S2. IMS Session Initiation signalling flow —
mobile origination and termination in home network
S2-2a. SIP 183 Session Progress response:
from UE2 to P-CSCF2
(9 of 70)
: UE2 provides the access-type and access-info, related to the serving access network.
: a tag is added to the To header.
: Contains a SIP URI with the IP address or FQDN of the UE; it includes the comp=sigcomp parameter.
: Contains the set of codecs supported by 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.