Emergency Services are provided to support IMS emergency sessions. "Emergency Services" refers to functionalities provided by the serving network when the network is configured to support Emergency Services. Emergency Services are provided to normally registered UEs and to Emergency Registered UEs, that can be either normally registered or in limited service state. Depending on local regulation, receiving Emergency Services in limited service state does not require a valid subscription. Depending on local regulation and on operator's policy, the network may allow or reject a registration request for Emergency Services (i.e. Emergency Registration) from UEs that have been identified to be in limited service state. Four different behaviours of Emergency Services as defined in TS 23.401, clause 18.104.22.168
Emergency Services shall not be provided to a UE over 3GPP access and untrusted non-3GPP access concurrently, except for the following case:
a UE may be Emergency Registered and have an emergency PDU session over non-3GPP access or may be attached for emergency session to ePDG over untrusted WLAN (as defined in TS 23.402) when 3GPP access becomes available. In which case the UE may have to register over 3GPP access and check first the support for Emergency Services over the 3GPP RAT it has selected (e.g. based on Emergency Services Support indication, Emergency Services Fallback, AS broadcast indicator). If there is native support for Emergency Services in the selected 3GPP RAT the UE will attempt to transfer the emergency PDU session from non-3GPP access to 3GPP access (see TS 23.502, clause 4.9.2). If there is no native support for Emergency Services in the selected RAT, but Emergency Services Fallback to another RAT in 5GS or to another System where Emergency Services may be supported (based on the conditions defined in clause 22.214.171.124), the UE may trigger first Emergency Services Fallback (see TS 23.502, clause 126.96.36.199) and then attempt to transfer the emergency PDU session from non-3GPP access to 3GPP access (see TS 23.502, clause 4.9.2). In these cases the UE may thus briefly be emergency registered and receive emergency services over both 3GPP access and non-3GPP access concurrently.
A UE may only attempt to use Emergency Services over untrusted non-3GPP access if it is unable to use Emergency Services over 3GPP access as specified in TS 23.167
To provide Emergency Services, the AMF is configured with Emergency Configuration Data that are applied to Emergency Services that are established by an AMF based on request from the UE. The AMF Emergency Configuration Data contains the S-NSSAI and Emergency DNN which is used to derive an SMF. In addition, the AMF Emergency Configuration Data may contain the statically configured SMF for the Emergency DNN. The SMF may also store Emergency Configuration Data that contains statically configured UPF information for the Emergency DNN.
When the UE is camped normally in the cell, i.e. not in limited service state, during Registration procedure described in TS 23.502, clause 188.8.131.52
, the serving AMF includes an indication for Emergency Services Support within the Registration Accept to the UE. For 3GPP access, the Emergency Services Support indication is valid within the current Registration Area per RAT (i.e. this is to cover cases when the same registration area supports multiple RATs and they have different capability).
The Emergency Services Support is configured in the AMF according to local regulations and network capabilities. AMF includes Emergency Services Support indicator in the Registration Accept message to indicate that the UE can setup emergency PDU Session to obtain emergency services. The AMF may include additional local emergency numbers associated with the serving network for the UE, further defined in TS 24.501
During Registration procedures over 3GPP access, the 5GC includes the Emergency Services Support indicator, valid for the current Registration Area and indicating per RAT that Emergency Services are supported if any of the following conditions is true within the current Registration Area:
the Network is able to support Emergency Services natively over 5GS;
E-UTRA connected to 5GC supports IMS Emergency Services (e.g. voice), and the NG-RAN is able to trigger handover or redirection from NR to E-UTRA connected to 5GC at QoS Flow establishment for IMS Emergency Services (e.g. voice);
NG-RAN is able to trigger handover to EPS at QoS Flow establishment for IMS Emergency Services (e.g. voice);
NG-RAN is able to trigger redirection to EPS at QoS Flow establishment for IMS Emergency Services (e.g. voice); or
NG-RAN is able to trigger 5G SRVCC handover to UTRAN for IMS Emergency Services (i.e. voice).
During Registration procedures over non-3GPP access, the 5GC indicates that Emergency Services are supported if the Network is able to support Emergency Services natively over 5GS.
The 5GC includes an indication per RAT whether it supports Emergency Services Fallback (as defined in clause 184.108.40.206
) to another RAT in 5GS or to another System where Emergency Services are supported natively. The Emergency Services Fallback support indicator is valid within the current Registration Area per RAT.
If a certain RAT is restricted for Emergency Services, AMF signals that the corresponding RAT is restricted for Emergency Services Support to the Master RAN Node. This helps assist the Master RAN node determine whether to set up Dual Connectivity for Emergency Services.
UEs that are in limited service state, as specified in TS 23.122
, or that camp normally on a cell but failed to register successfully to the network under conditions specified in TS 24.501
, initiate the Registration procedure by indicating that the registration is to receive Emergency Services, referred to as Emergency Registration, and a Follow-on request is included in the Registration Request to initiate PDU Session Establishment procedure with a Request Type indicating "Emergency Request". UEs that had registered for normal services and do not have emergency PDU Sessions established and that are subject to Mobility Restriction in the present area or RAT (e.g. because of restricted tracking area) shall initiate the UE Requested PDU Session Establishment procedure to receive Emergency Services, i.e. with a Request Type indicating "Emergency Request". Based on local regulation, the network supporting Emergency Services for UEs in limited service state provides Emergency Services to these UE, regardless whether the UE can be authenticated, has roaming or Mobility Restrictions or a valid subscription.
For Emergency Services over 3GPP access, other than eCall over IMS, the UEs in limited service state determine that the cell supports Emergency Services over NG-RAN from a broadcast indicator in AS. The cell connected to EPC and 5GC broadcasts separate broadcast indicator for EPC and 5GC to indicate support of emergency services by the EPC and 5GC. For Emergency Services over untrusted non-3GPP access, other than eCall over IMS, the UE in limited service state selects any N3IWF as specified in clause 6.3.6
. Emergency calls for eCall Over IMS may only be performed if the UE has a USIM.
A serving network shall provide an Access Stratum broadcast indication from E-UTRA connected to 5GC to UEs indicating whether eCall Over IMS is supported:
When a cell is connected to EPC and 5GC, the cell broadcasts separate Access stratum broadcast indication for 5GC and EPC to indicate support of eCall over IMS by 5GC and EPC.
A UE that is not in limited service state determines that the E-UTRA cell supports eCall Over IMS via 5GC using the broadcast indicator for eCall over IMS. UE shall originate emergency calls for eCall Over IMS only over E-UTRA connected to 5GC and shall not originate emergency calls for eCall Over IMS over NR. Emergency calls for eCall over IMS are not supported over non-3GPP access.
The Access Stratum broadcast indicator is determined according to operator policies and minimally indicates that the PLMN, or all of the PLMNs in the case of network sharing, and at least one emergency center or PSAP to which an eCall Over IMS can be routed, support eCall Over IMS.
There is no restriction on handoff of an emergency call for eCall Over IMS to NR or on use of NR for call back by a PSAP.
A UE in limited service state determines that the cell supports eCall Over IMS using both the broadcast indicator for support of Emergency Services over E-UTRA connected to 5GC and the broadcast indicator of E-UTRA for eCall over IMS. Emergency calls for eCall Over IMS are not supported over NR and Non-3GPP access.
The broadcast indicator for eCall Over IMS does not indicate whether UEs in limited service state are supported. So, the broadcast indicator for support of Emergency Services over E-UTRA connected to 5GC that indicates limited service state support needs to be applied in addition.
For a UE that is Emergency Registered, if it is unauthenticated the security context is not set up on UE.
In order to receive Emergency Services, UEs that camp on a suitable cell in RM-DEREGISTERED state (i.e. without any conditions that result in limited service state), or that decide to access 5GC via untrusted non-3GPP access (and not in limited service state over untrusted non-3GPP access), initiate the Initial Registration procedure for normal service instead of Emergency Registration. Upon successful registration, such UEs shall initiate the UE Requested PDU Session Establishment procedure with a Request Type indicating "Emergency Request" to receive Emergency Services if the AMF indicated support for Emergency Services in 5GC (for the RAT the UE is currently camped on when UE is camping on 3GPP access). The UEs that camp normally on a cell or that are connected via untrusted Non-3GPP access are informed that the PLMN supports Emergency Services over 5G-AN from the Emergency Services Support indicator in the Registration procedure. This applies to both 3GPP and non-3GPP Access Types.
The Emergency Services Support indicator in the Registration procedures does not indicate support for eCall Over IMS.
For a UE that is Emergency Registered, normal PLMN selection principles apply after the end of the IMS emergency session.
For Emergency Services, there is no support for inter PLMN mobility thus there is a risk of service disruption due to failed inter PLMN mobility attempts.
The UE shall set the RRC establishment cause to emergency as defined in TS 38.331
when it requests an RRC Connection in relation to an emergency session.
In the case of Limited Service state, UE shall not include any Network Slice related parameters when communicating with the network.
When a PLMN supports IMS and Emergency Services:
all AMFs in that PLMN shall have the capability to support Emergency Services.
at least one SMF shall have this capability.
For other emergency scenarios (e.g. UE autonomous selection for initiating Emergency Services), refer to TS 23.167
for domain selection principles.
For emergency service support in Public network integrated NPNs, refer to clause 220.127.116.11
When Emergency Services are supported and local regulation requires IMS Emergency Sessions to be provided regardless of the Mobility Restrictions (see clause 18.104.22.168
), or access should not be applied to UEs receiving Emergency Services. When the (R)AN resources for Emergency Services are established, the ARP value for Emergency Services indicates the usage for Emergency Services to the 5G-AN.
During handover, the source NG-RAN and source AMF ignore any UE related restrictions during handover evaluation when there is an active PDU Session associated with emergency service.
During Mobility Registration Update procedures, including a Mobility Registration Update as part of a handover, the target AMF ignores any Mobility Restrictions or access restrictions for UE with emergency services where required by local regulation. Any non-emergency services are not allowed, by the target network when not allowed by the subscription for the target location. To allow the UE in limited service state (either Emergency Registered or registered for normal service) over a given Access Type to get access to normal services over this Access Type after the Emergency Session has ended and when it has moved to a new area that is not stored by the UE as a forbidden area, after allowing a period of time for subsequent Emergency Services, the UE may explicitly deregister and register for normal services over this Access Type without waiting for the emergency PDU Session Release by the SMF.
This functionality applies to all mobility procedures.
Over 3GPP access, an Emergency Registered UE when its Periodic Registration Update timer expires shall not initiate a Periodic Registration Update procedure but shall enter the RM-DEREGISTERED state. For such UEs, the AMF runs a mobile reachable timer with a similar value to the UE's Periodic Registration Update timer. After expiry of this timer the AMF may change the UE RM state for 3GPP Access in the AMF to RM-DEREGISTERED. The AMF assigns the Periodic Registration Update timer value to Emergency Registered UEs. This timer keeps the Emergency Registered UE registered for Emergency Services after change to CM-IDLE state to allow for a subsequent Emergency Service without a need for a new Emergency Registration.
Over untrusted non-3GPP access, an Emergency Registered UE is only reachable in CM-CONNECTED state: since the UE may only use Emergency Services over untrusted Non-3GPP access when it is not possible over 3GPP access, 3GPP access is assumed to be unavailable for paging the UE.
When a SMF is selected for Emergency Services, the SMF selection function described in clause 6.3.2
for normal services is applied to the Emergency DNN or the AMF selects the SMF directly from the AMF Emergency Configuration Data. If the SMF selection function described in clause 6.3.2
is used it shall always derive a SMF in the Serving PLMN, which guarantees that the IP address is also allocated by the Serving PLMN. When a UPF is selected for Emergency Services, the UPF selection function described in clause 6.3.3
for normal services is applied to the Emergency DNN or the SMF selects the UPF directly from the SMF Emergency Configuration Data. The information in the AMF Emergency Configuration Data and the SMF Emergency Configuration Data is specified in clause 22.214.171.124
Local regulation may require supporting emergency calls from an unauthorised UE. In such a case, the SMF may not have subscription data. Additionally, the local network may want to provide Emergency Services support differently than what is allowed by a UE subscription. Therefore, the initial QoS parameters used for establishing Emergency Services are configured in the V-SMF (local network) in the SMF Emergency Configuration Data.
This functionality is used by the UE Requested PDU Session Establishment procedure when establishing Emergency Services.
Dynamic PCC is used for UEs establishing emergency service and shall be used to manage IMS emergency sessions when an operator allows IMS emergency sessions. When establishing Emergency Services with a SMF, the PCF provides the SMF with the QoS parameters, including an ARP value reserved for the Emergency Services to prioritize the QoS Flows when performing admission control, as defined in TS 23.503
The PCF rejects an IMS session established via the emergency PDU Session if the AF (i.e. P-CSCF) does not provide an emergency indication to the PCF.
Emergency service is provided by the serving PLMN. The UE and serving PLMN must have compatible IP address versions in order for the UE to obtain a local emergency PDU Session.
The QoS Flows of a PDU Session associated with the emergency DNN shall be dedicated for IMS emergency sessions and shall not allow any other type of traffic. The emergency contexts shall not be changed to non-emergency contexts and vice versa. The UPF shall block any traffic that is not from or to addresses of network functions (e.g. P-CSCF) providing Emergency Services. If there is already an emergency PDU Session over a given Access Type (3GPP access or untrusted non-3GPP access), the UE shall not request another emergency PDU Session over the other Access Type except for handing over the emergency PDU Session to this other Access Type. The network shall reject any emergency PDU Session requests over a given Access Type (3GPP access or untrusted non-3GPP access) if it knows the UE already has an emergency PDU Session over the other Access Type. The ARP reserved for emergency service shall only be assigned to QoS Flows associated with an emergency PDU Session. If the UE is Emergency Registered over a given access, it shall not request a PDU Session to any other DNN over this access.
For service requirements for eCall only mode, refer to TS 22.101
A UE configured for eCall Only Mode shall remain in RM-DEREGISTERED state, shall camp on a network cell when available but shall refrain from any Registration Management, Connection Management or other signalling with the network. The UE may instigate Registration Management and Connection Management procedures in order to establish, maintain and release an eCall Over IMS session or a session to any non-emergency MSISDN(s) or URI(s) configured in the USIM for test and/or terminal reconfiguration services. Following the release of either session, the UE starts a timer whose value depends on the type of session (i.e. whether eCall or a session to a non-emergency MSISDN or URI for test/reconfiguration). While the timer is running, the UE shall perform normal RM/CM procedures and is permitted to respond to paging to accept and establish an incoming session (e.g. from an emergency centre, PSAP or HPLMN operator). When the timer expires, the UE shall perform a UE-initiated Deregistration procedure if still registered and enter RM-DEREGISTERED state.
An HPLMN operator can change the eCall Only Mode configuration state of a UE in the USIM. An HPLMN operator can also instead add, modify or remove a non-emergency MSISDN or URI in the USIM for test and/or terminal reconfiguration services. This can occur following a UE call to a non-emergency MSISDN or URI configured for reconfiguration. When the eCall Only Mode configuration is removed, the UE operates as a normal UE that can support eCall over IMS.
A test call and a reconfiguration call can be seen as normal (non-emergency) call by a serving PLMN and normal charging rules can apply depending on operator policy.
An MSISDN configured in the USIM for test and/or terminal reconfiguration services for eCall Over IMS can differ from an MSISDN configured in the USIM for test services for eCall over the CS domain.
In order to support various deployment scenarios for obtaining Emergency Services, the UE and 5GC may support the mechanism to direct or redirect the UE either towards E-UTRA connected to 5GC (RAT fallback) when only NR does not support Emergency Services or towards EPS (E-UTRAN connected to EPC System fallback) when the 5GC does not support Emergency Services. Emergency Services fallback may be used when the 5GS does not indicate support for Emergency Services (see clause 126.96.36.199
) and indicates support for Emergency Services fallback.
Following principles apply for Emergency Services Fallback:
If the AMF indicates support for Emergency Services fallback in the Registration Accept message, then in order to initiate Emergency Service, normally registered UE supporting Emergency Services fallback shall initiate a Service Request with Service Type set to Emergency Services fallback as defined in TS 23.502, clause 188.8.131.52.
AMF uses the Service Type Indication within the Service Request to redirect the UE towards the appropriate RAT/System. The 5GS may, for Emergency Services, trigger one of the following procedures:
Handover or redirection to EPS.
Handover or redirection to E-UTRA connected to 5GC.
After receiving the Service Request for Emergency Fallback, the AMF triggers N2 procedure resulting in either CONNECTED state mobility (Handover procedure) or IDLE state mobility (redirection) to either E-UTRA/5GC or to E-UTRAN/EPC depending on factors such as N26 availability, network configuration and radio conditions. In the N2 procedure, the AMF based on support for Emergency Services in 5GC or EPC may indicate the target CN for the RAN node to know whether inter-RAT fallback or inter-system fallback is to be performed. The target CN indicated in the N2 procedure is also conveyed to the UE in order to be able to perform the appropriate NAS procedures (S1 or N1 Mode).
Emergency Services Fallback to EPS can be followed by an onward movement to GERAN or UTRAN via CSFB procedures if the PLMN does not support IMS emergency services.