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Mastering 5G Network Design, Implementation, and Operations
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In the previous section, we saw how an IMS PDU session is established. In this section, we will go over the VoNR call flow, which is used when a user places a voice call.
Figure 7.25 – VoNR call flow – part 1
Step 1: The UE initiates SIP registration toward the called party via UPF, and P-CSCF through the IMS core network in the backend.
Step 2: P-CSCF sends Npcf_PolicyAuthorization_Update
to the PCF to enforce policies, modify service information, apply gate control for traffic shaping and policing, modify subscription to SDF notification/deactivation, and so on.
Step 3: The PCF sends an HTTP POST
request (/callbacks/v1/smPoliciesUpdate
Notification/imsi-123xxxxxx:1:1591309591702656285/update
) to the SMF to update PCC rules (SIP VoNR audio), policy control request triggers, SDF, and charging-related information.
Step 4: The SMF processes the received PCC rules and sends a 204 No Content
(200 OK) message for...
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