om the UE entity contains the identity of the S-CSCF entity in the header route. The P-CSCF entity detects emergency calls and forwards them to the E-CSCF entity. The P-CSCF entity generates the data necessary for the generation of charging tickets. The P-CSCF entity establishes an IPSec (IP Security) association with the UE at its registration. During session establishment, the P-CSCF entity controls the type of resources required by the UE on the basis of the capacities authorized by the EPS network, using the DIAMETER messages exchanged with the PCRF entity. VoLTE and ViLTE During session establishment, the P-CSCF entity checks resource availability in the EPS network. 1.2.1.2. I-CSCF entity The I-CSCF entity is the specific point of contact within the IMS network for some transactions coming from the P-CSCF or S-CSCF entities. It performs the function of a PROXY SERVER. Upon receipt of the first SIP REGISTER request, the I-CSCF assigns an S-CSCF entity to the UE entity and transfers the request to the S-CSCF entity chosen. To fulfill this function, an exchange of DIAMETER messages with the HSS entity is necessary. Upon receipt of the second SIP REGISTER request and the first SIP INVITE request, for an incoming call, the I-CSCF entity queries the HSS entity for the IP address of the S-CSCF entity attributed to the UE entity and transfers the request to that S-CSCF entity. The I-CSCF entity forwards the data necessary for the generation of charging tickets. 1.2.1.3. S-CSCF entity The S-CSCF entity provides the UE entity with session control services. It performs different roles depending on the type of request received: - that of a REGISTRAR for the registration of the UE entity; - that of a LOCATION SERVER for the storage of the correspondence between the IP address and the URI identity of the UE entity; - that of a PROXY SERVER for the establishment of a session; - that of an UA, in abnormal operating conditions, when it has to terminate or generate SIP transactions. On receiving the first REGISTER request, t