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

OL-4556-01

 

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order.  The second step multiplexes 7 of the DS-2 signals using pulse stuffing synchronization to 
generate the DS-3 signal.  Demultiplexing is also accomplished in a two-step process.  In the first 
step, a DS-3 signal is decomposed into 7 DS-2 signals.  In the second step, each of the DS-2 
signals is decomposed into 4 DS-1 signals. 
 

 
Synchronous multiplexing is the SONET process used when multiple lower-order path-layer 
signals are adapted into a higher-order path signal, or when the higher-order path signals are 
adapted into the Line Overhead.  The multiplexing principles of SONET are: 
 

    Mapping – A process used when tributaries are adapted into Virtual Tributaries (VTs) by 

adding justification bits and Path Overhead (POH) information. 

 

    Aligning – This process takes place when a pointer is included in the STS Path or VT Path 

Overhead, to allow the first byte of the Virtual Tributary to be located. 

 

    Multiplexing – This process is used when multiple lower-order path-layer signals are 

adapted into a higher-order path signal, or when the higher-order path signals are adapted 
into the Line Overhead. 

 

    Stuffing – SONET has the ability to handle various input tributary rates from asynchronous 

signals.  As the tributary signals are multiplexed and aligned, some spare capacity has 
been designed into the SONET frame to provide enough space for all these various 
tributary rates 

 
Figure B-7 shows the basic multiplexing structure of SONET.  Any type of service, ranging from 
voice to high-speed data and video, can be accepted by various types of service adapters.  A 
service adapter maps the signal into the payload envelope of the STS-1 or virtual tributary (VT).  
New services and signals can be transported by adding new service adapters at the edge of the 
SONET network. 
 

 

OC-192

STS-192

x4

OC-48

STS-48

x4

OC-12

STS-12

x4

OC-3

STS-3

x3

OC-1

STS-1

SPE

45 Mb

x7

VT Grp

VT6

6 Mb

x2

VT3

3 Mb

x3

VT2

2 Mb

x4

VT1.5

1.5 Mb

 

 
Except for concatenated signals, all inputs are eventually converted to a base format of a 
synchronous STS-1 signal (51.84 Mb/s or higher).  Lower speed inputs such as DS1s are first bit- 
or byte-multiplexed into virtual tributaries.  Several synchronous STS-1s are then multiplexed 
together in either a single- or two-stage process to form an electrical STS-N signal (N = 1 or 
more).