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主要信令流程

开机附着流程

UE刚开机时, 先进行物理下行同步, 搜索测量进行小区选择, 选择到一个合适或者可接纳的小区后, 驻留并进行附着过程. 附着流程图如下:

@startuml
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autonumber "<b><font color=red >[00]"

title 开机附着流程
UE -> eNB: **MSG1** Random Access Preamble
eNB -> UE: **MSG2** Random Access Response
UE -> eNB: **MSG3** RRC Connection Request
eNB -> UE: **MSG4** RRC Connection Setup
UE -> eNB: RRC Connection Setup Complete
eNB -> MME: Initial UE message
UE <--> MME: Identity/Authentication/Security
MME -> eNB: Initial Context Setup Request
eNB -> UE: UE Capability Enquiry
UE -> eNB: UE Capability Information
eNB -> MME: UE Capability Info Indication
eNB -> UE: Security Mode Command
UE -> eNB: Security Mode Complete
eNB -> UE: RRC Connection Reconfiguration
UE -> eNB: RRC Connection Reconfiguration Complete
eNB -> MME: Initial context setup response
UE -> eNB: UL Information Transfer
eNB -> MME: UPLINK NAS TRANSPORT

@enduml

  1. 处在RRC_IDLE态的UE进行Attach过程, 首先发起随机接入过程, 即MSG1消息; [Random Access Request]

  2. eNB检测到MSG1消息后, 向UE发送随机接入响应消息, 即MSG2消息;[Random Access Response]

  3. UE收到随机接入响应后, 根据MSG2的TA调整上行发送时机, 向eNB发送RRCConnectionRequest消息;[RRC Connection Request]

  4. eNB向UE发送RRCConnectionSetup消息, 包含建立SRB1承载信息和无线资源配置信息; [RRC Connection Setup]

  5. UE完成SRB1承载和无线资源配置, 向eNB发送RRCConnectionSetupComplete消息, 包含NAS层Attach request信息; [RRC Connection Setup Complete]

  6. eNB选择MME, 向MME发送INITIAL UE MESSAGE消息, 包含NAS层Attach request消息; [InitialUEMessage]

  7. NAS message

  8. MME向eNB发送INITIAL CONTEXT SETUP REQUEST消息, 请求建立默认承载, 包含NAS层Attach Accept, Activate default EPS bearer context request消息;[Inital Contest Setup Request]

  9. eNB接收到INITIAL CONTEXT SETUP REQUEST消息, 如果不包含UE能力信息, 则eNB向UE发送UECapabilityEnquiry消息, 查询UE能力; [UE Capability Enquiry]

  10. UE向eNB发送UECapabilityInformation消息, 报告UE能力信息; [UE Capability Information]

  11. eNB向MME发送UE CAPABILITY INFO INDICATION消息, 更新MME的UE能力信息; [UE Capability Info Indication]

  12. eNB根据INITIAL CONTEXT SETUP REQUEST消息中UE支持的安全信息, 向UE发送SecurityModeCommand消息, 进行安全激活; [Security Mode Command]

  13. UE向eNB发送SecurityModeComplete消息, 表示安全激活完成;[Security Mode Complete]

  14. eNB根据INITIAL CONTEXT SETUP REQUEST消息中的ERAB建立信息, 向UE发送RRCConnectionReconfiguration消息进行UE资源重配, 包括重配SRB1和无线资源配置, 建立SRB2, DRB(包括默认承载)等; [RRC Connection Reconfiguration]

  15. UE向eNB发送RRCConnectionReconfigurationComplete消息, 表示资源配置完成; [RRC Connection Reconfiguration Complete]

  16. eNB向MME发送INITIAL CONTEXT SETUP RESPONSE响应消息, 表明UE上下文建立完成; [Inital Context Setup Response]

  17. UE向eNB发送ULInformationTransfer消息, 包含NAS层Attach Complete, Activate default EPS bearer context accept消息;

  18. eNB向MME发送上行直传UPLINK NAS TRANSPORT消息, 包含NAS层Attach Complete, Activate default EPS bearer context accept消息.

随机接入

随机接入分为基于冲突的随机接入和基于非冲突的随机接入两个流程. 其区别为针对两种流程其选择随机接入前缀的方式.

  • 基于冲突的随机接入 UE从基于冲突的随机接入前缀中依照一定算法随机选择一个随机前缀

  • 基于非冲突的随机接入 基站侧通过下行专用信令给UE指派非冲突的随机接入前缀.

基于冲突的随机接入

@startuml
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autonumber "<b><font color=red >[00]"

title 基于冲突的随机接入
UE -> eNB: Random Access Preamble
eNB -> UE: Random Access Response
UE -> eNB: Scheduled Transmission
eNB -> UE: Contention Resolution

@enduml

  1. UE在RACH上发送随机接入前缀;

  2. ENb的MAC层产生随机接入响应, 并在DL-SCH上发送;

  3. UE的RRC层产生RRC Connection Request 并在映射到UL–SCH上的CCCH逻辑信道上发送;

  4. RRC Contention Resolution 由ENb的RRC层产生, 并在映射到DL–SCH上的CCCH or DCCH(FFS)逻辑信道上发送.

基于非冲突的随机接入

@startuml
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autonumber "<b><font color=red >[00]"

title 基于非冲突的随机接入
eNB -> UE: RA Preamble assignment
UE -> eNB: Random Access Preamble
eNB -> UE: Radom Access Response

@enduml

  1. ENb 通过下行专用信令给UE指派非冲突的随机接入前缀(non-contention Random Access Preamble), 这个前缀不在BCH上广播的集合中.

  2. UE在RACH上发送指派的随机接入前缀.

  3. ENb的MAC层产生随机接入响应, 并在DL-SCH上发送.

S1初始化

@startuml
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autonumber "<b><font color=red >[00]"

title S1 Setup Request
eNB -> MME: S1 Setup Request
MME -> eNB: S1 Setup Response
eNB -> MME: ENB Direct Information Transfer

@enduml

  1. S1 Setup Request. [S1 Setup Request]

  2. S1 Setup Response. [S1 Setup Response]

  3. ENB Direct Information Transfer.[ENB Direct Information Transfer]

X2初始化

@startuml
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autonumber "<b><font color=red >[00]"

title X2 Setup Request
eNB1 -> eNB2: X2 Setup Request
eNB2 -> eNB1: X2 Setup Response
eNB1 -> eNB2: ENB Configuration Update
eNB2 -> eNB1: ENB Configuration Update Acknowledge
@enduml

  1. X2 Setup Request. [X2 Setup Request]

  2. X2 Setup Response. [X2 Setup Response]

  3. ENB Configuration Update.[ENB Configuration Update]

  4. ENB Configuration Update Acknowledge.[ENB Configuration Update Acknowledge]

Service Request

UE在IDLE模式下, 需要发送业务数据时, 发起service request过程.

@startuml
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autonumber "<b><font color=red >[00]"

title Service Request
UE -> eNB: **MSG1** Random Access Preamble
eNB -> UE: **MSG2** Random Access Response
UE -> eNB: **MSG3** RRC Connection Request
eNB -> UE: **MSG4** RRC Connection Setup
UE -> eNB: RRC Connection Setup Complete, Service request
eNB -> MME: Initial UE message, Service request
UE <--> MME: Identity/Authentication/Security
MME -> eNB: Initial Context Setup Request
eNB -> UE: UE Capability Enquiry
UE -> eNB: UE Capability Information
eNB -> MME: UE Capability Info Indication
eNB -> UE: Security Mode Command
UE -> eNB: Security Mode Complete
eNB -> UE: RRC Connection Reconfiguration
UE -> eNB: RRC Connection Reconfiguration Complete
eNB -> MME: Initial context setup response
UE -> eNB: UL Information Transfer
eNB -> MME: UPLINK NAS TRANSPORT

@enduml

Paging

s_TMSI Paging

UE在IDLE模式下, 当网络需要给该UE发送数据(业务或者信令)时, 发起寻呼过程.

@startuml
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autonumber "<b><font color=red >[00]"

title s_TMSI Paging
participant UE
participant eNB
MME -> eNB: NAS: Paging(S_TMSI)
eNB -> UE: NAS: Paging(S_TMSI)
note over MME, UE: Continue with Service Request

@enduml

IMSI Paging

当网络发生错误需要恢复时(例如S-TMSI不可用), 可发起IMSI寻呼, UE收到后执行本地detach, 然后再开始attach.

@startuml
hide footbox
autonumber "<b><font color=red >[00]"

title s_TMSI Paging
participant UE
participant eNB
MME -> eNB: NAS: Paging(IMSI)
eNB -> UE: NAS: Paging(IMSI)
note over MME, UE: Continue with Attach Request

@enduml

TAU

当UE进入一个小区, 该小区所属TAI不在UE保存的TAI list内时, UE发起正常TAU流程, 分为IDLE和CONNECTED(即切换时)下. 如果TAU accept分配了一个新的GUTI, 则UE需要回复TAU complete, 否则不用回复.

IDLE态

IDLE下, 如果有上行数据或者上行信令(与TAU无关的)发送, UE可以在TAU request消息中设置an "active"标识, 来请求建立用户面资源, 并且TAU完成后保持NAS信令连接. 如果没有设置"active"标识, 则TAU完成后释放NAS信令连接. IDLE下发起的也可以带EPS bearer context status IE, 如果UE带该IE, MME回复消息也带该IE, 双方EPS承载通过这个IE保持同步.

@startuml
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autonumber "<b><font color=red >[00]"

title IDLE TAU
UE -> eNB: **MSG1** Random Access Preamble
eNB -> UE: **MSG2** Random Access Response
UE -> eNB: **MSG3** RRC Connection Request
eNB -> UE: **MSG4** RRC Connection Setup
UE -> eNB: RRC Connection Setup Complete (with TAU request)
eNB -> MME: initialUEMessage, Tracking area update request
MME -> eNB: downlinkNASTransprot, Tracking area update accept
eNB -> UE: DL Information Transfer, Tracking area update accept
UE -> eNB: UL Information Transfer, Tracking area update commplete
eNB -> MME: uplinkNASTransport, Tracking area update commplete
MME -> eNB: UEContextReleaseCommand [NAS-cause=normal-release]
eNB -> UE: RRC Connection Release
eNB -> MME: UEContextRelease

@enduml

CONNECTED态

  1. 如果TAU accept未分配一个新的GUTI, 则无过程5,6

  2. 切换下发起的TAU, 完成后不会释放NAS信令连接

  3. CONNECTED下发起的TAU, 不能带"active"标识

@startuml
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autonumber "<b><font color=red >[00]"

title CONNECTED TAU
UE -> eNB: UL Information Transfer, Tracking area update request
eNB -> MME: uplinkNASTransport, Tracking area update request
rnote over MME: Update UE CONTEXT between MMEs
MME -> eNB: downlinkNASTransprot, Tracking area update accept
eNB -> UE: DL Information Transfer, Tracking area update accept
UE -> eNB: UL Information Transfer, Tracking area update commplete
eNB -> MME: uplinkNASTransport, Tracking area update commplete

@enduml

测量报告

@startuml
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autonumber "<b><font color=red >[00]"

title 测量报告
UE -> eNB: Measurement Report
eNB -> UE: RRC Connection Reconfiguration
UE -> eNB: RRC Connection Reconfiguration Complete
UE -> eNB: Measurement Report
eNB -> UE: RRC Connection Reconfiguration
UE -> eNB: RRC Connection Reconfiguration Complete

@enduml

  1. 测量报告

  2. RRC重配置, 设置添加测量报告. [RRC Connection Reconfiguration]

  3. RRC重配置完成.[RRC Connection Reconfiguration Complete]

  4. 测量报告 [Measurement Report]

  5. RRC测量配置, 设置测量报告. [RRC Connection Reconfiguration]

  6. RRC重配置完成.

E-RAB承载管理

在CN和eNodeB上为UE建立业务通道.

@startuml
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autonumber "<b><font color=red >[00]"

title E-RAB承载管理
participant eNB
MME -> eNB: E-RAB Setup Request
eNB -> MME: E-RAB Setup Response

@endumll

  1. E-RAB Setup Request [E-RAB Setup Request]

  2. E-RAB Setup Response [E-RAB Setup Response]

X2切换

@startuml
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autonumber "<b><font color=red >[00]"

title X2切换
participant UE

== Handover Preparation ==
s_eNB -> UE: RRC Connection Reconfigration
UE -> s_eNB: RRC Connection Reconfigration Complete
s_eNB -> UE: Measurement Report
rnote over s_eNB: HO decision
s_eNB -> d_eNB: Handover Request
d_eNB -> s_eNB: Handover Request Ack

== Handover  Execution ==
s_eNB -> UE: RRC Connection Reconfigration
UE -> d_eNB: RRC Connection Reconfigration Complete

== Handover  Completion ==
MME -> d_eNB: Path Switch Request
d_eNB -> MME: Path Switch Request Ack
d_eNB -> s_eNB: UE Context Release
rnote over s_eNB: Release Resource

@endumll