计算机网络复习主要知识点

TCP: Transmission Control Protocol 传输控制协议

FDM: Frequency-division multiplexing 频分多路复用

CSMA/CD: Carrier Sense Multiple Access/Collision Detect 载波监听多路访问/冲突检测方法FTP：File Transfer Protocol 文件传输协议

IP：Internet Protocol 网络之间互连的协议

NAT：Network Address Translation 网络地址转换

UDP: User Datagram Protocol 用户数据报协议

MAC: Medium Access Control 介质访问控制层

CRC：Cyclical Redundancy Check 循环冗余码

VLNA: Virtual Local Area Netwok 虚拟局域网

URL：Uniform/Universal Resource Locator 统一资源定位符

RIP：Routing Information Protocol 路由信息协议

DNS: Domain Name System 域名系统

HDLC: High-Level Data Link Control 高级数据链路控制

DHCP: Dynamic Host Configuration Protocol 动态主机设置协议

ICMP: Internet Control Message Protocol 网络控制报文协议

SMTP: Simple Mail Transfer Protocol 简单邮件传输协议

ARP: Address Resolution Protocol 地址解析协议

ATM：Asynchronous Transfer Mode 异步传输模式

CDMA: Code Division Multiple Access 码分多址

CHAP.1

Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages, called packets in certain contexts, sent by any machine are received by all others.

When a packet with this code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting.

Some broadcast systems also support transmission to a subnet of the machines, something known as multicasting.

Point-to-point networks consist of many connections between individual pairs of machines. To go from the source to the destination, a packet on this type of network may have to first visit one or more intermediate machines. Often multiple routes, of different lengths, are possible, so finding good ones is important in point-to-point networks.

Point-to-point transmission with one sender and one receiver is sometimes called unicasting. (P15)

Connection-oriented service is modeled after the telephone system. To talk to someone, you pick up the phone, dial the number, talk, and then hang up. Similarly, to use a connection-oriented network service, the service user first establishes connection, uses the connection, and then releases the connection. In most cases the order is preserved so that the bits arrive in the order they were sent.

Connectionless service is modeled after the postal system. Each message carries the full destination address, and each one is routed through the system independent of all others. It is

possible that the first one sent can be delayed so that the second one arrives first. (P32)

The physical layer is concerned with transmitting raw bits over a communication channel.

The main task of the data link layer is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer.

The network layer controls the operation of the subnet. A key design issue is determining how packets are routed from source to destination.

The basic function of the transport layer is to accept data from above, split it up into smaller units if need be, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end.(P38)

TCP is a reliable connection-oriented protocol that allows a byte stream originating on one machine to be delivered without error on any other machine in the internet.

UDP is an unreliable, connectionless protocol for applications that do not TCP’s sequencing or flow control and wish to provide their own.

CHAP.2

Maximum data rate = 2H log2 V bits/sec

Maximum data rate:最大数据传输率

H：带宽

V：离散级数

Maximum number of bits/sec = H log2 (1+S/N)

Maximum number of bits/sec:最大信道容量

S/N:信噪比

求分贝: dB = 10 log10S/N

QSPK: V = 4

T1 PCM: V = 27

QAM-64: V = 64

Two different switching techniques are used nowadays: circuit switching and packet switching. When you or your computer places a telephone call, the switching equipment within the telephone system seeks out a physical path all the way from your telephone to the receiver’s telephone. This technique is called circuit switching.