OSCAR protocol

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

Despite its name, the specifications for the protocol are proprietary. AOL has gone to great lengths to keep competitors, namely Microsoft, Jabber, and Cerulean Studios, from implementing compatible clients for their proprietary messaging system. 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 let iChat users 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.)

Large parts of the protocol are nowadays understood after reverse-engineering the protocol, 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.


[edit] Packet structure

[edit] FLAP header

Every packet enclosed in a special FLAP container. 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

[edit] External links

[edit] Protocol information

[edit] Implementations

C libpurple
C# NOscar
C# 2.0 OscarLib
Java joscar
Instant Messenger Lib
OCaml mlOscar
Python TwistedWords
Perl Net::Oscar
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