4.1.2 Direct network applications
Most applications that work in a networked environment are classified as client-server applications. These applications, such as FTP, web browsers, and e-mail all have two components which allow them to function, the client side and the server side. The client side is located on the local computer and is the requestor of the services. The server side is located on a remote computer and provides services in response to the client's requests.
A client-server application works by constantly repeating the following looped routine. Client-request, server-response; client-request, server-response, and so on. For example, a web browser accesses a web page by requesting a uniform resource locator (URL), or web address, on a remote web server. After it locates the URL, the web server that is identified by that URL responds to the request. Then, based on the information received from the web server, the client can request more information from the same web server, or can access another web page from a different web server.
Netscape Navigator and Internet Explorer, are probably the most commonly used web browser applications. An easy way to understand a Web browser is to compare it to a television remote control. A remote control gives you the ability to directly control a TV's functions. For example, volume, channels, brightness, and so on. For the remote control to function properly, you do not need to understand how the remote control functions electronically. The same is true of a Web browser, in that the browser gives you the ability to navigate through the Web by clicking on hyperlinks. For the Web browser to function properly, it is not necessary for you to understand how the lower layer OSI protocols work and interact.
4.1.3 Indirect network support
Within a LAN environment, indirect-application network support is a client-server function. If a client wants to save a file from a word processor to a network server, the redirector enables the word processing application to become a network client.
The redirector is a protocol that works with computer operating systems and network clients instead of specific application programs.
Examples of redirectors are:
• Apple File Protocol
• NetBIOS Extended User Interface (NetBEUI)
• Novell IPX/SPX protocols
• Network File System (NFS) of the TCP/IP protocol suite
The redirector process is as follows:
1. The client requests that the network file server allow the data file to be stored.
2. The server responds by saving the file to its disk, or by rejecting the client's request.
3. If the client requests that the network print server allow the data file to be printed by a remote (network) printer, the server processes the request by printing the file on one of its print devices, or by rejecting the request.
參考答案:4.1.2 指示网络申请
在被网络的环境中工作的大多数的申请被归类为客户- 伺候器的申请。像文件传送协议这样的这些申请, 设圈套浏览器, 而且全部发电子邮件给有二个允许他们动作的成份，客户边和伺候器边。 客户边位于地方计算机之上并且是服务的 requestor 。 伺候器边回应客户的请求位于一部遥远的计算机之上而且提供服务。
一个客户- 伺候器的申请被不变地重复被使常式成环的下列各项工作。 客户-请求,伺候器-回应; 客户-请求,伺候器-回应,等等。 在一个遥远的网伺候器身上举例来说，一个网浏览器藉由请求一个统一的资源定位器 (网址), 或网住址存取一个网页。 在它之后位于网址,被那一个网址识别的网伺候器回应请求。然后,被基于的从网伺候器被收到的数据,客户能请求来自相同的网伺候器的较多数据, 或能存取来自一个不同的网伺候器的另外一个网页。
网景航海家和英特网探险家,或许是那最普遍使用过的网浏览器申请。 一个容易的方法了解一个网络浏览器是比较它和一台电视遥远的控制。 遥远的控制给你能力直接地控制电视的功能。 举例来说,体积，频道，光亮,等等。 对于遥远的控制适当地动作,你不需要了解遥远的控制如何电子地动作。 一样的适用于一个网络浏览器,在那个浏览器中给你能力藉由按下超链接经过网络航行。对于网络浏览器适当地动作, 它不是必需的让你了解较低的层 OSI 记录如何工作而且互相影响。
4.1.3 间接的网络支持
在区域网络环境里面，间接- 申请网络支持是一个客户- 伺候器的功能。 如果一位客户想要解救从一台文件处理机到一个网络伺候器的一个文件,再指导者使处理成为一位网络客户的申请字能够。
再指导者是一个记录以以操作系统和网络客户代替特定的申请计画的计算机工作。
再指导者的例子是:
? 苹果文件记录
? NetBIOS 延长了使用者接口 (NetBEUI)
? Novell公司 IPX/ SPX 记录
? 传输控制协议/ IP 记录随员的网络文件系统 (NFS)
再指导者程序是依下列各项:
1. 客户请求网络文件伺候器允许数据文件被储存。
2. 伺候器藉由解救对它的磁盘片的文件回应, 或藉由拒绝客户的请求。
3. 如果客户请求，网络版伺候器允许数据文件被一台遥远的 (网络) 打印机印刷,伺候器处理印刷在它的版装置之一上的文件请求, 或藉由拒绝请求。
