"Instant Messenging"

Skype (IPA: [skaɪp]) is software that allows users to make telephone calls over the Internet. Calls to other users of the service and to free-of-charge numbers are free, while calls to other landlines and mobile phones can be made for a fee. Additional features include instant messaging, file transfer and video conferencing.

The system was created by entrepreneurs Niklas Zennström, Janus Friis, and a team of software developers based in Tallinn, Estonia.^[1] The Skype Group has its headquarters in Luxembourg, with offices in London, Tallinn, Tartu, Stockholm, Prague,^[2] and San Jose.

Skype has experienced rapid growth in popular usage since the launch of its services. The company was acquired by eBay in September 2005 for $2.6 billion.

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Skype uses a proprietary Internet telephony (VoIP) network, called the Skype protocol. The protocol has not been made publicly available by Skype and official applications using the protocol are proprietary and closed-source. The main difference between Skype and standard VoIP clients is that Skype operates on a peer-to-peer model (originally based on the Kazaa^[65]) rather than the more usual client-server model. The Skype user directory is entirely decentralized and distributed among the nodes of the network—i.e., users' computers—which allows the network to scale very easily to large sizes (currently about 240 million users)^[66] without a complex centralized infrastructure costly to the Skype Group. The disadvantage of this approach is that Skype offers no interoperability with SIP-based VOIP networks.

softwareExtensible Messaging and Presence Protocol (XMPP) is an open, XML-inspired protocolinstant messaging (IM) and presence informationmessage oriented middleware.^[1]Jabber Instant Messaging and Presence technology. Built to be extensible, the protocol has accumulated features over time such as Voice over IP and file transfer signaling.

Reaction:Unlike most instant messaging protocols, XMPP is an open standard. Like e-mail, it is an open system where anyone who has a domain name and a suitable Internet connection can run his own Jabber server and talk to users on other servers. The standard server implementations and many clients are also free and open source software.

originally aimed at near-real-time, extensible (e.g. buddy lists), but now expanded into the broader realm of It remains the core protocol of the

AOL Instant Messenger (AIM) is an instant messaging and presence computer program which uses the proprietary OSCAR instant messaging protocol and the TOC protocol to allow registered users to communicate in real time. It was released by AOL in May 1997. Stand-alone official AIM client software includes advertisements and is available for Microsoft Windows, Mac OS, Mac OS X, and Linux. The software, maintained by AOL, LLC, has a large share of the instant messaging market, especially in the United States (with 52% of the total reported as of 2006.

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AIM is different from other clients such as Yahoo Messenger in that it does not require approval from one buddy to be added to another's buddy list. As a result, it is possible for users to keep other unsuspecting users on their buddy list to see when they are online, read their status and away messages, and read their profiles. However, one can block another user from communicating and also enhance privacy by selecting a menu option allowing communication only with those on one's buddy list.