osi模型:七层模型介绍

应用层-OSI模型 (Application Layer - OSI Model)

It is the top most layer of OSI Model. Manipulation of data(information) in various ways is done in this layer which enables user or software to get access to the network. Some services provided by this layer includes: E-Mail, transferring files, distributing the results to user, directory services, network resources, etc.

它是OSI模型的最顶层。 在此层中以各种方式处理数据（信息），使用户或软件能够访问网络。 该层提供的一些服务包括：电子邮件，传输文件，将结果分发给用户，目录服务，网络资源等。

The Application Layer contains a variety of protocols that are commonly needed by users. One widely-used application protocol is HTTP(HyperText Transfer Protocol), which is the basis for the World Wide Web. When a browser wants a web page, it sends the name of the page it wants to the server using HTTP. The server then sends the page back.

应用层包含用户通常需要的各种协议。 一种广泛使用的应用协议是HTTP（超文本传输​​协议） ，它是万维网的基础。 当浏览器需要网页时，它将使用HTTP将其想要的页面的名称发送到服务器。 然后，服务器将页面发回。

Other Application protocols that are used are: File Transfer Protocol(FTP), Trivial File Transfer Protocol(TFTP), Simple Mail Transfer Protocol(SMTP), TELNET, Domain Name System(DNS) etc.

使用的其他应用程序协议是： 文件传输协议（FTP） ， 普通文件传输协议（TFTP） ， 简单邮件传输协议（SMTP） ， TELNET ， 域名系统（DNS）等。

应用层的功能 (Functions of Application Layer)

1. Mail Services: This layer provides the basis for E-mail forwarding and storage. 邮件服务：此层为电子邮件转发和存储提供了基础。
2. Network Virtual Terminal: It allows a user to log on to a remote host. The application creates software emulation of a terminal at the remote host. User's computer talks to the software terminal which in turn talks to the host and vice versa. Then the remote host believes it is communicating with one of its own terminals and allows user to log on.网络虚拟终端：它允许用户登录到远程主机。 该应用程序在远程主机上创建终端的软件仿真。 用户的计算机与软件终端对话，而软件终端又与主机对话，反之亦然。 然后，远程主机认为它正在与其自己的终端之一进行通信，并允许用户登录。
3. Directory Services: This layer provides access for global information about various services.目录服务：此层提供对各种服务的全局信息的访问。
4. File Transfer, Access and Management (FTAM): It is a standard mechanism to access files and manages it. Users can access files in a remote computer and manage it. They can also retrieve files from a remote computer.文件传输，访问和管理（FTAM）：这是访问文件并进行管理的标准机制。 用户可以访问远程计算机中的文件并进行管理。 他们还可以从远程计算机检索文件。

应用层的设计问题 (Design Issues with Application Layer)

There are commonly reoccurring problems that occur in the design and implementation of Application Layer protocols and can be addressed by patterns from several different pattern languages:

在应用层协议的设计和实现中，经常会发生一些常见的问题，可以通过几种不同的模式语言来解决：

• Pattern Language for Application-level Communication Protocols
  应用程序级通信协议的模式语言
• Service Design Patterns
  服务设计模式
• Patterns of Enterprise Application Architecture
  企业应用程序架构的模式
• Pattern-Oriented Software Architecture
  面向模式的软件架构

翻译自: https://www.studytonight.com/computer-networks/osi-model-application-layer

osi模型:七层模型介绍