OSCAR or Open System for CommunicAtion in Realtime is AOL's flagship instant messaging and presence information protocol. Currently, OSCAR is in use for AOL's two main instant messaging systems: ICQ and AIM.

Despite its name, the specifications for the protocol remain proprietary. AOL has gone to great lengths to keep competitors (namely Microsoft, XMPP, and Cerulean Studios) from implementing compatible clients for their proprietary messaging systems. In 2002, AOL signed a contract with Apple, Inc., allowing them to use OSCAR (as well as AOL's own code libraries) in their iChat application. This allowed iChat users to interact with ICQ and AIM users directly. The deal also permitted users of Apple's .Mac service to log into the AIM network using their .Mac email addresses. (This has carried over to Apple's MobileMe service.)

As of 2009^[update] large parts of the protocol have been reverse-engineered and implemented by an ever-increasing number of 3rd party clients.

On March 6, 2006, AOL released the AIM SDK and launched a developer website, allowing developers to build plugins for AIM Triton, and build their own custom clients, which connect over the OSCAR protocol. They had not, at that point, however, released any information about the protocol itself.

On March 5, 2008, AOL released portions of the OSCAR protocol documentation. Google also provides the ability to sign into AIM network via the Google Talk client built into Gmail.

Contents 1 Packet structure 1.1 FLAP header 2 See also 3 External links 3.1 Protocol information 3.2 Implementations 4 Footnotes

[edit] Packet structure

[edit] FLAP header

A special FLAP (Frame Layer Protocol^[1]) container encloses every packet. It carries information about packet size, channel, and its number in sequence.

Offset (hex)	Field	Type/Size (in bytes)	Remarks
00	FLAP ID	byte/1	Always contains 2A. It is mark of packet start.
01	Channel	byte/1
02	Number in sequence	int16/2	Incremented by 1 each time a packet sent. Wraps to 0 after 7FFF.
04	Data size	int16/2	Size does not include FLAP header

[edit] See also

• Comparison of instant messaging clients
• Comparison of instant messaging protocols
• TOC protocol, AOL's free but deprecated messaging protocol
• TOC2 protocol, as of 2009^[update], the current version of the TOC protocol

[edit] External links

[edit] Protocol information

• Official OSCAR-Documentation
• OSCAR Protocol Terminology
• OSCAR (ICQ v7/v8/v9) Documentation
• UnOfficial AIM/OSCAR Protocol Specification

[edit] Implementations

Programming language	Implementations
C	libpurple GnomeICU
C#	NOscar
C# 2.0	OscarLib
Java	joscar Instant Messenger Lib daim
OCaml	mlOscar
Python	TwistedWords
Perl	Net::Oscar
PHP	WebIcqPro

[edit] Footnotes

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