RRC services and features
The main services and functions RRC sub-layer include:
- Broadcasting AS and NAS with the relevant system information;
- NG-RAN or a 5GC initiated paging;
- Establishment, RRC connection between the UE and the maintenance and release of NG-RAN, comprising:
- Carrier aggregation add, modify and release;
- Or between E-UTRA and NR NR add, modify, and release the double connector.
- Safety features include key management;
- Establishing a signaling radio bearer (SRB) and data radio bearer (the DRB), configuration, maintenance and release;
- Mobile features include:
- Transfer and context transfer;
- UE cell selection and reselection and cell selection and reselection control;
- Inter-RAT mobility.
- QoS management functions;
- UE measurement reporting and control report;
- Radio link failure detection and recovery;
- NAS to / from the UE transmits the NAS message.
Protocol Specifications
It supports the following RRC state, the following characteristics:
RRCJDLE:
- PLMN selection;
- Broadcast system information;
- Cell reselection mobility;
- Paged mobile terminated data initiated by 5GC;
- Mobile terminated data area managed by the paging 5GC;
- CN configured by NAS for paging DRX.
RRC_INACTIVE ：
- PLMN selection;
- Broadcast system information;
- Cell reselection mobility;
- Paging is initiated by NG-RAN (RAN paging);
- Notification area on the RAN (RNA) managed by NG-RAN;
- Configured by the DRX NG-RAN RAN paging;
- UE is establishing 5GC-NG-RAN connection (two C / user plane);
- UE context stored in the AS NG-RAN and the UE;
- NG-RAN know RNA UE belongs.
RRC_CONNECTED ：
- UE is establishing 5GC-NG-RAN connection (two C / user plane);
- UE context stored in the AS NG-RAN and the UE;
- NG-RAN knows that the UE belongs to cells;
- To / from the UE unicast data transmission;
- Mobility control network includes a measurement.
Information processing system
Outline
System Information (SI) and the other into a minimum SI SI, SI used wherein different minimum message (MIB and SIB1) at two different downlink channels
transmitted on other SI message transmission SystemInformation (SIB2 and up) :
SI comprises minimum basic information required for initial access and access to any other information SI.
SI minimum include:
- MIB contains system information needed to receive further information and the prohibition state cell basic physical layer information;
- SIB1 defined schedules another system information block, and contains the information needed to initial access;
Other SI SIB not contain all the SI broadcast a minimum. The SIB may be periodically broadcast in a DL-SCH, on-demand broadcast DL-SCH (i.e., according to the request of the UE in RRC_IDLE or from RRC_INACTIVE), or transmitted to RRC_CONNECTED in the DL-SCH in a specific manner UE.
Other SI include:
- SIB2 comprising cell reselection information, mainly related to the serving cell;
- SIB3 contains information regarding the cell reselection within an associated service frequency and the frequency of the neighboring cells (including a common frequency cell reselection parameters and cell reselection parameters specific);
- SIB4 contains information regarding the cell reselection other inter-frequency and frequency-dependent NR neighbor cell (including a common frequency cell reselection parameters and cell reselection parameters specific);
- SIB5 contains information about the E-UTRA frequencies and a cell reselection associated with E-UTRA neighboring cells (including a common frequency cell reselection parameters and cell reselection parameters specific);
- SIB6 contains ETWS primary notification;
- SIB7 contains ETWS secondary notification;
- SIB8 include CMAS alert notification;
- SIB9 contains information relating to the GPS time and Coordinated Universal Time (UTC).
Supply system as shown below:
For the UE considered for cell / camped frequency, UE does not need to acquire the content of the SI minimal cell / frequency from the other cell / frequency layer. This does not exclude the SI memory cell from the UE applies the previously accessed.
If the UE can not determine the minimum SI entire contents of the cell it should be taken to prohibit the cell (the cell or by receiving from a previously stored valid cell receiving SI), the UE.
In the case of BA, UE SI acquired only on the active BWP.
Dispatch
1, MIB is mapped on the BCH and carried on the BCCH, and all other SI messages on the BCCH is mapped, and carried on the DL-SCH, which are carried on dynamic DL-SCH. Other scheduling SI SI message portion indicated by SIB1.
2, for the UE in RRC_IDLE and RRC_INACTIVE, triggers a random access procedure for the other SI request, wherein the request message MSG3 comprises SI, SI unless requested subset associated PRACH resource, in this case is MSG1 indicating that the requested additional SI.
3, when MSG1, a minimum particle size is SI request message (i.e., a group of the SIB), a RACH preamble and / or a plurality of PRACH resources for the SI request message, and acknowledges the request in gNB MSG2. 3, gNB acknowledges the request when used in the MSG4 MSG.
4, may broadcast other SI configured to be a specific duration and periodicity. When the UE requests the RRC_IDLE / RRC_INACTIVE may also broadcast other SI.
5, in order to allow the UE is camped on a cell, it must obtain from the content of the SI smallest cell. It may exist in the SI broadcast minimum cell system, the UE can not camp.
SI modification
1, a change of system information (except ETWS / CMAS) occurs only in a specific radio frame, i.e., using the concept of a modification period. The system information may be transmitted multiple times to the same content within the modification period, as is defined by the schedule. Configured by the system information modification period.
2, when the network changes (some of the) system information, it first notifies the change to the UE, i.e. it can be done in the entire modification period. In the next modification period, the network transmits the updated system information. Upon receiving a change notification, the UE acquires the system information from the new beginning of the next modification period. UE application of previously acquired system information until the UE to acquire new information system.
3, indicating the paging message or the PDCCH for notifying RRC_IDLE, RRC_INACTIVE RRC_CONNECTED and the UE information about the system change. As
if this UE receives paging message, it knows that the system information (except ETWS / CMAS) the next modification period boundary changes.
Access Control
NG-RAN overload and supports access control functions, e.g. RACH back, reject the RRC connection, the RRC connection release and access restriction mechanism UE based; access control framework for all UE status of NR (RRC_IDLE, RRC_INACTIVE and RRC_CONNECTED). NG-RAN broadcasts control information prohibiting access classes and an associated access identification (in the case of network sharing, restriction control information may be provided separately for each PLMN). The restriction information for the selected UE and the access attempt and the access category of the selected PLMN broadcast access identifier, determining whether to authorize access attempt:
- Triggering a request for NAS, NAS and the access identifier to determine access category;
- Request for triggered AS, the RRC determine the access category, and the determined NAS access identifier.
gNB processing having a high priority establishment cause "urgent", "mps-PriorityAccess" and "mcs-PriorityAccess" (i.e. an emergency call, MPS, MCS subscriber) access attempts, and only in response to extreme network load RRC reject access try conditions that could threaten the stability of the gNB.
UE capability retrieval framework
UE reports at least static UE radio access capabilities in the network request. gNB which can request the UE capability reporting information based on the band.
Transmission of the NAS message
NR order to provide reliable delivery of the NAS message, except when re-establishing PDCP handover may occur in the loss or duplication of RRC SRB.
In the RRC, NAS message sent in a transparent container. Piggybacked NAS message may occur in the following scenarios:
- Established in bearer / modify / release;
- Initial NAS message for transmission during connection establishment and restore the connection in the UL.
Note: In addition to the NAS integrity protection and ciphering executed, NAS messages can be encrypted and integrity protected by PDCP.
Carrier aggregation
When configuring CA, UE only has one RRC connection with the network. When the RRC connection establishment / re / handover, the NAS mobility information to provide a service cell, and a connection re-establishment / handover RRC, one serving cell provides the security input. This cell is called the primary cell (PCell). Depending on UE capability, a secondary cell (SCell) may be configured to form a set of serving cells with PCell. Thus, configured serving cell for the UE always consists of a set of one or more PCell and SCell composition.
SCell may perform a reconfiguration by RRC, add and remove. When switching the NR, the RRC may also be added, removed, or reconfigured target PCell SCell for use. When adding a new SCell, dedicated RRC signaling is used to transmit all the required system information SCell, i.e., when in the connected mode, the UE does not need to obtain information directly from the broadcasting system SCell.
Bandwidth Adaptation
To enable BA in PCell, gNB use UL and DL BWP configuration UE. To enable BA on the SCell in the case of CA, gNB least configured to UE DL BWP (i.e., UL may not). For PCell, initial BWP BWP for initial access. For SCell, initial BWP BWP is configured for the UE is first activated under SCell operation.
In unpaired spectrum, DL, and UL BWP can be switched independently. Unpaired spectrum, DL, and while switching the UL BWP. BWP configured to switch between DCI or by an inactivity timer. When configured as a serving cell inactivity timer, the inactivity timer expires and the cell associated with the active switch to default BWP BWP configured by the network.
UE Support Information
If configured to do so, the UE may send a signal to the network through UEAssistanceInformation, if it prefers to adjust a connected mode DRX
cycle length, or is experiencing internal overheating. In the latter case, the UE may represent transient a secondary component carrier to reduce the maximum
number, the maximum number and the maximum aggregate bandwidth of MIMO layers. In both cases, it decides whether to adapt gNB request.
