Internet Relay Chat

Internet Relay Chat (IRC) is a text-based chat (instant messaging) system. It enables discussions among any number of participants in so-called conversation channels, as well as discussions between only two partners — for example, in question-and-answer dialogues.[1] Any participant may open a new conversation channel, and a single computer user can also take part in several such simultaneous channels.

The first IRC server, tolsun.oulu.fi, a Sun-3 server on display near the University of Oulu computer centre. (2001)

In order to establish or join a chat, a network program, called an IRC client, is required for accessing a channel by connecting to a server. The IRC client can be either an independent program on the local computer (e.g. mIRC, XChat) or take the form of a special user interface from within a larger program such as an Internet browser; the Opera browser, for example, includes an IRC client, and clients such as Mibbit and IRCCloud or the open source KiwiIRC and MIT's The Lounge Chat can work in connection with many popular browsers.

An IRC network of interconnected servers operating as relay stations is used to mediate the calls in the IRC. The essential feature of this network is its BITNET communication topology, which permits only one communication path between any two participants. Historically, this ensured efficient communication, because in the early days of IRC, intercontinental data lines had a very limited capacity. The topology enabled a message from a client on one continent not to be sent individually for each client on another continent, but only once to a local server, which then distributed it to clients. Despite limited management capacities, very large “chat landscapes” were possible. The disadvantage is the lack of redundancy, which manifests itself in so-called net splits: if any server fails, the network automatically breaks into separate parts until a new connection is established between the parts.

The largest IRC networks consist of several dozen IRC servers that simultaneously connect over 100,000 users and manage tens of thousands of channels, on each of which several thousand people can simultaneously participate. Despite these enormous proportions, the delay in a sent text is usually on the order of tenths of a second and seldom exceeds one second's time.

IRC usage has been declining steadily since 2003, losing 60 percent of its users (from 1 million to about 400,000 in 2021) and half of its channels (from half a million in 2003 to under 200,000 in 2021).[2] In April 2011, the top 100 IRC networks served more than half a million users at a time,[3] hosting hundreds of thousands of channels[3] operating on a total of roughly 1 500 servers[3] out of roughly then 3 200 IRC servers worldwide.[4] As of June 2021, there are 481 different IRC networks known to be operating,[5] of which the open source Libera Chat, founded in May 2021, has the most users, with 21,348 channels on 15,433 servers; between them, the top 100 IRC networks share 188,336 channels operating on 96,708 servers.[6]

From a technical standpoint, Internet Relay Chat is implemented as an application layer protocol to facilitate communication in the form of text. The chat process works on a client–server networking model. As already discussed, IRC clients can be stand-alone computer programs or web-based applications running either locally in the browser or on a third party server. These clients communicate with chat servers to transfer messages to other clients.[7] IRC is mainly designed for group communication in discussion forums, called channels,[8] but also allows one-on-one communication via private messages[9] as well as chat and data transfer,[10] including file sharing.[11]

Client software is available for every major operating system that supports Internet access.[12]