Section: 6.4.9.2 Security procedures not applied
Content: As a serving network option, emergency calls, or PS connections for emergency sessions, may be established without the network having to apply the security mode procedure as defined in TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ]  [35]. The following are the only cases where the "security procedure not applied" option may be used: a) Authentication is impossible because the (U)SIM is absent; b) Authentication is impossible because the serving network cannot obtain authentication vectors due to a network failure; c) Authentication is impossible because the (U)SIM is not permitted to receive non-emergency services from the serving network (e.g. there is no roaming agreement or the IMSI is barred); d) Authentication is possible but the serving network cannot successfully authenticate the (U)SIM.