bed-QoS Profile MSISDN VPLMN-Dynamic-Address-Allowed STN-SR ICS-Indicator Figure 5.1. Subscription data to EPS network The home subscriber server (HSS) stores the service profile data that is transmitted to the mobility management entity (MME) when attaching the mobile or when changing the profile service. The "PDP-Type" field indicates the version of IP (Internet Protocol): IPv4, IPv6, IPv4 or IPv6, IPv4 and IPv6. 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. 148 VoLTE and ViLTE The "service-selection" field contains the access point name (APN): ims in the case of voice or conversational video service, SOS in the case of emergency call. The "EPS-subscribed-QoS profile" field indicates the value of the QoS class identifier (QCI) and the allocation and retention priority (ARP). The "VPLMN-dynamic-address-allowed" field indicates whether roaming is allowed or not. The "subscriber-status" field indicates whether the telephone service is allowed or not. The "network-access-mode" field indicates whether the telephone service is available in packet-switched (PS) and circuit-switched (CS) mode or in PS mode only. The "MSISDN" field contains the mobile subscriber number. The "STN-SR" field contains the session transfer number for SRVCC, used during the PS-CS inter-system handover, in the case of the implementation of the e-SRVCC function (enhanced Single Radio Voice Call Continuity). The "ICS-indicator" field indicates whether IMS centralized services are available or not. 5.1.2. Subscription to the IMS network When subscribing to the IP multimedia subsystem (IMS), the user is assigned a IMS private user identity (IMPI) to which are associated one or more service profiles (Figure 5.2). The HSS entity stores data relating to a user's service profile which is transmitted to the serving call session control function (S-CSCF) when the registration of the user or when a change of the service pr