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Content for  TS 24.229  Word version:  17.0.0

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U (Normative)  IP-Connectivity Access Network specific concepts when using 5GS to access IM CN subsystem |R15|Word‑p. 936

U.1  Scope

The present annex defines IP-CAN specific requirements for a call control protocol for use in the IP Multimedia (IM) Core Network (CN) subsystem based on the Session Initiation Protocol (SIP), and the associated Session Description Protocol (SDP), where the IP-CAN is 5G System (5GS). The 5GS IP-CAN has a 5GS core network which can be supported by a NG-RAN.

U.2  IP-CAN aspects when connected to the IM CN subsystem

U.2.1  Introduction

A UE accessing the IM CN subsystem, and the IM CN subsystem itself, utilise the services provided by 5GS to provide packet-mode communication between the UE and the IM CN subsystem.
Requirements for the UE on the use of these packet-mode services are specified in this clause.
When using the 5GS, each IP-CAN bearer is provided by a 5GS QoS flow.

U.2.2  Procedures at the UE

U.2.2.1  Establishment of IP-CAN bearer and P-CSCF discovery

Prior to communication with the IM CN subsystem, the UE shall:
a)
if not registered for 5GS services, perform a registration procedure in 5GS as specified in TS 24.501;
b)
ensure that a 5GS PDU session and a QoS flow used for SIP signalling of that PDU session is available. This 5GS QoS flow shall remain active throughout the period the UE is connected to the IM CN subsystem, i.e. from the initial registration and at least until the deregistration. As a result, the 5GS PDU session provides the UE with information that makes the UE able to construct an IPv4 or an IPv6 address;
when establishing a 5GS PDU session, if a service which requires service continuity provided by SSC mode 1 as specified in TS 23.501, (e.g. IMS Multimedia Telephony Service as specified in TS 24.173), is to be used within that PDU session, the UE shall set SSC mode 1 for that PDU session;
when establishing a 5GS PDU session with a QoS flow used for SIP signaling, the UE shall indicate to the network, by setting the IM CN Subsystem Signalling Flag in the extended Protocol Configuration Options information element specified in TS 24.501 in the PDU SESSION ESTABLISHMENT REQUEST message, that the request is for SIP signalling;
c)
use the QoS flow associated with the default QoS rule for SIP signalling. The UE may also use this 5GS QoS flow for Domain Name Server (DNS) and Dynamic Host Configuration Protocol (DHCP) signalling; and
d)
acquire a P-CSCF address(es).
The methods for P-CSCF discovery are:
  1. When using IPv4, employ the DHCP RFC 2132, the DHCPv4 options for SIP servers RFC 3361, and RFC 3263 as described in subclause 9.2.1. When using IPv6, employ Dynamic Host Configuration Protocol for IPv6 (DHCPv6) RFC 3315, the DHCPv6 options for SIP servers RFC 3319 and DHCPv6 options for DNS RFC 3646 as described in subclause 9.2.1.
  2. Transfer P-CSCF address(es) within the 5GS PDU session establishement procedure.
    The UE shall indicate the request for a P-CSCF address to the network within the extended Protocol Configuration Options information element of the PDU SESSION ESTABLISHMENT REQUEST message.
    If the network provides the UE with a list of P-CSCF IPv4 or IPv6 addresses in the PDU SESSION ESTABLISHMENT ACCEPT message, the UE shall assume that the list is ordered top-down with the first P-CSCF address within the extended Protocol Configuration Options information element as the P-CSCF address having the highest preference and the last P-CSCF address within the extended Protocol Configuration Options information element as the P-CSCF address having the lowest preference.
  3. The UE selects a P-CSCF from the list (see TS 31.103) stored in the ISIM.
  4. The UE selects a P-CSCF from the list in IMS management object.
The UE shall use method IV to select a P-CSCF, if
  • a P-CSCF is to be discovered in the home network;
  • the UE is roaming; and
  • the IMS management object contains the P-CSCF list.
The UE shall use method III to select the P-CSCF, if:
  • a P-CSCF is to be discovered in the home network;
  • the UE is roaming;
  • either the UE does not contain the IMS management object, or the UE contains the IMS management object but the IMS management object does not contain the P-CSCF list; and
  • the ISIM residing in the UICC supports the P-CSCF list.
The UE can freely select method I or II for P-CSCF discovery, if:
  • the UE is in the home network; or
  • the UE is roaming and the P-CSCF is to be discovered in the visited network.
The UE can select method IV, if:
  • the UE is in the home network; and
  • the IMS management object contains the P-CSCF list.
In case method I is selected and several P-CSCF addresses or FQDNs are provided to the UE, the selection of P-CSCF address or FQDN shall be performed as indicated in RFC 3361 when using IPv4 or RFC 3319 when using IPv6. If sufficient information for P-CSCF address selection is not available, selection of the P-CSCF address by the UE is implementation specific.
If the UE is designed to use I above, but receives P-CSCF address(es) according to II, then the UE shall either ignore the received address(es), or use the address(es) in accordance with II, and not proceed with the DHCP request according to I.
If the UE is configured to use Option II above and detects that all P-CSCFs known by the UE have been used when the UE selects a different P-CSCF as a result of:
  • receiving 305 (Use Proxy) to the REGISTER request;
  • receiving 504 (Server Time-out); or
  • expiration of the timer F at the UE,
then unless the PDU session is in use by other applications, the UE shall:
  1. release the PDU session of the 5GS QoS flow that is used only for the transport of SIP signalling and that are not used for other non-IMS applications, but shall not release emergency PDU session; and
  2. unless the UE decides the service is no longer needed,
    1. perform a new P-CSCF discovery procedure as described in subslause 9.2.1; and
    2. perform the procedures for initial registration as described in subclause 5.1.1.2.
When using IPv4, the UE may request a DNS Server IPv4 address(es) via RFC 2132 or by the extended Protocol Configuration Options information element when establishing the PDU session according to TS 24.501.
When using IPv6, the UE may request a DNS Server IPv6 address(es) via RFC 3315 and RFC 3646 or by the extended Protocol Configuration Options information element when establishing the PDU session according to TS 24.501.
When:
  • the UE obtains a 5GS QoS flow used for SIP signalling by performing handover of the connection from another IP-CAN;
  • IP address of the UE is not changed during the handover; and
  • the UE already communicates with the IM CN subsystem via the connection with the other IP-CAN, e.g. the UE determines that its contact with host portion set to the UE IP address (or FQDN of the UE) associated with the connection with the other IP-CAN has been bound to a public user identity;
the UE shall continue using the P-CSCF address(es) acquired in the other IP-CAN.
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U.2.2.1A  Modification of the PDU session of the 5GS QoS flow used for SIP signallingWord‑p. 938
The UE shall not modify the 5GS QoS flow from being used exclusively for SIP signalling.
When a 5GS QoS flow used for SIP signalling is established, the UE shall not set the IM CN Subsystem Signalling Flag in the extended Protocol Configuration Options information element specified in TS 24.501 of any subsequent PDU SESSION MODIFICATION REQUEST message for that DNN.
The UE shall ignore the IM CN Subsystem Signalling Flag if received from the network in the extended Protocol Configuration Options information element.
After the establishment of a 5GS QoS flow used for SIP signalling, the UE shall not indicate the request for a P-CSCF address to the network within the extended Protocol Configuration Options information element of any subsequent PDU SESSION MODIFICATION REQUEST message for that DNN.
The UE shall ignore P-CSCF address(es) if received from the network in the extended Protocol Configuration Options information element of a PDU SESSION MODIFICATION COMMAND message which is triggered by a PDU SESSION MODIFICATION REQUEST message.
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U.2.2.1B  Re-establishment of the PDU session with the 5GS QoS flow used for SIP signalling

If the UE registered a public user identity with an IP address allocated for the DNN of the PDU session with the 5GS QoS flow used for SIP signalling, the PDU session with the 5GS QoS flow used for SIP signalling is deactivated as result of signalling from the network and:
  1. if the UE is required to perform an initial registration according to subclause U.3.1.2;
  2. if the signalling from the network results in requiring the UE to initiate activation of the PDU session of the 5GS QoS flow used for SIP signalling; or
  3. if the UE needs to continue having a public user identity registered with an IP address allocated for the DNN;
the UE shall:
  1. if the non-access stratum is performing the UE requested PDU session establishment procedure for the DNN triggered as result of the signalling from the network, wait until the UE requested PDU session establishment procedure for the DNN finish; and
  2. perform the procedures in subclause U.2.2.1, bullets a), b) and c).
If none of the bullets i), ii) and iii) of this subclause evaluate to true, or the procedures in bullet B) of this subclause were unable to ensure that the 5GS QoS flow used for SIP signalling is available or were unable to acquire any P-CSCF address(es):
  1. if the SIP signalling was carried over a 5GS QoS flow not associated with the default QoS rule, the UE shall release all resources established as a result of SIP signalling by sending to the network either:
    1. a PDU SESSION MODIFICATION REQUEST message, if there are 5GS QoS flows of this PDU session that are not related SIP sessions; or
    2. a PDU SESSION RELEASE REQUEST message if all the 5GS QoS flows of this PDU session are related to SIP sessions.
If the 5GS QoS flow associated with default QoS rule used for SIP signalling was deactivated as described at the start of this subclause, and the procedures in bullet B) of this subclause ensured that the 5GS QoS flow used for SIP signalling is available and acquired the P-CSCF address(es), the UE shall perform a new initial registration according to subclause 5.1.1.2.
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U.2.2.1C  P-CSCF restoration procedureWord‑p. 939
A UE supporting the P-CSCF restoration procedure performs one of the following procedures:
  1. if the UE used method II for P-CSCF discovery and if the UE receives one or more P-CSCF address(es) in the extended Protocol Configuration Options information element of a PDU SESSION MODIFICATION COMMAND message and the one or more P-CSCF addresse(s) do not include the address of the currently used P-CSCF, then the UE shall acquire a different P-CSCF address from the one or more P-CSCF addresse(s) in the PDU SESSION MODIFICATION COMMAND message. If more than one P-CSCF address with the same container identifier (i.e. "P-CSCF IPv6 Address" or "P-CSCF IPv4 Address") are included, then the UE shall assume that the more than one P-CSCF addresses with the same container identifier are prioritised with the first P-CSCF address with the same container identifier within the Protocol Configuration Options information element as the P-CSCF address with the highest priority.
    If the UE used method II for P-CSCF discovery and if the UE has previously sent the "P-CSCF Re-selection support" PCO indicator at PDU session creation and if the UE receives one or more P-CSCF address(es) in the extended Protocol Configuration Options information element of a PDU SESSION MODIFICATION COMMAND message, then the UE shall acquire a P-CSCF address from the one or more P-CSCF addresse(s) in the PDU SESSION MODIFICATION COMMAND message. If more than one P-CSCF address with the same container identifier (i.e. "P-CSCF IPv6 Address" or "P-CSCF IPv4 Address") are included, then the UE shall assume that the more than one P-CSCF addresses with the same container identifier are prioritised with the first P-CSCF address with the same container identifier within the Protocol Configuration Options information element as the P-CSCF address with the highest priority;
  2. if the UE uses RFC 6223 as part of P-CSCF restoration procedures, and if the P-CSCF fails to respond to a keep-alive request, then the UE shall acquire a different P-CSCF address using one of the methods I, III and IV for P-CSCF discovery described in the subclause U.2.2.1.
If the UE has an ongoing session and acquired the new P-CSCF address by using procedure A described above, the UE may wait until the UE has detected that the ongoing session has ended before performing an initial registration as specified in subclause 5.1.
In all other cases, when the UE has acquired the P-CSCF address, the UE not having an ongoing session shall perform an initial registration as specified in subclause 5.1.
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U.2.2.2  Session management proceduresWord‑p. 940
The procedures for session management as described in TS 24.501 shall apply while the UE is connected to the IM CN subsystem.

U.2.2.3  Mobility management procedures

The procedures for mobility management as described in TS 24.501 shall apply while the UE is connected to the IM CN subsystem.

U.2.2.4  Cell selection and lack of coverage

The existing mechanisms and criteria for cell selection as described in TS 38.304 or TS 36.304 shall apply while the UE is connected to the IM CN Subsystem.

U.2.2.5  5GS QoS flow for media

U.2.2.5.1  General requirements
If the resource allocation is initiated by the UE, the UE starts reserving resources whenever it has sufficient information about the media streams, and used codecs available as specified in TS 24.501.
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U.2.2.5.1A  Activation or modification of QoS flows for media by the UE
If the UE is configured not to initiate resource allocation for media according to TS 24.167, then the UE shall refrain from requesting additional 5GS QoS flow(s) for media until the UE considers that the network did not initiate resource allocation for the media.
U.2.2.5.1B  Activation or modification of QoS flows for media by the network
If the UE receives an activation request from the network for a 5GS QoS flow for media which is associated with the 5GS QoS flow used for signalling, the UE shall correlate the media 5GS QoS flow with a currently ongoing SIP session establishment or SIP session modification.
If the UE receives a modification request from the network for a 5GS QoS flow that is used for one or more media streams in an ongoing SIP session, the UE shall:
1) modify the related PDU session context in accordance with the request received from the network.
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U.2.2.5.1C  Deactivation of a QoS flow for mediaWord‑p. 941
When a data stream for media related to a session is released, if the 5GS QoS flow transporting the data stream is no longer needed and allocation of the 5GS QoS flow was requested by the UE, then the UE releases the 5GS QoS flow.
U.2.2.5.1D  Default QoS flow usage restriction policy
The default QoS flow usage restriction policy consists of zero or more default QoS flow usage restriction policy parts.
The default QoS flow usage restriction policy part consists of a mandatory media type condition and an optional ICSI condition.
The default QoS flow usage restriction policy does not apply to UE detected emergency calls.
Sending media is restricted according to the default QoS flow usage restriction policy, if sending media is restricted according to at least one default QoS flow usage restriction policy part of the default QoS flow usage restriction policy.
Sending media is restricted according to the default QoS flow usage restriction policy part if:
  1. the media is to be sent for a media stream negotiated in a session offered or established by SIP signalling;
  2. the media stream is of a media type indicated in the media type condition of the QoS flow usage restriction policy part;
  3. the following is true:
    1. the default QoS flow usage restriction policy part does not have the ICSI condition; or
    2. the session is offered or established by SIP signalling related to an IMS communication service identified in the ICSI condition of the default QoS flow usage restriction policy part; and
  4. the media is to be sent via the default QoS flow of the PDU session for SIP signalling.
The UE may support the default QoS flow usage restriction policy.
If the UE supports the default QoS flow usage restriction policy:
  1. the UE shall not send media restricted according to the default QoS flow usage restriction policy; and
  2. the UE may support being configured with the default QoS flow usage restriction policy using one or more of the following methods:
    1. the Default_QoS_Flow_usage_restriction_policy node of the EFIMSConfigData file described in TS 31.102;
    2. the Default_QoS_Flow_usage_restriction_policy node of the EFIMSConfigData file described in TS 31.103; and
    3. the Default_QoS_Flow_usage_restriction_policy node of TS 24.167.
If the UE is configured with both the Default_QoS_Flow_usage_restriction_policy node of TS 24.167 and the Default_QoS_Flow_usage_restriction_policy node of the EFIMSConfigData file described in TS 31.102 or TS 31.103, then the Default_QoS_Flow_usage_restriction_policy node of the EFIMSConfigData file shall take precedence.
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U.2.2.5.2  Special requirements applying to forked responses
Since the UE does not know that forking has occurred until a second, provisional response arrives, the UE requests resource allocation as required by the initial response received. If a subsequent provisional response is received, different alternative actions may be performed depending on the requirements in the SDP answer:
  1. The resource requirements of the subsequent SDP can be accommodated by the existing resources requested. The UE performs no further resource requests.
  2. The subsequent SDP introduces different QoS requirements or additional IP flows. The UE requests further resource allocation according to subclause U.2.2.5.1.
  3. The subsequent SDP introduces one or more additional IP flows. The UE requests further resource allocation according to subclause U.2.2.5.1.
When a final answer is received for one of the early dialogs, the UE proceeds to set up the SIP session. The UE shall release all the unneeded IP-CAN resources. Therefore, upon the reception of the first final 200 (OK) response for the INVITE request (in addition to the procedures defined in RFC 3261 subclause 13.2.2.4), the UE shall:
  1. in case resources were established or modified as a consequence of the INVITE request and forked provisional responses that are not related to the accepted 200 (OK) response, send release request to release the unneeded resources.
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U.2.2.5.3  Unsuccessful situationsWord‑p. 942
The UE can receive resource reservation related error codes in a PDU SESSION MODIFICATION REJECT as described in TS 24.501. If the UE receives a resource reservation related error code, the UE shall either handle the resource reservation failure as described in subclause 6.1.1 or retransmit the message up to three times.

U.2.2.6  Emergency service

U.2.2.6.1  General
For the purposes of this document, an emergency PDU session is the equivalent of emergency bearers; i.e. the 5GS defines emergency bearers for the support of emergency calls. Emergency PDU session is defined for use in emergency calls in 5GS and core network support of emergency PDU session is indicated to the UE in NAS signalling. Where the UE recognises that a call request is an emergency call and the core network supports emergency PDU session, the UE shall use emergency PDU session for both signalling and media for emergency calls made using the IM CN subsystem.
Some jurisdictions allow emergency calls to be made when the UE does not contain an UICC, or where the credentials are not accepted. Additionally, where the UE is in state 5GMM-REGISTERED.LIMITED-SERVICE or 5GMM-REGISTERED.PLMN-SEARCH, a normal registration in 5GS has been attempted but it can also be assumed that a registration in the IM CN subsystem will also fail. In such cases, subject to the lower layers indicating that the network does support emergency bearer services in limited service state (see TS 36.331 or TS 38.331), the procedures for emergency calls without registration can be applied, as defined in subclause 5.1.6.8.2. If the 5GS primary authentication procedure has already succeeded during the latest normal or emergency registration procedure in 5GS, the UE shall perform an initial emergency registration, as described in subclause 5.1.6.2 before attempting an emergency call as described in subclause 5.1.6.8.3.
To perform emergency registration, the UE shall request to establish an emergency PDU session as described in TS 24.501. The procedures for PDU session establishment and P-CSCF discovery, as described in subclause U.2.2.1 of this specification apply accordingly.
In the present document, "EMS is Y" as described in TS 23.167 refers to one of the following conditions:
  1. if the UE is in an NR cell connected to 5GCN, the network indicates in the REGISTRATION ACCEPT message that EMC is set to either "Emergency services supported in NR connected to 5GCN only" or "Emergency services supported in NR connected to 5GCN and E-UTRA connected to 5GCN" as described in TS 24.501; or
  2. if the UE is in an E-UTRA cell connected to 5GCN, the network indicates in the REGISTRATION ACCEPT message that EMC is set to either "Emergency services supported in E-UTRA connected to 5GCN only" or "Emergency services supported in NR connected to 5GCN and E-UTRA connected to 5GCN" as described in TS 24.501.
In the present document, "EMS is N" as described in TS 23.167 refers to one of the following conditions:
  1. if the UE is in an NR cell connected to 5GCN, the network indicates in the REGISTRATION ACCEPT message that EMC is set to either "Emergency services not supported" or "Emergency services supported in E-UTRA connected to 5GCN only" as described in TS 24.501; or
  2. if the UE is in an E-UTRA cell connected to 5GCN, the network indicates in the REGISTRATION ACCEPT message that EMC is set to either "Emergency services not supported" or "Emergency services supported in NR connected to 5GCN only" as described in TS 24.501.
In the present document, "ESFB is Y" as described in TS 23.167 refers to one of the following conditions:
  1. if the UE is in an NR cell connected to 5GCN, the network indicates in the REGISTRATION ACCEPT message that EMF is set to either "Emergency service fallback supported in NR connected to 5GCN only" or "Emergency service fallback supported in NR connected to 5GCN and E-UTRA connected to 5GCN" as described in TS 24.501; or
  2. if the UE is in an E-UTRA cell connected to 5GCN, the network indicates in the REGISTRATION ACCEPT message that EMF is set to either "Emergency service fallback supported in E-UTRA connected to 5GCN only" or "Emergency service fallback supported in NR connected to 5GCN and E-UTRA connected to 5GCN" as described in TS 24.501.
In the present document, "ESFB is N" as described in TS 23.167 refers to one of the following conditions:
  1. if the UE is in an NR cell connected to 5GCN, the network indicates in the REGISTRATION ACCEPT message that EMF is set to either "Emergency service fallback not supported" or "Emergency service fallback supported in E-UTRA connected to 5GCN only" as described in TS 24.501; or
  2. if the UE is in an E-UTRA cell connected to 5GCN, the network indicates in the REGISTRATION ACCEPT message that EMF is set to either "Emergency service fallback not supported" or "Emergency service fallback supported in NR connected to 5GCN only" as described in TS 24.501.
Emergency services fallback is defined to direct or redirect the UE towards either E-UTRA connected to 5GCN or EPS and support of emergency service fallback is indicated to the UE in NAS signalling.
In order to find out whether the UE is attached to the home PLMN or to the visited PLMN, the UE shall compare the MCC and MNC values derived from its IMSI with the MCC and MNC of the PLMN the UE is attached to. If the MCC and MNC of the PLMN the UE is attached to do not match with the MCC and MNC derived from the IMSI, then for the purpose of emergency calls in the IM CN subsystem the UE shall consider to be attached to a VPLMN.
If the dialled number is equal to a local emergency number stored in the Extended Local Emergency Number List (as defined in TS 24.301), then the UE shall recognize such a number as for an emergency call and:
  • if the dialled number is equal to an emergency number stored in the ME, or in the USIM, then the UE shall perform either procedures in the subclause U.2.2.6.1B or the procedures in subclause U.2.2.6.1A; and
  • if the dialled number in not equal to an emergency number stored in the ME, or in the USIM, then the UE shall perform procedures in the subclause U.2.2.6.1B.
If the dialled number is not equal to a local emergency number stored in the Extended Local Emergency Number List (as defined in TS 24.301) and:
  • if the dialled number is equal to an emergency number stored in the ME, in the USIM or in the Local Emergency Number List (as defined in TS 24.008), then the UE shall recognize such a number as for an emergency call and performs the procedures in subclause U.2.2.6.1A.
    • the PLMN attached to relies on the Local Emergency Number List for deriving a URN; or
    • the previously received Extended Emergency Number List Validity field indicated "Extended Local Emergency Numbers List is valid only in the PLMN from which this IE is received".
If the UE detected an emergency number, the UE subsequently performs a registration procedure or an emergency registration procedure with a different PLMN than the PLMN from which the UE received the last Extended Local Emergency Number List, the dialled number is not stored in the ME, in the USIM and in the Local Emergency Number List, and:
  • the REGISTRATION ACCEPT message received from the different PLMN contains the Extended Local Emergency Number List and the emergency number is present in the updated Extended Local Emergency Number List then the UE uses the updated Extended Local Emergency Number List when it performs the procedures in subclause U.2.2.6.1B; and
  • the REGISTRATION ACCEPT message received from the different PLMN contains no Extended Local Emergency Number List or the emergency number is no longer present in the updated Extended Local Emergency Number List then the UE shall attempt UE procedures for SIP that relate to emergency using emergency service URN "urn:service:sos".
Upon reception of a 380 (Alternative Service) response to an INVITE request as defined in subclause 5.1.2A.1.1 and subclause 5.1.3.1, if:
  • the 380 (Alternate Service) response contains a Contact header field;
  • the value of the Contact header field is a service URN; and
  • the service URN has a top-level service type of "sos";
then the UE determines that "emergency service information is included" as described TS 23.167.
Upon reception of a 380 (Alternative Service) response to an INVITE request as defined in subclause 5.1.3.1 if the 380 (Alternate Service) response does not contain a Contact header field with service URN that has a top-level service type of "sos", then the UE determines that "no emergency service information is included" as described TS 23.167.
If the "emergency service information is included" as described TS 23.167:
  1. if the URN in the Contact header field matches an emergency service URN in table U.2.2.6.1, then the type of emergency service is the value corresponding to the matching entry in table U.2.2.6.1; and
  2. if the URN in the Contact header field does not match any emergency service URN in table U.2.2.6.1, then the type of emergency service is not identified.
When the emergency registration expires, the UE should disconnect the emergency PDU session.
Upon receiving a 3xx other than 380 (Alternative service), 4xx, 5xx or 6xx response to an INVITE request for a UE detectable emergency call, the UE shall perform domain selection as specified in TS 23.167 annex H, to re-attempt the emergency call.
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U.2.2.6.1A  Type of emergency service derived from emergency service category valueWord‑p. 944
The type of emergency service for an emergency number is derived from the settings of the emergency service category value (bits 1 to 5 of the emergency service category value as specified in subclause 10.5.4.33 of TS 24.008). Table U.2.2.6.1 below specifies mappings between a type of emergency service and an emergency service URN. The UE shall use the mapping to match an emergency service URN and a type of emergency service. If a dialled number is an emergency number but does not map to a type of emergency service the service URN shall be "urn:service:sos".
Type of emergency service
Emergency service URN

Police
urn:service:sos.police
Ambulance
urn:service:sos.ambulance
Fire Brigade
urn:service:sos.fire
Marine Guard
urn:service:sos.marine
Mountain Rescue
urn:service:sos.mountain

If an IP-CAN, capable of providing local emergency numbers, did not provide a local emergency number that matches the dialled number (see subclause 5.1.6.1) and multiple types of emergency service can be derived for a dialled number from the information configured on the UICC then:
  • if the UE is in the HPLMN, the UE shall map any one of these types of emergency service to an emergency service URN as specified in table U.2.2.6.1; and
  • if the UE is in the VPLMN, the UE shall select "urn:service:sos".
If an IP-CAN, capable of providing local emergency numbers, provided a local emergency number that matches the dialled number (see subclause 5.1.6.1), and:
  • if the UE can derive one or more types of emergency service from the information received from the IP-CAN for the dialled number and the UE cannot derive types of emergency service from the information configured on the UICC for the dialled number; or
  • if the UE is able to derive identical types of emergency service from both the information received from the IP-CAN for the dialled number and from the information configured on the UICC for the dialled number,
then the UE shall map any one of these emergency service types to an emergency service URN as specified in table U.2.2.6.1.
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U.2.2.6.1B  Type of emergency service derived from extended local emergency number listWord‑p. 945
The Extended Local Emergency Number List (defined in TS 24.301) can contain sub-services of the associated emergency service URN for the detected emergency number.
If:
  • the length of sub-services field is greater than "0", the UE shall construct the emergency service URN using "urn:service:sos" followed by adding a dot followed by the content of the sub-services field; and
  • the length of sub-services field is "0", the UE shall use the emergency service URN "urn:service:sos".
EXAMPLE 1:
For a detected number, if the sub-service is "gas", then the UE constructs "urn:service:sos.gas" as the associated emergency service URN.
EXAMPLE 2:
For a detected number, if no sub-service is provided, then the UE uses "urn:service:sos" as the associated emergency service URN.
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U.2.2.6.2  eCall type of emergency serviceWord‑p. 946
If the IP-CAN indicates the eCall support indication or the CS domain is not available to the UE, the UE can send an INVITE request with Request-URI set to "urn:service:sos.ecall.manual" or "urn:service:sos.ecall.automatic".
If the IP-CAN does not indicate the eCall support indication and the CS domain is available to the UE, the UE shall not send an INVITE request with Request-URI set to "urn:service:sos.ecall.manual" or "urn:service:sos.ecall.automatic".
U.2.2.6.3  Current location discovery during an emergency call
Void.
U.2.2.6.4  Emergency services in single-registration mode
When the UE operates in single-registration mode as described in TS 24.501 and the UE recognises that a call request is an emergency call, if:
  1. the IM CN subsystem is selected in accordance with the conventions and rules specified in TS 23.167; and
  2. the UE is currently registered to the 5GS services while the UE is in an NR cell connected to 5GCN;
then the following treatment is applied:
  1. if the EMC indicates "Emergency services not supported":
    1. if the UE supports emergency services fallback as specified in TS 23.501 and the emergency services fallback is available (i.e., "ESFB is Y" as described in TS 23.167), the UE shall attempt emergency services fallback as specified in TS 24.501. If the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may behave as described in bullet b) below assuming that the emergency services fallback is not available;
    2. if the UE supports emergency services fallback as specified in TS 23.501 and the emergency services fallback is not available (i.e., "ESFB is N" as described in TS 23.167) and if:
      1. the EMF is set to "Emergency services fallback supported in E-UTRA connected to 5GCN only" and the UE is capable of accessing 5GCN via E-UTRA, the UE shall either:
        1. attempt to select an E-UTRA cell connected to 5GCN. If the UE finds a suitable E-UTRA cell connected to 5GCN, the UE shall attempt emergency services fallback as specified in TS 24.501 via E-UTRA connected to 5GCN. If the UE does not find a suitable E-UTRA cell connected to 5GCN or the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
        2. attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
      2. the EMF is set to "Emergency services fallback not supported" or the UE is not capable of accessing 5GCN via E-UTRA, the UE shall disable the N1 mode capability for 3GPP access as specified in TS 24.501 and attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; and
    3. if the UE does not support emergency services fallback as specified in TS 23.501, the UE shall disable the N1 mode capability for 3GPP access as specified in TS 24.501 and attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration;
  2. if the EMC indicates "Emergency services supported in E-UTRA connected to 5GCN only":
    1. if the UE supports emergency services fallback as specified in TS 23.501 and the emergency services fallback is available (i.e., "ESFB is Y" as described in TS 23.167), the UE shall attempt emergency services fallback as specified in TS 24.501. If the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may behave as described in bullet b) below assuming that the emergency services fallback is not available; and
    2. if the UE does not support emergency services fallback as specified in TS 23.501 or the emergency services fallback is not available (i.e., "ESFB is N" as described in TS 23.167) and if:
      1. the UE is capable of accessing 5GCN via E-UTRA, the UE shall attempt to select an E-UTRA cell connected to 5GCN. If the UE finds a suitable E-UTRA cell connected to 5GCN, the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501 via E-UTRA connected to 5GCN. If the UE does not find a suitable E-UTRA cell connected to 5GCN, the UE may attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
      2. the UE is not capable of accessing 5GCN via E-UTRA, the UE shall disable the N1 mode capability for 3GPP access as specified in TS 24.501 and attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; and
  3. if the EMC indicates "Emergency services supported in NR connected to 5GCN only" or "Emergency services supported in NR connected to 5GCN and E-UTRA connected to 5GCN", the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501.
When the UE operates in single-registration mode as described in TS 24.501 and the UE recognises that a call request is an emergency call, if:
  1. the IM CN subsystem is selected in accordance with the conventions and rules specified in TS 23.167; and
  2. the UE is currently registered to the 5GS services while the UE is in an E-UTRA cell connected to 5GCN;
then the following treatment is applied:
  1. if the EMC indicates "Emergency services not supported":
    1. if the UE supports emergency services fallback as specified in TS 23.501 and the emergency services fallback is available (i.e., "ESFB is Y" as described in TS 23.167), the UE shall attempt emergency services fallback as specified in TS 24.501. If the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may behave as described in bullet b) below assuming that the emergency services fallback is not available;
    2. if the UE supports emergency services fallback as specified in TS 23.501 and the emergency services fallback is not available (i.e., "ESFB is N" as described in TS 23.167) and if:
      1. the EMF is set to "Emergency services fallback supported in NR connected to 5GCN only" and the UE is capable of accessing 5GCN via NR, the UE shall either:
        1. attempt to select an NR cell connected to 5GCN. If the UE finds a suitable NR cell connected to 5GCN, the UE shall attempt emergency services fallback as specified in TS 24.501 via NR connected to 5GCN. If the UE does not find a suitable NR cell connected to 5GCN or the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
        2. attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
      2. the EMF is set to "Emergency services fallback not supported" or the UE is not capable of accessing 5GCN via NR, the UE shall disable the N1 mode capability for 3GPP access as specified in TS 24.501 and attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; and
    3. if the UE does not support emergency services fallback as specified in TS 23.501, the UE shall disable the N1 mode capability for 3GPP access as specified in TS 24.501 and attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration;
  2. if the EMC indicates "Emergency services supported in NR connected to 5GCN only":
    1. if the UE supports emergency services fallback as specified in TS 23.501 and the emergency services fallback is available (i.e., "ESFB is Y" as described in TS 23.167), the UE shall attempt emergency services fallback as specified in TS 24.501. If the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may behave as described in bullet b) below assuming that the emergency services fallback is not available; and
    2. if the UE does not support emergency services fallback as specified in TS 23.501 or the emergency services fallback is not available (i.e., "ESFB is N" as described in TS 23.167) and if:
      1. the UE is capable of accessing 5GCN via NR, the UE shall attempt to select an NR cell connected to 5GCN. If the UE finds a suitable NR cell connected to 5GCN, the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501 via NR connected to 5GCN. If the UE does not find a suitable NR cell connected to 5GCN, the UE may attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
      2. the UE is not capable of accessing 5GCN via NR, the UE shall disable the N1 mode capability for 3GPP access as specified in TS 24.501 and attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; and
  3. if the EMC indicates "Emergency services supported in E-UTRA connected to 5GCN only" or "Emergency services supported in NR connected to 5GCN and E-UTRA connected to 5GCN", the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501.
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U.2.2.6.5  Emergency services in dual registration modeWord‑p. 949
When the UE operates in dual-registration mode as described in TS 24.501 and the UE recognises that a call request is an emergency call, if:
  1. the IM CN subsystem is selected in accordance with the conventions and rules specified in TS 23.167; and
  2. the UE currently camps on an NR cell connected to 5GCN;
then the following treatment is applied:
  1. if the EMC indicates "Emergency services not supported" and:
    1. if the UE is attached for EPS services and the network provided the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
    2. if the UE is not attached for EPS services, and:
      1. if emergency services fallback is available (i.e. "ESFB is Y" as described in TS 23.167) and the UE supports emergency services fallback as specified in TS 23.501, the UE shall attempt emergency services fallback as specified in TS 24.501. If the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may behave as described in bullet ii) below assuming that the emergency services fallback is not available; or
      2. if emergency services fallback is not available (i.e. "ESFB is N" as described in TS 23.167) or the UE does not support emergency services fallback as specified in TS 23.501, the UE shall attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration;
  2. if the EMC indicates "Emergency services supported in E-UTRA connected to 5GCN only" and:
    1. if the UE is attached for EPS services and:
      1. if the network provided the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
      2. if the network provided the UE with the EMC BS set to "emergency bearer services in S1 mode not supported" as described in TS 24.301 and the UE is capable of accessing 5GCN via E-UTRA, the UE shall be locally detached for EPS services and the UE shall attempt to select an E-UTRA cell connected to 5GCN. If the UE finds a suitable E-UTRA cell connected to 5GCN, the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501 via E-UTRA connected to 5GCN; or
    2. if the UE is not attached for EPS services and:
      1. if emergency services fallback is available (i.e., "ESFB is Y" as described in TS 23.167) and the UE supports emergency services fallback as specified in TS 23.501, the UE shall attempt emergency services fallback as specified in TS 24.501. If the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may behave as described in bullet ii) below assuming that the emergency services fallback is not available; or
      2. if emergency services fallback is not available (i.e., "ESFB is N" as described in TS 23.167) or the UE does not support emergency services fallback as specified in TS 23.501, and:
        1. if the UE is capable of accessing 5GCN via E-UTRA, the UE shall attempt to select an E-UTRA cell connected to 5GCN. If the UE finds a suitable E-UTRA cell connected to 5GCN, the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501 via E-UTRA connected to 5GCN. If the UE does not find a suitable E-UTRA cell connected to 5GCN, the UE may attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; or
        2. if the UE is not capable of accessing 5GCN via E-UTRA, the UE shall attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; and
  3. if the EMC indicates "Emergency services supported in NR connected to 5GCN only" or "Emergency services supported in NR connected to 5GCN and E-UTRA connected to 5GCN", and:
    1. if the UE is not attached for EPS services or the UE is attached for EPS services but the network provided the UE with the EMC BS set to "emergency bearer services in S1 mode not supported" as described in TS 24.301, the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501; or
    2. if the UE is attached for EPS services and the network provided the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall either:
      1. trigger establishment of an emergency PDU session as specified in TS 24.501; or
      2. perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration.
When the UE operates in dual-registration mode as described in TS 24.501 and the UE recognises that a call request is an emergency call, if:
  1. the IM CN subsystem is selected in accordance with the conventions and rules specified in TS 23.167; and
  2. the UE currently camps on an E-UTRA cell connected to 5GCN and the UE is not attached for EPS services;
then the following treatment is applied:
  1. if the EMC indicates "Emergency services not supported" and:
    1. if emergency services fallback is available (i.e. "ESFB is Y" as described in TS 23.167) and the UE supports emergency services fallback as specified in TS 23.501, the UE shall attempt emergency services fallback as specified in TS 24.501. If the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may behave as described in bullet b) below assuming that the emergency services fallback is not available; or
    2. if emergency services fallback is not available (i.e. "ESFB is N" as described in TS 23.167) or the UE does not support emergency services fallback as specified in TS 23.501, the UE shall attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; and
  2. if the EMC indicates "Emergency services supported in NR connected to 5GCN only" and:
    1. if emergency services fallback is available (i.e., "ESFB is Y" as described in TS 23.167) and the UE supports emergency services fallback as specified in TS 23.501, the UE shall attempt emergency services fallback as specified in TS 24.501. If the UE receives from the lower layers an indication that the emergency services fallback attempt failed, the UE may behave as described in bullet b) below assuming that the emergency services fallback is not available; or
    2. if emergency services fallback is not available (i.e., "ESFB is N" as described in TS 23.167) or the UE does not support emergency services fallback as specified in TS 23.501 and:
      1. if the UE is capable of accessing 5GCN via NR, the UE shall attempt to select an NR cell connected to 5GCN. If the UE finds a suitable NR cell connected to 5GCN, the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501 via NR connected to 5GCN. If the UE cannot find a suitable NR cell connected to 5GCN, the UE may attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; and
      2. if the UE is not capable of accessing 5GCN via NR, the UE shall attempt to select an E-UTRA cell connected to EPC. If the UE finds a suitable E-UTRA cell connected to EPC and the network provides the UE with the EMC BS set to "emergency bearer services in S1 mode supported" as described in TS 24.301, the UE shall perform the procedures as described in subclause L.2.2.6 to activate an EPS bearer context to perform emergency registration; and
  3. if the EMC indicates "Emergency services supported in E-UTRA connected to 5GCN only" or "Emergency services supported in NR connected to 5GCN and E-UTRA connected to 5GCN", the UE shall trigger establishment of an emergency PDU session as specified in TS 24.501.
If the UE operating in dual-registration mode and camping on an E-UTRA cell connected to 5GCN, is also attached for EPS service, the domain selection is out of the scope of the specification.
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