S3. IMS Session Initiation signalling flow —
origination in CS Network
mobile termination in home network
S3-2a. SIP 183 Session Progress response:
from UE2 to P-CSCF2
(7 of 48)
: the UE 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.
: the SDP contains the set of codecs supported by UE; it requests a confirmation of the QoS preconditions for establishing the session.