Instant Messaging

An instant messenger is a client which hooks up to an instant messaging service. Instant messaging differs from e-mail in that conversations happen in realtime. Also, most services convey an "online status" between users, such as if a contact is actively using the computer. Generally, both parties in the conversation see each line of text right after it is typed (line-by-line), thus making it more like a telephone conversation than exchanging letters. Instant messaging applications may also include the ability to post an away message, the equivalent of the message on a telephone answering machine.

Popular instant messaging services on the public Internet include AOL Instant Messenger, Yahoo! Messenger, .NET Messenger Service and ICQ. These services owe many ideas to an older (and still popular) online chat medium known as Internet Relay Chat (IRC).

Instant messaging has arisen in parallel in many places, and each application has its own protocols. This has led to users running many instant messaging applications simultaneously to be available on several networks. Alternately they could use a client which supports many protocols, such as Gaim or Trillian.

Jabber

Jabber is an open, XML-based protocol for instant messaging and presence. Jabber-based software is deployed on thousands of servers across the internet and is used by over ten million people worldwide, according to the Jabber Software Foundation.

Jeremie Miller began the project in 1998; its first major public release occurred in May 2000. The project's main product is jabberd, a server to which Jabber clients connect in order to chat. This server can either create a private Jabber network (behind a firewall, for instance) or it can join the global public Jabber network.

A key concept of the Jabber system is that of transports, also known as gateways, which allow users to access networks using other protocols - such as AIM, ICQ, MSN Messenger/Windows Messenger, SMS or E-mail. Unlike multi-protocol clients like Trillian or Gaim, Jabber provides this access at the server level by communicating via special gateway services running on a remote computer. Any Jabber user can 'register' with one of these gateways by providing the information needed to log on to that network, and can then communicate with users of that network as though they were Jabber users. This means that any client which fully supports the Jabber protocol can be used to access any network to which a gateway exists, without the need for any extra code in the client.

The basis of the Jabber protocol, now managed by the Jabber Software Foundation, has been submitted as an IETF draft under the name XMPP, so it can become the official standard for instant messaging. However, SIMPLE, based on the SIP protocol, is competing for the same status.