LTE信令流程
目 录
第一章 协议层与概念 .......................................................................................................... 5
1.1 1.2
控制面与用户面 ........................................................................................................... 5 接口与协议 ................................................................................................................... 5
1.2.1 NAS协议（非接入层协议） ..................................................................................... 7 1.2.2 RRC层（无线资源控制层） ...................................................................................... 7 1.2.3 PDCP层（分组数据汇聚协议层） ............................................................................. 8 1.2.4 RLC层（无线链路控制层） ...................................................................................... 8 1.2.5 MAC层（媒体接入层） ........................................................................................... 9 1.2.6 PHY层（物理层） ................................................................................................. 10
1.3 1.4 1.5
空闲态和连接态 ......................................................................................................... 12 网络标识 ..................................................................................................................... 13 承载概念 ..................................................................................................................... 14
第二章 主要信令流程 ........................................................................................................ 16
2.1 开机附着流程 ................................................................................................................. 16 2.2随机接入流程 .................................................................................................................. 19 2.3 UE发起的service request流程 ................................................................................. 23 2.4寻呼流程 .......................................................................................................................... 26 2.5切换流程 .......................................................................................................................... 27
2.5.1 切换的含义及目的 .................................................................................................... 27 2.5.2 切换发生的过程 ....................................................................................................... 28 2.5.3 站内切换.................................................................................................................. 28 2.5.4 X2切换流程 ............................................................................................................. 30 2.5.5 S1切换流程 ............................................................................................................. 32 2.5.6 异系统切换简介 ....................................................................................................... 34
2.6 CSFB流程 ....................................................................................................................... 35
2.6.1 CSFB主叫流程 ......................................................................................................... 36 2.6.2 CSFB被叫流程 ......................................................................................................... 37 2.6.3 紧急呼叫流程 ........................................................................................................... 39
2.7 TAU流程 ......................................................................................................................... 40
2.7.1 空闲态不设置“ACTIVE”的TAU流程 ...................................................................... 41
2.7.2 空闲态设置“ACTIVE”的TAU流程 ......................................................................... 43 2.7.3 连接态TAU流程 ...................................................................................................... 45
2.8专用承载流程 .................................................................................................................. 46
2.8.1 专用承载建立流程 .................................................................................................... 46 2.8.2 专用承载修改流程 .................................................................................................... 48 2.8.3 专用承载释放流程 .................................................................................................... 50
2.9去附着流程 ...................................................................................................................... 52
2.9.1 关机去附着流程 ....................................................................................................... 52 2.9.1 非关机去附着流程 .................................................................................................... 53
2.10 小区搜索、选择和重选 ............................................................................................... 55
2.10.1 小区搜索流程 ......................................................................................................... 55 2.10.1 小区选择流程 ......................................................................................................... 56 2.10.3 小区重选流程 ......................................................................................................... 57
第三章 异常信令流程 ........................................................................................................ 60
3.1 附着异常流程 ................................................................................................................. 61
3.1.1 RRC连接失败 ........................................................................................................... 61 3.1.2 核心网拒绝 .............................................................................................................. 62 3.1.3 eNB未等到Initial context setup request消息 ........................................................ 63 3.1.4 RRC重配消息丢失或eNB内部配置UE的安全参数失败 ............................................ 64
3.2 ServiceRequest异常流程 ............................................................................................ 65
3.2.1 核心网拒绝 .............................................................................................................. 65 3.2.2 eNB建立承载失败 .................................................................................................... 66
3.3 承载异常流程 ................................................................................................................. 68
3.3.1核心网拒绝 ............................................................................................................... 68 3.3.2 eNB本地建立失败（核心网主动发起的建立） ........................................................... 68 3.3.3 eNB未等到RRC重配完成消息，回复失败 ................................................................ 69 3.3.4 UE NAS层拒绝 ........................................................................................................ 70 3.3.5上行直传NAS消息丢失 ............................................................................................ 71
第四章 系统消息解析 ........................................................................................................ 72
4.1 系统消息 ......................................................................................................................... 73 4.2 系统消息解析 ................................................................................................................. 74
4.2.1 MIB （Master Information Block）解析 ................................................................. 74 4.2.2 SIB1 （System Information Block Type1）解析 ..................................................... 75 4.2.3 SystemInformation消息 ......................................................................................... 77
第五章 信令案例解析 ........................................................................................................ 83
5.1实测案例流程 .................................................................................................................. 84
5.2 流程中各信令消息解析 ................................................................................................. 84
5.2.1 RRC_CONN_REQ:RRC连接请求 ............................................................................... 85 5.2.2 RRC_CONN_SETUP:RRC连接建立 ........................................................................... 86 5.2.3 RRC_CONN_SETUP_CMP:RRC连接建立完成 ........................................................... 90 5.2.4 S1AP_INITIAL_UE_MSG:初始直传消息 ..................................................................... 90 5.2.5 S1AP_INITIAL_CONTEXT_SETUP_REQ:初始化文本建立请求 ..................................... 91 5.2.6 RRC_UE_CAP_ENQUIRY:UE能力查询....................................................................... 94 5.2.7 RRC_UE_CAP_INFO:UE能力信息 ............................................................................. 95 5.2.8 S1AP_UE_CAPABILITY_INFO_IND:UE能力信息指示 ................................................. 99 5.2.9 RRC_SECUR_MODE_CMD:RRC安全模式命令 ........................................................ 103 5.2.10 RRC_CONN_RECFG:RRC连接重配置 ................................................................... 104 5.2.11 RRC_SECUR_MODE_CMP:RRC安全模式完成 ....................................................... 107 5.2.12 RRC_CONN_RECFG_CMP:RRC连接重配置完成 ................................................... 107 5.2.13 S1AP_INITIAL_CONTEXT_SETUP_RSP:初始化文本建立完成 ................................. 108 5.2.14 S1AP_ERAB_MOD_REQ:ERAB修改请求 ............................................................... 109 5.2.15 RRC_DL_INFO_TRANSF:RRC下行直传消息 .......................................................... 110 5.2.16 S1AP_ERAB_MOD_RSP:ERAB修改完成 ............................................................... 110 5.2.17 RRC_CONN_RECFG:RRC连接重配置 ................................................................... 111 5.2.18 RRC_UL_INFO_TRANSF:RRC上行直传消息 .......................................................... 116 5.2.19 S1AP_UL_NAS_TRANS:上行NAS直传消息 .......................................................... 116 5.2.20 RRC_CONN_RECFG_CMP:RRC连接重配置完成 ................................................... 117 5.2.21 RRC_CONN_RECFG:RRC连接重配置 ................................................................... 117 5.2.22 RRC_CONN_RECFG_CMP:RRC连接重配置完成 ................................................... 119 5.2.23 RRC_MEAS_RPRT:RRC测量报告 .......................................................................... 119 5.2.24 RRC_UL_INFO_TRANSF:RRC上行信息传输 .......................................................... 120 5.2.25 S1AP_UL_NAS_TRANS:上行NAS信息传输 .......................................................... 120 5.2.26 S1AP_UE_CONTEXT_MOD_REQ:UE文本更改请求 ............................................... 121 5.2.27 S1AP_UE_CONTEXT_MOD_RSP:UE文本更改响应................................................ 122 5.2.28 RRC_CONN_REL:RRC连接释放 ............................................................................ 123 5.2.29 S1AP_UE_CONTEXT_REL_REQ:UE文本释放请求 .................................................. 124 5.2.30 S1AP_UE_CONTEXT_REL_CMD:UE文本释放命令 ................................................ 124 5.2.31 S1AP_UE_CONTEXT_REL_CMP:UE文本释放完成 ................................................. 125
概述
本文通过对重要概念的阐述，为信令流程的解析做铺垫，随后讲解LTE中重要信令流程，让大家熟悉各个物理过程是如何实现的，其次通过异常信令的解读让大家增强对异常信令流程的判断，再次对系统消息的解析，让大家了解系统消息的特点和携带的内容。最后通过实测信令内容讲解，说明消息的重要信元字段。
第一章 协议层与概念
1.1 控制面与用户面
在无线通信系统中，负责传送和处理用户数据流工作的协议称为用户面；负责传送和处理系统协调信令的协议称为控制面。用户面如同负责搬运的码头工人，控制面就相当于指挥员，当两个层面不分离时，自己既负责搬运又负责指挥，这种情况不利于大货物处理，因此分工独立后，办事效率可成倍提升，在LTE网络中，用户面和控制面已明确分离开。
1.2 接口与协议
接口是指不同网元之间的信息交互时的节点，每个接口含有不同的协议，同一接口的网元之间使用相互明白的语言进行信息交互，称为接口协议，接口协议的架构称为协议栈。在LTE中有空中接口和地面接口，相应也有对应的协议和协议栈。
非常详细的LTE信令流程 - 图文
