A

N

Y

Y

Y

PS

CS if available and supported (NOTE 7, NOTE 8)

B

N

Y

N

Y

PS or CS if the emergency session includes at least voice.

PS if the emergency session contains only media other than voice.

PS if first attempt in CS

CS if first attempt in PS (NOTE 7, NOTE 8)

C

N

Y

Y or N

N

PS if ESFB is "Y" (NOTE 5).

Else CS or PS for another 3GPP RAT with EMS or ESFB set to "Y" if available and supported and if the emergency session includes at least voice.

Else PS for another 3GPP RAT with EMS or ESFB set to "Y" if available and supported if the emergency session contains only media other than voice.

PS if first attempt in CS

CS if first attempt in PS (NOTE 7, NOTE 8)

D

Y

N

Y or N

Y or N

CS if the emergency session includes at least voice.

PS if available and EMS or ESFB is "Y" and emergency session contains only media other than voice.

PS if available and EMS or ESFB is "Y"

E

Y

Y

Y

Y

If the emergency session includes at least voice, follow rules in TS 22.101 [8] which say to use the same domain as for a non-EMC (NOTE 2)

PS if the emergency session contains only media other than voice.

PS if first attempt in CS

CS if first attempt in PS

F

Y

Y

Y or N

N

PS if ESFB is "Y" (NOTE 5).

Else PS for another 3GPP RAT with EMS if available and supported or CS, if the emergency session includes at least voice.

CS if first attempt in PS

PS for another 3GPP RAT if available and supported and EMS or ESFB is "Y" if first attempt in CS.

G

Y

Y

N

Y

CS if the emergency session includes at least voice.

PS if the emergency session contains only media other than voice.

PS

EMC = Emergency Session. EMC includes also normal calls initiated in the CS domain that are treated by the CS CN as emergency calls.

VoIMS = Voice over IMS over PS sessions support as indicated by IMS Voice over PS session supported indication as defined in TS 23.401 [28], TS 23.060 [2] and TS 23.502 [49].

EMS = IMS Emergency Services supported as indicated by Emergency Service Support indicator as defined in TS 23.401 [28], TS 23.060 [2], TS 23.501 [48] and TS 23.502 [49].

ESFB = Emergency Services Fallback for 5GS as defined in TS 23.501 [48] and TS 23.502 [49].

NOTE 1: If the UE selects the CS domain and initiates a normal call using the dialled local emergency number (see clause 7.1.2), and the UE enters limited service state (e.g. due to a Location Registration failing), then the UE camps on an acceptable cell (see TS 23.122 [41]) and may proceed with the EMC by initiating an emergency call in limited service state.

NOTE 2: Use of the same domain as for a non-EMC is restricted to UTRAN, E-UTRAN and NG-RAN access (e.g. excludes WLAN).

NOTE 3: This NOTE applies to a UE in dual registration mode as defined in TS 23.501 [48]. A dual registration mode UE that is registered to both EPC and 5GC assumes attachment, for the purpose of the "PS Attached" column, to whichever of EPC or 5GC indicates EMS as "Y". When both EPC and 5GC indicate EMS as "Y", the UE shall assume attachment to either EPC or 5GC based on implementation. A UE that is registered to both EPC and 5GC does not use emergency services fallback and ignores the ESFB condition when performing domain selection.

NOTE 4: The other 3GPP RAT for row C and row F can be any of UTRA, E-UTRAN connected to EPC, E-UTRA connected to 5GC or NR connected to 5GC that is supported by the UE and differs from the RAT to which the UE is currently attached in the PS domain (or is assumed to be attached based on NOTE 3).

NOTE 5: The condition ‘ESFB is "Y"’ only applies for a UE that is camped on or connected to 5GS via NR or via E-UTRA and that supports Emergency Services Fallback. In that case the emergency call will be provided over E-UTRAN or E-UTRA connected to 5GC as defined in procedures in TS 23.502 [49]. The condition ‘ESFB is "Y"’ is taken into consideration by the UE only when the network has indicated EMS = "N" for the RAT on which the UE is camping or connected.

NOTE 6: For 5GS, the value of the column "EMS" is for the RAT that UE is camped on or is connected to.

NOTE 7: As an implementation option, when the first attempt uses PS and fails for reasons other than related to IMS, the second attempt may use PS with a different 3GPP RAT. In this case the UE can make a third attempt using CS.

NOTE 8: As an implementation option, when the first attempt uses PS and fails because the first discovered P-CSCF is not available, additional attempts may use PS with alternate P-CSCFs (see clause E.1.1.1 of TS 23.228 [1] and clause 4.3.2.2.1 of TS 23.502 [49]). In this case the UE can make an attempt using CS after making failed PS attempts on all discovered alternate P-CSCFs.