 SMS-DELIVER-REPORT/RP-ACK is transmitted from the mobile to acknowledge the message SMS/SMS-DELIVER/RP-DATA. 13) The message SMS-DELIVER-REPORT/RP-ACK/CP-DATA is carried by the message NAS UPLINK NAS TRANSPORT, between the mobile and the MME entity. 14) The message SMS-DELIVER-REPORT/RP-ACK/CP-DATA is transported by the message SGsAP UPLINK UNITDATA between the MME and MSC server entities. 15) The message SMS-DELIVER-REPORT/RP-ACK is transported by the message MAP FORWARD SHORT MESSAGE ACK, between the MSC server and SMS-GMSC entities. 16) The SMS-GMSC entity sends the message SMS-DELIVER- REPORT to the SMS-SC entity. The CP-ACK message is transmitted by the MSC server entity to acknowledge the message SMS-DELIVER-REPORT/RP-ACK/CP-DATA. 282 VoLTE and ViLTE 17) The CP-ACK message is the message conveyed by SGsAP DOWNLINK UNITDATA between the MSC server and MME entities. 18) The CP-ACK message is conveyed by the message NAS UPLINK NAS TRANSPORT between the MME entity and the mobile. 19) The entity MSC server informs the MME entity that the transfer of the SMS messages is done by sending the message SGsAP RELEASE REQUEST. 10.3. SMS over SIP 10.3.1. Functional architecture The functional architecture of the SMS over SIP is given in Figure 10.6. The IP-SM-GW entity is an application server of the IMS network. The IP-SM-GW entity provides the protocol interworking between, firstly, the IMS network and secondly, the SMS-IWMSC entity for outgoing SMS messages or the SMS-GMSC entity for incoming SMS messages. Outgoing SMS IWMSC IP-SM UTRAN Incoming SMS Figure 10.6. Functional architecture for SMS over SIP When the mobile registers with the S-CSCF entity, the S-CSCF entity registers the mobile to the IP-SM-GW entity. To receive incoming SMS messages, the IP-SM-GW entity registers in turn the mobile to the HLR entity and provides also its address. The entities SMS-IWMSC, SMS-GMSC and SMSC are not affected by the architecture of SMS over SIP. Short Message Service 10.3.2. Procedures 10.3.2.1. Originating side The transfer p