17 UE radio capability signalling optimization

21.9163GPPRelease 16Release descriptionTS

17.1 Optimisations on UE radio capability signalling

840054

Optimisations on UE radio capability signalling

RACS

S2

RP-191460

Haris Zisimopoulos

800025

Study on RACS

FS_RACS

S2

SP-180599

Haris Zisimopoulos, Qualcomm

830027

Stage 2 of RACS

RACS

S2

SP-190180

Haris Zisimopoulos

840003

CT aspects of RACS

RACS

ct

CP-191061

Chaponniere, Lena, Qualcomm

840055

CT1 aspects of RACS

RACS

C1

CP-191061

Chaponniere, Lena, Qualcomm

840056

CT3 aspects of RACS

RACS

C3

CP-191061

Chaponniere, Lena, Qualcomm

840057

CT4 aspects of RACS

RACS

C4

CP-191061

Chaponniere, Lena, Qualcomm

830079

Optimisations on UE radio capability signalling – NR/E-UTRA Aspects

RACS-RAN

R2

RP-190657

MediaTek

800097

Study on optimisations on UE radio capability signalling – NR/E-UTRA Aspects

FS_RACS_RAN

R2

RP-181459

MediaTek

830179

Core part: Optimisations on UE radio capability signalling – NR/E-UTRA Aspects

RACS-RAN-Core

R2

RP-191088

MediaTek

Summary based on the input provided by Qualcomm Incorporated, MediaTek and CATT in SP-200273 (SP-200273 superseds RP-201235, which provides the summary only on the RAN part).

This section summarizes the feature “Optimisations of UE radio capability signalling” across 3GPP specifications (RAN, SA, CT).

Background

With the increase in the size of UE radio capabilities driven by additional supported bands, the size of the UE Radio Capabilities will significantly grow from Rel-15 onwards, therefore an efficient approach to signal UE Radio Capability information is needed.

SA2 concluded that additional optimisation of UE radio capabilities handling should be investigated as part of a dedicated study towards Release 16. A study item [1] was drafted accordingly, along with a corresponding RAN study item [13]. The SA2 study item conclusions are documented in TR 23.743 [2]. The conclusions of the RAN study item are documented in TR 37.873 [14]. Subsequent to the study items, work items were drafted in SA ([5]) and RAN ([10]) to implement optimisations to the UE radio capability signalling.

The work is divided into two subfeatures, UE radio capability ID and UE capability segmentation.

UE Radio Capability ID

The SA2 work item [5] specified system optimisations for the 5GS (documented in TS 23.501 [3]) and for the EPS (documented in TS 23.401 [4]), that apply to both NR and E-UTRA, but not NB-IoT, consisting of using UE Radio Capability IDs as an alternative to signaling the UE Radio Capabilities container in system procedures:

– between the UE and the CN (over Uu)

– between the CN and the RAN (impacting N2/S1 interfaces)

– within the RAN in e.g. the handover procedures (impacting Xn/X2/S1/N2 interfaces)

– within the CN.

Work was done in collaboration with RAN WGs for the related RAN interfaces and CT WGs for the CN interfaces and NFs. Interworking with nodes that support the feature and those that do not support the feature was also defined.

The UE Radio Capability ID format is defined in TS 23.003 [7]. The UE Radio Capability ID is signaled by the UE in NAS as specified in TS 24.501 [8] for the 5GS and as specified in TS 24.301 [9] for the EPS. Two possible options for the assignment of UE Radio Capability ID exist:

– Manufacturer-assigned: The UE Radio Capability ID may be assigned by the UE manufacturer in which case it includes a UE manufacturer identification (i.e. a Vendor ID). In this case, the UE Radio Capability ID uniquely identifies a set of UE radio capabilities for a UE by this manufacturer in any network.

– Network-assigned: If a manufacturer-assigned UE Radio Capability ID is not used by the UE or the serving network, or it is not recognised by the serving network’s UE Capability Management Function (UCMF), the UCMF may allocate UE Radio Capability IDs for the UE corresponding to each different set of UE radio capabilities which the network may receive from the UE at different times. In this case, the UE Radio Capability IDs which the UE receives are applicable to the serving network and uniquely identify the corresponding sets of UE radio capabilities in this network. The network-assigned UE Radio Capability ID includes a Version ID in its format. The value of the Version ID is the one configured in the UCMF, at the time when the UE Radio Capability ID value is assigned. The Version ID value makes it possible to detect whether a UE Radio Capability ID is current or outdated.

UE Radio Capability IDs and the mapping to the corresponding UE radio capabilities are stored in a new function called the UE Capability Management Function (UCMF) in the CN. The UCMF is used for:

– storage of dictionary entries corresponding to either Network-assigned or Manufacturer-assigned UE Radio Capability IDs.

– assigning Network-assigned UE Radio Capability ID values.

– provisioning of Manufacturer-assigned UE Radio Capability ID entries in the UCMF performed from an AF that interacts with the UCMF either directly or via the NEF/SCEF (or via Network Management).

Figure 1: UCMF architecture and related reference points in 5GS (left) and EPS (right)

System procedures are defined for 5GS in TS 23.502 [6] and for EPS in TS 23.401 [4].

UE Capability Segmentation

The RAN work item [10] calls for specification of a segmentation mechanism, so that in cases of excessively large UE capability signalling (e.g. capability information messages exceeding the maximum size of a PDCP SDU), the capability can be segmented into multiple RRC messages. Segmentation applies to both NR and E-UTRA and is captured respectively in [11] and [12].

Segmentation is performed in the RRC protocol layer, with a separate RRC PDU for each segment. The UE encodes the capability information message, then divides the encoded message into segments such that the size of each segment does not exceed the maximum size of a PDCP SDU (8188 octets in E-UTRA, 9000 octets in NR); the RAN node (eNB or gNB) receives the segments and reassembles them to reconstruct the original capability information message. Segmentation is applied only in case the size of the encoded capability information message exceeds the maximum size of a PDCP SDU. The signalling formats support up to 16 segments for a single capability information message.

References

List of related CRs: select "TSG Status = Approved" in:
https://portal.3gpp.org/ChangeRequests.aspx?q=1&workitem=840054,800025,830027,840003,840055,840056,840057,830079,800097,830179

[1] SP-180599, “Study on optimisations on UE radio capability signaling”

[2] TR 23.743, “Study on optimisations on UE radio capability signaling”

[3] TS 23.501, “System architecture for the 5G System (5GS)”

[4] TS 23.401, “General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access”

[5] SP-190180, “Work item on optimisations on UE radio capability signaling”

[6] TS 23.502, “Procedures for the 5G System (5GS)”

[7] TS 23.003, “Numbering, addressing and identification”

[8] TS 24.501, “Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3”

[9] TS 24.301, “Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3”

[10] RP-191088, “Updated WID: Core part: Optimisations on UE radio capability signalling – NR/E-UTRA Aspects”

[11] TS 38.331, “NR; Radio Resource Control (RRC); Protocol specification”

[12] TS 36.331, “Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification”

[13] RP-181459, “Study on optimisations on UE radio capability signalling – NR/E-UTRA Aspects”

[14] TR 37.873, “Study on optimizations of UE radio capability signalling; NR / Evolved Universal Terrestrial Radio Access Network (E-UTRAN) aspects”