rfc2810.txt

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Network Working Group                                           C. Kalt
Request for Comments: 2810                                   April 2000
Updates: 1459
Category: Informational


                   Internet Relay Chat: Architecture

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   The IRC (Internet Relay Chat) protocol is for use with text based
   conferencing. It has been developed since 1989 when it was originally
   implemented as a mean for users on a BBS to chat amongst themselves.

   First formally documented in May 1993 by RFC 1459 [IRC], the protocol
   has kept evolving. This document is an update describing the
   architecture of the current IRC protocol and the role of its
   different components.  Other documents describe in detail the
   protocol used between the various components defined here.

Table of Contents

   1.  Introduction ...............................................   2
   2.  Components .................................................   2
      2.1  Servers ................................................   2
      2.2  Clients ................................................   3
         2.2.1  User Clients ......................................   3
         2.2.2  Service Clients ...................................   3
   3.  Architecture ...............................................   3
   4.  IRC Protocol Services ......................................   4
      4.1  Client Locator .........................................   4
      4.2  Message Relaying .......................................   4
      4.3  Channel Hosting And Management .........................   4
   5.  IRC Concepts ...............................................   4
      5.1  One-To-One Communication ...............................   5
      5.2  One-To-Many ............................................   5
         5.2.1  To A Channel ......................................   5
         5.2.2  To A Host/Server Mask .............................   6



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RFC 2810           Internet Relay Chat: Architecture          April 2000


         5.2.3  To A List .........................................   6
      5.3  One-To-All .............................................   6
         5.3.1  Client-to-Client ..................................   6
         5.3.2  Client-to-Server ..................................   7
         5.3.3  Server-to-Server ..................................   7
   6.  Current Problems ...........................................   7
      6.1  Scalability ............................................   7
      6.2  Reliability ............................................   7
      6.3  Network Congestion .....................................   7
      6.4  Privacy ................................................   8
   7.  Security Considerations ....................................   8
   8.  Current Support And Availability ...........................   8
   9.  Acknowledgements ...........................................   8
   10.  References ................................................   8
   11.  Author's Address ..........................................   9
   12.  Full Copyright Statement ..................................  10

1. Introduction

   The IRC (Internet Relay Chat) protocol has been designed over a
   number of years for use with text based conferencing.  This document
   describes its current architecture.

   The IRC Protocol is based on the client-server model, and is well
   suited to running on many machines in a distributed fashion.  A
   typical setup involves a single process (the server) forming a
   central point for clients (or other servers) to connect to,
   performing the required message delivery/multiplexing and other
   functions.

   This distributed model, which requires each server to have a copy
   of the global state information, is still the most flagrant problem
   of the protocol as it is a serious handicap, which limits the maximum
   size a network can reach.  If the existing networks have been able to
   keep growing at an incredible pace, we must thank hardware
   manufacturers for giving us ever more powerful systems.

2. Components

   The following paragraphs define the basic components of the IRC
   protocol.

2.1 Servers

   The server forms the backbone of IRC as it is the only component
   of the protocol which is able to link all the other components
   together: it provides a point to which clients may connect to talk to




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RFC 2810           Internet Relay Chat: Architecture          April 2000


   each other [IRC-CLIENT], and a point for other servers to connect to
   [IRC-SERVER].  The server is also responsible for providing the basic
   services defined by the IRC protocol.

2.2 Clients

   A client is anything connecting to a server that is not another
   server.  There are two types of clients which both serve a different
   purpose.

2.2.1 User Clients

   User clients are generally programs providing a text based
   interface that is used to communicate interactively via IRC.  This
   particular type of clients is often referred as "users".

2.2.2 Service Clients

   Unlike users, service clients are not intended to be used manually
   nor for talking.  They have a more limited access to the chat
   functions of the protocol, while optionally having access to more
   private data from the servers.

   Services are typically automatons used to provide some kind of
   service (not necessarily related to IRC itself) to users.  An example
   is a service collecting statistics about the origin of users
   connected on the IRC network.

3. Architecture

   An IRC network is defined by a group of servers connected to each
   other.  A single server forms the simplest IRC network.

   The only network configuration allowed for IRC servers is that of
   a spanning tree where each server acts as a central node for the rest
   of the network it sees.

                       1--\
                           A        D---4
                       2--/ \      /
                             B----C
                            /      \
                           3        E

   Servers: A, B, C, D, E         Clients: 1, 2, 3, 4

                    [ Fig. 1. Sample small IRC network ]




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RFC 2810           Internet Relay Chat: Architecture          April 2000


   The IRC protocol provides no mean for two clients to directly
   communicate.  All communication between clients is relayed by the
   server(s).

4. IRC Protocol Services

   This section describes the services offered by the IRC protocol.  The
   combination of these services allow real-time conferencing.

4.1 Client Locator

   To be able to exchange messages, two clients must be able to locate
   each other.

   Upon connecting to a server, a client registers using a label which
   is then used by other servers and clients to know where the client is
   located.  Servers are responsible for keeping track of all the labels
   being used.

4.2 Message Relaying

   The IRC protocol provides no mean for two clients to directly
   communicate.  All communication between clients is relayed by the
   server(s).

4.3 Channel Hosting And Management

   A channel is a named group of one or more users which will all
   receive messages addressed to that channel.  A channel is
   characterized by its name and current members, it also has a set of
   properties which can be manipulated by (some of) its members.

   Channels provide a mean for a message to be sent to several clients.
   Servers host channels, providing the necessary message multiplexing.
   Servers are also responsible for managing channels by keeping track
   of the channel members.  The exact role of servers is defined in
   "Internet Relay Chat: Channel Management" [IRC-CHAN].

5. IRC Concepts

   This section is devoted to describing the actual concepts behind the
   organization of the IRC protocol and how different classes of
   messages are delivered.








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RFC 2810           Internet Relay Chat: Architecture          April 2000


5.1 One-To-One Communication

   Communication on a one-to-one basis is usually performed by clients,
   since most server-server traffic is not a result of servers talking
   only to each other.  To provide a means for clients to talk to each
   other, it is REQUIRED that all servers be able to send a message in
   exactly one direction along the spanning tree in order to reach any
   client.  Thus the path of a message being delivered is the shortest
   path between any two points on the spanning tree.

   The following examples all refer to Figure 1 above.

   Example 1: A message between clients 1 and 2 is only seen by server
       A, which sends it straight to client 2.

   Example 2: A message between clients 1 and 3 is seen by servers A &
       B, and client 3.  No other clients or servers are allowed see the
       message.

   Example 3: A message between clients 2 and 4 is seen by servers A, B,
       C & D and client 4 only.

5.2 One-To-Many

   The main goal of IRC is to provide a forum which allows easy and
   efficient conferencing (one to many conversations).  IRC offers
   several means to achieve this, each serving its own purpose.

5.2.1 To A Channel

   In IRC the channel has a role equivalent to that of the multicast
   group; their existence is dynamic and the actual conversation carried
   out on a channel MUST only be sent to servers which are supporting
   users on a given channel.  Moreover, the message SHALL only be sent
   once to every local link as each server is responsible to fan the
   original message to ensure that it will reach all the recipients.

   The following examples all refer to Figure 2.

   Example 4: Any channel with 1 client in it. Messages to the channel
       go to the server and then nowhere else.

   Example 5: 2 clients in a channel. All messages traverse a path as if
       they were private messages between the two clients outside a
       channel.






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