网络原理期末复习整理

第一章：

UDP：The second protocol in this layer, UDP(User Datagram Protocol),is an unreliable, connectionless protocol for applications that do not want TCP’s

sequencing or flow control and wish to provide their own.

UDP: 第二个协议是UDP(User Datagram Protocol，用户数据报协议)，它是一个不可靠的、无连接的协议，主要用于那些“不想要TCP的序列化或者

流控制功能，而希望自己提供这些功能”的应用程序。

OSI TCP/IP

7.Application应用层Application应用层

6.Presentation表示层Not present在模型

In the model中不存在

5.Session会话层

4.Transport传输层Transport

work网络层Internet互连网层

2.Data link数据链路层Host-to-network

主机至网络

1.Physical物理层

The Physical Layer:物理层

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

物理层涉及到在通信信道上传输的原始数据位。

The Dada Link Layer数据链路层

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.

数据链路层的主要任务是将一个原始的传输设施转变成一条逻辑的传输线路，在这条传输线路上，所有未检测出来的传输错误也会反映到网络层上。

The Network Layer网络层

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

网络层控制子网的运行过程。一个关键的设计问题是确定如何将分组从源端路由到目标端。

Network Hardware网络硬件

Broadcast networks:广播网络

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 the others.

广播网络只有一个通信信道，网络上所有的机器都共享该信道。在机器之间传递的是短消息（在有些上下文环境中称为分组或包，packet），任何一台机器发送的短消息都可以被其他所有的机器接收到。

Point-to-point links点到点连接

In contrast, 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.

与此相反，点到点网络则是由许多连接构成的，每一对连接对应着一对机器。

在这种网络中，为了将一个分组从源端传送到目的地，该组可能首先要经过一台或者多台中间机器。

习题：

1-18．Which of the OSI layers handles each of the following:

(a)dividing the transmitted bit stream into frames.

(b)determining which route through the subnet to use.

OSI模型中的哪一层处理以下问题：

(a)把传输的位流分成帧

(b)在通过子网的时候决定使用哪条路由路径。

Answer:

(a):The data link layer数据链路层

(b):The network layer网络层

1-22.What is the main difference between TCP and UDP?

TCP与UDP之间的主要区别是什么？

Answer:

TCP is a reliable connection-oriented protocol

TCP是一个可靠的面向连接的协议。

UDP is an unreliable, connectionless protocol.

UDP是一个不可靠的无连接协议。

第二章

最大数据传输率maximum data rate=2Hlog2Vbits/sec(H-带宽，V-离散级数)

最大数据传输率maximum number of bits/sec=Hlog2(1+S/N)(包含有信噪比的)

(S/N为信噪比，用公式10log10S/N=？dB计算出)

习题：

2-3.Television channels are 6 MHz wide. How many bits/sec can be sent if four-level digital signals are used? Assume a noiseless channel.

电视频道的带宽是6MHz。如果使用4级数字信号，则每秒钟可以发送多少位？假设电视频道为无噪声信道。

Answer:

Maximum data rate = 2 H log2V =2*6 *log 2 4 =24Mbits/s

2-4.If a binary signal is sent over a 3-KHz channel whose signal-to-noise ratio is 20 dB, what is the maximum achievable data rate?

如果在一条3KHz的信道上发送一个二进制信号，该信道的信噪比为20dB，则最大可达到的数据传输率为多少？

Answer:

Maximum data rate = 2 H log2V= 2*3 log22= 6Kbps