LTE必知必会笔记

1.Attach Type

The Attach Type indicates the purpose of the attach and as in most of other procedure, the attach type is also determined by a kind of mutual agreement between UE and Network. It means that UE indicates the attatch type I want to get and Network finaly determines available attach type and informs it to UE as in following procedure.

There are three different types of attach as listed below.

连接type 代表了连接目的。Attach type 由UE和网络之间的相互协议确定。

有三种不同的Attach Type.

（在modem log 中的attach request 和attach accept 中可以看到）

一. EPS attach（indicate the attach for EPS services only）

二：Combined EPS/IMSI attch（indicate the attach for both EPS and non-EPS services）

什么是Combined Attach?

It's attach for both EPS and non-EPS services, or both EPS services and "SMS only".

The combined attach procedure is also used by a UE in CS/PS to attach for EPS services if it is already IMSI attached for non-EPS services.

Combined Attach 是怎么触发的呢？

三：EPS emergency attch（indicate the attach for emergency bearer services）

2.apn 的简单理解

apn是一种网关，UE连接到该网关以访问大多数数据服务的核心网络。

问题1：apn 是怎么分配的？

根据UE的请求由网络配置的，因此apn是UE setting 和Network  Configuration的组合。

跟IP throughput (吞吐量 ) 、Browsing 、IMS等相关。

问题2：协议层次怎么看apn?

apn assignment的典型步骤有两步：

i) UE -> NW : PDN Connectivity Request // Usually UE request PDN with a specific APN (or no specified APN)

ii) UE <- NW : Activate Default EPS Bearer Context Request // Network always specifies a specific APN

问题3： default apn 和additional apn之间的区别是什么？

首先是default apn

i) RRC : RRC Connection Setup Complete + NAS : Attach Request + ESM : PDN Connectivity Request

ii) RRC : RRC Connection Reconfiguration + NAS : Attach Accept + NAS : Activate Default EPS Bearer Context Req

然后是additional apn

i) RRC : ulinformationTransfer + ESM : PDN Connectivity Request

ii) RRC : RRC Connection Reconfiguration + NAS : Activate Default EPS Bearer Context Req

思考：在modem log 中，经常能见到RRC Connection Reconfiguation ，是不是都是建立其他的apn连接呢？

3.RRC的几种状态

LTE 中是有两种状态：RRC_IDLE 和RRC_CONNECTED

NR 中是有三种状态：RRC_IDLE 、RRC_CONNECTED 和RRC_INACTIVE

可以查看文档 2 RRC 三种状态_天使恐龙蛋-优快云博客_rrc状态RRC 三种状态5G NR下RRC有三种状态：IDLE、INACTIVE、CONNECTED4G LTE只有RRC IDLE和RRC CONNECTED两种RRC状态，5G NR引入了一个新状态——RRC INACTIVE1、为何引入INACTIVE？引入INACTIVE态是为了减少信令和功耗。影响手机耗电的主要原因是与网络的连接，5G要面向万物互联，在速率要求高的情况下RRC是耗电的关键，另外，大量的设备零星传送少量的数据，又会带来过高的信令开销。一边是功耗，一边是快速接入，还要减少信令开销，要https://blog.youkuaiyun.com/dandan920107/article/details/111386372?utm_medium=distribute.pc_relevant.none-task-blog-2~default~BlogCommendFromBaidu~default-8.control&dist_request_id=1328760.154.16171691235538661&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2~default~BlogCommendFromBaidu~default-8.control