All the call flows illustrate that the CC delivery begins once the SDP offer and answer is completed (i.e., when the media bearer is setup). In all the call flows, the first reliable response is SIP 200 OK.
In all the call flows, the originating end of the call sends the SDP offer and terminating end gives the SDP answer. Since, the first reliable response is SIP 200 OK, the SDP answer is always given in the SIP 200 OK message.
The call flows assume that per clause 7A
, the IRI for VoIP is nothing but the delivery encapsulated SIP messages. The call flows do not show the method used for correlating the IRI with IRI and IRI with CC. It is presumed that those are stage 3 details.
All the call flows assume the presence of a Voice Application Server (shown as AS) that provides the voice services like digit translation, invoking the call forwarding, etc.
IRI in the visited CSP is intercepted by the P-CSCF and IRI in the home CSP is intercepted by the S-CSCF.
The call flows show that CC interception is done at the IP-CAN (and it should be interpreted to mean that the interception is done in the PDN-GW or GGSN depending on the packet core network), or at the TrGW or at the IM-MGW. The other possible CC interception options (e.g., IMS-AGW) are not shown.
Not all the functional elements are shown in the call flows. For example, the call flows do not show I-CSCF, HSS, PCRF.
All the call flows show a summary of SIP messages that are delivered to the LEA (not all SIP messages are shown). The term LEMF, used in some call flows, means it is an equivalent of LEA.
For each call flow, references are required to identify MMTEL service that it illustrates (for further study).