参考资料：3Gpp 38.413
1. NGAP服务
NGAP提供NG-RAN节点与AMF节点之间的信令服务。服务分为两类：
- 非UE相关服务：在NG-RAN与AMF之间建立NG接口实例。
-
UE相关服务：为UE接入核心网提供信令和数据连接。
2. NGAP一般过程分类
（1）NGAP一般过程按是否有响应，可分为两类：
- Class 1：应答类消息，需要等待响应消息。
| 一般过程 | 发起消息 | 成功响应 | 失败响应 |
|---|---|---|---|
| AMF Configuration Update | AMF CONFIGURATION UPDATE | AMF CONFIGURATION UPDATE ACKNOWLEDGE | AMF CONFIGURATION UPDATE FAILURE |
| RAN Configuration Update | RAN CONFIGURATION UPDATE | RAN CONFIGURATION UPDATE ACKNOWLEDGE | RAN CONFIGURATION UPDATE FAILURE |
| Handover Cancellation | HANDOVER CANCEL | HANDOVER CANCEL ACKNOWLEDGE | |
| Handover Preparation | HANDOVER REQUIRED | HANDOVER COMMAND | HANDOVER PREPARATION FAILURE |
| Handover Resource Allocation | HANDOVER REQUEST | HANDOVER REQUEST ACKNOWLEDGE | HANDOVER FAILURE |
| Initial Context Setup | INITIAL CONTEXT SETUP REQUEST | INITIAL CONTEXT SETUP RESPONSE | INITIAL CONTEXT SETUP FAILURE |
| UE Context Modification | UE CONTEXT MODIFICATION REQUEST | UE CONTEXT MODIFICATION RESPONSE | UE CONTEXT MODIFICATION FAILURE |
| UE Context Release | UE CONTEXT RELEASE COMMAND | UE CONTEXT RELEASE COMPLETE | |
| Path Switch Request | PATH SWITCH REQUEST | PATH SWITCH REQUEST ACKNOWLEDGE | PATH SWITCH REQUEST FAILURE |
| PDU Session Resource Setup | PDU SESSION RESOURCE SETUP REQUEST | PDU SESSION RESOURCE SETUP RESPONSE | |
| PDU Session Resource Release | PDU SESSION RESOURCE RELEASE COMMAND | PDU SESSION RESOURCE RELEASE RESPONSE | |
| PDU Session Resource Modify | PDU SESSION RESOURCE MODIFY REQUEST | PDU SESSION RESOURCE MODIFY RESPONSE | |
| PDU Session Resource Modify Indication | PDU SESSION RESOURCE MODIFY INDICATION | PDU SESSION RESOURCE MODIFY CONFIRM | |
| UE Radio Capability Check | UE RADIO CAPABILITY CHECK REQUEST | UE RADIO CAPABILITY CHECK RESPONSE | |
| Write-Replace Warning | WRITE-REPLACE WARNING REQUEST | WRITE-REPLACE WARNING RESPONSE | |
| PWS Cancel | PWS CANCEL REQUEST | PWS CANCEL RESPONSE | |
| NG Reset | NG RESET | NG RESET ACKNOWLEDGE | |
| NG Setup | NG SETUP REQUEST | NG SETUP RESPONSE | NG SETUP FAILURE |
- Class 2：通知类消息，无response消息。
| 一般过程 | 消息 |
|---|---|
| Downlink RAN Configuration Transfer | DOWNLINK RAN CONFIGURATION TRANSFER |
| Uplink RAN Configuration Transfer | UPLINK RAN CONFIGURATION TRANSFER |
| Downlink RAN Status Transfer | DOWNLINK RAN STATUS TRANSFER |
| Uplink RAN Status Transfer | UPLINK RAN STATUS TRANSFER |
| Downlink NAS Transport | DOWNLINK NAS TRANSPORT |
| Uplink NAS Transport | UPLINK NAS TRANSPORT |
| Downlink UE Associated NRPPa Transport | DOWNLINK UE ASSOCIATED NRPPA TRANSPORT |
| Uplink UE Associated NRPPa Transport | UPLINK UE ASSOCIATED NRPPA TRANSPORT |
| Downlink Non UE Associated NRPPa Transport | DOWNLINK NON UE ASSOCIATED NRPPA TRANSPORT |
| Uplink Non UE Associated NRPPa Transport | UPLINK NON UE ASSOCIATED NRPPA TRANSPORT |
| Handover Notification | HANDOVER NOTIFY |
| Initial UE Message | INITIAL UE MESSAGE |
| NAS Non Delivery Indication | NAS NON DELIVERY INDICATION |
| Error Indication | ERROR INDICATION |
| Paging | PAGING |
| PDU Session Resource Notify | PDU SESSION RESOURCE NOTIFY |
| Reroute NAS Request | REROUTE NAS REQUEST |
| UE Context Release Request | UE CONTEXT RELEASE REQUEST |
| AMF Status Indication | AMF STATUS INDICATION |
| PWS Restart Indication | PWS RESTART INDICATION |
| PWS Failure Indication | PWS FAILURE INDICATION |
| Trace Start | TRACE START |
| Trace Failure Indication | TRACE FAILURE INDICATION |
| Deactivate Trace | DEACTIVATE TRACE |
| Cell Traffic Trace | CELL TRAFFIC TRACE |
| Location Reporting Control | LOCATION REPORTING CONTROL |
| Location Reporting Failure Indication | LOCATION REPORTING FAILURE INDICATION |
| Location Report | LOCATION REPORT |
| UE TNLA Binding Release | UE TNLA BINDING RELEASE REQUEST |
| UE Radio Capability Info Indication | UE RADIO CAPABILITY INFO INDICATION |
| RRC Inactive Transition Report | RRC INACTIVE TRANSITION REPORT |
| Overload Start | OVERLOAD START |
| Overload Stop | OVERLOAD STOP |
| Secondary RAT Data Usage Report | SECONDARY RAT DATA USAGE REPORT |
（2）NGAP一般过程按功能分类，大致可以分为以下14类：
| 功能 | 过程 |
|---|---|
| 接口管理过程 | NG Setup RAN Configuration Update AMF Configuration Update NG Reset Error Indication Overload Start Overload Stop AMF Status Indication |
| 寻呼过程 | Paging |
| UE上下文管理过程 | Initial Context Setup UE Context Release Request (NG-RAN initiated) UE Context Release Request (AMF initiated) UE Context Modification RRC Inactive Transition Report |
| UE移动性管理过程 | Handover Preparation Handover Resource Allocation Handover Notification Path Switch Request Handover Cancellation Uplink RAN Status Transfer Downlink RAN Status Transfer |
| UE无线能力管理过程 | UE Radio Capability Info Indication UE Radio Capability Check |
| PDU会话管理过程 | PDU Session Resource Setup PDU Session Resource Release PDU Session Resource Modify PDU Session Resource Notify PDU Session Resource Modify Indication |
| NAS消息传输过程 | Initial UE Message Downlink NAS Transport Uplink NAS Transport NAS Non Delivery Indication Reroute NAS Request |
| 配置传输过程 | Uplink RAN Configuration Transfer Downlink RAN Configuration Transfer |
| 告警消息传输过程 | Write-Replace Warning |
| NRPPa传输过程 | DOWNLINK UE ASSOCIATED NRPPA TRANSPORT DOWNLINK NON UE ASSOCIATED NRPPA TRANSPORT UPLINK UE ASSOCIATED NRPPA TRANSPORT UPLINK NON UE ASSOCIATED NRPPA TRANSPORT |
| 跟踪过程 | Trace Start Trace Failure Indication Deactivate Trace Deactivate Trace Cell Traffic Trace |
| 位置报告过程 | Location Reporting Control Location Reporting Failure Indication Location Report |
| UE TNLA绑定过程 | UE TNLA Binding Release |
| 数据使用率报告过程 | Secondary RAT Data Usage Report |