An Internet technology for sending short messages to other users who are online. The concept of instant messaging started in early networked UNIX environments; users who were logged on could use commands such as talk, write, and finger to determine who else was logged on and to send them messages. However, the term “instant messaging” now generally applies to a technology popularized by America Online (AOL) and supported by Microsoft and other companies.
AOL users can send instant messages to other AOL users online by using client software called AOL Instant Messenger (AIM). To use AIM, a user signs on at an AOL central server, indicating that he or she is online and can receive instant messages from other users. The central server records the user’s IP address for that session.
(The user’s IP address is assigned by Dynamic Host Configuration Protocol [DHCP] and can vary from session to session.) Other users can then send instant messages to that user via the server.
The user’s AIM client sends the server a copy of the user’s “buddy list” (a list of other users that he or she frequently exchanges messages with), and the server responds by telling the user which buddies are currently online and can receive messages.
The user can select a buddy from the list and submit a message to the server, which forwards the message to the buddy.
Graphic I-2. The instant messaging system used by AOL.
Microsoft has an instant messaging client called MSN Messenger Service. An Internet Engineering Task Force (IETF) working group is developing a standard for an Instant Messaging and Presence Protocol (IMPP) to make sure that instant messaging offerings from different vendors are fully compatible with each other. Microsoft plans to ensure that its instant messaging clients and servers support IMPP.