UE Capability Handling

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5.11        UE Capability Handling
5.11.1        General
The UE Capability information is made up of the UE Radio Capability information and the UE Core Network Capability information.
The UE Radio Capability for Paging Information is separate from both the UE Radio Capability information and the UE Core Network Capability information. The UE Radio Capability for Paging Information may be used to enhance the paging in the E-UTRAN.
5.11.2        UE Radio Capability Handlin
The UE Radio Capability information contains information on RATs that the UE supports (e.g. power class, frequency bands, etc). Consequently, this information can be sufficiently large (e.g. >50 octets) that it is undesirable to send it across the radio interface at every transition from ECM IDLE to ECM CONNECTED. To avoid this radio overhead, the MME stores the UE Capability information during ECM IDLE state and the MME shall, if it is available, send its most up to date UE Radio Capability information to the E UTRAN in the S1 interface INITIAL CONTEXT SETUP REQUE8ST message unless the UE is performing an Attach procedure or a Tracking Area Update procedure for the "first TAU following GERAN/UTRAN Attach" or for a "UE radio capability update".
NOTE 1:        For a GERAN/UTRAN/E-UTRAN capable UE, the UE Radio Capability information that the MME stores is broadly equivalent to the combination of the MS Radio Access capability sent in the TS 24.008 [47] Attach Request or RAU Request messages plus the E UTRAN Inter RAT Handover information sent in the TS 24.008 [47] Attach Complete or RAU Complete messages. The UTRAN Radio Capabilities are excluded owing to issues with the handling of dynamic UMTS security parameters.
If a UE supports both NB-IoT and WB-E-UTRAN, the UE handles the UE Radio capability information as follows:
-        When the UE is camping on NB-IoT the UE provides only NB-IoT UE radio capabilities to the network.
-        When the UE is camping on WB-E-UTRAN, the UE provides UE radio capabilities including WB-E-UTRAN UE radio capabilities but not NB-IoT UE radio capabilities to the network.
In order to handle the distinct UE radio capabilities, the MME stores a separate NB-IoT specific UE Radio Capability information when the UE provides the UE Radio Capability information while camping on NB-IoT.
When the UE is camping on NB-IoT, the MME sends, if available, the NB-IoT specific UE Radio Capability information to the E-UTRAN.
When the UE is camping on WB-E-UTRAN, the MME sends, if available, UE radio capabilities including WB-E-UTRAN UE radio capabilities but not NB-IoT radio capabilities.
If the UE is performing an Attach procedure or a Tracking Area Update procedure for the "first TAU following GERAN/UTRAN Attach" or for "UE radio capability update", the MME shall delete (or mark as deleted) any UE Radio Capability information that it has stored, and, if the MME sends an S1 interface INITIAL CONTEXT SETUP REQUEST or UE RADIO CAPABILITY MATCH REQUEST message during that procedure, the MME shall not send any UE Radio Capability in-formation to the E UTRAN in that message. This triggers the E UTRAN to request the UE Radio Capability from the UE and to upload it to the MME in the S1 interface UE CAPABILITY INFO INDICATION message. The MME stores the UE Radio Capability information, and include it in further INITIAL CONTEXT SETUP REQUEST or UE RADIO CAPABILITY MATCH REQUEST messages in other cases than Attach procedure, Tracking Area Update procedure for the "first TAU following GERAN/UTRAN Attach" and "UE radio capability update" procedure.
If the UE is performing a Service Request (or other) procedure and the MME does not have UE Radio Capability information available (or it is available, but marked as "deleted"), then the MME sends an S1 interface INITIAL CONTEXT SETUP REQUEST message to the E UTRAN without any UE Radio Capability information in it. This triggers the E UTRAN to request the UE Radio Capability from the UE and upload it to the MME in the S1 interface UE CAPABILITY INFO INDICATION message.
NOTE 2:        This use of the INITIAL CONTEXT SETUP REQUEST message means that for a signalling only procedure such as a periodic Tracking Area Update, the UE Radio Capability would not be sent to the E UTRAN.
NOTE 3:        If a "first TAU following GERAN/UTRAN Attach" Tracking Area Update is performed during ECM-CONNECTED mode, e.g. after an inter RAT handover, no INITIAL CONTEXT SETUP REQUEST is sent and the UE Radio Capability information in the MME will remain deleted until the next ECM-IDLE to ECM-CONNECTED transition (or later, e.g. if the next activity from the UE is another Tracking Area Update).
For the EPS CIoT Optimisations, during the Attach procedure or the Tracking Area Update procedure, e.g. for the "first TAU following GERAN/UTRAN Attach", if the MME does not send an S1 interface INITIAL CONTEXT SETUP REQUEST to the E-UTRAN, the MME should obtain the UE Radio Capability information by sending the Connection Establishment Indication message without UE Radio Capability information included to the E-UTRAN. This triggers the E UTRAN to request the UE Radio Capability from the UE and upload it to the MME in the S1 interface UE CAPABILITY INFO INDICATION message. In subsequent ECM connections, if the MME does not send an S1 interface INITIAL CONTEXT SETUP REQUEST to the E UTRAN, the MME sends the UE Radio Capability to the E-UTRAN in the Connection Establishment Indication message or Downlink NAS Transport message.
The UE Radio Capability is not provided directly from one CN node to another. It will be uploaded to the MME when the E-UTRAN requests the UE Radio Capability information from the UE.
During handover via the MME (both intra RAT and inter RAT), the radio capability information for the source and target 3GPP RATs (with the possible exception of UTRAN and E-UTRAN) are transferred in the "source to target transparent container". Information on additional 3GPP RATs is optionally transferred in the "source to target transparent container". Transfer of the radio capability information related to the source and/or additional RATs is beneficial as it avoids the need for the target RAT to retrieve the information from the UE prior to a subsequent inter-RAT handover.
Owing to issues with dynamic UTRAN security parameters, special rules apply to the handling of the UTRAN radio capability information at inter-RAT handover (see e.g. the HandoverPreparationInformation message description in TS 36.331 [37] and the usage of the PS Handover Complete Ack message in TS 43.129 [8] and TS 48.018 [42])
To allow for the addition of future radio technologies, frequency bands, and other enhancements, the MME shall store the UE Radio Capability Information as defined in TS 23.008 [28].
The E UTRAN stores the UE Radio Capability information, received in the S1 interface INITIAL CONTEXT SETUP REQUEST message or obtained from the UE, for the duration of the RRC connection for that UE. Before any handover attempt from E UTRAN to UTRAN, the E UTRAN retrieves the UE's UTRAN Radio Capabilities from the UE.
If the UE's non-UTRAN UE Radio Capability information changes while in ECM-IDLE state (including cases of being in GERAN/UTRAN coverage), the UE shall perform a Tracking Area Update indicating "UE radio capability update" when it next returns to E UTRAN coverage.
NOTE 4:        In this release of the specifications, "UE radio capability update" is only supported for changes of GERAN radio capabilities in ECM-IDLE. Any change in the UE's E UTRAN capabilities requires the UE to detach and then re-attach to the system.
The MME may also request for Voice Support Match Information. If requested, the eNB then derives and provides an indication to the MME whether the UE radio capabilities are compatible with the network configuration (e.g. whether the UE supports the frequency bands that the network may rely upon for providing "full" PS voice coverage or whether the UE supports the SRVCC configuration of the network e.g. E-UTRAN to GERAN) as defined in clause 5.3.14.
5.11.3        UE Core Network Capability
The UE Core Network Capability is split into the UE Network Capability IE (mostly for E-UTRAN access related core network parameters) and the MS Network Capability IE (mostly for UTRAN/GERAN access related core network parameters) and contains non radio-related capabilities, e.g. the NAS security algorithms etc. Both the UE Network Capability and the MS Network Capability are transferred between CN nodes at MME to MME, MME to SGSN, SGSN to SGSN, and SGSN to MME changes.
In order to ensure that the UE Core Network Capability information stored in the MME is up to date (e.g. to handle the situation when the USIM is moved into a different device while out of coverage, and the old device did not send the Detach message; and the cases of inter-RAT Tracking Area Update), the UE shall send the UE Core Network Capability information to the MME during the Attach and non-periodic Tracking Area Update procedure within the NAS message.
The MME shall store always the latest UE Core Network Capability received from the UE. Any UE Core Network Capability that an MME receives from an old MME/SGSN is replaced when the UE provides the UE Core Network Capability with Attach and the Tracking Area Update signalling. The MME shall remove the stored MS Network Capability, if MS Network Capability is not included in Attach or non-periodic Tracking Area Update signaling e.g. UE is only capable of E-UTRAN.
If the UE's UE Core Network Capability information changes (in either ECM-CONNECTED or in ECM-IDLE state (including cases of being in GERAN/UTRAN coverage and having ISR activated)), the UE shall perform a Tracking Area Update ('type' different to 'periodic') when it next returns to E UTRAN coverage - see clause 5.3.3.0.
If the UE supports multiple user plane radio bearers on the NB-IoT RAT (see TS 36.306 [82], TS 36.331 [37]), then the UE shall indicate this in the UE Network Capability IE.
To allow for the addition of future features, the MME shall store the UE Network Capability and the MS Network Capability even if either or both is larger than specified in TS 24.008 [47]/TS 24.301 [46], up to a maximum size of 32 octets for each IE.
5.11.4        UE Radio Capability for Paging Information
The aim of this procedure is to assist the E-UTRAN in optimising the radio paging procedures.
As specified in TS 36.413 [36] , the eNB uploads the UE Radio Capability for Paging Information to the MME in the S1 interface UE CAPABILITY INFO INDICATION message (in a separate IE from the UE Radio Capability). As specified in TS 36.331 [37], the UE Radio Capability for Paging Information may contain UE Radio Paging Information provided by the UE to the eNB, and other information derived by the eNB (e.g. band support information) from the UE Radio Capability information.
Typically this is at the same time as the eNB uploads the UE Radio Capability information. The MME stores the UE Radio Capability for Paging Information in the MME context. When it needs to page, the MME provides the UE Radio Capability for Paging Information to the eNB as part of the S1 paging message. The eNB may use the UE Radio Capability for Paging Information to enhance the paging towards the UE.
If the UE Radio Capability for Paging Information changes, the UE shall follow the same procedures as if the UE Radio Capability changes.
In order to handle the situations of connected mode inter-MME change, the UE Radio Capability for Paging Information is sent to the target MME as part of the MM Context information. The UE Radio Capability for Paging Information is only applicable for MMEs, i.e. it is not applicable for SGSNs. Therefore, it will not be included by MME during context transfers towards SGSNs.