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

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At the far end of a SDH circuit, the reverse process takes place, transitioning the signal from 
SONET to SDH as follows: 
 

    Drop STS-Nc from OC-N facility (SPE pointer processed and J1 byte of the HO-POH 

located) 

 

    STS-Nc mapping into a VC-4-Nc where M=3xN  

 

    AU pointer creation with the value 10 for the SS bits as required for SDH 

 

    STM-N signal generation with MSOH and RSOH 

 
During this process, the only bytes modified are the H1, H2 and H3 bytes.  All the other bytes are 
passed transparently.  The H bytes are modified to allow 1) pointer justifications that may be 
necessary and 2) the SS bits are set to 10 when the frame leaves the OC-N card provisioned as 
SDH. 
 

If any connected SDH equipment is using any different interpretation of SS bits, LOP may 

result. 
 

 
The SDH to SONET mapping depends on the SDH payload type being transported and is 
manually set by the user during the creation of the SONET circuits used to transport the SDH 
traffic.  For example, an STM-4 port can be mapped in a number of alternative ways, depending 
upon the content of the signal including:  
 

    One STS-12c circuit to transport a 622Mb/s concatenated data payload. 

    Four (4) STS-3c circuits for an Au4 mapped SDH interface (see Table 3-1). 

    Twelve (12) STS-1 circuits for an Au3 mapped SDH interface (see Table 3-2). 

 
Figure 3-1 shows how the SDH and SONET multiplexing structures meet at AU4 (i.e., STS-3c) by 
byte interleaving 3 STS-1s.  The STM-1 (i.e., OC-3c) granularity corresponds to the minimum rate 
where both SONET and SDH systems share.  Multiplex structures below VC-3 and/TUG-3 are 
not compatible between SDH & SONET.  Services carried below VC-3 (i.e., E1) need SDH based 
ADMs to be added or dropped onto the fiber network.