quest for deregistration, Alice's UA entity (or Bob's) starts the detachment phase and passes to the MME entity the EMM DETACH REQUEST message. 86 VoLTE and ViLTE EMM ATTACH REQUEST message carries ESM PDN DISCONNECT REQUEST message. ESM PDN DISCONNECT REQUEST EMM DETACH REQUEST RRC ULInformationTransfer S1 -AP UPLINK NAS TRANSPORT GTPv2-C DELETE SESSION REQUEST GTPv2-C DELETE SESSION RESPONSE GTPv2-C DELETE SESSION REQUEST GTPv2-C DELETE SESSION RESPONSE ESM DEACTIVATE EPS BEARER CONTEXT REQUEST DIAMETER CCR EMM DETACH ACCEPT DIAMETER CCA S1-AP UE CONTEXT RELEASE COMMAND RRC ConnectionRelease S1-AP UE CONTEXT RELEASE COMPLETE Figure 3.4 Mobile detachment to EPS network EMM ATTACH REQUEST message is carried by RRC ULInformation Transfer message on the radio interface LTE-Uu and S1-AP UPLINK NAS TRANSPORT message on the S1-MME interface. 2) The MME entity sends to the SGW entity the GTPv2-C DELETE SESSION REQUEST message to deactivate the default bearer used for telephone signaling. 3) The SGW entity responds with the GTPv2-C DELETE SESSION RESPONSE message. 4) The SGW entity sends to the PGW entity the GTPv2-C DELETE SESSION REQUEST message to deactivate the default bearer. 5) The PGW entity responds with the GTPv2-C DELETE SESSION RESPONSE message. 6) The PGW entity sends to the PCRF entity the DIAMETER CCR message to inform about the deactivation of the default bearer. Basic Procedures 7) The PCRF entity responds to the PGW entity with the DIAMETER CCA message. 8) The MME entity confirms the detachment to Alice's UA entity in the EMM DETACH ACCEPT message. EMM DETACH ACCEPT message carries ESM DEACTIVATE EPS BEARER CONTEXT REQUEST message. EMM DETACH ACCEPT message is carried by RRC Connection Release message on the radio interface LTE-Uu and S1-AP UE CONTEXT RELEASE COMMAND message on the S1-MME interface. 9) The eNB entity confirms the context deactivation in S1-AP EU CONTEXT RELEASE COMPLETE message. 3.5. Establishment of VoLTE session The establishment of the VoLTE session includes the following operations: