TCPIP Applications and Technologies

TCP/IP Applications and Technologies

TCP/IP actually is a suite of protocols used on the Internet for routing and transporting information. The following sections discuss the major application protocols that rely on TCP/IP.

ISP

An ISP (Internet service provider) provides the connection between an individual PC or network and the Internet. ISPs use routers connected to high-speed, high-bandwidth connections to route Internet traffic from their clients to their destinations.

HTTP/ HTTPS

Hypertext Transfer Protocol ( HTTP ) is the protocol used by Web browsers, such as Internet Explorer and Netscape Navigator, to access Web sites and content. Normal (unsecured sites) use the prefix http:// when accessed in a Web browser. Sites that are secured with various encryption schemes are identified with the prefix https:// .

Most browsers connecting with a secured site will also display a closed padlock symbol onscreen.

SSL

Secure Socket Layers ( SSL ) is the encryption technology used by secured (https://) Web sites. To access a secured Web site, the Web browser must support the same encryption level used by the secured Web site (normally 128-bit encryption) and the same version(s) of SSL used by the Web site (normally SSL version 2.0 or 3.0).

HTML

Hypertext Markup Language (HTML) is the language used by Web pages. An HTML page is a specially formatted text page that uses tags (commands contained in angle brackets) to change text appearance, insert links to other pages, display pictures, incorporate scripting languages, and provide other features. Web browsers, such as Microsoft Internet Explorer and Netscape Navigator, are used to view and interpret the contents of Web pages, which have typical file extensions such as .HTM, .HTML, .ASP (Active Server pages generated by a database), and others.

The World Wide Web Consortium (http://www.w3c.org) sets the official standards for HTML tags and syntax, but major browser vendors , such as Microsoft and Netscape, often modify or extend official HTML standards with their own tags and syntax.

You can see the HTML code used to create the Web page in a browser by using the View Source or View Page Source menu option provided by your browser. Figure 21.6 compares what you see in a typical Web page (top window) with the HTML tags used to set text features and the underlined hyperlink (bottom window). The figure uses different text size and shading to distinguish tags from text, and so do most commercial Web-editing programs used to make Web pages.

Figure 21.6. A section of an HTML document as seen by a typical browser (top window) uses the HTML tags shown in the bottom window for paragraph breaks ( <P> tags), font settings ( <FONT> tags), and hyperlinks ( <A HREF> tags).

Tags such as <P> are used by themselves , and other tags are used in pairs. For example, <A HREF...> is used to indicate the start of a hyperlink (which will display another page or site in your browser window), and </A> indicates the end of a hyperlink.

FTP

File Transfer Protocol ( FTP ) is a protocol used by both Web browsers and specialized FTP programs to access dedicated file transfer servers for file downloads and uploads. When you access an FTP site, the site uses the prefix ftp://.

tip

Although you can use Windows's built-in FTP client for file uploads and downloads with both secured and unsecured FTP sites, you should consider using third-party FTP products such as CuteFTP or WS_FTP Pro. These programs enable you to create a customized setup for each FTP site you visit, and will store passwords, server types, and other necessary information. They also enable faster downloads than typical Web browsers running in ftp:// mode.

Windows contains ftp.exe , a command-line FTP program; type FTP , press Enter, and then type ? at the FTP prompt to see the commands you can use.

FTP sites with downloads available to any user support anonymous FTP; if any credentials are required, it's typically the user's email address as a password (the username is preset to anonymous). Some FTP sites require the user to log in with a specified username and password.

Telnet

Telnet enables a user to log in to a particular computer on the Internet and use it as if he were a regular user sitting in front of it, rather than simply downloading pages and files as he would with an http:// or ftp:// connection.

The remote computer must be configured to accept a Telnet login. Typically, TCP port 23 on the remote computer must be open before a login can take place.

Windows contains a command-line Telnet program. To open a connection to a remote computer, enter a command such as

  telnet a.computer.com  

To use other commands, open a command prompt, type telnet , and press the Enter key. To see other commands, type ?/help .

DNS

The domain name system ( DNS ) is the name for the network of servers on the Internet that translate domain names such as www.selectsystems.com into the matching IP addresses. If you manually configure an IP address, you typically provide the IP addresses of one or more DNS servers as part of the configuration process.

If you want a unique domain name for either a Web site or email, the ISP that you will use to provide your email or Web hosting service often provides a registration wizard you can use to access the domain name registration services provided by various companies such as VeriSign.

caution

Can't access the site you're looking for? Got the wrong site? You might have made one of these common mistakes:

• Don't assume that all domain names end in .com ” Other popular domain name extensions include .net, .org, .gov, .us, .cc, and various national domains such as .uk (United Kingdom), .ca (Canada), and many others.

• Don't forget to use the entire domain name in the browser ” Some browsers will add the www. prefix used on most domain names, but others will not. For best results, spell out the complete domain name.

A domain name has three major sections, from the end of the name to the start:

• The top-level domain (.com, .org, .net, and so on)

• The name of the site

• The server type; www indicates a Web server, ftp indicates an FTP server, mail indicates a mail server, and search indicates a search server

For example, Microsoft.com is located in the .com domain, typically used for commercial companies. Microsoft is the domain name. The Microsoft.com domain has the following servers:

• www.microsoft.com hosts Web content, such as product information.

• search.microsoft.com hosts the Microsoft.com search features, enabling users to search all or selected parts of the Microsoft.com domain.

• ftp.microsoft.com hosts the File Transfer Protocol server of Microsoft.com; this portion of the Microsoft.com domain can be accessed by either a Web browser or an FTP client.

Some small Web sites use a folder under a domain hosted by an ISP:

 www.anisp.com/~asmallsite 

Many companies have only WWW servers, or only WWW and FTP servers.

Email

All email systems provide transfer of text messages, and most have provisions for file attachments, enabling you to send documents, graphics, video clips, and other types of computer data files to receivers for work or play. Email clients are included as part of Web browsers, and are also available as limited-feature, freely downloadable, or more-powerful commercially purchased standalone email clients. Some email clients, such as Microsoft Outlook, are part of application suites (like Microsoft Office) and also feature productivity and time-management features.

tip

Users who travel away from corporate networks might prefer to use a Web-based email account, such as Hotmail, or use Outlook Web Access to get access to email from any system with a properly configured Web browser.

To configure any email client, you need

• The name of the email server for incoming mail

• The name of the email server for outgoing mail

• The username and password for the email user

• The type of email server (POP, IMAP, or HTTP)

To access Web-based email, you need

• The Web site for the email service

• The username and password