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1.1 Overview of computer network
1.1.1 Computer network concept
1. Broad perspective
Any 远程信息处理system that can be implemented is a computer network
2. Resource sharing perspective
（1）目的：Resource Sharing
（2）组成单元： "Autonomous computers" in different geographical locations
（3）Must be obeyed统一的协议
1.1.2 Composition of computer network
（1） 从组成部分来看： Hardware, software, protocol
（2）从工作方式来看： Edge part, core part
（3）从功能上来看: Communication subnet, resource subnet
1.1.3 Function of computer network
1.数据通信
2.资源共享
3.分布式处理
4.提高可靠性
5.负载均衡
1.1.4 Classification of computer networks
一、按分布范围分类
(1) Wide area network (WAN) wide area network
(2) Metropolitan Area Network (MAN) metropolitan area network
(3) Local area network (LAN) local area network
(4), personal area network (PAN) personal area network
局域网接入广域网通过router实现
二、按分传输技术分类
- Broadcast network
- Peer-to-peer network
三、按拓扑结构分类
- Star network
- Bus network
- Ring network
- Mesh network
四、按使用者分类
- Public network
- Private network
五、按交换技术分类
1）电路交换网络
2）报文交换网络
3）分组交换网络
六、按传输介质分类
wiredwithwireless
1.1.5 Computer network performance indicators
1）带宽 The original unit is HZ; now it represents the transmission rate in bits per second bit/s
2）时延
Transmission delay: 数据量/带宽
Propagation delay:信道长度/电磁波在信道传输速率
3）时延带宽积：Propagation delay* The amount of data passing through the network through the network during the
4）往返时间（RTT） 从发送端发送数据开始，到发送端收到来自接收端的确认total time delay of the bandwidth kb/s, Mb/s, Gb/s
5）吞吐量
6）速率Usually the highest rate is called bandwidth
1.2 Computer network architecture and reference model
1.2.1 Computer network layered structure
n层实体实现的服务为n+1层利用The lower layer provides services to the upper layer
1.2.2 The concept of computer network protocols, interfaces and services
The service is mainly This layer serves the upper layer
计算机网络主要提供三中服务方式
（1）面向连接服务于无连接服务
（2）可靠服务和不可靠服务
（3）有应答和无应答服务
1.2.3 ISO/OSI Reference Model
1.2.3.1 Application layer
Typical agreements are: FTP、SMTP、HTTP
1.2.3.2 Presentation layer
数据压缩、加密解密
1.2.3.3 Session layer
- Allow sessions between processes on different hosts.
1.2.3.4 Transport layer (TCP/IP)
Transmission units TCP报文段or 用户数据报（UDP）
The functions of the transport layer are summarized as: 流量控制、拥塞控制、差错控制
主要负责主机中两个进程之间的通信，端到端连接的可靠传输服务
1.2.3.5 Network layer
网际层、IP层
Typical ICMPprotocols: IGMP, IP, OSPF, ,IP
Function: the network layer protocol data unit (packet) from a source to destination, and implement 流量控制, 拥塞控制,差错控制
The transmission unit is IP datagram
1.2.3.6 Data Link Layer
The transmission unit of the data link layer is 帧
The functions of the data link layer are summarized as: 成帧、流量控制、拥塞控制、差错控制
Typical SDLCprotocols: HDLC, PPP, ,STP
1.2.3.7 Physical layer
The transmission unit is:比特流
1.2.4 TCP/IP model
