Protocol
The standard protocol that AIM clients use to communicate is called Open System for CommunicAtion in Realtime (OSCAR). Most AOL-produced versions of AIM and popular third party AIM clients use this protocol. However, AOL also created a simpler protocol called TOC that lacks many of OSCAR's features but is sometimes used for clients that only require basic chat functionality. The TOC/TOC2 protocol specifications were made available by AOL, while OSCAR is a closed protocol that third parties have had to reverse-engineer.
In January 2008, AOL introduced experimental Extensible Messaging and Presence Protocol (XMPP) support for AIM, allowing AIM users to communicate using the standardized, open-source XMPP. However, in March 2008, this service was discontinued. As of May 2011, AOL offers limited XMPP support.
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