Extensible Messaging and Presence Protocol

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Extensible Messaging and Presence Protocol (XMPP) is an open-standard communications protocol for message-oriented middleware based on XML (Extensible Markup Language).[1] The protocol was originally named Jabber,[2] and was developed by the Jabber open-source community in 1999 for, originally, near-real-time, extensible instant messaging (IM), presence information, and contact list maintenance. Designed to be extensible, the protocol today also finds application in VoIP and file transfer signaling.

Unlike most instant messaging protocols, XMPP uses an open systems approach of development and application, by which anyone may implement an XMPP service and interoperate with other organizations' implementations. The software implementation and many client applications are distributed as free and open source software.

The Internet Engineering Task Force (IETF) formed an XMPP Working Group in 2002 to formalize the core protocols as an IETF instant messaging and presence technology. The XMPP WG produced four specifications (RFC 3920, RFC 3921, RFC 3922, RFC 3923), which were approved by the Internet Engineering Steering Group as Proposed Standards in 2004. The XMPP Standards Foundation (formerly the Jabber Software Foundation) is active in developing open XMPP extensions. In 2011, RFC 3920 and RFC 3921 have been superseded by RFC 6120 and RFC 6121 respectively, and RFC 6122 comes to specify XMPP address format.

XMPP-based software is deployed widely across the Internet and by 2003 was used by over ten million people worldwide, according to the XMPP Standards Foundation.[3]

Apache Wave's federation protocol is an extension to the XMPP protocol.[4]

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Contents

[edit] History

Jeremie Miller began working on the Jabber technology in 1998 and released the first version of the jabberd server on January 4, 1999.[5] The early Jabber community focused on open-source software, mainly the jabberd server (e.g., version 1.0 in May 2000, version 1.2 in October 2000, and version 1.4 in February 2001), but its major outcome proved the development of the XMPP protocol.

The early Jabber protocol as developed in 1999 and 2000 formed the basis for XMPP as published in RFC 3920 and RFC 3921 (the primary changes during formalization by the IETF's XMPP Working Group were the addition of TLS for channel encryption and SASL for authentication). XMPP has often been regarded as a competitor to SIMPLE, based on the Session Initiation Protocol (SIP) protocol, as the standard protocol for instant messaging and presence notification.[6][7]

The first IM service based on XMPP was Jabber.org, which has operated continuously since 1999 and has offered free accounts to users of XMPP.[8] From 1999 until February 2006 the service used jabberd as its server software, at which time it migrated to ejabberd (both of which are free software application servers). In January 2010, the service plans to migrate to proprietary M-Link software produced by Isode Ltd.[9]

In August 2005, Google introduced Google Talk, a combination VoIP and IM system that uses XMPP for instant messaging and as a base for a voice and file transfer signaling protocol. (The initial launch did not include server-to-server communications; Google enabled that feature on January 17, 2006).[10]

In September 2008 Cisco Systems acquired Jabber, Inc. the creators of the commercial product Jabber XCP.[11]

In February 2010, the social-networking site Facebook opened up its chat feature to third-party applications via XMPP.[12] The Facebook developers' site notes that Facebook Chat does not actually run an XMPP server internally, but merely presents an XMPP interface to clients; consequently, some server-side features like roster editing cannot be done via XMPP.[13]

In addition to Google Talk, many other public IM services use XMPP, including

Furthermore, several enterprise IM software products that do not natively use XMPP nevertheless include gateways to XMPP, including

[edit] Strengths

Decentralization
The architecture of the XMPP network is similar to email; anyone can run their own XMPP server and there is no central master server.
Open standards
The Internet Engineering Task Force has formalized XMPP as an approved instant messaging and presence technology under the name of XMPP, and the XMPP specifications have been published as RFC 3920 and RFC 3921. No royalties are required to implement support of these specifications and their development is not tied to a single vendor.
History
XMPP technologies have been in use since 1998. Multiple implementations of the XMPP standards exist for clients, servers, components, and code libraries, with the backing of large companies such as Sun Microsystems and Google.
Security
XMPP servers may be isolated from the public XMPP network (e.g., on a company intranet), and robust security (via SASL and TLS) has been built into the core XMPP specifications. To encourage use of channel encryption, the XMPP Standards Foundation currently runs an intermediate certification authority at StartSSL (formerly at xmpp.net) offering free digital certificates to XMPP server administrators under the auspices of the StartCom Certification Authority (which is the root CA for the intermediate CA).
Flexibility
Custom functionality can be built on top of XMPP; to maintain interoperability, common extensions are managed by the XMPP Software Foundation. XMPP applications beyond IM include network management, content syndication, collaboration tools, file sharing, gaming, and remote systems monitoring.

[edit] Weaknesses

In-band binary data transfer is inefficient
Because XMPP is not yet encoded as Efficient XML Interchange but as a single long XML document, binary data must be first base64 encoded before it can be transmitted in-band. Therefore any significant amount of binary data (e.g., file transfers) is best transmitted out-of-band, using in-band messages to coordinate. The best example of this is the Jingle XMPP Extension Protocol, XEP-0166.

[edit] Decentralization and addressing

The XMPP network uses a client–server architecture (clients do not talk directly to one another). However, it is decentralized—by design there is no central authoritative server, as there is with services such as AOL Instant Messenger or Windows Live Messenger. Some confusion often arises on this point as there is a public XMPP server being run at jabber.org, to which a large number of users subscribe. However, anyone may run their own XMPP server on their own domain. The standard TCP port for XMPP is 5222.

Every user on the network has a unique Jabber ID (usually abbreviated as JID). To avoid requiring a central server to maintain a list of IDs, the JID is structured like an e-mail address with a username and a domain name (or IP address[19]) for the server where that user resides, separated by an at sign (@), such as username@example.com.

Since a user may wish to log in from multiple locations, they may specify a resource. A resource identifies a particular client belonging to the user (for example home, work, or mobile). This may be included in the JID by appending a slash followed by the name of the resource. For example, the full JID of a user's mobile account would be username@example.com/mobile.

Each resource may have specified a numerical value called priority. Messages simply sent to username@example.com will go to the client with highest priority, but those sent to username@example.com/mobile will go only to the mobile client.

JIDs without a username part are also valid, and may be used for system messages and control of special features on the server. A resource remains optional for these JIDs as well.

[edit] Message delivery scenario

Suppose juliet@capulet.com wants to chat with romeo@montague.net. Juliet and Romeo each respectively have accounts on the capulet.com and montague.net servers. When Juliet types in and sends her message, a sequence of events is set in motion:

  1. Juliet's client sends her message to the capulet.com server
    • If montague.net is blocked on capulet.com, the message is dropped.
  2. The capulet.com server opens a connection to the montague.net server.
    • If capulet.com is blocked on montague.net, the message is dropped.
  3. Montague.net checks to see if Romeo is currently connected. If not, the message is stored for later delivery.
  4. If Romeo is online, the montague.net server delivers the message to Romeo.
Juliet → capulet.com → montague.net → Romeo

[edit] Connecting to other protocols

Alice sends a message through the XMPP net to the ICQ transport. The message is next routed to Bob via the ICQ network.

Another useful feature of the XMPP system is that of transports, also known as gateways, which allow users to access networks using other protocols. This can be other instant messaging protocols, but also protocols such as SMS or Email. Unlike multi-protocol clients, XMPP provides this access at the server level by communicating via special gateway services running on a remote computer. Any user can "register" with one of these gateways by providing the information needed to log on to that network, and can then communicate with users of that network as though they were XMPP users. This means any client that fully supports XMPP can access any network with a gateway without extra code in the client, and without the need for the client to have direct access to the Internet. This may violate terms of service on the protocol used—but such terms of service are not legally enforceable in several countries. This also requires sending your IM username and password to the third-party site that operates the transport, which may raise privacy concerns.

[edit] XMPP via HTTP transport

Another aspect of XMPP is the HTTP binding for users behind restricted firewalls. In the original specification, XMPP could use HTTP in two ways: polling[20] and binding.[21] The polling method, now deprecated, essentially implies messages stored on a server-side database are being fetched (and posted) regularly by an XMPP client by way of HTTP 'GET' and 'POST' requests. With HTTP binding, the client uses longer-lived HTTP connections to receive messages as soon as they are sent. This push model of notification is more efficient than polling, where many of the polls return no new data.

Because the client uses HTTP, most firewalls allow clients to fetch and post messages without any hindrances. Thus, in scenarios where the TCP port used by XMPP is blocked, a server can listen on the normal HTTP port and the traffic should pass without problems. Various websites let people sign in to XMPP via a browser. Furthermore, there are open public servers that listen on standard http (port 80) and https (port 443) ports, and hence allow connections from behind most firewalls.

[edit] Implementations

XMPP is implemented by a large number of XMPP clients, servers, and code libraries.

[edit] Development

The IETF XMPP working group has produced a number of RFC protocol documents: RFC 3920, RFC 3921, RFC 3922, RFC 3923, RFC 4622, RFC 4854, RFC 4979

The XMPP Standards Foundation (XSF) develops and publishes extensions to XMPP through a standards process centered on XMPP Extension Protocols (XEPs, previously known as Jabber Enhancement Proposals - JEPs). The following extensions are in especially wide use:

XMPP is currently being extended to handle signaling / negotiation for VoIP and other media sessions. This signaling protocol is called Jingle. Jingle is designed to be consistent with the Google Talk service and bridgeable with the Session Initiation Protocol.

[edit] See also

[edit] References

  1. ^ Johansson, Leif (18 April 2005). "XMPP as MOM". Greater NOrdic MIddleware Symposium (GNOMIS). Oslo: University of Stockholm. http://www.gnomis.org/presentasjoner/oslo2005/xmpp.pdf 
  2. ^ Jabber Inc.
  3. ^ XMPP Standards Foundation (22 September 2003). "Jabber Instant Messaging User Base Surpasses ICQ". Press release. http://xmpp.org/xsf/press/2003-09-22.shtml. Retrieved 30 November 2007. 
  4. ^ "Google Wave Federation Protocol". Google. http://www.waveprotocol.org/draft-protocol-specs/draft-protocol-spec#intro-overview. 
  5. ^ Open Real Time Messaging System
  6. ^ "XMPP rises to face SIMPLE standard", Infoworld magazine, April 17, 2003 XMPP rises to face SIMPLE standard
  7. ^ "XMPP vs SIMPLE: The race for messaging standards", Infoworld magazine, May 23, 2003 Infoworld.com
  8. ^ Chatting Up the Chef Linux Journal March 1, 2003 by Marcel Gagné
  9. ^ "Jabber.org - XMPP Server Migration". 12 August 2009. http://www.jabber.org/2009/08/xmpp-server-migration/. Retrieved 14 December 2009. 
  10. ^ Burd, Gary (17 January 2006). "XMPP Federation". http://googletalk.blogspot.com/2006/01/xmpp-federation.html. Retrieved 30 November 2007. 
  11. ^ "Cisco Announces Definitive Agreement to Acquire Jabber". http://newsroom.cisco.com/dlls/2008/corp_091908.html. Retrieved 2 January 2010. 
  12. ^ "Facebook Chat Now Available Everywhere". http://blog.facebook.com/blog.php?post=297991732130. Retrieved 11 February 2010. 
  13. ^ "Integrating with Facebook Chat". http://wiki.developers.facebook.com/index.php/Integrating_with_Facebook_Chat. Retrieved 21 February 2010. 
  14. ^ Question FAQ #270
  15. ^ Ovi Contacts
  16. ^ "Lotus Sametime 7.5 Interoperates with AIM, Google Talk", eWeek, December 6, 2006 Eweek.com
  17. ^ "Lotus ships gateway to integrate IM with AOL, Yahoo, Google", Network World, December 6, 2006 Networkworld.com
  18. ^ "Unified Communications: Uniting Communication Across Different Networks", Microsoft Press Release, October 1, 2009 Microsoft.com
  19. ^ RFC-Standard 6122 for XMPP
  20. ^ XEP-0025: Jabber HTTP Polling
  21. ^ a b XEP-0124: Bidirectional-streams Over Synchronous HTTP (BOSH)
  22. ^ XEP-0027: Current Jabber OpenPGP Usage
  23. ^ XEP-0004: Data Forms
  24. ^ XEP-0030: Service Discovery
  25. ^ XEP-0045: Multi-User Chat
  26. ^ XEP-0071: XHTML-IM
  27. ^ XEP-0096: File Transfer
  28. ^ XEP-0115: Entity Capabilities
  29. ^ XEP-0163: Personal Eventing Protocol

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