When a P-CSCF receives the 200 OK to REGISTER SIP message, it stores the P-Associated-URIs present in the response in AoR RCB list. P-CSCF supports a total of 20 SIP/Tel URIs in the P-Associated0-URI header for a 200 OK response to REGISTER message.
Future SIP requests from the registered users which contain P-Preferred-Identity values are compared with the stored list of URIs in the AoR RCB list (internally stored registration info). If the P-Preferred-Identity is present in the list, the egress SIP request is added with the P-Asserted-Identity with the URI present. If the ingress SIP request does not contain the P-Preferred-Identity or the P-Preferred-Identity values are not matching with the AoR RCB list, the default public user identity picked from the top of the AoR list is added as P-Asserted-Identity.
This behavior is configurable by enabling the enableDefaultPuiProcedures flag in the SBC IP Signaling Profile.
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