J.3 High Level Procedures for IMS emergency calls
23.1673GPPIP Multimedia Subsystem (IMS) emergency sessionsRelease 17TS
For the high level procedures (as described in clause 7.1.1) the following statements apply for UE detected emergency calls when EPC access over WLAN is used:
– the IP-CAN bearer resource is a PDN connection dedicated for emergency services. The TS 23.402 [29] describes how to indicate that a PDN connection request is for emergency;
– For registration requests received from an emergency PDN connection, the P-CSCF shall reject any IMS registration which is not for the emergency purpose.
NOTE 1: When the IMS network detects that the UE is establishing an emergency session over WLAN access to EPC while the UE is not in its Home country, local policies in the Home IMS network may determine whether to nevertheless handle the emergency session
For the high level procedures (as described in clause 7.1.2) the following statements apply for Non UE detectable emergency calls when WLAN access to EPC is used:
– The P-CSCF may reject the session initiation request with an indication that this is an emergency session or may allow the session initiation request to continue.
The following flow contains a high level description of the emergency service procedures performed over WLAN access to EPC when the UE can detect that an emergency PDN connection is being needed. This flow provides details (or references) related with WLAN access to EPC on top of the general procedure described in clause 7.1.
Figure J.3: Terminal Detected Emergency Calls (WLAN access to EPC)
The following steps are performed:
1. Same as step 1 of Figure 7.1.
2. The UE releases any PDN connection it may have over untrusted access to EPC.
3. Void.
4. As described in TS 23.402 [29]:
– in the case of untrusted access, the UE selects an ePDG for emergency services and sets-up a PDN connection for emergency services;
– in the case of trusted access, the UE sets-up a PDN connection for emergency services.
The UE is assigned an IP address at this stage.
NOTE 2: No specific WLAN AP selection is carried out to support emergency services.
5. Same as step 5 of Figure 7.1.
6. Same as step 6 of Figure 7.1.
7. Same as step 7 of Figure 7.1.