Simple analysis of the channel process of the mobile phone caller and Modem Log
RR, Radio Resource, radio resource;
MM, Mobile Management, mobility management;
CC, Call Control, call control.
During the call establishment process, the signaling connection of the access layer needs to be established first, which is the established RR connection at this time, and this connection is between the UE and the BSC. Subsequently, a non-access stratum connection needs to be established, that is, an MM connection needs to be established. This connection is a channel for transmitting signaling between the UE and the CN (MSC). After this channel is established, the related negotiation and establishment process of the call needs to be carried out. At this time, it is the process of CC signaling, such as setup, alerting, connect and so on.
Recently, the group learned and shared some basic knowledge about Modem, and wrote it down for future reference.
1. Related concepts
Signaling: There are various signals transmitted in the network, some of which are what we need (such as the voice of making calls, the data packets of Internet access, etc.), and the other part that we do not need (it can only be said that it is not directly required) it Used to specifically control the circuit, this type of signal is called signaling. The transmission of any practical application information between communication devices is always accompanied by the transmission of some control information. They work according to the established communication protocol and transmit the application information to the destination safely, reliably and efficiently. This information is called protocol control information in computer networks , and called signaling in telecommunication networks . (Baidu Encyclopedia) Simple understanding: The interaction process between Modem and base station is based on signaling.
The processor of the smart machine: divided into AP and BP.
AP: Application Processor, that is, an application processor. An AP can be regarded as a computer. The operating system and application software are running on the AP. The dual-core mobile phone we usually say refers to the AP.
BP: Baseband Processor, that is, the baseband processor, BP can be regarded as the wireless modem of the computer. This wireless modem provides calls and short messages through the AT interface (equivalent to the interface between the computer and the modem, but each manufacturer has extended commands). , Internet access, UIM card and other functions.
2. Mobile phone calling process:
(1). The overall general process is as follows:
The signaling process when a mobile user makes a call starts from the MS requesting a channel from the BTS, and ends when the calling user's TCH traffic channel assignment is completed. Generally speaking, the calling party goes through several major stages: the access stage, the authentication and encryption stage, and the TCH domination stage.
* Access stage: including channel request, channel activation, channel response activation, immediate control, service request and other steps. After this stage, the mobile phone and BTS (BSC) have established a temporarily fixed relationship.
* Authentication and encryption stage: including authentication request, authentication response, encryption mode command, encryption mode completion, call establishment and other steps. After this stage, the identity of the calling user has been confirmed, and the network considers the calling user to be a legitimate user and is allowed to continue processing the call.
*TCH Domination Phase: Including Domination Commands, Domination Completed. After this stage, the voice channel of the calling user has been determined. If it cannot be connected in the process of being connected by the calling party later, the calling user can hear the voice prompt of the MSC through the voice channel.
(2). The information transfer process from the mobile phone to the base station requires a unified regulation. This is the GSM, CDMA and other protocols. The hierarchical structure of the protocol layer of the mobile phone and the base transceiver station is as follows:
RRM (Radio Resource Management): manages the radio interface, including channel configuration, transmission mode, measurement of uplink and downlink levels and communication quality, and handover operations;
MM (Mobility Management): A functional group mainly built on RRM for handling mobile security and security confidentiality;
CM (connection management): located on two groups, used to complete the establishment of point-to-point communication, it is divided into CC (call control), SS (supplementary services, such as call transfer, call waiting), SMS (short message processing);
这三者之间的关系如下：RRM建立好了手机与基站的道路，并负责监控这条路。CM相当于物流，比如说打电话，它建立电话连接，不过在你运输之前，MM需要检查你是不是授权了，并且保证你传输过程中是保密的。
三. 主叫的三个阶段分析：
（1）. 接入阶段（RRM的初始化）：
通过随机接入信道RACH发出申请，要求网络提供SDCCH信道用于信令的传递，BTS收到信号之后，会通过与BSC交互之后，向MS发送“立即指配”。
（2）. 鉴权加密阶段
鉴权阶段：RR建立之后，MS发送“CM业务请求”，MSC/VLR收到MS发送的CM业务请求消息之后，需要鉴定移动用户的身份， 于是MSC发送“鉴权请求”给
MS，MS将结果发送给MSC/VLR，VLR进行比对之后如果一致则鉴权通过，如果不一致则拒绝MS接入。
加密阶段：鉴权之后，VLR首先向MSC下发加密模式命令，然后下发“接受接入请求”，MSC下发这两个消息给MS，MS返回“加密模式完成”
（3）.TCH支配阶段
(1)MS的呼叫类型信息：移动台在SDCCH信道上向网络发送“Setup”消息
(2)话音信道指配过程：MSC收到“Setup”消息后，首先向VLR查询该用户的相关业务信息，然后通过比较决定呼叫是否可以继续(如果没开漫游，就直接拒绝掉)，如
果不能继续，则向MS发送“release complete”消息；如果可以向MSC发回“完成呼叫能力查询”的消息，指示MSC可以进行下一步动作，只有呼叫继续才给你分配
TCH信道。MSC收到消息后，向MS发送“呼叫进程(call proceeding)”消息，告诉MS别急，还在处理。然后MSC通知BSC来给此次呼叫分配TCH信道，BSC向MS
发送“信道指配”消息，安排MS到TCH信道进行话务接续，至此TCH信道建立，通话建立。
主叫的TCH信道建立完成后，接下来就是等待被叫的响应了，被叫的响应分为“提醒(Alerting)”和“连接(connect)”，当收到被叫的“提醒”消息，则表示已经建立了通
路；当收到被叫用户“应答”消息后，主叫MSC给主叫MS发送一条“连接”消息，告诉主叫可以进行通话了，主叫MS收到之后向系统发送“连接证实(connect ACK)”告
诉系统可以收费了
四. Modem Log 分析
（1）. 打电话正常时Modem LOG分析
红色字体：MS －> NW，表明是从手机到基站发送信令。
蓝色字体：NW －> MS，表明是从基站到手机端发送信令。
（2）.欠费时打电话Modem LOG分析
