The values of the TEID parameter of the GTP-U protocol are exchanged via the GTPv2-C (GPRS Tunnel Protocol Control), S1-AP and X2-AP protocols. VoLTE and ViLTE The TEID parameter used for the signaling exchanged over the S5 interface is unique. The same parameter is used for all signaling messages relating to the activation of the various S5 bearers for the different mobiles. The TEID parameter used for the signaling exchanged over the S10 and S11 interfaces is unique for each mobile. The same parameter is used for all signaling messages relating to the establishment of the various S1-U bearers for the same mobile. Table 2.6 summarizes the GTPv2-C messages exchanged for the management of support and mobility. Type of messages Request Response CREATE / DELETE CREATE / DELETE SESSION REQUEST SESSION RESPONSE CREATE / MODIFY / CREATE /MODIFY / DELETE BEARER DELETE BEARER REQUEST RESPONSE DOWNLINK DATA NOTIFICATION Bearer management DOWNLINK DATA ACKNOWLEDGE or NOTIFICATION DOWNLINK DATA NOTIFICATION FAILURE INDICATION CREATE / DELETE CREATE / DELETE INDIRECT DATA INDIRECT DATA FORWARDING TUNNEL FORWARDING TUNNEL REQUEST RESPONSE Type of messages Request Response FORWARD RELOCATION FORWARD RELOCATION REQUEST RESPONSE FORWARD RELOCATION FORWARD RELOCATION NOTIFICATION ACKNOWLEDGE Mobility management FORWARD ACCESS FORWARD ACCESS CONTEXT CONTEXT NOTIFICATION ACKNOWLEDGE CONTEXT REQUEST CONTEXT RESPONSE CONTEXT ACKNOWLEDGE Table 2.6. GTPv2-C messages Signaling Protocols 2.5.1. Bearer management The signaling bearer related to a mobile is created by the CREATE SESSION REQUEST message. It is reinforced by the use of a TEID parameter. The message is transmitted: - by the MME entity to the serving gateway (SGW), over the S11 interface; - by the target SGW entity for the PDN gateway (PGW), over the S5 interface. The request is transmitted when any of the following procedures are initiated: - attachment of the mobile, - traffic request from the mobile, - updating of the tracking area code (TAC), - handover. The SGW entity (or