K.2.1 General

23.1673GPPIP Multimedia Subsystem (IMS) emergency sessionsRelease 17TS

This clause lists the additional functionality in the network that is required to support IMS emergency sessions for roaming users in network deployments where there are no IMS-level roaming interfaces between the serving IMS network and the home IMS network.

K.2.2 P-CSCF

In addition to the functionality described in clause 6.2.1, the P-CSCF supports the functionality listed below:

– P-CSCF shall be able to retrieve the UE/user’s IMSI, IMEI and MSISDN (if available) from the PCRF/PCF.

– P-CSCF may support the GIBA procedure over Gm as defined in TS 24.229 [19].

– P-CSCF may verify the IMSI/IMEI provided in the SIP REGISTER message against the IMSI/IMEI provided by the PCRF or PCF.

K.2.3 PCRF or PCF

– PCRF or PCF shall be able to provide the IMSI, the ME Identity (IMEISV), and MSISDN (if available) over Rx to the P-CSCF.

K.2.4 PGW or SMF/UPF

– PGW or SMF/UPF shall be able to prevent "source IP address spoofing" for IMS emergency PDN connections if GIBA authentication, defined in TS 33.203 [44], is used as part of emergency IMS registration.

K.2.4 HSS or UDM

– The EPS user subscription at the HSS should contain exactly one MSISDN which should be the same as that in the IMS profile.

– The 5GS user subscription at the UDM should contain exactly one MSISDN based GPSI which should be the same as that in the IMS profile.