How instant messaging works

June 27, 2003

Some popular instant messaging utilities include America Online's Instant Messenger (AIM) and ICQ, Microsoft's MSN Messenger and Yahoo! Messenger. While some of the details vary between utilities, the basic steps outlined below for ICQ apply to all of the other IM utilities on the market today.

  • Visit the download page for ICQ to get a copy of the free software program, called a "client" for your computer.

  • Install the software and open the client.

  • The client tries to connect to the ICQ server.

  • Once the client is connected to the server, you can enter your name and password to log in to the server. If this is your first time on, you can sign up for an account and immediately begin using it. When the server verifies your name and password, you are logged in.

  • The client sends the server the connection information of the computer you are using. It also provides the user with the names of everyone in your ICQ contacts list.

  • The server creates a temporary file that has the connection information for you and the list of your contacts. It then checks to see if any of the users in your contact list are currently logged in.

  • If the server finds any of your contacts logged in, it sends a message back to the ICQ client on your computer with the connection information for that user. The ICQ server also sends your connection information to the people in your contact list that are signed on.

  • When your ICQ client gets the connection information for a person in your contact list, it changes the status of that person to "online."

  • You click on the name of a person in your contact list who is online, and a window opens that you can enter text into. You enter a message and click "Send" to communicate with that person.

  • Your message is sent directly to the ICQ client on that person's computer.

  • The other person gets your instant message and responds. The ICQ window that each of you sees on your respective computers expands to include a scrolling dialog of the conversation. Each person's instant messages appears in this window on both computers.

  • Close the message window after you finish the conversation. When you go offline and exit ICQ, your ICQ client sends a message to the ICQ server to terminate the session. The ICQ server sends a message to the ICQ client of each person on your contact list that is currently online to indicate that you have logged off. The ICQ server then deletes the temporary file that contained the connection information for your ICQ client. In the ICQ clients of your contacts that are online, your name moves to the "offline" status section.

- Source: How Stuff Works Web site at


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