Jabber is the trade name of the XMPP instant messaging protocol. XMPP, or Extensible Messaging and Presence Protocol, is an open source IM protocol designed to facilitate email using similar resources. Any email server or other webserver can be modified to accommodate Jabber technologies, even those isolated from the public Internet. As the Jabber project is open source, Jabber instant messaging clients have been developed for all major operating systems including Linux, Windows, and Macintosh, as well as mobile solutions for PDAs, cellphones, and even telephone interfaces. Additionally, the term "Jabber" also refers to faulty network equipment, which broadcast redundant or excessive data packets.
Unlike other IM protocols, Jabber is decentralized, meaning that there is no central server regulating it's use. This differs from popular proprietary IM protocols such as AIM, ICQ, MSN Messenger, and Yahoo Messenger, which all must communicate, or at least establish a connection, via a central server. A Jabber user who wants to send a message to another user contacts his own XMPP server, which relays the message to the recipient's server. Only then is the message pushed to the recipient's client. For this reason, Jabber addresses mimic email addresses, with each part of the address serving the same purpose as it's counterpart in an email address. Additionally, as messages can be delivered to multiple clients, Jabber addresses can have specific clients specified by appending a slash and the client's name to the end of the address. A full Jabber address would then look like this: firstname.lastname@example.org/client. The asynchronous nature of Jabber, along with the relatively long daisy-chain delivery service, adds to the latency of two-way communication via standard Jabber implementations. However, as Jabber is based upon XML, the protocol is easily extensible. Extensions to the protocol, many of which are now standardized, have been written which greatly reduce the latency. VOIP service and video streaming are two high-bandwidth and latency-sensitive applications that are now possible to perform via Jabber thanks to these extensions. Other Jabber extensions enable file sharing, remote system access, media streaming, and even real-time gaming.
XMPP was standardized as an Application Level protocol by the Internet Engineering Task Force. Thus, all fully compliant TCP/IP implementations support Jabber. This standardization has helped fuel Jabber adoption, and many popular services, such as Google's Gmail, have adopted Jabber as their internal messaging protocol. Gateway interfaces which enable Jabber to communicate with other IM protocols, notably Microsoft's MSN Messenger, are being developed and perfected in both proprietary implementations and reverse-engineered open-source efforts. This fact, combined with the fact that SMS, telephone, and other interfaces can communicate with Jabber servers via standard XMPP interfaces, has led to controversy regarding Jabber's use to provide alternative interfaces to Microsoft's proprietary IM client.
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