Cisco Cisco ONS 15454 SONET Multiservice Provisioning Platform (MSPP) Guía De Diseño

OL-4556-01

 

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Through-timing and per-port loop timing are additional timing modes available, but are not 
supported for the optical synchronous interfaces.  DS1 and DS3 asynchronous interfaces are 
through-timed and do not reference the system timing.  For these asynchronous ports, transmit 
timing is derived from the received timing for that asynchronous signal. 
 
The transmit timing on all optical synchronous interfaces is derived from the system timing 
reference provided by the TCC cards.  Figure 2-15 illustrates how timing signals flow through the 
ONS 15454.  The TCC selects a timing reference from one of several sources as discussed 
above and distributes this reference to the synchronous interface cards. 
 

 
The TCC synchronization functions include: 
 

    Reference monitoring, qualification and selection 

    Filtering and locking to the active reference 

    Distribution of 19.44MHz system clock 

    Termination of two BITS inputs 

    Generation of two BITS outputs 

    Processing and generating SSM (Synchronization Status Messages) 

 

 
The external timing input signal on the Cisco ONS 15454 must come from a synchronization 
source whose timing characteristics are better than the stratum 3 internal clock.  The TCC will 
track the external reference with the internal clock. 
 
The BITS signal is a DS-1 level, 1.544 MHz signal, formatted either as Superframe (SF, 12 
frames per superframe) or the Extended Superframe (ESF, 24 frames per superframe) ESF.  For 
the ONS 15454, the default setting for the BITS framing reference is ESF, but you may change