he mobile starts the attachment procedure to the evolved packet system (EPS) which comprises the following steps: - the mutual authentication between user equipment (UE) and mobility management entity (MME) corresponding to the AKA (Authentication and Key Agreement) mechanism; - the security of non-access stratum (NAS) messages; - the location of the mobile related to the tracking area identity (TAI) and to the E-UTRAN cell global identifier (ECGI); - the establishment of a default bearer. In the case where the voice or video conversational call is supported by the EPS network, a default bearer (QCI = 5) is established for transporting the signaling exchanged between the mobile and the IP multimedia sub-system (IMS); - the granting of a globally unique temporary identity (GUTI). The UE mobile attachment procedure to the EPS network is described in Figure 3.1: 1) The attachment procedure is triggered by the UE entity when it sends to the eNB entity the EMM ATTACH REQUEST message containing the international mobile subscriber identity (IMSI) of the mobile. VoLTE and ViLTE: Voice and Conversational Video Services over the 4G Mobile Network, First Edition. André Perez. C ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc. VoLTE and ViLTE ESM PDN CONNECTIVITY REQUEST EMM ATTACH REQUEST RRC ConnectionSetupComplete S1-AP INITIAL UE MESSAGE DIAMETER AIR DIAMETER AIA EMM AUTHENTICATION REQUEST EMM AUTHENTICATION RESPONSE EMM SECURITY MODE COMMAND EMM SECURITY MODE COMPLETE DIAMETER ULR DIAMETER ULA GTPv2-C CREATE SESSION REQUEST GTPv2-C CREATE SESSION REQUEST DIAMETER CCR DIAMETER CCA GTPv2-C CREATE SESSION RESPONSE GTPv2-C CREATE SESSION RESPONSE ESM ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST EMM ATTACH ACCEPT S1-AP INITIAL CONTEXT SETUP REQUEST RRC ConnectionReconfiguration RRC SecurityModeCommand RRC SecurityModeComplete ESM ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT EMM ATTACH COMPLETE RRC ConnectionReconfiguration Complete S1-AP INITIAL CONTEXT SETUP RESPONSE GTPv2-C MODIFY BEARER REQUEST GTPv2-C MODIFY