Content for TS 23.167 Word version: 17.2.0

H.1 General H.2 UE specific behaviour H.3 High Level Procedures for IMS emergency calls H.4 Location handling H.5 Domain Priority and Selection Rules for Emergency Session Attempts H.6 eCall over IMS
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E Emergency support in different IP-CANs Word‑p. 44

Support for emergency services in the IP Multimedia Core Network can be provided by certain IP-CANs according to Table E.1, which shows the level of possible emergency support in this version of the specification. The UE may be able to use also other IP-CANs that are not included in Table E.1 to access emergency services in the IP Multimedia Core Network, but the support of such access technologies is out of scope of this specification.

Table E.1: Support for IMS Emergency Services by Different IP-CANs

IP-CAN	Normal Access	Emergency support	Insufficient Security Credentials
GPRS (UTRAN)	X	X	X
Fixed Broadband	X	X	X
cdma2000 HRPD/PDS	X	X	X
cdma2000 HRPD/EPC	X	X	X
EPS (UTRAN and E-UTRAN)	X	X	X
WLAN access to EPS	X (Note 1)	X	–
5GS (NG-RAN)	X	X	X
non-3GPP access to 5GC	X (Note 1)	X	–
NOTE 1: Emergency Sessions use a normal access to EPC/5GC only in the case of emergency sessions not detected by the UE and nevertheless served by the IMS network.

The term "normal access" in Table E.1 means that the IP-CAN is not made aware of the UE intent to establish an emergency services session and therefore provides no special emergency support e.g. call priority.

The term "emergency support" in the table means that the IP-CAN is made aware of the UE intent to establish an emergency services session, or at least of the priority nature of the access, so that the access network is able to handle the emergency call with appropriate priority.

The term "insufficient security credentials" in the table means that the IP CAN is able to allow a UE with no UICC card or a UICC card with insufficient credentials to obtain IP bearer access for emergency services in the IP Multimedia Core Network.

F (Normative) IMS Emergency Services Using HRPD/PDS Network Word‑p. 45

F.1 cdma2000 HRPD/PDS Options |R8| Word‑p. 45

The following options from the normative clauses of this TS are applicable in cdma2000 HRPD systems with a PDS core network:

Clause 7.1.1, step 4 "The IP-CAN may support a UE indication that this request is for an emergency service".

The following options from the normative clauses of this TS are not applicable in cdma2000 HRPD/PDS systems:

Clause 4.1 "The P-CSCF serving the emergency call is the IMS network entity which may retrieve the location identifier from the IP CAN".

F.2 Requirements on the HRPD Network as an IP-CAN |R8| Word‑p. 45

For an emergency call over HRPD, the requirements on the IP CAN are specified in 3GPP2 X.S0060 [25].

F.3 Information Flows |R8| Word‑p. 45

The informational flows for emergency calls over HRPD are provided in 3GPP2 X.S0060 [25].

G TEL URI provisioning considerations for IMS emergency call back |R8| Word‑p. 46

In order to support emergency call-back from the PSTN or CS Domain:

For a single or multiple device subscription that contain both a SIP URI and TEL URI in at least one implicit registration set for each device (including subscriptions that share SIP-URIs and TEL URIs between devices), IMS emergency sessions can already be supported. If the user registers with a temporary public user identity (e.g. the subscription has a device containing a USIM) ensure that a TEL URI is provisioned in the same implicit registration set as the temporary public user identity.
For a multiple device subscription that has TEL URIs for some devices but has one or more devices that are not assigned an implicit registration set containing a TEL URI (e.g. because these devices in the subscription are not allowed to use a TEL URI in normal originations), the existing TEL URIs in the subscription cannot be shared between all devices for the purposes of IMS emergency sessions.

H (Normative) IMS emergency services using UTRAN, E-UTRAN and NG-RAN radio access network |R9| Word‑p. 47

H.1 General Word‑p. 47

This annex includes additional requirements and clarifications when the IP-CAN is a PS Domain supporting UTRAN, E-UTRAN or NG-RAN radio access network.

If a PLMN supports other emergency numbers than those listed in TS 22.101, the UE is connected to the PLMN using UTRAN, E-UTRAN or NG-RAN radio access network and the UE needs to know these other emergency numbers, then such emergency numbers shall be provided to the UE via the mobility management procedures as described in TS 24.301, TS 24.008 and TS 24.501.

If an SNPN supports other emergency numbers than those listed in TS 22.101, the UE is connected to the SNPN using NR access and the UE needs to know these other emergency numbers, then such emergency numbers shall be provided to the UE via the mobility management procedures as described in TS 24.501.

For registration requests received from an emergency PDN connection or emergency PDU session, the P-CSCF shall reject any IMS registration which is not for the emergency purpose.

eCall is supported with E-UTRAN and NG-RAN for PLMNs only, i.e. eCall is not supported for SNPNs. UE configured for eCall Only Mode can receive a PSAP call back for a limited duration following the termination of the eCall due to its specific mobility management procedures requirement as defined in TS 22.101.

H.2 UE specific behaviour Word‑p. 47

For the specific case where the UE has selected to make an emergency call over EPS, GPRS or 5GS the UE shall use the following procedures:

A UE shall establish an emergency PDN connection or emergency PDU session and perform an IMS emergency registration before initiating a UE detectable emergency session via UTRAN, E-UTRAN or NG-RAN.
A UE shall not establish an emergency PDN connection or emergency PDU session if the UE initiated a non UE detectable emergency session and is subsequently informed by the network that the ongoing session is an emergency session.

NOTE 1:
If SRVCC is required in the network, an operator could download the local emergency numbers to avoid non UE detectable emergency sessions since UTRAN and E-UTRAN will not be able to identify emergency SRVCC handling without an emergency PDN connection.
If the UE initiates a non UE detectable emergency session, and the session initiation request is rejected by the P-CSCF with an indication that this is an emergency session, the UE shall select a domain according to the requirements for domain priority and selection in clause H.5 when applying the requirements in clause 7.1.2.
A UE in 5GS shall not initiate establishment of an IMS emergency session over Non-3GPP access unless the emergency session could not be established via 3GPP access.
If the UE has not been authenticated in the PS domain, the UE shall initiate an IMS emergency session establishment without registration according to clause 7.4.
The UE shall include the latest available Cell Global Identification (CGI) in the IMS emergency request establishing the emergency call.
When the UE is using NR satellite access to 5GC, the UE shall include an indication of NR satellite access in the IMS request.

NOTE 2:
When using UTRAN, the UE is not always able to read the current cell identity and in some cases the UE can be connected to several cells simultaneously.

NOTE 3:
For NR satellite access to 5GC the NR CGI (NCGI) available to the UE and the NCGI provided from NG-RAN to 5GC might be different. The NCGI provided by the UE might not relate to the UE's geographic location. A P-CSCF relying only on the UE provided NCGI could then lead to errors.
If the UE is required to include an equipment identifier (according to clause 4.1 and clause 6.1) the equipment identifier shall be the IMEI.
For the media supported during IMS emergency sessions in clause 10.4 of TS 22.101, media codec and format support is specified in TS 26.114.
UE shall only perform eCall procedure over IMS as specified in clause 7.7.1 when it detects the "eCall supported" indication as defined in TS 23.401 and TS 23.501.
When PS access is available, but the UE does not detect the "eCall supported" indication as defined in TS 23.401 and TS 23.501, and there is no CS access available, the UE shall establish a regular IMS emergency call.
If the broadcast indicators in an E-UTRA cell connected to 5G and EPC as defined in TS 23.501 indicate only one core network (EPC or 5GC) supports emergency services then the UE shall register to the core network which supports emergency services when the UE initiates emergency services. If broadcast indicators indicate that both 5GC and EPC support emergency services then the UE initiates emergency services to either EPC or 5GC according to the UE implementation.
If the broadcast indicator in an NR cell indicates that the cell provides access to SNPNs and that 5GC supports emergency services, the UE shall only register to the core network of the SNPN that indicates support for emergency services. If broadcast indicators indicate that one or more SNPNs and/or PLMNs support emergency services, then the UE initiates emergency services to either a SNPN or a PLMN according to UE implementation.

H.3 High Level Procedures for IMS emergency calls Word‑p. 48

For the high level procedures (as described in clause 7.1.1) the following statements apply for UE detected emergency calls when PS domain with UTRAN, E-UTRAN or NG-RAN access is used:

the bearer registration to the IP-CAN is the PS attach or PS Registration procedure;
the IP-CAN bearer resource is the PDP context for GPRS, EPS Bearer for EPS and QoS Flow for 5GS, and TS 23.060, TS 23.401 and TS 23.501 respectively describe how to indicate that the request is for emergency;
the release of reserved bearer resources is the release of a PDP context, an EPS Bearer or a QoS Flow.

For the high level procedures (as described in clause 7.1.2) the following statements apply for Non UE detectable emergency calls when PS domain with UTRAN, E-UTRAN or NG-RAN access is used:

The P-CSCF rejects the session initiation request with an indication that this is an emergency session; or
the P-CSCF allows the session initiation request to continue and the E-CSCF informs the UE that it is an emergency session. Such a session will not use an emergency PDN connection or emergency PDU session and will not have SRVCC or SRVCC for IMS emergency session support.

For the IMS Emergency Session Establishment without Registration (as described in clause 7.4), P-CSCF retrieves the additional subscriber related identifier(s) from IP-CAN via PCC in TS 23.203 when PS domain with UTRAN and E-UTRAN access is used.

H.4 Location handling Word‑p. 49

The applicable location solutions are specified in TS 23.271 for control plane with UTRAN and E-UTRAN access, in TS 23.501 and TS 23.502 for control plane with NG-RAN access and in SUPL 2.0 (OMA AD SUPL [15], OMA TS ULP [16]) for user plane. For SUPL, SUPL Initiation Function using UDP/IP (OMA AD SUPL [15]) shall be supported by the SET.

If the operator policy requires network provided location using PCC-based solutions for the UE location (e.g. serving cell), the P-CSCF retrieves location information from the access network and includes it in the emergency service request, as described in TS 23.228. The UE location is marked as being network provided to distinguish it from location information that the UE provided.

If the operator policy requires network provided location using the LRF-based solution for the UE location (e.g. serving cell), the P-CSCF forwards the emergency request to E-CSCF. The E-CSCF retrieves location information from LRF as described in clause 6.2.2.

Operator policies in the P-CSCF and E-CSCF should be aligned to ensure that the E-CSCF doesn't attempt to retrieve location information from the LRF if network-provided location information is present in the initial emergency request. However, as described in clause 6.2.2, the E-CSCF may request the LRF to retrieve additional location information (e.g. the UE's geographical location information).

H.5 Domain Priority and Selection Rules for Emergency Session Attempts Word‑p. 49

This clause details the domain priority and selection (see clause 7.3) for UE that attempts to make an emergency session for UTRAN, E-UTRAN or NG-RAN radio access networks based on the UE attach status to CS or PS domains and the network support for IMS emergency and IMS voice over PS.

The following table (Table H.1) defines these rules based on the UE (last 2 columns) for different initial conditions (first 4 columns) when an emergency session is initiated and when the UE is not in limited service state.

For NG-eCall (eCall over IMS) domain selection in clause H.6 applies. This clause is not applicable for NG-eCall.

Table H.1: Domain Selection Rules for emergency session attempts for UTRAN, E-UTRAN or NG-RAN radio access networks

	CS Attached	PS Attached	VoIMS	EMS	First EMC Attempt	Second EMC Attempt
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 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, TS 23.060 and TS 23.502. EMS IMS Emergency Services supported as indicated by Emergency Service Support indicator as defined in TS 23.401, TS 23.060, TS 23.501 and TS 23.502. ESFB Emergency Services Fallback for 5GS as defined in TS 23.501 and TS 23.502. 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) 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. 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. 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 and clause 4.3.2.2.1 of TS 23.502). In this case the UE can make an attempt using CS after making failed PS attempts on all discovered alternate P-CSCFs.

H.6 eCall over IMS |R14| Word‑p. 52

This clause details the domain priority and selection (see clause 7.3) for a UE that attempts to make an eCall over IMS session using E-UTRAN or NG-RAN radio access networks based on the availability of the CS or PS domains and the network support for IMS emergency, eCall over IMS and IMS voice over PS.

The following table (Table H.2) defines these rules based on the UE (last 2 columns) for different initial conditions (first 4 columns) when an eCall over IMS session is initiated and when the UE is not in limited service state.

Table H.2: Domain Selection Rules for eCall over IMS session attempts for E-UTRAN or NG-RAN radio access networks

	PS Available	VoIMS	EMS	ECL	First eCall Attempt	Second eCall Attempt
A	Y	Y	Y	Y	PS	PS on another PS RAT if available with EMS=Y and ECL=Y or CS if available
B	Y	Y	Y	N	CS if available	PS (UE establishes IMS emergency session)
C	Y	Y or N	N	N	CS if available	PS on another PS RAT if available with EMS=Y or EMS unknown
D	Y	N	Y	Y	PS or CS if available	CS if first attempt in PS PS if first attempt in CS
E	Y	N	Y	N	CS if available	PS (UE establishes IMS emergency session)
F	N		-	-	CS if available
VoIMS Voice over IMS over PS sessions support as indicated by IMS Voice over PS session supported indication as defined in TS 23.401 and TS 23.502. EMS IMS Emergency Services supported as indicated by Emergency Service Support indicator as defined in TS 23.401 and TS 23.501 and TS 23.502. ECL eCall Over IMS support as indicated by the eCall support indicator defined in TS 23.401 and TS 23.501. NOTE 1: 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.