XMPP Instant Messaging From: http://www.jabber.org/ietf/draft-miller-xmpp-im-02.txt Reference: draft-miller-xmpp-im-02 ------------------------------------------------------------------------ Network Working Group J. Miller Internet-Draft P. Saint-Andre Expires: May 4, 2003 Jabber Software Foundation November 03, 2002 XMPP Instant Messaging draft-miller-xmpp-im-02 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 4, 2003. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes the specific extensions to and applications of the eXtensible Messaging and Presence Protocol (XMPP) that are necessary to create a basic instant messaging and presence application (specificlaly, an application that is compatible with the open-source Jabber instant messaging system). Miller & Saint-Andre Expires May 4, 2003 [Page 1] Internet-Draft XMPP Instant Messaging November 2002 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4 Conventions Used in this Document . . . . . . . . . . . . . 4 1.5 Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 5 1.6 Intellectual Property Notice . . . . . . . . . . . . . . . . 5 2. Registration . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1 Registration Data Flow . . . . . . . . . . . . . . . . . . . 6 2.2 Cancellation Data Flow . . . . . . . . . . . . . . . . . . . 8 2.3 Definition of the 'jabber:iq:register' Namespace . . . . . . 8 2.3.1 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3.2 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3.3 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3. Authentication . . . . . . . . . . . . . . . . . . . . . . . 12 3.1 Authentication Using SASL . . . . . . . . . . . . . . . . . 12 3.2 Authentication Using' jabber:iq:auth . . . . . . . . . . . . 13 3.3 Definition of the 'jabber:iq:auth' Namespace . . . . . . . . 14 3.3.1 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.3.2 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.3.3 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4. Exchanging Messages . . . . . . . . . . . . . . . . . . . . 17 4.1 Specifying an Intended Recipient . . . . . . . . . . . . . . 17 4.2 Specifying a Message Type . . . . . . . . . . . . . . . . . 17 4.3 Specifying a Message Subject . . . . . . . . . . . . . . . . 18 4.4 Specifying a Message Thread . . . . . . . . . . . . . . . . 18 4.5 Specifying a Message Body . . . . . . . . . . . . . . . . . 19 4.6 Specifying Additional Information . . . . . . . . . . . . . 19 4.7 Message-Related Errors . . . . . . . . . . . . . . . . . . . 19 5. Exchanging Presence Information . . . . . . . . . . . . . . 20 5.1 Node and Host Responsibilities . . . . . . . . . . . . . . . 20 5.2 Sending Initial Presence . . . . . . . . . . . . . . . . . . 20 5.3 Specifying Availability Status . . . . . . . . . . . . . . . 21 5.4 Specifying Detailed Status Information . . . . . . . . . . . 21 5.5 Probing for Presence . . . . . . . . . . . . . . . . . . . . 21 5.6 Sending Final Presence . . . . . . . . . . . . . . . . . . . 21 6. Managing Subscriptions . . . . . . . . . . . . . . . . . . . 22 6.1 Requesting a Subscription . . . . . . . . . . . . . . . . . 22 6.2 Handling a Subscription Request . . . . . . . . . . . . . . 22 6.3 Cancelling a Subscription from Another Entity . . . . . . . 23 6.4 Unsubscribing from Another Entity's Presence . . . . . . . . 23 7. Managing One's Roster . . . . . . . . . . . . . . . . . . . 24 7.1 Receiving One's Roster on Login . . . . . . . . . . . . . . 24 7.2 Adding a Roster Item . . . . . . . . . . . . . . . . . . . . 25 7.3 Deleting a Roster Item . . . . . . . . . . . . . . . . . . . 26 7.4 Definition of the 'jabber:iq:roster' Namespace . . . . . . . 27 Miller & Saint-Andre Expires May 4, 2003 [Page 2] Internet-Draft XMPP Instant Messaging November 2002 7.4.1 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.4.2 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 7.4.3 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 8. Routing and Delivery Guidelines . . . . . . . . . . . . . . 30 9. Security Considerations . . . . . . . . . . . . . . . . . . 31 References . . . . . . . . . . . . . . . . . . . . . . . . . 32 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 32 Full Copyright Statement . . . . . . . . . . . . . . . . . . 33 Miller & Saint-Andre Expires May 4, 2003 [Page 3] Internet-Draft XMPP Instant Messaging November 2002 1. Introduction 1.1 Overview The core features of the XMPP protocol are defined in XMPP Core [1]. These features, specifically XML streams as well as the 'jabber:client' and 'jabber:server' namespaces, provide the building blocks for many types of near-real-time applications, which may be layered on top of the core by sending XML chunks that are scoped by specific XML namespaces. This document describes the specific extensions to and applications of XMPP Core that are used to create the basic functionality expected of an instant messaging and presence application as defined in RFC 2779 [2]. Extended namespaces for many other functionality areas have been defined and continue to be defined by the Jabber Software Foundation [3], including service discovery, multi-user chat, search, remote procedure calls, data gathering and forms submission, encryption, feature negotiation, message composing events, message expiration, delayed delivery, and file transfer; however, such functionality is not described herein because it is not required by [2]. 1.2 Terminology This document inherits the terminology defined in [1]. 1.3 Requirements For the purposes of this document, we stipulate that a basic instant messaging and presence application needs to enable a node to perform the following functionality: o Register an account with a host o Authenticate with a host o Exchange messages with other nodes o Exchange presence information with other nodes o Manage subscriptions to and from other nodes o Manage the items in the node's contact list (called a "roster") 1.4 Conventions Used in this Document The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and Miller & Saint-Andre Expires May 4, 2003 [Page 4] Internet-Draft XMPP Instant Messaging November 2002 "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [4]. 1.5 Discussion Venue The authors welcome discussion and comments related to the topics presented in this document, preferably on the "xmppwg@jabber.org" mailing list (archives and subscription information are available at http://www.jabber.org/cgi-bin/mailman/listinfo/xmppwg/). 1.6 Intellectual Property Notice This document is in full compliance with all provisions of Section 10 of RFC 2026. Parts of this specification use the term "jabber" for identifying namespaces and other protocol syntax. Jabber[tm] is a registered trademark of Jabber, Inc. Jabber, Inc. grants permission to the IETF for use of Jabber trademark in association with this specification and its successors, if any. Miller & Saint-Andre Expires May 4, 2003 [Page 5] Internet-Draft XMPP Instant Messaging November 2002 2. Registration Registering with a host is necessary in order for a node to engage in any desired functionality. Certainly such registration MAY (and frequently does) occur outside the context of an instant messaging and presence application. However, XMPP also enables a node to register with a host within the context of an IM system. This functionality is enabled by sending and receiving IQ chunks in a request-response pattern, where the IQ chunks contain elements in the 'jabber:iq:register' namespace. 2.1 Registration Data Flow Step 1: Node queries host regarding information that is required in order to register: Step 2: Host responds with the required registration fields: Choose a username and password to register with this service. Note: the node is REQUIRED to provide information for all of the elements (other than ) contained in the IQ result. (Note also that the XML chunk shown above does not include a 'to' attribute, since the connected socket does not yet have an account.) Miller & Saint-Andre Expires May 4, 2003 [Page 6] Internet-Draft XMPP Instant Messaging November 2002 Step 3: Node provides required information: juliet@capulet.com R0m30 juliet Step 4: Host informs node of successful registration: Step 4 (alt 1): Host informs node of failed registration (required field not provided): juliet@capulet.com R0m30 Not Acceptable Miller & Saint-Andre Expires May 4, 2003 [Page 7] Internet-Draft XMPP Instant Messaging November 2002 Step 4 (alt 2): Node is already registered: juliet@capulet.com R0m30 juliet Bad Request 2.2 Cancellation Data Flow The 'jabber:iq:register' namespace also makes it possible for a user to cancel a registration with a host by sending a element as shown below. Step 1: Node sends request to unregister: Step 2: Host informs node of successful unregistration: 2.3 Definition of the 'jabber:iq:register' Namespace 2.3.1 Children While numerous fields are available for use in the 'jabber:iq:register' namespace, only those fields (other than ) sent from the host in an IQ result are REQUIRED in order to register. The officially-recognized fields available for Miller & Saint-Andre Expires May 4, 2003 [Page 8] Internet-Draft XMPP Instant Messaging November 2002 use are as follows: o instructions o username o password o name o email o address o city o state o zip o phone o url o date o misc o text o remove - request to unregister (sent only in an IQ set) Miller & Saint-Andre Expires May 4, 2003 [Page 9] Internet-Draft XMPP Instant Messaging November 2002 2.3.2 DTD 2.3.3 Schema Miller & Saint-Andre Expires May 4, 2003 [Page 10] Internet-Draft XMPP Instant Messaging November 2002 Miller & Saint-Andre Expires May 4, 2003 [Page 11] Internet-Draft XMPP Instant Messaging November 2002 3. Authentication In order to gain access to the network of XMPP-compliant applications and thus engage in standard IM functionality such as exchanging messages and presence, a node must authenticate with a host. The preferred authentication method is SASL. Authentication using the older 'jabber:iq:auth' method is OPTIONAL and MAY be used if a node does not support SASL. 3.1 Authentication Using SASL If a node is capable of authenticating with SASL, it MUST include the agreed-upon SASL namespace within the opening element with which it initiated communications with the host. For the protocol describing how a node authenticates with a host, refer to [1]. Once a node has authenticated its streams with a host, it MUST provide a resource associated with the connection. This is accomplished by means of the 'jabber:iq:auth' namespace. The protocol for doing so is described below. Step 1: Node queries host regarding information that is still required to begin a session: juliet Step 2: Host responds with the required fields (in this case, only the username and resource): juliet Miller & Saint-Andre Expires May 4, 2003 [Page 12] Internet-Draft XMPP Instant Messaging November 2002 Step 3: Node sends resource information: juliet balcony Step 4: Host informs node of successful session initiation: 3.2 Authentication Using' jabber:iq:auth Earlier iterations of XMPP contained a client-server authentication protocol that was enforced after the stream was negotiated; this protocol, which uses the 'jabber:iq:auth' namespace, is described for completeness in this section. The 'jabber:iq:auth' namespace provides two things: (1) a simple way for a node to authenticate with a host and (2) a way to create a resource representing a specific connection or session associated with the node. The following is the data flow for a complete example of a node authenticating with a host. Step 1: Node queries host regarding information that is required in order to authenticate: juliet Miller & Saint-Andre Expires May 4, 2003 [Page 13] Internet-Draft XMPP Instant Messaging November 2002 Step 2: Host responds with the required authentication fields: juliet Step 3: Node sends authentication information (encrypted password): juliet 64d60e40febe09264c52bc9cbddd5dd1147fae97 balcony Step 4: Host informs node of successful authentication: Step 4 (alt): Host informs node of failed authentication: juliet 64d60e40febe09264c5wrongpassword2bc9cbddd5dd1147fae97 balcony Unauthorized 3.3 Definition of the 'jabber:iq:auth' Namespace 3.3.1 Children o username - the unique username for this node (usually an IM user). o password - the secret key or passphrase for the node's access to the host. Miller & Saint-Andre Expires May 4, 2003 [Page 14] Internet-Draft XMPP Instant Messaging November 2002 o digest - the concatenation of the stream id and the password, encrypted according to the SHA1 Secure Hash Algorithm [5] and represented as all lowercase hex. o resource - unique value to represent current connection. 3.3.2 DTD Miller & Saint-Andre Expires May 4, 2003 [Page 15] Internet-Draft XMPP Instant Messaging November 2002 3.3.3 Schema Miller & Saint-Andre Expires May 4, 2003 [Page 16] Internet-Draft XMPP Instant Messaging November 2002 4. Exchanging Messages Exchanging messages is simple within XMPP: using a message chunk, a node can send a message to any other node (or, more generally, any entity). 4.1 Specifying an Intended Recipient A node SHOULD specify an intended recipient for the message by providing an appropriate JID in the 'to' attribute of the element. Normally, the value of the 'to' attribute specifies an entity other than the sending node (for exceptions, see the next paragraph). The intended recipient MAY be any valid JID (e.g., a node on the same host, a node on a different host, the host itself, or another host). If no 'to' address is specified, it is implied that the message is addressed to the sending node itself (i.e., the node@host sending the chunk); furthermore, a message explicitly or implicitly addressed to the sending node itself is processed by the host on behalf of that node. A message addressed to a specific connected resource associated with the sending node is delivered to that node@host/ resource (which MAY be different from the connected resource that generated the message). 4.2 Specifying a Message Type As mentioned in [1], there are several defined types of messages (specified by means of a 'type' attribute within the element). In the context of an instant messaging application, a node MAY include a message type in order to capture the conversational context of the message, thus providing a hint regarding presentation (e.g., in a GUI). If included, the 'type' attribute SHOULD have one of the following values (any other value MAY be ignored): o chat -- The message is sent in the context of a one-to-one chat conversation. o groupchat -- The message is sent in the context of a multi-user chat environment. o headline -- The message is generated by an automated service that delivers content (news, sports, market information, etc.). o error - A message returned to a sender specifying an error associated with a previous message sent by the sender (for a full list of error messages, see [1]) Miller & Saint-Andre Expires May 4, 2003 [Page 17] Internet-Draft XMPP Instant Messaging November 2002 4.3 Specifying a Message Subject A message chunk MAY contain a child element specifying the subject of the message. The subject MUST NOT contain mixed content. A message with a subject: Imploring Wherefore art thou, Romeo? 4.4 Specifying a Message Thread A message chunk MAY contain a child element specifying the thread of the message for the purpose of tracking a conversation thread. The content of the element is a random string that is generated by the sender; this string MAY be copied back to the sender in subsequent replies. If included, the element MUST have no attributes and MUST NOT contain mixed content. A simple threaded conversation: Art thou not Romeo, and a Montague? 283461923759234 Neither, fair saint, if either thee dislike. 283461923759234 How cam'st thou hither, tell me, and wherefore? 283461923759234 Miller & Saint-Andre Expires May 4, 2003 [Page 18] Internet-Draft XMPP Instant Messaging November 2002 4.5 Specifying a Message Body A message chunk MAY (and usually will) contain a child element specifying the body of the message. The body MUST NOT contain mixed content. If it is necessary to provide the message body in an alternate form (e.g., encrypted using the public key infrastructure or formatted using XHTML), the alternate form SHOULD be contained in an appropriately-namespaced child of the message chunk other than the element. 4.6 Specifying Additional Information A message chunk MAY house an element containing content that extends the meaning of the message (e.g., an encrypted form of the message body). In common usage this child element is often the element but MAY be any element, as long as the 'xmlns' namespace declaration is something other than the streams namespace and the default namespace; this extended namespace defines all elements contained within the child element. 4.7 Message-Related Errors If a message sent by a sender cannot be delivered, a host SHOULD return that message to the sender in a message chunk of type "error" along with an appropriate error message (for a list of error messages, see [1]). A message-related error: Sleep dwell upon thine eyes Sleep dwell upon thine eyes No Such JID Miller & Saint-Andre Expires May 4, 2003 [Page 19] Internet-Draft XMPP Instant Messaging November 2002 5. Exchanging Presence Information Exchanging presence information is made relatively simple within XMPP by using presence chunks. However, we see here a contrast to the handling of messages: although a node MAY send directed presence information to another entity, in general presence information is sent from a node to a host and then broadcasted by the host to any entities that are subscribed to the presence of the sending entity. 5.1 Node and Host Responsibilities When a node connects to a host, it sends an initial presence chunk to the host to express default availability. This presence chunk MUST have no type. Upon receiving initial presence from a node, the host sends presence probes to any remote entities that are subscribed to that node's presence (as represented in the node's roster) in order to determine if they are available. (The remote host is responsible for responding to the presence probe only when (1) the probing entity has been allowed to access the probed entity's presence, e.g., by server rules or user subscriptions, and (2) the probed entity is available; the probing entity's host then informs the probing entity of the probed entity's last known available presence, for all of the probed entity's resources if applicable.) The host then sends the node's initial presence chunk to any subscribed entities that are available. Throughout the active session of a connected resource associated with the node, the host is responsible for broadcasting any changes in the availability status of the connected resource to the subscribed entities that are available, so that such entities are apprised of availability changes. Finally, the host MUST notify all of the subscribed and available entities when a connected resource becomes unavailable. 5.2 Sending Initial Presence Upon authenticating, a node SHOULD send initial presence to its host indicating that the connected resource is available for communications. This presence chunk MUST have no type. Initial presence sent from node to host: Miller & Saint-Andre Expires May 4, 2003 [Page 20] Internet-Draft XMPP Instant Messaging November 2002 5.3 Specifying Availability Status A node MAY provide further information about its availability status by using the element. As defined in [1], the recognized values for the show element are "away", "chat", "xa", and "dnd". Availability status: away 5.4 Specifying Detailed Status Information In conjunction with the element, a node MAY provide detailed status information by using the element. The content of this element is a natural-language description of the node's current availability status. Detailed status information: dnd Busy fighting the Romans 5.5 Probing for Presence A node or a host MAY probe for the current presence of another entity. A node probing for the presence of another node MUST have permission to view the presence of the probed node. Presence probe: 5.6 Sending Final Presence Upon ending its session with a host, a node SHOULD send a final presence chunk that is explicitly of type unavailable. Sending final presence to express unavailable state: Miller & Saint-Andre Expires May 4, 2003 [Page 21] Internet-Draft XMPP Instant Messaging November 2002 6. Managing Subscriptions In order to protect the privacy of instant messaging users and any other entities, presence and availability information is made available only to other entities that the user has approved. When a user has agreed that another entity may view its presence, the entity is said to have a subscription to the user's presence information. Note well that a subscription lasts across sessions; indeed, it lasts until the subscriber unsubscribes or the subscribee cancels the previously-granted subscription. Subscriptions are completed within XMPP by sending presence chunks containing specially-defined attributes of presence chunks. 6.1 Requesting a Subscription A request to subscribe to another entity's presence is made by sending a presence chunk of type "subscribe". Sending a subscription request: 6.2 Handling a Subscription Request When a node receives a subscription request from another entity, it MAY accept the request by sending a presence chunk of type "subscribed" or decline the request by sending a presence chunk of type "unsubscribed". Accepting a subscription request: Miller & Saint-Andre Expires May 4, 2003 [Page 22] Internet-Draft XMPP Instant Messaging November 2002 Denying a presence subscription request: 6.3 Cancelling a Subscription from Another Entity If a node would like to cancel a previously-granted subscription request, it sends a presence chunk of type "unsubscribed". Cancelling a previously granted subscription request: 6.4 Unsubscribing from Another Entity's Presence If a node would like to unsubscribe from the presence of another entity, it sends a presence chunk of type "unsubscribe". Unsubscribing from an entity's presence: Miller & Saint-Andre Expires May 4, 2003 [Page 23] Internet-Draft XMPP Instant Messaging November 2002 7. Managing One's Roster One's list of contacts is called a roster. A roster is stored by the host so that a user may access roster information from any connected resource. 7.1 Receiving One's Roster on Login Upon connecting to the host, a node SHOULD request the roster (however, because receiving the roster may not be desirable for all resources, e.g., a connection with limited bandwidth, the node's request for the roster is OPTIONAL). Node requests current roster from host: Node receives roster from the host: Friends Friends Miller & Saint-Andre Expires May 4, 2003 [Page 24] Internet-Draft XMPP Instant Messaging November 2002 7.2 Adding a Roster Item At any time, a node MAY add an item to its roster. Node adds a new item: Servants The host is responsible for updating the roster information in persistent storage, and also for pushing that change out to all connected resources for the node using an IQ chunk of type "set". This enables all connected resources to remain in sync with the host- based roster information. Miller & Saint-Andre Expires May 4, 2003 [Page 25] Internet-Draft XMPP Instant Messaging November 2002 Host replies with an IQ result to the sending resource and pushes the updated roster information to all connected resources: Servants Servants 7.3 Deleting a Roster Item At any time, a node MAY delete an item from its roster by doing an IQ set and making sure that the value of the 'subscription' attribute is "remove". Miller & Saint-Andre Expires May 4, 2003 [Page 26] Internet-Draft XMPP Instant Messaging November 2002 Node removes a item: Servants Note: as with adding a roster item, when deleting a roster item the host is responsible for updating the roster information in persistent storage, and also for pushing that change out to all connected resources for the node using an IQ chunk of type "set". 7.4 Definition of the 'jabber:iq:roster' Namespace 7.4.1 Children A element scoped by the 'jabber:iq:roster' namespace MAY contain zero or more elements. An item element MAY contain the following attributes: o jid - A REQUIRED attribute that contains the complete JID of the contact that this item represents o name - An OPTIONAL attribute that contains a natural-language name for the contact o subscription - The current status of the subscription related to this item. Should be one of the following (all other values are ignored): * none - no subscription. * from - this entity has a subscription to the contact. * to - the contact has a subscription to this entity. * both - subscription is both to and from. * remove - item is to be removed. o ask - An OPTIONAL attribute specifying the current status of a request to this contact. Should be one of the following (all Miller & Saint-Andre Expires May 4, 2003 [Page 27] Internet-Draft XMPP Instant Messaging November 2002 other values are ignored): * subscribe - this entity is asking to subscribe to that contact's presence. * unsubscribe - this entity is asking unsubscribe from that contact's presence. An element MAY contain zero or more instances of the following element: o group - Natural-language name of a user-specified group for the purpose of categorizing contacts into groups. 7.4.2 DTD 7.4.3 Schema Miller & Saint-Andre Expires May 4, 2003 [Page 28] Internet-Draft XMPP Instant Messaging November 2002 Miller & Saint-Andre Expires May 4, 2003 [Page 29] Internet-Draft XMPP Instant Messaging November 2002 8. Routing and Delivery Guidelines XML chunks that are not handled directly by a host (e.g., for the purpose of data storage or rebroadcasting) are routed or delivered to the intended recipient of the chunk as represented by a JID in the 'to' attribute. The following rules apply: o If the JID contains a resource identifier (to="node@host/ resource"), the chunk is delivered first to the resource that exactly matches the resource identifier, or secondarily to a resource that matches partially (e.g., resource "foo" partially matches resource identifier "foobar"). o If the JID contains a resource identifier and there are no matching resources, but there are other connected resources associated with the node, then message chunks are further processed as if no resource is specified (see next item). For all other chunks, the host should return them to the sender with a type of "error" and an appropriate error code (503) and message. o If the JID contains only a node@host and there is at least one connected resource available for the node, the host should deliver the chunk to an appropriate resource based on the availability state, priority, and connect time of the connected resource(s). (Existing XMPP implementations contain some hardcoded rules, based on and most recent connection time, for the routing of such chunks. A more flexible approach to routing would be desirable.) o If the JID contains only a node@host and there are no connected resources available for the node (e.g., an IM user is offline), the host MAY choose to store the chunk (usually only message and presence subscription chunks) on behalf of the node and deliver the chunk when a resource becomes available for that node. Miller & Saint-Andre Expires May 4, 2003 [Page 30] Internet-Draft XMPP Instant Messaging November 2002 9. Security Considerations For security considerations, refer to the relevant section of [1]. Miller & Saint-Andre Expires May 4, 2003 [Page 31] Internet-Draft XMPP Instant Messaging November 2002 References [1] Miller, J. and P. Saint-Andre, "XMPP Core (draft-miller-xmpp- core-02, work in progress)", November 2002. [2] Day, M., Aggarwal, S., Mohr, G. and J. Vincent, "A Model for Presence and Instant Messaging", RFC 2779, February 2000, . [3] Jabber Software Foundation, "Jabber Software Foundation", August 2001, . [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [5] World Wide Web Consortium, "Secure Hash Algorithm - Version 1.0", October 1997, . Authors' Addresses Jeremie Miller Jabber Software Foundation 1899 Wynkoop Street, Suite 600 Denver, CO 80202 US EMail: jeremie@jabber.org URI: http://www.jabber.org/people/jer.php Peter Saint-Andre Jabber Software Foundation 1899 Wynkoop Street, Suite 600 Denver, CO 80202 US EMail: stpeter@jabber.org URI: http://www.jabber.org/people/stpeter.php Miller & Saint-Andre Expires May 4, 2003 [Page 32] Internet-Draft XMPP Instant Messaging November 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Miller & Saint-Andre Expires May 4, 2003 [Page 33]