If these inputs have been selected as the primary and
secondary synchronization sources, the active and standby TCC cards will monitor both inputs. If
the primary input fails, the secondary input will be selected. Failure switching is discussed in
more detail later. It is recommended, but not necessary, to have redundant BITS inputs.
However, if only a single BITS source is available, the secondary source can be set to Internal or
Line synchronization.
Note that DS-1s delivered over traffic links are not suitable BITS sources. The primary reason is
that SONET compensation for off-frequency DS-1s results in jitter since controlled slips are not
performed.
Table 2-15 provides a summary of the BITS input physical connections and signal formats for the
ONS 15454.
Table 2-15: Summary of BITS Inputs and Signal Formats
Number of BITS Inputs
BITS Input Physical Connection
BITS Input Signal Format
2
4 wire-wrap pins provide
connections for redundant BITS
clock inputs.
connections for redundant BITS
clock inputs.
1.544 Mb/s DSX-1 with either
SF or ESF (required for SSM
support) framing format.
SF or ESF (required for SSM
support) framing format.
Line Timing
The ONS 15454 can accept reference timing from any optical port. For increased reliability,
optical cards with multiple ports (e.g. 4-port OC-3) can only have one of its ports provisioned as a
timing reference. The optical cards divide down the recovered clock to 19.44 MHz and transmit it
to the working and protect TCC cards, where it is qualified for use as a timing reference.
Synchronization Status Messaging (SSM) can be optionally enabled or disabled on an optical
port. A controller on the optical card monitors the received SSM and reports any changes to the
TCC synchronization process. If an optical port (receiver) is selected as the active timing
reference, the SSM value DUS (Don’t Use for Synchronization) is transmitted (on the transmit
port) to help prevent timing loops. If SSM is disabled, the controller does not monitor the received
SSM value and transmits the SSM value STU (Synchronized, Traceability Unknown). More
information on SSM is available later in this chapter.
Mixed Mode Timing
Mixed Mode Timing allows you to select both external and line timing sources. However,
Cisco does not recommend its use because it can create timing loops. Caution must be used
when using Mixed Mode timing as it can result in inadvertent timing loops. The most common
reason for using Mixed Mode Timing is so that an OC-N timing source can be provisioned as a
backup for the BITS timing source.
The Mixed Mode Timing feature enhances the provisioning options for the NE Reference only.
The rules associated with the BITS Out timing source have not changed. To review these rules,
Figure 2-16 has been provided to show the ONS 15454 timing circuit.
when using Mixed Mode timing as it can result in inadvertent timing loops. The most common
reason for using Mixed Mode Timing is so that an OC-N timing source can be provisioned as a
backup for the BITS timing source.
The Mixed Mode Timing feature enhances the provisioning options for the NE Reference only.
The rules associated with the BITS Out timing source have not changed. To review these rules,
Figure 2-16 has been provided to show the ONS 15454 timing circuit.