LESSON 3 PORTS AND PROTOCOLS part II

3.3 TCP/IP model
3.3.1 Introduction
TCP/IP was developed by the DoD (Department of Defense) of the United States and DARPA
(Defense Advanced Research Project Agency) in the 1970s. TCP/IP was designed to be an
open standard that anyone could use to connect computers together and exchange
information between them. Ultimately, it became the basis for the Internet.

3.3 TCP/IP 模型

3.3.1 简介

TCP/IP 是美国国防部和美国国防部高级研究计划局在20世纪70年代提出。TCP/IP 以公开的标准设计，所有人

都可以用它来连接电脑，并传递信息。最终，它成为了互联网的基础。

 

3.3.2 Layers
The TCP/IP model defines four totally independent layers into which it divides the process of
communication between two devices. The layers through which it passes information
between two devices are:

3.3.2 层次结构

TCP/IP 模型由4个独立的层次组成，两台设备之间的通信过程被划分为四个部分。这四个部分为：

  应用

  传输

  因特网

  网络接入

 

3.3.2.1 Application
The application layer is the layer nearest the end user. This is the layer that is in charge of
translating data from applications into information that can be sent through the network.
The basic functions of this layer are:
- Representation
- Codification
- Dialog Control
- Application Management

 

3.3.2.1 应用

应用层最接近终端用户。这一层负责将从应用软件接收到的数据翻译成能送到网络中的数据，应用层的基本功能：

-陈述

-汇编

-对话框控件

-应用管理

 

3.3.2.2 Transport
The transport layer establishes, maintains and finishes virtual circuits for information transfer. It
provides control mechanisms for data flow and allows broadcasting, and it provides
mechanisms for the detection and correction of errors. The information that arrives at this
layer from the application layer is divided into different segments. Information that comes to
the transport layer from the internet layer is delivered back to the application layer through
ports. (See Section 3.3.5 Ports for details on ports.)

The basic functions of this layer are:
- Reliability
- Flow Control
- Error Correction
- Broadcasting

 

3.3.2.2  传输

 传输层建立，维护完成信息传输的虚拟电路。它给数据流提供控制机制和广播信息，同时提供探测机制和纠错机制。从

应用层发送到传输层的数据被分成不同的片段。从英特网层传送到传输层的数据通过借口送回应用层。

传输层的基本功能：

-可靠性

-流控制

-纠错

-广播

 

3.3.2.3 Internet
This layer divides the segments of the transport layer into packets and sends the packets
across the networks that make up the Internet. It uses IP, or internet protocol addresses to
determine the location of the recipient device. It does not ensure reliability in the
connections, because this is already taken care of by the transport layer, but it is responsible
for selecting the best route between the originating device and the recipient device.

 

3.3.2.3 因特网

这一个层次将从传输层送过来的数据片段分解成数据包，将这数据包送到网络中。通过IP地址或者互联网通信协议地址

确定接受器的地址。它不能保证连接过程的可靠性，因为这由传输层负责，但是它负责选择从发送器到接收器的最佳传输

路径。

3.3.2.4 Network Access
This layer is in charge of sending information at both the LAN level and the physical level. It
transforms all the information that arrives from the superior layers into basic information (bits)
and directs it to the proper location. At this level, the destination of the information is
determined by the MAC, or media access control, address of the recipient device.

 

3.3.2.4 网络接入

这一层次负责在局域网级和物理级传送信息。它将从上级层次传送的信息转换成基本信息（位），并送到适当的位置。

在这一层次上，信息的目的地（接收器的地址）由MAC（媒体存取控制）决定。

3.3.3 Protocols
To be able to send information between two devices, both must speak the same language.
This language is called the protocol.
The protocols that appear in the application layer of the TCP/IP model are:
      - File Transfer Protocol (FTP)
      - Hypertext Transfer Protocol (HTTP)
      - Simple Mail Transfer Protocol (smtp)
      - Domain Name Service (DNS)
      - Trivial File Transfer Protocol (TFTP)
The protocols of the transport layer are:
      - Transport Control Protocol (TCP)
      - User Datagram Protocol (UDP)
The protocols of the internet layer are:
      - Internet Protocol (IP)
The protocol most often used in the network access layer is:
      - Ethernet
The protocols listed above and their associated ports will be described in the following
sections.

 

3.3.3 协议

为了在两个设备间传输数据，需要能说一种语言，这种语言被称作协议。

出现在TCP/IP模式应用层的协议有：

    -文件传输协议（FTP）

    -超文本传输协议（HTTP）

    -简单邮件传送协议（smtp）

    -域名服务（DNS）

    -简单文件传输协议（TFTP）

传输层的协议有：

    -传输控制协议（TCP）

    -用户数据报协议（UDP）

因特网层协议有：

    -互联网协议（IP）

在网络接入中经常用到的协议有：

    -局域网

以上列出的协议和他们联系的接口在后续部分会介绍。