4. The overall architecture and functional distinction
4.1 overall architecture
NG-RAN may be:
GNB: NR providing user plane and control plane protocol terminations to the UE
ng-eNB: providing E-UTRA user plane and control plane protocol terminations to the UE
4.2 functional distinction
gNb ng-eNB bearer and the following features:
Radio resource management: radio bearer control, radio admission control, mobility control, dynamic allocation of resources to the UE in uplink and downlink (scheduling); and
IP header compression, ciphering and integrity protection;
When the UE access, information can not be provided from the UE determines to route the AMF, AMF is selected UE;
The user plane data is routed to the UPF;
The control plane data is routed to the AMF;
Connection establishment and release;
Paging scheduling and transmission;
Scheduling and transmission of broadcast information system (AMF or derived from the OAM);
Measurement and measurement reporting configuration for mobility and scheduling;
Uplink transport level packet marking (?)
Session management;
Support network sections;
QoS Flow management and to drb mapping;
Support RRC_INACTIVE state of the UE;
Distribution NAS message;
Wireless network sharing;
Dual Link;
Tight interoperability between NR-EUTRA;
AMF bearer following functions:
NAS signaling termination;
NAS signaling security
AS security control;
Between 3GPP mobile networks, signaling between nodes CN;
Idle mode UE reachability (including control and execution of retransmission Paging);
Registration Area Management;
The supporting system and inter-system mobility;
Access authentication;
Roaming access authorization;
Mobility Management Control (subscriptions and policies)
Support network sections;
SMF choice;
UPF carries the following main functions:
And the system of inter-system mobility anchor (if applicable);
The external data network interconnection point session PDU
Packet routing and forwarding
Policy rules planar portion and a user data packet inspection embodiment
Traffic usage reports;
Route traffic to uplink data network classifier;
Branch point to support multiple host sessions PDU
QoS user plane processing such as packet filtering, gated, UL / DL rate enhancement;
Verify upstream traffic (SDF to flow mapping QoS)
Buffering a downlink data packet and the downlink data notification trigger
Session management function (SMF) carries the following main functions:
Session management;
UE IP address allocation and management;
UPF flow configuration in turn, will route traffic to the correct destination;
Control portion and QoS policy enforcement;
A downlink data notification;
4.3 Network Interface
4.3.1NG Interface
4.3.1.1 NG user plane interface
NG user plane interface (NG-U) is defined between the NG-RAN node and UPF. IP-based transport network layer construct, GTP-U over UDP / IP PDU for user plane bearer between the node NG-RAN and UPF.
NG-U PDU providing a user plane between the NG-RAN node UPF and non-guaranteed delivery. For further details on NG-U, see TS 38.410
4.3.1.2NG control plane interface
NG control plane interface (NG-C) is defined between the NG-RAN node and the AMF. Construction of IP-based transport network layer. In order to reliably transmit a signaling message, SCTP is added on top of IP. Application layer signaling protocol called NGAP (NG Application Protocol). SCTP layer provides the application layer message delivery guarantee. In transmission, IP layer signaling point transmission for transmitting the PDU.
NG-C provides the following functions: NG interface management; the UE context manager; the UE mobility management; NAS transport message; Paging; PDU session management; transmission configuration; the warning message transmission.
For further details on NG-C, see TS 38.410 [16].
4.3.2 Xn Interface
4.3.2.1 Xn user plane interface
User plane interface definition Xn (Xn-U) between two NG-RAN node. IP-based transport network layer construct, GTP-U over UDP / IP user plane for carrying the PDU.
Xn-U provides the user plane PDU can not guarantee delivery, and supports the following functions: data forwarding; flow control
For more information on Xn-U, see TS 38.420
4.3.2.2 control plane interface
Control plane interface Xn (Xn-C) is defined between two NG-RAN node. The transport network layer built on top of the SCTP over IP. The application layer signaling protocol called XnAP (Xn Application Protocol). SCTP layer provides the application layer message delivery guarantee. In transmission, IP layer signaling point transmission for transmitting the PDU.
Xn-C interface supports the following functions: Xn interface management; the UE mobility management context including transmission and RAN Paging; dual link.
For more information on Xn-C, see TS 38.420
4.4 wireless protocol architecture
4.5 MRDC
NG-RAN supports MR-DC operation, wherein the UE is in RRC_CONNECTED configuration using two different radio resources provided by the scheduler, the scheduler is located at two different NG-RAN nodes, connected by a non-ideal backhaul, providing a NR visit, the other provides E-UTRA or NR visit. For more detailed information about MR-DC operation, see TS 37.340
4.6 Network Share
NG-RAN supports TS 23.501 [3] as defined in a shared radio access network. If the system information broadcast NR shared access, the sharing unit indicates the identity of each unit of TAC and PLPN subset (up to 12). NR visit only a TAC and each PLMN for each unit of a unit identification. Each unit identifier associated with the subset identity PLPN its serving node NG-RAN.
5.Physical Layer
6.Layer 2
7 RRC
7.1 services and features
The main services and functions RRC sub-layer include:
AS and NAS systems related to information broadcast;
5GC and NG-RAN triggered Paging;
Between the UE and NG-RAN establishment, maintenance and release of RRC connection,
They include: add, modify and release of CA;
Or between E-UTRA and NR NR add, modify, and release the connection bis
Security features include key management;
SRB and DRB build configuration maintenance and release;
Mobility: context switching and transmission; cell selection and reselection the UE and its control; heterologous system mobility;
QOS management functions;
UE measurement reports and control;
RLF detection and recovery;
The NAS message
7.2 protocol state
RRC supports the following states:
RRC_IDLE:
PLMN selection;
System information broadcast;
Cell reselection mobility;
5gc triggered Paging;
NAS is configured DRX CN Paging;
RRC_INACTIVE：
PLMN selection;
System information broadcast;
Cell reselection mobility;
NG-RAN triggered Paing;
NG-RAN of RNA (RAN-based notification area) management;
NG-RAN DRX RNA Paging is arranged;
UE is establishing 5GC-NG-RAN connection (control plane and a user plane);
NG-RAN and the UE, the AS UE context memory error;
NG-RAN know RNA belongs UE;
RRC_CONNECTED：
UE is establishing 5GC-NG-RAN connection (control plane and a user plane);
NG-RAN and the UE, the AS UE context memory error;
NG-RAN know RNA belongs UE;
Unicast data transmission to the UE;
Comprising measuring the mobility control by a network;
7.3 Information Processing System
System Information (SI) by a plurality of MIB and SIB, which are divided into Minimum SI and Other SI.
Minimum SI includes basic information required for the initial visit and obtain any additional information needed for SI
Minimum SI include:
MIB contains the cell information and the prohibition state basic physical layer information necessary for the cell to receive further system information, e.g. CORESET # 0 configuration. MIB periodic broadcast on the BCH.
SIB1 define additional scheduling system information block, and contains the information needed to initial access. SIB1 also referred Remaining Minimum SI (RMSI), periodic broadcast on the DL-SCH, or transmitted in a dedicated manner to the UEs in RRC_CONNECTED on DL-SCH.
OTHER SI contains all but the smallest of the SI broadcast SIB. The IB may be periodically broadcast in a DL-SCH, on-demand broadcast DL-SCH (i.e. RRC_IDLE or RRC_INACTIVE should request the UE for broadcast), or in a dedicated manner in RRC_CONNECTED sent to the UE on the DL-SCH.
Other SI include:
SIB2 comprising cell reselection information, mainly related to the serving cell;
SIB3 comprising (reselection parameter comprises frequency of the common cell reselection parameters and cell-specific) information about the frequency and intra-frequency neighboring cell related services reselection
SIB4 comprising (reselection parameter comprises frequency of the common cell reselection parameters and cell-specific) information relating to other frequencies and NR neighboring inter-frequency cell reselection and
SIB5 comprising (reselection parameter comprises frequency of the common cell reselection parameters and cell-specific) information about the E-UTRA and E-UTRA frequency associated with the neighboring cell reselection
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).
Consider a UE 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 preclude the application from the storage UE previously accessed cell case of SI.
If the UE can not determine the minimum SI entire contents of the cell should be taken to prohibit the cell (the cell or by receiving from a previously stored valid cell receiving SI), the UE.
When a plurality of digital mixed on a single carrier, only the default values for the system information broadcast and paging.
7.3.2 Scheduling
MIB is mapped on the BCCH and BCH, and all other mappings SI messages on the BCCH, dynamics on the DL-SCH. Other SIB1 indicating the scheduling portion SI SI messages.
For RRC_INACTIVE RRC_IDLE and the UEs, Other SI request triggers a random access procedure (see 9.2.6), a subset of the SI and PRACH resource if the associated request, comprising the MSG3 SI request message, MSG1 Other SI is used to indicate the request . When using MSG1, a minimum particle size for the SI request message (i.e., a group of SIB), a RACH preamble and / or a plurality of PRACH resources for the SI message request and request acknowledgment in gNB MSG2. 3 using MSG, gNB confirmation request in MSG4.
Other SI at a certain period and a configurable duration for broadcast. When the UE requests the RRC_IDLE / RRC_INACTIVE, the broadcast may Other SI.
To allow the UE is camped on a cell, it must obtain from the content Minimum SI cell. The system may not have the Minimum SI broadcast cell, the UE can not camp on such a cell.
7.3.3 SI modification
Change system information (ETWS / CMAS, see Section 16.4) occurs only on a specific radio frame, that is, using the concept of modification period. System information may (defined by schedule) multiple times during the modification to the transmission of the same content. Modification of the system configuration information.
7.4 Access Control
NG-RAN support overload and access control features such as RACH fall-back, RRC connection reject, RRC connection release and prohibit access mechanism based on UE.
A unified access control framework specified in TS 22.261 applies to all NR UE state (RRC_IDLE, RRC_INACTIVE and RRC_CONN). NG-RAN broadcast prohibit access category associated with identification and access control information (in the case of network sharing can be set individually for each PLMN prohibiting control information). Depending on the selected PLMN the UE prohibits the broadcast information and access to selected categories of identity and access access attempts (attempts to determine whether access is authorized:
For NAS request triggered, NAS access category to determine identity and access;
AS request triggered, RRC determine access categories, and access the NAS to determine identity.
gNB in dealing with a "emergency", when "mps-PriorityAccess" and "mcs-PriorityAccess" (ie emergency call, MPS, MCS subscribers) high priority access attempts, only that could threaten the stability of the extreme network conditions gNB RRC_REJECt refused to use these access attempts.
7.5 UE capability
UE reports its UE capabilities, at least when the network request, these functions are static. gNB may request the UE reports based band which features information.
7.6 NAS transport message
NR provided on the RRC SRB reliable NAS message sequence delivery, but at the time of reconstruction PDCP handover, may result in lost or duplicated. In the RRC, NAS message transparently transmitted. Piggybacked NAS message may occur in the following scenarios:
In the DL bearer setup / modify / release.
In the UL connection establishment and connection recovery during initial NAS message transmission.
NOTE: In addition to NAS integrity protection and ciphering performed outside, NAS messages can be encrypted and integrity protected by the PDCP
During session establishment or modification PDU resources, a plurality of NAS messages may be transmitted in a single downlink RRC message. In this case, an RRC message sequence NAS message to be included in the same order as the corresponding NG-AP message so as to ensure an orderly transfer of the NAS message.
7.7 CA
7.8 Bandwidth Adaptation
7.9 UE Assistance Information
8 THE Identities
8.1 UE Identities
In this clause, it lists the identity connected to 5GC the use of NR. For cell-based scheduling, the following identity:
C_RNTI: unique UE identifier, and an RRC connection as scheduling.
CS_RNTI, INT_RNTI, MCS_C_RNTI, P_RNTI, SI_RNTI, SP_CSI_RNTI
SFI_hrinti, Tfc_fucrcः_hrinti, Tfc_fushcः_hrinti, Tfc_srs_hrinti
RA_RNTI, Temporary C_RNTI, Random value for contention resolution
I_RNTI
8.2 Network Identities
In NG-RAN, the following identity is used to identify a particular network entity:
AMF Name,
NR Cell Global Identifier(NCGI),
gNB Identifier(gNB ID),
Global gNB ID,
TAI(Tracking Area identity),
S-NSSAI
9 and a mobility state conversion
NR load balancing through a handover, the redirection mechanism at the RRC release and by using inter-frequency and inter-system and inter-frequency absolute priority Qoffset parameters to achieve.
Links to measure the mobility state UE performs into at least three measurement types:
NR intra-frequency measurements, inter-frequency measurement NR, E-UTRA inter-system measurement
For each measurement type, you may define one or more measurement object (measurement target is defined to monitor the carrier frequency).
For each measurement object can define one or more report configurations (reporting condition reporting configuration defined). Three reporting standards: event-triggered reports, periodic reports and event-triggered periodic reports.
The association between the measurement and reporting configuration objects created (a measure identifies the object to be measured the same RAT and a report configuration linked together) by a measurement identity. By using a plurality of measurement identities (each measurement object, configuration report) may be:
A plurality of measurement reporting configuration object associated with
The reporting configuration associated with a plurality of measuring objects
In reporting the measurement results are also used to measure identity.
Measuring the amount of each RAT considered separately.
NG-RAN instructs the UE to use the measurement start command, modify or stop the measurement.
RAT handover may be performed in the same and / or CN, the RAT may be directed and / or CN changes.
When 5GC does not support emergency services, voice services, load balancing, will perform down to between E-UTRAN system. The availability factors CN interfaces, wireless network configuration and conditions, the process will lead to RRC_CONNECTED state down movement (handover procedure), or mobile RRC_IDLE state (redirection), see TS 23.501 [3] and TS38.331 [12]
9.2 NR within the system
9.2.1 RRC_IDLE move
9.2.1.1 cell selection
NR PLMN selection principles based on 3GPP PLMN selection principle. Select from the cell to the RM-DEREGISTERED RM-REGISTERED, from the CM-IDLE principle to CM-CONNECTED to and from the CM-CONNECTED CM-IDLE, and is based on:
UE NAS layer identity of the selected PLMN and equivalent PLMN
Cell selection is always based on CD-SSB located on the synchronous grid (see clause 5.2.4)
The UE searches for the frequency band NR, each carrier frequency to identify the strongest cell in accordance with CD-SSB. Then the reading unit system information broadcast to identify its PLMN
The UE may search sequentially each carrier ( "initial cell selection") or a shorter search information stored ( "stored cell selection information")
UE seeks to establish a suitable cell; if not identified a suitable cell, it seeks to identify an acceptable cell. When a suitable cell is found or only found acceptable cell, the cell resides, and starts the cell reselection process.
Suitable cell is a cell attribute satisfies cell selection conditions; cell PLMN is the selected PLMN, equivalent PLMN or the registered; part of the tracking area list of the cell is not prohibited or reserved, and not "tracking area roaming not allowed"
The acceptable cell is a cell attribute measured cell selection conditions are not prohibited cell.
Go RRC_IDLE status:
When switching from the RRC_CONNECTED or RRC_INACTIVE RRC_IDLE, UE should (if any) resides cell selected according to the frequency allocated in the RRC state transition message.
Recover from the coverage:
The above UE should attempt to find a suitable cell for the stored information or initial cell selection as described. If a suitable cell is not found on any frequency or RAT, the UE should try to find the acceptable cell.
In the multi-beam operation, the cell mass derived cell corresponding to the same beam (see subclause 9.2.4)
9.2.1.2 cell reselection
RRC_IDLE the UE performs cell reselection. Principles of the program are as follows:
Cell reselection always based on the CD-SSB located on the synchronous grid (see clause 5.2.4)
Properties UE measures the neighbor and serving cell, to enable reselection procedure:
For inter-frequency search and neighboring cell measurement simply indicating the carrier frequency
A cell identifier of the UE cell reselection should reside. It is based on cell reselection criteria, which involves measurements of serving and neighboring cell.
With frequency re-election based on cell ranking.
Absolute inter-frequency reselection priorities, wherein the UE attempts to camp on an available frequency of the highest priority.
Blacklist provided, to prevent the UE reselects to a specific intra-frequency and inter-frequency cells.
Cell reselection may be dependent on speed.
Service-specific priorities.
In the multi-beam operation, the cell mass derived cell corresponding to the same beam (see subclause 9.2.4)
9.2.1.3 State Transition
The following figure depicts the UE triggers a transition from RRC_IDLE to RRC_CONNECTED (for NAS member, see TS 23.502)
1 UE requesting a new connection is provided from RRC_IDLE
2 / 2a gNB RRC setup complete
The first NAS message 3 UE by RRCSetupCmp, Initial Ue Message sent by AMF
4 / 4a / 5 / 5a may exchange other NAS message between the UE and the AMF.
6. AMF preparation UE context data (PDU including a session context security key, the wireless UE capability and UE security capabilities, etc.), and sends it to gNB.
7 / 7a gNb activate safety
8 / 8a gNB remakes by establishing SRB2 and DRB
9 gNB inform the AMF build process is complete.
9.2.2 RRC_INACTIVE move
9.2.2.1 overview
CM is to maintain RRC_INACTIVE UE connection state, can move within a region (RNA) NG-RAN configuration without notice NG-RAN. In RRC_INACTIVE, the last service node reserves the NG gNB UE context and service associated UPF AMF and the UE connection.
When the UE RRC_INACTIVE state, if the last service gNB UPF receives downlink data from the downlink or a UE associated signaling received from the AMF (except UE Context Release Command message), paging RNA corresponding to this cell, if RNA with cross gNB neighbor to neighbor sent XnAP paging gNB
When the UE receives UE Context Release Command message RRC_INACTIVE, the cell corresponding to this paging RNA, RNA containing cross GNB if neighboring paging to transmit neighbor XnAP GNB, in order to release the UE display.
When the UE receives RRC_INACTIVE NG RESET message, the cell corresponding to this paging RNA, RNA containing cross GNB if neighboring paging to transmit neighbor XnAP GNB, in order to release the UE display.
When RAN paging fails, gNB processing in accordance with TS 23.501.
AMF provides the core network assistance information to the NG-RAN nodes to help NG-RAN node can decide whether to convert the UE to RRC_INACTIVE. The auxiliary information comprises a core network configured for the UE registration area, periodic update timer register index value and a UE identifier, and may include specific UE in the DRX, indicating whether the UE is configured by the AMF start moving only the connection (the MICO) mode, and the UE is expected behavior. When configuring RNA, NG-RAN node will consider the UE registration area. NG-RAN node uses the UE-specific DRX UE and RAN paging identification index value. NG-RAN node will consider periodically updated registration timer to configure RNA regularly update timer. NG-RAN node will consider the expected UE behavior to help UE RRC state transition decisions.
When converted to RRC_INACTIVE, NG-RAN node may use the periodic update timer value configuration RNA UE. When RNA regularly update timer expires without UE notice, gNB behavior specified in TS 23.501
If the UE visit last gNB outside gNB service, the receiver will trigger XnAP gNB UE context retrieval process, in order to obtain gNB UE context from the last service, and may also trigger Xn-U address indication process, including the possibility of gNB from the last service recover data. After the UE context is successfully retrieved, the receiving GNB slice should be performed upon receiving information of the slice sensing admission control, and as a service GNB, and further triggers a path switch request and NGAP RRC procedures applicable. After the path switching process, service gNB trigger the release of UE context in the last service gNB by XnAP UE context release process.
If you can not access the UE, gNB the last service gNB should:
Failure associated with any AMF UE initiated procedure class 1, the enable signal issued operation is unsuccessful in the corresponding response message
Send NAS non-delivery indication of the program, a non-delivery report any NAS PDU received from UE AMF
If the UE to access a service gNB last beyond gNB, and receives gNB not find a valid UE context, the receiver can perform gNB establish a new RRC connection, rather than restore the previous RRC connection. UE context will also fail to retrieve, so if AMF service changes, the need to establish a new RRC connection
When the UE moves RNA configuration, UE needs to be in a state of starting RNA RRC_INACTIVE updates. When the update request from the UE receives an RNA, receiving gNB triggered XnAP retrieval UE Context procedure to gNB acquire a UE context from the last service, and may decide the UE sends back RRC_INACTIVE state, the UE moves to RRC_CONNECTED status, or a UE transmits to RRC_IDLE. In the case of RNA periodically updated, if the last service gNB decided not to reposition the UE context, the UE context it is unsuccessful retrieval process, and transmitted back to UE RRC_INACTIVE, or to a RRC_IDLE message encapsulation directly by RRCRelease
9.2.2.2 cell reselection
RC_INACTIVE the UE performs cell reselection. This process is the same principle with RRC_IDLE state (see clause 9.2.1.2).
9.2.2.3 RAN-Based Notification Area
In the UE RRC_INACTIVE state may be configured by a last NG-RAN node service RNA, wherein:
RNA may cover a single or a plurality of cells, and should be included in the registration area CN; In this version, Xn are connected in RNA should be available;
Update (RNAU) periodically sent by the UE based RAN notification area, and also when the UE transmits the selected cell reselection procedure does not belong to the configuration of the cell the RNA
There are several different alternative in terms of how to configure the RNA:
Cell list: UE provides the RNA constituting a cell (s) explicitly list
RAN area list: providing a UE (at least one) region RAN ID, where RAN tracking area is CN or equal to a subset of the region CN tracking area. RAN RAN area is selected by a region ID, which the RAN TAC area code and optionally the composition; cell broadcast in system information or a plurality of regions RAN ID