S4. IMS Session Initiation signalling flow —
mobile origination in home network
termination in CS network
S4-3a. SIP PRACK request (UE1 to UE2):
from UE1 to P-CSCF1
(12 of 48)
The request does not contain SDP because in the initial SDP offer/answer there was a single media stream with a single codec.