解读NG Application Protocol (NGAP)——38413

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概述

基本流程（EP）：

NGAP协议由一些基本流程组成。以个基本流程是NG-RAN和AMF间的交互单元。

具有独立性和灵活性。

EP的消息构成类型：

Class1：应答类消息，有request和response过程，response会响应success或failure

Class2：通知类消息，发送notify，不用等response

Class1类response种类：

Successful，信令消息明确表明EP成功完成，
Unsuccessful，信令消息表明EP失败，
Successful & Unsuccessful，信令消息中同时带有成功和失败结果。

Class2类消息则认为一直是成功的。

NGAP提供UE相关和非UE相关服务：

非UE相关服务，在NG-RAN和AMF间建立NG口实例。
UE相关服务，为UE接入核心网提供信令和数据连接。

NGAP基本流程（EP）列表

Table 8.1-1: Class 1 procedures

Elementary Procedure	Initiating Message	Successful Outcome	Unsuccessful Outcome
Elementary Procedure	Initiating Message	Response message	Response message
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
NG Reset	NG RESET	NG RESET ACKNOWLEDGE
NG Setup	NG SETUP REQUEST	NG SETUP RESPONSE	NG SETUP FAILURE
Path Switch Request	PATH SWITCH REQUEST	PATH SWITCH REQUEST ACKNOWLEDGE	PATH SWITCH REQUEST FAILURE
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
PDU Session Resource Release	PDU SESSION RESOURCE RELEASE COMMAND	PDU SESSION RESOURCE RELEASE RESPONSE
PDU Session Resource Setup	PDU SESSION RESOURCE SETUP REQUEST	PDU SESSION RESOURCE SETUP RESPONSE
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
Write-Replace Warning	WRITE-REPLACE WARNING REQUEST	WRITE-REPLACE WARNING RESPONSE
PWS Cancel	PWS CANCEL REQUEST	PWS CANCEL RESPONSE
UE Radio Capability Check	UE RADIO CAPABILITY CHECK REQUEST	UE RADIO CAPABILITY CHECK RESPONSE

Table 8.1-2: Class 2 procedures

Elementary Procedure	Message
Downlink RAN Configuration Transfer	DOWNLINK RAN CONFIGURATION TRANSFER
Downlink RAN Status Transfer	DOWNLINK RAN STATUS TRANSFER
Downlink NAS Transport	DOWNLINK NAS TRANSPORT
Error Indication	ERROR INDICATION
Uplink RAN Configuration Transfer	UPLINK RAN CONFIGURATION TRANSFER
Uplink RAN Status Transfer	UPLINK RAN STATUS TRANSFER
Handover Notification	HANDOVER NOTIFY
Initial UE Message	INITIAL UE MESSAGE
NAS Non Delivery Indication	NAS NON DELIVERY 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
Uplink NAS Transport	UPLINK NAS TRANSPORT
AMF Status Indication	AMF STATUS INDICATION
PWS Restart Indication	PWS RESTART INDICATION
PWS Failure Indication	PWS FAILURE INDICATION
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
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 Capability Info Indication	UE CAPABILITY INFO INDICATION

PDU会话管理过程

包括PDU会话资源建立、释放、修改、通知以及PDU会话资源修改指示。

1、PDU会话建立过程，主要是为一个或多个PDU会话资源和相应的QoS流分配Uu和NG-U的资源，并给特定的UE建立相应的DRB。

该过程有AMF发起，NG-RAN收到请求消息，NG-RAN判断是否有AMF请求的配置资源，如果有，则执行执行被请求的NG-RAN配置并为PDU会话列表中在NG和Uu间分配资源。

2、PDU会话资源释放，目的是释放已经为特定UE建立的PDU会话资源。

该过程有AMF发起，NG-RAN在释放NG和Uu间释放通信资源。

3、PDU会话资源修改，目的是为特定的UE修改已建立好的PDU会话，并为已建立好的PDU会话发起QoS的建立、修改和释放。

该过程由AMF发起，NG-RAN判断是否有修改请求的配置资源，如果有，则NG-RAN节点将为请求的PDU会话执行修改配置。

4、PDU会话资源通知，目的是通知已经为给定UE建立的QoS流或PDU会话被释放或不再被执行，或由发出通知的NG-RAN节点再次执行。

该过程由NG-RAN节点发起。

5、PDU会话资源修改指示，目的是为NG-RAN节点请求修改已建好的PDU会话。

NG-RAN节点发起该过程，AMF将透传PDU会话资源修改指示给每个PDU资源相关的SMF。

UE上下文管理过程

1、初始上下文建立，目的是在NG-RAN节点建立需要的所有的UE上下文，包括PDU会话上下文，安全Key，移动性约束列表，UE无线能力和UE的安全能力等。如果有一个UE相关的NG连接链路存在（即NG口与AMF已建立连接）或者AMF已收到在INITIAL UE MESSAGE 中包含RAN UE NGAP ID（也表明NG口实例已建好），AMF将发起该过程。