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The goal is to design a system where a caller can call from a POTS phone to a SIP device and neither the caller nor the SSP nor the STP nor the SCP know the call is going to a SIP device.
STEP 1) The SSP initiates a call as though the Media Gateway Controller (MGC) is another SSP.
STEP 2) The STP forwards the call request to the MGC as though it were a tandem SSP.
STEP 3) The MGC does all of the SSP functions that the distant end SSP did in the previous example plus it sends all of the commands to the Media Gateway (MG) that the MG needs to connect to the SSP and translate from TDM to RTP. It also initiates all call messages necessary to set up a session with the distant UA (one portion of the MGC acts as a UA).
STEP 4) The SIP Servers locate and validate the distant UA and provide all functions necessary to build a session to the MG.
STEP 5) Once the session is prepared, the MG completes a voice path from the UA to a selected TDM channel to the SSP.
Posted by yogendra
Posted by sagitraz
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