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SIMPLE, the Session Initiation Protocol for Instant Messaging and Presence Leveraging Extensions, is an instant messaging (IM) and presence protocol suite based on Session Initiation Protocol (SIP) managed by the IETF.[1] Like XMPP, and in contrast to the vast majority of IM and presence protocols used by software deployed today, SIMPLE is an open standard.



SIMPLE applies SIP to the problems of:

  • registering for presence information and receiving notifications when such events occur, for example when a user logs-in or comes back from lunch;
  • sending short messages, analogous to SMS or two-way paging;
  • managing a session of real-time messages between two or more participants.

Implementations of the SIMPLE based protocols can be found in SIP Softphones and also in SIP Hardphones.

Technical description


The SIMPLE presence specifications can be broken up into:

  • The core protocol machinery. This provides the actual SIP extensions for subscriptions, notifications and publications. RFC 3265 defines the SUBSCRIBE and NOTIFY methods. SUBSCRIBE allows to subscribe to an event on a server, the server responds with NOTIFY whenever the event come up. RFC 3856 defines how to make use of SUBSCRIBE/NOTIFY for presence. Two models are defined: an end-to-end model in which each User Agent handles presence subscriptions itself; and a centralized model. The latter introduces the concept of a presence server; all subscriptions are handled by this server. The message PUBLISH (RFC 3903) allows User Agents to inform the presence server about their subscription states.
  • Presence documents. The presence information is coded in XML documents, that are carried in the bodies of the respective SIP messages. RFC 3863 and RFC 4479 describe this procedure, RFC 4480 (RPID), RFC 4481, RFC 4482 (CPID) and various drafts describe contents and formats of the presence documents.
  • Privacy, policy and provisioning. If the centralized model is used, the User Agents need a way to define who may subscribe to which amount of their presence information. RFC 4745 and RFC 5025 define a framework for authorization policies controlling access to application-specific data. The XCAP protocol (RFC 4825), carried by HTTP, allows User Agents to communicate their presence rules to a XCAP server, which rules the information exposed by the presence server. RFC 3857 and RFC 3858 define a subscription event "watcher info". User Agents may subscribe to this event to be informed who is subscribing to their presence information.


SIP defines two modes of instant messaging:

  • The Page Mode makes use of the SIP method MESSAGE, as defined in RFC 3428. This mode establishes no sessions.
  • The Session Mode. The Message Session Relay Protocol (RFC 4975, RFC 4976) defines text-based protocol for exchanging arbitrarily sized content of any time between users. An MSRP session is set up by exchanging certain information, such as an MSRP URI, within SIP and SDP signaling.


  1. ^ SIMPLE Working Group

External links


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary



Most common English words: smile « walk « places « #709: simple » fresh » noble » appearance


< Middle English simple < Old French and French simple < Latin simplex (simple, literally 'onefold', as opposed to duplex, twofold, double) < sim- (the same) + plicare (to fold): see same and ply. Cf. single, singular, simultaneous, etc.



simple (comparative simpler, superlative simplest)

  1. Having few parts or features; having no special features.
    • 2001, Sydney I. Landau, Dictionaries: The Art and Craft of Lexicography, Cambridge University Press (ISBN 0-521-78512-X), page 167,
      There is no simple way to define precisely a complex arrangement of parts, however homely the object may appear to be.
  2. (colloquial) Feeble-minded.
  3. (mathematics, of a group) Having no normal subgroup.
  4. (mathematics, of a Lie group) Having no connected normal subgroup.



Derived terms





simple (plural simples)

  1. (medicine) A preparation made from one plant, as opposed to something made from more than one plant.
  2. (logic) A simple or atomic proposition



to simple

Third person singular

Simple past

Past participle

Present participle

to simple (third-person singular simple present simples, present participle simpling, simple past and past participle simpled)

  1. (transitive, intransitive, archaic) To gather simples, ie, medicinal herbs.

Derived terms




From Latin simplex.


  • (Eastern Catalan) IPA: [ˈsimpɫə]
  • (Western Catalan) IPA: [ˈsimpɫe]


simple m. and f. (plural simples, obsolete feminine simpla)

  1. simple (uncomplicated)
  2. single (not divided into parts)


  • senzill

Derived terms

  • fulla simple (“simple leaf”)
  • simplement (“simply”)

Related terms

  • símplex (“simplex”)
  • simplicitat (“simplicity”)
  • ximple



simpl- + -e


  • IPA: /ˈsimple/



  1. simply




simple (epicene, plural simples)

  1. simple
  2. one-way
    Un billet simple.
    A one-way ticket.

Related terms



simple m. and f. (plural simples)

  1. simple



  • IPA: [ˈsim.ple]



  1. feminine plural nominative form of simplu.
  2. feminine plural accusative form of simplu.
  3. neuter plural nominative form of simplu.
  4. neuter plural accusative form of simplu.



simple m. and f. (plural simples)

  1. simple
  2. mere, uncomplicated, easy
  3. single
  4. insipid


simple m. and f. (plural simples)

  1. simpleton, fool
  2. (pharmacology, masculine) simple

Simple English

When something is simple, it is very easy to understand or do. The opposite is hard or difficult. Simplicity is the measurement of how simple something is.

This Wikipedia is in Simple English so all people can understand this. When a page (or article) is too hard, a complex template ({{Complex}}) is used. This is what the complex template says:

  • 2+2 is a very simple sum (an easy sum).
  • Boiling an egg is very simple (very easy).

Simple can mean something that is only made up of a few parts. It is not complicated:

Simple can mean that something or someone is humble (lowly) or common:

Simple can also be used to refer to someone whose mind thinks in a very simple way. Calling a person "simple minded" is usually rude.

Other pages

Simple, easy. Something that anyone can do.

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