- The P-CSCF adds itself to the Record-Route header and Via header. As the request is forwarded to an interface that is not compressed, the own P-CSCF SIP URI does not contain the "comp=sigcomp" parameter.
- The P-CSCF removes the Security-Verify header and associated "sec-agree" option-tags prior to forwarding the request. As the Proxy-Require header is empty, it removes this header completely.
- P-Asserted-Identity: P-CSCF inserts the TEL URI in the P-Asserted-Identity header field and it also removes P-Preferred-Identity header field.
- P-Charging-Vector: The P-CSCF inserts this header and populates the icid parameters with a globally unique value.