18 UE capabilities

36.3003GPPEvolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)Overall descriptionRelease 17Stage 2TS

RRC signalling carries AS capabilities and NAS signalling carries NAS capabilities. When a capability ID is used as described below, the ID representing AS capabilities may be carried in NAS signalling. The UE capability information is stored in the MME. In the uplink, except of NB-IoT no capability information is sent early in e.g. RRCConnectionRequest message. For NB-IoT, early indications for multi-tone support (IOT bit) and multi-carrier support (IOT bit) are sent in RRCConnectionRequest-NB message. In the downlink, enquiry procedure of the UE capability is supported.

Figure 18-1: Initial UE Capability Handling

The MME stores the UE Radio Capability uploaded in the UE CAPABILITY INFO INDICATION message.

The possible RAT-Types are: EUTRAN, UTRAN, GERAN-PS, GERAN-CS, CDMA2000-1XRTT. The GERAN capability is divided into separate parts. MS Classmark 2 and Classmark 3 are used for CS domain (in both AS and NAS) and MS Radio Access Capability is used for PS domain. The main part of CDMA2000 capabilities is not handled by the eNB or the MME, but is exchanged via tunnelling (see 10.3.2). The small part of CDMA2000 capabilities (for CDMA2000-1XRTT) is needed for the eNB to be able to build messages for the target CDMA2000 RNC (see 10.3.2).

The eNB may acquire the UE capabilities after a Handover completion. The UE capabilities are then uploaded to the MME.

Usually during handover preparation, the source RAN node transfers both the UE source RAT capabilities and the target RAT capabilities to the target RAN node, in order to minimize interruptions and to follow the principles in clause 10.2.2. The source RAN is not mandated to acquire other RAT capabilities (i.e. other than the source and target RAT capabilities) in order to start a handover preparation. This is described in clause 19.2.2.5.6. However, there are exceptions to this principle:

– For handover from GERAN to EUTRAN, due to limitations in GERAN radio interface signalling, source RAT (GERAN) never provides the EUTRA capabilities to the target RAN node.

– At handover from UTRAN to EUTRAN, it is optional to forward the UTRAN capabilities to the target RAN.

The UTRAN capabilities, i.e. the INTER RAT HANDOVER INFO, include START-CS, START-PS and "predefined configurations", which are "dynamic" IEs. In order to avoid the START values desynchronisation and the key replaying issue, the eNB always enquiry the UE UTRAN capabilities at transition from RRC_IDLE to RRC_CONNECTED and before Handover to UTRAN. The eNB does not upload the UE UTRAN capabilities to the MME.

Due to limitations in radio interface signalling, transfer of EUTRA capabilities is not supported in GERAN.

For BL UEs, UEs supporting Enhanced Coverage and NB-IoT UEs, the S1 signalling includes the UE Radio Capability for Paging. The eNB uploads the UE Radio Capability for Paging to the MME in the UE CAPABILITY INFO INDICATION message separately from the UE Radio Capability. The MME includes the UE Radio Capability for Paging in the paging request to the eNB. The eNB may use the UE Radio Capability for Paging to determine how to page the UE.

For a NB-IoT UE that supports S1-U data transfer or User Plane CIoT EPS optimisations, as defined in TS 24.301 [20], the procedure in Figure 18-1 is applicable except that RAT-Types and handover are not supported.

If a request to retrieve the UE Radio Capability is included in the DOWNLINK NAS TRANSPORT message, the eNB may request the UE Radio Capability from the UE and provide it to the MME in the UE CAPABILITY INFO INDICATION message. The detailed procedure is defined in TS 36.413 [25].

For a UE that supports Control Plane CIoT EPS optimisation, as defined in TS 24.301 [20], the MME may initiate Connection Establishment Indication procedure to provide UE Radio Capability to the eNB after receiving INITIAL UE MESSAGE message. If the UE Radio Capability is not included in the procedure, this may trigger the eNB to request the UE Radio Capability from the UE and to provide it to the MME in the UE CAPABILITY INFO INDICATION message. The detailed procedure is defined in TS 36.413 [25].

In NB-IoT, for a UE that supports Control Plane CIoT EPS optimisations, as defined in TS 24.301 [20], the eNB, based on configuration, may retrieve the UE Radio capability from the MME upon reception of RRC Connection Request as defined in TS 23.401 [17], clauses 5.3.4B.2 and 5.3.4B.3.

If supported by the UE and the network, the UE may provide an ID in NAS signalling that represents its radio capabilities for one or more RATs in order to reduce signalling overhead. The ID may be assigned either by the manufacturer or by the serving PLMN. The manufacturer-assigned ID corresponds to a pre-provisioned set of capabilities. In the case of the PLMN-assigned ID, assignment takes place in NAS signalling.