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

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The transport network using SONET provides much more powerful networking capabilities than 
existing asynchronous systems.  The key benefits provided by SONET include the following: 
 

 
As a result of SONET transmission, the network’s clocks are referenced to a highly stable 
reference point.  Therefore, the need to align the data streams or synchronize clocks is 
unnecessary.  Therefore, a lower rate signal such as DS1 is accessible, and demultiplexing is not 
needed to access the bitstreams.  Also, the signals can be stacked together without bit stuffing. 
 
For those situations in which reference frequencies may vary, SONET uses pointers to allow the 
streams to “float” within the payload envelope.  Synchronous clocking is the key to pointers.  It 
allows a very flexible allocation and alignment of the payload within the transmission envelope. 
 

 
Separate M13 multiplexers (DS-1 to DS-3) and fiber optic transmission system terminals are used 
to multiplex a DS-1 signal to a DS-2, DS-2 to DS-3, and then DS-3 to an optical line rate.  The 
next stage is a mechanically integrated fiber/multiplex terminal. 
 
In the existing asynchronous format, care must be taken when routing circuits in order to avoid 
multiplexing and demultiplexing too many times since electronics (and their associated capital 
cost) are required every time a DS-1 signal is processed.  With SONET, DS-1s can be 
multiplexed directly to the OC-N rate.  Because of synchronization, an entire optical signal doesn’t 
have to be demultiplexed, only the VT or STS signals that need to be accessed. 
 

 
Because of different optical formats among vendors’ asynchronous products, it’s not possible to 
optically connect one vendor’s fiber terminal to another.  For example, one manufacturer may use 
417 Mb/s line rate, another 565 Mb/s. 
 
A major SONET value is that it allows mid-span meet with multi-vendor compatibility.  Today’s 
SONET standards contain definitions for fiber-to-fiber interfaces at the physical level.  They 
determine the optical line rate, wavelength, power levels, pulse shapes, and coding.  Current 
standards also fully define the frame structure, overhead, and payload mappings.  Enhancements 
are being developed to define the messages in the overhead channels to provide increased 
OAM&P functionality. 
 
SONET allows optical interconnection between network providers regardless of who makes the 
equipment.  The network provider can purchase one vendor’s equipment and conveniently 
interface with other vendors’ SONET equipment at either the different carrier locations or 
customer premises sites.  Users may now obtain the OC-N equipment of their choice and meet 
with their network provider of choice at that OC-N level. 
 

 
The difference between point-to-point and multipoint systems was shown previously in this 
appendix.  Most existing asynchronous systems are only suitable for point-to-point, whereas 
SONET supports a multipoint or hub configuration. 
 
A hub is an intermediate site from which traffic is distributed to three or more spurs.  The hub 
allows the four nodes or sites to communicate as a single network instead of three separate