back to TS 24.228
- P-Access-Network-Info: UE2 provides the access-type and access-info, related to the serving access network.
- To: A tag is added to the To header.
- Contact: Contains a SIP URI with the IP address or FQDN of UE2. It includes the comp=sigcomp parameter.
- SDP: The SDP contains the set of codecs supported UE2. It requests a confirmation of the QoS preconditions for establishing the session.
- P-CSCF2 authorizes the resources necessary for this session. The approval of QoS commitment either happens at this stage or after 200 OK of INVITE based on operator local policy.