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Table Of Contents
14.3 Synchronization Status Messaging
Timing Reference
This chapter provides information about Cisco ONS 15454 users and node timing. To provision timing, refer to the Cisco ONS 15454 DWDM Procedure Guide.
Note
Unless otherwise specified, "ONS 15454" refers to both ANSI and ETSI shelf assemblies.
Chapter topics include:
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14.1 Node Timing Parameters
SONET timing parameters must be set for each ONS 15454. Each ONS 15454 independently accepts its timing reference from one of three sources:
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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/STM-N card, set the timing to line. In typical ONS 15454 networks:
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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 tab show current timing information for an ONS 15454, including the timing mode, clock state and status, switch type, and reference data.
Caution
14.2 Network Timing
Figure 14-1 shows an ONS 15454 network timing setup example. Node 1 is set to external timing. Two timing references are set to BITS. These are Stratum 1 timing sources wired to the BITS input pins on the Node 1 backplane. The third reference is set to internal clock. The BITS output pins on the backplane of Node 3 are used to provide timing to outside equipment, such as a digital access line access multiplexer.
In the example, Slots 5 and 6 contain the trunk (span) cards. Timing at Nodes 2, 3, and 4 is set to line, and the timing references are set to the trunk cards based on distance from the BITS source. Reference 1 is set to the trunk card closest to the BITS source. At Node 2, Reference 1 is set to Slot 5 because it is connected to Node 1. At Node 4, Reference 1 is set to Slot 6 because it is connected to Node 1. At Node 3, Reference 1 could be either trunk card because they are at an equal distance from Node 1.
Figure 14-1 ONS 15454 Timing Example
14.3 Synchronization Status Messaging
Synchronization status messaging (SSM) is a SONET protocol that communicates information about the quality of the timing source. SSM messages are carried on the S1 byte of the SONET Line layer. They enable SONET devices to automatically select the highest quality timing reference and to avoid timing loops.
SSM messages are either Generation 1 or Generation 2. Generation 1 is the first and most widely deployed SSM message set. Generation 2 is a newer version. If you enable SSM for the ONS 15454, consult your timing reference documentation to determine which message set to use. Table 14-1 and Table 14-2 show the Generation 1 and Generation 2 message sets.
Posted: Mon Oct 22 05:58:07 PDT 2007
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