Cisco Model D-PCG1000 PowerKEY CAS Gateway Technical References

  

 

Operations Alert Bulletin 
Configuring Stat Mux Dejitter Groups  
on the DNCS 
 

Statistical multiplexing is the process of using a statistical multiplexer (or stat mux) 

to combine a number of MPEG programs so that the sum total bit rate of the 

included programs does not exceed a programmed limit. This allows system 

operators to change the bit rates of channels dynamically according to the 

bandwidth requirements of each channel.  
The GQAM does not provide statistical multiplexing, but it does process the stat 

mux data with an algorithm that uses time shifting of information, glue frame (valid 

frames with no video data) replacement, and/or frame dropping to reduce the 

individual program bit rates, as required by the bandwidth limitations. 
This GQAM algorithm can introduce jitter as compared to the input signal, so 

dejitter techniques are applied as part of the processing. 
A stat mux dejitter group (SMDG) processes the stat mux stream as a group of 

programs (as a single unit). In the GQAM, it ensures that the stream realizes the 

optimum dejittering. Using SMDGs, the GQAM uses just one buffer dedicated to 

one, and only one, transport stream. This produces an output stream closest in 

quality to the original. 
The SMDG provides the following functions: 

 

Processes the variable bit rate (VBR) stream as a group of programs 

 

Ensures optimum dejitter by using one buffer that is dedicated to only one 

transport stream 

 

Produces an output stream closer to the received jitter 

 

Processes the SMDG as a session, so it can be created and torn down as needed