An Introduction to the InternetInternet Applications [Archives:2003/641/Education]

June 12 2003

Adnan A. Al-Harazi
Academic Head
NCC Education, Yemen Center

We have seen how the Internet uses a set of protocols to enable reliable communications between networks and computers. The Internet provides a robust, standardized communications infrastructure, but it is the applications that make use of that infrastructure, the main concern for users. There are wide ranges of such applications, most of which are defined just the same way as the basic underlying TCP/IP infrastructure. It is the quality and usefulness of these applications that account for the Internet success.
The most important Internet applications are :
– e-mail.
– FTP (file transfer).
– Newsgroups.
– (WWW) World Wide Web.
– Instant messaging and Internet Relay Chat (IRC).
– Voice over IP (VoIP).

There are of course certain more developing applications than the ones mentioned above that are becoming important day by day, but we will try to discuss here only the above applications.

Electronic Mail
Electronic mail (e-mail) is one of the most heavily used Internet tools. People use this service to send messages to their friends and families using the Internet as the delivery mechanism. But do you think the e-mail message you write jumps from your computer to the recipients directly? Or does it go to a responsible host that carries it from one country to another? And if you are sending an e-mail message by using a free e-mail service like 'Yahoo' from Yemen to a friend in UK, will it take the same trip as if you are sending the same message by using the same e-mail account from USA?

E-mail is not delivered directly from the sender to the recipient. Instead it uses a store and forward approach. Mail messages progress from sender to recipients in a series of hops from host to host until the message is received at a computer that is responsible for holding the message ready for delivery to the recipient. There is no need for the sender and the recipient to be in simultaneous contact. As you can see in Fig1, the e-mail message moves from one host to another. Each host stores the message for a few moments and then forwards it to the next available host that, in turn, stores the message and forwards it until it gets to the host that holds the recipient e-mail account. When the recipient accesses his/her account, the host computer downloads the message to his/her computer.
The process of preparing, transmitting, receiving and readding e-mails can be carried out in a variety of different ways. The processes are handled in two sides, the e-mail client and e-mail server (the controlling computer). The e-mail client is used to prepare the e-mail messages using simple text editing features. The client then sends the message to an e-mail server that transmits the message onwards. This e-mail server is the target server for the incoming e-mails of the recipient. It stores messages of different users until they are ready to collect them. For sending the e-mail messages the e-mail server has to use an Internet protocol called Simple Mail Transfer Protocol (SMTP). Without this protocol the e-mail server is not able to move the message a step. At the recipient side, the e-mail server stores the incoming messages until the users logon into the e-mail server and download the messages. The e-mail server has to use a different protocol this time. This protocol is called Post Office Protocol (POP). This protocol is responsible for authorizing the user to access the e-mail server. It is also responsible for distributing the incoming messages between users in the same e-mail server. There are thousands of e-mail servers in the Internet, but the most famous ones are yahoo, and hotmail of Microsoft. You can get a free e-mail account from these sites and use it to send and receive e-mail messages. The major difference you might find between these sites is the available space that you have in your e-mail inbox.

File Transfer Protocol (FTP)
Another available Internet application is what's called File Transfer Protocol. As the name indicates, this service has something to do with the transferring of files. Yes, you can use this service to copy files from one computer to another in a different location smoothly and efficiently. FTP is extremely useful for retrieving information from Internet archives. Such Internet sites contain a wide variety of information. Most large software suppliers maintain their own archives containing upgrades to their software. When you download songs or newspapers from the Internet, you are actually accessing an FTP site that has an FTP server. To publish or update their websites, the designers usually use FTP service to upload their websites' files. So the usefulness of this Internet applications is copying files of different types from one host to another. To use this service you need to use an FTP application such as WS_FTP program or you can just use the tool that comes with Windows operating systems. You can do that by going to the command line and type “ftp”. Then, you have to use the “open” command to open any FTP server. For example, to open ftp server I write this command in the command line:
1. C:\ ftp
2. ftp> open
You can also use the internet browser instead of the command line. If you would like to try some of the FTP sites, you can visit the Linux RedHat * operating system site and download their latest version RedHat 9.0. You can go there by typing the following in your browser : It is impossible to download the whole operating system unless you have a real fast Internet connection, but check that for the sake of practicing.

Another application of the Internet is Telnet. Telnet is the Internet protocol used to allow you to remotely log in to another computer as if you were directly attached to the system. This is less frequently used than some of the other Internet protocols, but it is still important that Web site developers are able to use it, since it is useful for solving problems with web servers. It's worth bearing in mind that this application is the most frequently used tool by hackers, because when you know the authorized code to access a host in the Internet, you can just “telnet it” and enter the access code and you are in full control of the host. Windows comes with an application that you can use to telnet any host in the Internet, but be careful not to use it a lot against one host. To run telnet in your computer you need to go to the command line and do following:

1. C:\telnet
2. Microsoft Telnet > telnet
The next week's lesson discusses Newsgroups, World Wide Web, Chat and voice over IP.

* Linux Operating system is a free operating system that is considered as the new competitor for Microsoft Windows