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

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existing tunnel.  If a tunnel does not exist, or if an existing tunnel does not have sufficient 
capacity, CTC displays a dialog box asking whether you want to create a tunnel.  Before you 
create the tunnel, review the existing tunnel availability, keeping in mind future bandwidth needs.  
In some cases, you may want to manually route a circuit rather than create a new tunnel. 
 

 
Network synchronization and timing are critical elements within a SONET network.  The goal is to 
create a fully synchronous optical hierarchy by ensuring that all ONS 15454 nodes derive timing 
traceable to a primary reference source (PRS).  An ONS 15454 network may use more than one 
PRS.  A PRS is equipment that provides a timing signal whose long-term accuracy is maintained 
at 10-11 or better with verification to Universal Time Coordinated (UTC), and whose timing signal 
is used as the basis of reference for the control of other clocks within a network. 
 

 
A stratum 1 timing source is typically the Primary Reference Source (PRS) within a network, 
because it ensures the highest level of performance of a SONET network.  Other types of clocks 
used in the synchronized network include stratum 2, 3E, 3, 4E, and 4,  In most cases these 
clocks are components of a digital synchronization network and are synchronized to other 
clocks within that network using a hierarchical master-slave arrangement. In this arrangement, 
each clock receives timing, usually in the form of primary and secondary reference signals, from 
another clock of the same or better quality.  Figure 2-14 shows the timing accuracy hierarchy 
supported by the ONS 15454. 
 

 

 
The clocks used to synchronize ONS 15454 nodes must be stratum 3 (or better quality) to meet 
ANSI T1.101 synchronization requirements. 
 
Building Integrated Timing Supply (BITS) 
 
In the United States, a Building Integrated Timing Supply (BITS) clock is commonly used to 
distribute timing signals from Stratum clocks to an ONS 15454 node.  BITS timing references run 
over the working and protect SONET paths.