 the message body (value multipart/mixed) S-CSCF P-CSCF SIP INVITE (SDP) SIP INVITE (SDP) SIP INVITE (SDP / XML) SIP INVITE (SDP / XML) SIP INVITE (SDP / XML) SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing (Alert-Info) SIP 180 Ringing (Alert - Info) SIP 200 OK SIP 200 OK SIP 200 OK SIP 200 OK SIP 200 OK SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK Figure 5.9. CW The telephony application server also includes in this header a parameter boundary corresponding to the boundary between the messages (value boundary1). 166 VoLTE and ViLTE -boundary1 Content-Type application/sdp (SDP message) -boundary1 Content-Type: application/vnd.3gpp.cw+xml <?xml version="1.0"? <ims-cw xmlns="urn:3gpp:ns:cw:1.0"> <communication-waiting-indication/: </ims-cw> -boundary1- 6), 7), 8) On receiving the message 180 Ringing, the telephony application server implements the CFNR, to transfer the call to a third party, in case Bob does not pick the waiting communication up. 9), 10) To the message 180 Ringing received from the P-CSCF entity, the TAS may optionally add the indication to the caller of a call waiting in the header Alert-Info (value urn:alert: service: call-waiting). 11) to 15) Bob's UA entity decides to take the call and end the current call or park his correspondent, and responds to the INVITE request with the message 200 OK. 16) to 20) The caller's UA entity caller acknowledges the 200 OK response with the ACK message. In the second case, the telephony application server relays the INVITE request, without enriching the message body. However, as before, it inserts the header Alert-Info into the response 180 Ringing. 5.2.1.7. Communication rejection 5.2.1.7.1. ICB Incoming communication barring (ICB) enables the callee (Bob) to reject an incoming call belonging to a certain category of communication. The rule may include the URI of the caller, present in the header P-Asserted- Identity or Referred- - By (in the case of call forwarding). Bob's telephony application server responds to Alice's UA entity with the message 6