 identifier in the INVITE request that it transfers to the Emergency CSCF entity (E-CSCF), in the following two cases (Figure 3.13): Basic Procedures - the mobile is not registered, because it has no UICC card or because it is on a visited network that has no roaming agreement with the home network; - the mobile is already registered with the S-CSCF entity and a specific registration for the emergency call is not required. If a specific registration for the emergency call is required, the P-CSCF entity informs the mobile (Figure 3.13). User dials an emergency call The mobile detects the The mobile send a P-CSCFentity détects emergency call normal service request the emergency call P-CSCF entity inserts an emergency indication information Starting the procedure of the detected emergency call the mobile sends an P-CSCF entity accepts E-CSCF entity The mobile is emergency service processes the registered anonymous call request anonymous call the mobile sends an P-CSCF entity accepte emergency service the emergency service E-CSCF entity request awith normal processes the request awith normal emergency call registration registration Emergency registration procedure The mobile sends an E-CSCF entity emergency service request processes the with an emergency emergency call registration Figure 3.13. Conditions for the transmission of the emergency call The REGISTER request shall insert in the header Contact the parameter SOS to indicate that it is a registration for an emergency call. REGISTER sip: ims mnc01 mcc208 3gppnetwork.org SIP/2.0 Contact: <sip 192.0.2.101>; expires=600000; SOS; Radio Interface Procedures 4.1. Radio interface At the LTE-Uu radio interface, between the user equipment (UE) and the evolved node base station (eNB), traffic data, corresponding to an IP Internet protocol (IP) packet and signaling data, corresponding to an radio resource control (RRC) message, are encapsulated by the data link layer broken down into three sub-layers (Figure 4.1): - packet data convergence protocol (PDCP); - radio link co