Network Working Group P. Saint-Andre Internet-Draft Jabber Software Foundation Expires: December 11, 2005 A. Houri IBM J. Hildebrand Jabber, Inc. June 9, 2005 Basic Messaging and Presence Interoperability between the Extensible Messaging and Presence Protocol (XMPP) and Session Initiation Protocol (SIP) Extensions for Instant Messaging and Presence (SIMPLE) draft-saintandre-xmpp-simple-03 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 December 11, 2005. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document defines a bi-directional protocol mapping for use by gateways that enable the exchange of presence information and single instant messages between systems that implement the Extensible Saint-Andre, et al. Expires December 11, 2005 [Page 1] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Messaging and Presence Protocol (XMPP) and those that implement the basic extensions to the Session Initiation Protocol (SIP) for instant messaging and presence. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Architectural Assumptions . . . . . . . . . . . . . . . . 3 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 6 3. Instant Messages . . . . . . . . . . . . . . . . . . . . . . . 7 3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 8 3.3 SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 9 4. Presence Subscriptions . . . . . . . . . . . . . . . . . . . . 11 4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2 XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 12 4.3 SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 14 5. Presence Notifications . . . . . . . . . . . . . . . . . . . . 16 5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.2 XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 17 5.3 SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 19 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 7. Security Considerations . . . . . . . . . . . . . . . . . . . 21 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 9.1 Normative References . . . . . . . . . . . . . . . . . . . 22 9.2 Informative References . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 24 Intellectual Property and Copyright Statements . . . . . . . . 25 Saint-Andre, et al. Expires December 11, 2005 [Page 2] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 1. Introduction In order to help ensure interoperability between instant messaging and presence systems that conform to the requirements of RFC 2779 [IMP-REQS], it is important to clearly define mappings between such protocols. Within the IETF, work has proceeded on two such protocols: o Various extensions to the Session Initiation Protocol ([SIP]) for instant messaging and presence, work on which has been formalized under the SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE) Working Group o The Extensible Messaging and Presence Protocol (XMPP), which consists of a formalization of the core XML streaming protocols developed originally by the Jabber open-source community One approach to helping ensure interoperability between such protocols is to map each protocol to the abstract semantics described in [CPIM] and [CPP]; that is the approach taken by [SIMPLE-CPIM] and [XMPP-CPIM]. Another approach is that taken by [DRAFT-UMPP]. The approach taken in this document is to directly map semantics from one protocol to another (i.e., from SIP/SIMPLE to XMPP and vice-versa), mainly for use by gateways between systems that implement one or the other of these protocols. The mappings specified in this document cover three areas that address basic instant messaging and presence functionality: o Mapping of addresses o Mapping of single instant messages o Mapping of presence subscriptions o Mapping of presence notifications Mapping of more advanced functionality (e.g., messaging sessions rather than single messages) is out of scope for this document; however, the authors will attempt to address such issues in future documents. 1.1 Architectural Assumptions This document assumes that the mapping between protocols will most likely occur by means of a gateway between an XMPP network and a SIP network being used for instant messaging and presence. Such a gateway is a dedicated translator between the XMPP and SIP/SIMPLE protocols. Although such a gateway could use the [CPIM] and [CPP] specifications to define the common formats into which the protocols are translated for purposes of interworking (as specified in [SIMPLE- CPIM] and [XMPP-CPIM]), this document assumes that a gateway will Saint-Andre, et al. Expires December 11, 2005 [Page 3] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 translate directly from one protocol to the other. Naturally, a gateway need not be a distinct entity on the network and may be co- resident with an XMPP server or a SIMPLE "server" (although there is no such thing as a SIMPLE server, we use the term here to refer to a SIP proxy, redirect, or registrar server that supports the SIP extensions for instant messaging and/or presence). Within this document, we refer to a gateway from an XMPP network to a SIP network being used for instant messaging and presence as an "XMPP-SIMPLE gateway" and we refer to a gateway from a SIP network being used for instant messaging and presence to an XMPP network as a "SIMPLE-XMPP gateway". 1.2 Terminology The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [TERMS]. 2. Addresses 2.1 Overview The address formats used to identify XMPP entities are different from those used to identify SIP entities. The XMPP address format is specified in [XMPP-CORE]; as specified in [XMPP-IM], instant messaging and presence applications of XMPP must also support 'im:' and 'pres:' URIs as specified in [CPIM] and [CPP] respectively, although such support may simply involve leaving resolution of such addresses up to an XMPP server. The SIP address format for instant messaging is specified in [SIP-IM]; it may use either 'sip:' or 'sips:' URIs as specified in [SIP] or an 'im:' URI as specified in [CPIM]. The SIP address format for presence is specified in [SIP- PRES]; it may use either 'sip:' or 'sips:' URIs as specified in [SIP] or a 'pres:' URI as specified in [CPP]. In this document we describe mappings for addresses of the form only, ignoring any protocol-specific extensions such as XMPP resource identifiers or SIP telephone numbers and passwords. In addition, we have ruled the mapping of domain names as out of scope for now since that is a matter for the Domain Name System; specifically, the issue for interworking between SIP and XMPP relates to the translation of fully internationalized domain names (which the SIP address format does not allow, but which the XMPP address format does allow via [IDNA]) into non-internationalized domain names. Therefore, in the following sections we discuss local-part addresses only (these are called variously "usernames", "instant inboxes", "presentities", and "node identifiers" in the protocols at issue). Saint-Andre, et al. Expires December 11, 2005 [Page 4] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 The sip:/sips:, im:/pres:, and XMPP address schemes allow different sets of characters. In some cases, characters allowed in one scheme are disallowed in others; these characters must be mapped appropriately in order to ensure interoperable communications across systems. The table below summarizes our findings regarding the complement of allowable US-ASCII characters in each addressing scheme when compared individually to the other schemes. Table 1: Partial complements of allowable US-ASCII characters +----------+----------+-----------+-------+ | | SIP/SIPS | IM/PRES | XMPP | +----------+----------+-----------+-------+ | SIP/SIPS | N/A | (),; | &'/ | +----------+----------+-----------+-------+ | IM/PRES | #%^`{|} | N/A | &'/ | +----------+----------+-----------+-------+ | XMPP | none | none | N/A | +----------+----------+-----------+-------+ Note: Each cell shows US-ASCII characters that are disallowed in the column protocol but allowed in the row protocol; e.g., the last cell of the second row shows that the characters &'/ are allowed in sip:/ sips: URIs but disallowed in XMPP addresses. The table below is another way of looking at the same issue, since it shows the intersection of allowable US-ASCII characters in each addressing scheme when compared individually to the other schemes. Table 2: Partial intersections of allowable US-ASCII characters +-------------------+------------------+----------------------+ | SIP/SIPS & XMPP | IM/PRES & XMPP | SIP/SIPS & IM/PRES | +-------------------+------------------+----------------------+ | a-z A-Z 0-9 | a-z A-Z 0-9 | a-z A-Z 0-9 | | !$()*+,-.;=?_~ | !#$%*+-.=?^_` | !$*+-.=?_~ | | %hexhex | {|}~ | | +-------------------+------------------+----------------------+ Therefore the following US-ASCII characters are allowed in all three addressing schemes (i.e., the intersection of all three sets of allowable characters): a-z A-Z 0-9 ! $ * + - . = ? In addition to the US-ASCII characters described above, many non-US- ASCII (specifically, UTF-8) characters are allowed in XMPP addresses but not allowed in sip:/sips: or im:/pres: URIs, since XMPP allows Saint-Andre, et al. Expires December 11, 2005 [Page 5] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 internationalized local-part addresses. A straightforward mapping of these characters to US-ASCII characters is provided in Section 2.2.5 of [URL-GUIDE], namely to encode unsafe octets using the %hexhex encoding. 2.2 XMPP to SIP The following is a high-level algorithm for mapping an XMPP address to a sip:, sips:, im:, or pres: URI: 1. Split XMPP address into node identifier (local-part; mapping described in remaining steps), domain identifier (hostname; mapping is out of scope), and resource identifier (specifier for particular device or connection; discard this for cross-system interoperability) 2. Apply Nodeprep profile of [STRINGPREP] (as specified in [XMPP- CORE]) for canonicalization (OPTIONAL) 3. Translate "\26" to &, "\27" to ', and "\2f" to / respectively (this is consistent with [JEP-0106]) 4. For each byte, if the byte is not in the set -A-Za-z0-9!$*.?_~+= then change to %hexhex 5. Combine resulting local-part with mapped hostname to form local@domain address 6. Prepend with 'im:' scheme (for XMPP stanzas) or 'pres:' scheme (for XMPP stanzas) if foreign domain supports these (discovered via [SRV] lookup as specified in [XMPP-IM]), else prepend with 'sip:' or 'sips:' scheme according to local service policy 2.3 SIP to XMPP The following is a high-level algorithm for mapping a sip:, sips:, im:, or pres: URI to an XMPP address: 1. Remove URI scheme 2. Split at the first '@' character into local-part and hostname (mapping the latter is out of scope) 3. Translate %hexhex to equivalent octets 4. Treat result as a UTF-8 string 5. Translate & to "\26", ' to "\27", and / to "\2f" respectively (this is consistent with [JEP-0106]) 6. Apply Nodeprep profile of [STRINGPREP] (as specified in [XMPP- CORE]) for canonicalization (OPTIONAL) 7. Recombine local-part with mapped hostname to form local@domain address Saint-Andre, et al. Expires December 11, 2005 [Page 6] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 3. Instant Messages 3.1 Overview Both XMPP and IM-aware SIP systems enable entities (often but not necessarily human users) to send "instant messages" to other entities. The term "instant message" usually refers to messages sent between two entities for delivery in close to real time (rather than messages that are stored and forwarded to the intended recipient upon request). Generally there are three kinds of instant message: o Single messages, which are sent from the sender to the recipient outside the context of any one-to-one chat session or multi-user text conference. o Chat messages, which are sent from the sender to the recipient in the context of a "messaging session" between the two entities. o Groupchat messages, which are sent from a sender to multiple recipients in the context of a text conference (along the lines of [IRC]). This document covers single messages only, since they form the "lowest common denominator" for instant messaging on the Internet. It is likely that future documents will address chat messages as well, especially once the SIMPLE WG completes its work on one-to-one messaging sessions (a likely candidate for finalization is [MSRP]). Instant messaging using XMPP message stanzas of type "normal" is specified in [XMPP-IM]. Instant messaging using SIP requests of type MESSAGE (often called "pager-model" messaging) is specified in [SIP-IM]. As described in [XMPP-IM], a single instant message is an XML stanza of type "normal" sent over an XML stream (since "normal" is the default for the 'type' attribute of the stanza, the attribute is often omitted). In this document we will assume that such a message is sent from an XMPP client to an XMPP server over an XML stream negotiated between the client and the server, and that the client is controlled by a human user (this is a simplifying assumption introduced for explanatory purposes only; the XMPP sender could be a bot-controlled client, a component such as a workflow application, a server, etc.). Continuing the tradition of Shakespeare examples in XMPP documentation, we will say that the XMPP user has an XMPP address of . As described in [SIP-IM], a single instant message is a SIP MESSAGE request sent from a SIP user agent to an intended recipient who is most generally referenced by an Instant Message URI of the form but who may be referenced by a SIP or SIPS URI of Saint-Andre, et al. Expires December 11, 2005 [Page 7] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 the form or Here again we introduce the simplifying assumption that the user agent is controlled by a human user, whom we shall dub . 3.2 XMPP to SIP When Juliet wants to send an instant message to Romeo, she interacts with her XMPP client, which generates an XMPP stanza. The syntax of the stanza, including required and optional elements and attributes, is defined in [XMPP-IM]. The following is an example of such a stanza: Example: XMPP user sends message: | | Art thou not Romeo, and a Montague? | Upon receiving such a stanza, the XMPP server to which Juliet has connected either delivers it to a local recipient (if the hostname in the 'to' attribute matches one of the hostnames serviced by the XMPP server) or attempts to route it to the foreign domain that services the hostname in the 'to' attribute. Naturally, in this document we assume that the hostname in the 'to' attribute is an IM-aware SIP service hosted by a separate server. As specified in [XMPP-IM], the XMPP server needs to determine the identity of the foreign domain, which it does by performing one or more [SRV] lookups. For message stanzas, the order of lookups recommended by [XMPP-IM] is to first try the "_xmpp-server" service as specified in [XMPP-CORE] and to then try the "_im" service as specified in [IMP-SRV]. Here we assume that the first lookup will fail but that the second lookup will succeed and return a resolution "_im._simple.example.net.", since we have already assumed that the example.net hostname is running a SIP instant messaging service. (Note: The XMPP server may have previously determined that the foreign domain is a SIMPLE server, in which case it would not need to perform the SRV lookups; the caching of such information is a matter of implementation and local service policy, and is therefore out of scope for this document.) Once the XMPP server has determined that the foreign domain is serviced by a SIMPLE server, it must determine how to proceed. We here assume that the XMPP server contains or has available to it an XMPP-SIMPLE gateway. The XMPP server would then deliver the message stanza to the XMPP-SIMPLE gateway. The XMPP-SIMPLE gateway is then responsible for translating the XMPP message stanza into a SIP MESSAGE request from the XMPP user to the Saint-Andre, et al. Expires December 11, 2005 [Page 8] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 SIP user: Example: XMPP user sends message (SIP transformation): | MESSAGE sip:romeo@example.net SIP/2.0 | Via: SIP/2.0/TCP julietpc.example.com;branch=z9hG4bK776sgdkse | Max-Forwards: 70 | From: sip:juliet@example.com;tag=49583 | To: sip:romeo@example.net | Call-ID: Hr0zny9l3@example.com | CSeq: 1 MESSAGE | Content-Type: text/plain | Content-Length: 37 | | Art thou not Romeo, and a Montague? The mapping of XMPP syntax elements to SIP syntax elements SHOULD be as shown in the following table. (Mappings for elements not mentioned are undefined.) Table 3: Message syntax mapping from XMPP to SIP +-----------------------------+--------------------------+ | XMPP Element or Attribute | SIP Header or Contents | +-----------------------------+--------------------------+ | | body of MESSAGE | | | Subject | | | (no mapping) | | from | From | | id | (no mapping) | | to | To | | type | (no mapping) | | xml:lang | Content-Language | +-----------------------------+--------------------------+ 3.3 SIP to XMPP When Romeo wants to send an instant message to Juliet, he interacts with his SIP user agent, which generates a SIP MESSAGE request. The syntax of the MESSAGE request is defined in [SIP-IM]. The following is an example of such a request: Saint-Andre, et al. Expires December 11, 2005 [Page 9] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Example: SIP user sends message: | MESSAGE sip:juliet@example.com SIP/2.0 | Via: SIP/2.0/TCP romeopc.example.com;branch=eskdgs677Kb4Ghz9 | Max-Forwards: 70 | From: sip:romeo@example.net;tag=38594 | To: sip:juliet@example.com | Call-ID: M4spr4vdu@example.net | CSeq: 1 MESSAGE | Content-Type: text/plain | Content-Length: 26 | | Neither, fair saint, if either thee dislike. Section 5 of [SIP-IM] stipulates that a SIP User Agent presented with an im: URI should resolve it to a sip: or sips: URI. Therefore we assume that the To header of a request received by a SIMPLE-XMPP gateway will contain a sip: or sips: URI. The gateway SHOULD resolve that address to an im: URI for SIP MESSAGE requests, then follow the rules in [IMP-SRV] regarding the "_im" SRV service for the target domain contained in the To header. If SRV address resolution fails for the "_im" service, the gateway MAY attempt a lookup for the "_xmpp-server" service as specified in [XMPP-CORE] or MAY return an error to the sender (the SIP "502 Bad Gateway" error seems most appropriate). If SRV address resolution succeeds, the gateway is responsible for translating the request into an XMPP message stanza from the SIP user to the XMPP user and returning a SIP "200 OK" message to the sender: Example: SIP user sends message (XMPP transformation): | | Neither, fair saint, if either thee dislike. | The mapping of SIP syntax elements to XMPP syntax elements SHOULD be as shown in the following table. (Mappings for elements not mentioned in the foregoing table are undefined.) Saint-Andre, et al. Expires December 11, 2005 [Page 10] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Table 4: Message syntax mapping from SIP to XMPP +--------------------------+-----------------------------+ | SIP Header or Contents | XMPP Element or Attribute | +--------------------------+-----------------------------+ | Call-ID | (no mapping) | | Content-Language | xml:lang | | CSeq | id (OPTIONAL) | | From | from | | Subject | | | To | to | | body of MESSAGE | | +--------------------------+-----------------------------+ Note: When transforming SIP pager-model messages, a SIMPLE-XMPP gateway SHOULD specify no XMPP 'type' attribute or a 'type' attribute whose value is "normal". 4. Presence Subscriptions 4.1 Overview Both XMPP and presence-aware SIP systems enable entities (often but not necessarily human users) to subscribe to the presence of other entities. XMPP presence subscriptions are specified in [XMPP-IM]. Presence subscriptions using a SIP event package for presence are specified in [SIP-PRES]. As described in [XMPP-IM], XMPP presence subscriptions are managed using XMPP presence stanzas of type "subscribe", "subscribed", "unsubscribe", and "unsubscribed". The main subscription states are "none" (neither the user nor the contact is subscribed to the other's presence information), "from" (the user has a subscription from the contact), "to" (the user has a subscription to the contact's presence information), and "both" (both user and contact are subscribed to each other's presence information). As described in [SIP-PRES], SIP presence subscriptions are managed through the use of SIP SUBSCRIBE events sent from a SIP user agent to an intended recipient who is most generally referenced by an Instant Message URI of the form but who may be referenced by a SIP or SIPS URI of the form or . The subscription models underlying XMPP and SIP are quite different. For instance, XMPP presence subscriptions are long-lived (indeed permanent if not explicitly cancelled), whereas SIP presence subscriptions are short-lived (the default time to live of a SIP Saint-Andre, et al. Expires December 11, 2005 [Page 11] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 presence subscription is 3600 seconds, as specified in Section 6.4 of [SIP-PRES]). These differences are addressed below. 4.2 XMPP to SIP An XMPP user initiates a subscription by sending a subscription request to another entity (conventionally called a "contact"), which request the contact either accepts or declines. If the contact accepts the request, the user will have a subscription to the contact's presence information until (1) the user unsubscribes or (2) the contact cancels the subscription. The subscription request is encapsulated in a presence stanza of type "subscribe": Example: XMPP user subscribes to SIP contact: | Upon receiving such a stanza, the XMPP server to which Juliet has connected needs to determine the identity of the foreign domain, which it does by performing one or more [SRV] lookups. For presence stanzas, the order of lookups recommended by [XMPP-IM] is to first try the "_xmpp-server" service as specified in [XMPP-CORE] and to then try the "_pres" service as specified in [IMP-SRV]. Here we assume that the first lookup will fail but that the second lookup will succeed and return a resolution "_pres._simple.example.net.", since we have already assumed that the example.net hostname is running a SIP presence service. Once the XMPP server has determined that the foreign domain is serviced by a SIMPLE server, it must determine how to proceed. We here assume that the XMPP server contains or has available to it an XMPP-SIMPLE gateway. The XMPP server would then deliver the presence stanza to the XMPP-SIMPLE gateway. The XMPP-SIMPLE gateway is then responsible for translating the XMPP subscription request into a SIP SUBSCRIBE request from the XMPP user to the SIP user: Saint-Andre, et al. Expires December 11, 2005 [Page 12] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Example: XMPP user subscribes to SIP contact (SIP transformation): | SUBSCRIBE sip:romeo@example.net SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=ffd2 | To: | Call-ID: 1h4t3s1p@example.com | Event: presence | Max-Forwards: 70 | CSeq: 123 SUBSCRIBE | Contact: | Accept: application/pidf+xml | Expires: 3600 | Content-Length: 0 The SIP user then SHOULD send a response indicating acceptance of the subscription request: Example: SIP accepts subscription request: | SIP/2.0 200 OK | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: | To: ;tag=ffd2 | Call-ID: 1h4t3s1p@example.com | CSeq: 123 SUBSCRIBE | Contact: | Expires: 3600 | Content-Length: 0 The XMPP-SIMPLE gateway SHOULD transform the 200 OK into a presence stanza of type "subscribed": Example: XMPP user receives acknowledgement from SIP contact: | The SIP user also SHOULD immediately send a presence notification to the XMPP user (see Section 5). Note: It is the responsibility of the XMPP-SIMPLE gateway to set the value of the Expires header and to renew the subscription accordingly so that the subscription appears to be permanent to the XMPP user. At any time after subscribing, the XMPP user may unsubscribe from the contact's presence. This is done by sending a presence stanza of Saint-Andre, et al. Expires December 11, 2005 [Page 13] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 type "unsubscribe": Example: XMPP user unsubscribes from SIP contact: | The XMPP-SIMPLE gateway is responsible for translating the unsubscribe command into a SIP SUBSCRIBE request with the Expires header set to a value of zero: Example: XMPP user unsubscribes from SIP contact (SIP transformation): | SUBSCRIBE sip:romeo@example.net SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=ffd2 | To: ;tag=xfg9 | Call-ID: 1ckm32@example.com | Event: presence | Max-Forwards: 70 | CSeq: 789 SUBSCRIBE | Contact: | Accept: application/pidf+xml | Expires: 0 | Content-Length: 0 Upon sending the transformed unsubscribe, the XMPP-SIMPLE gateway SHOULD a presence stanza of type "unsubscribed" to the XMPP user: Example: XMPP user receives unsubscribed notification: | 4.3 SIP to XMPP A SIP user initiates a subscription to a contact's presence information by sending a SIP SUBSCRIBE request to the contact. The following is an example of such a request: Saint-Andre, et al. Expires December 11, 2005 [Page 14] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Example: SIP user subscribes to XMPP contact: | SUBSCRIBE sip:juliet@example.com SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=ffd2 | To: ;tag=xfg9 | Call-ID: 4wcm0n@example.net | Event: presence | Max-Forwards: 70 | CSeq: 263 SUBSCRIBE | Contact: | Accept: application/pidf+xml | Content-Length: 0 Upon receiving such a request, a SIMPLE-XMPP gateway is responsible for translating it into an XMPP subscription request from the SIP user to the XMPP user: Example: SIP user subscribes to XMPP contact (XMPP transformation): | Notice that the Expires header was not included in the SUBSCRIBE request; this means that the default value of 3600 (i.e., 3600 seconds = 1 hour) applies. It is the responsibility of the SIMPLE-XMPP gateway to properly handle the difference between short-lived SIP presence subscriptions and long-lived XMPP presence subscriptions. The gateway has two options when the SIP user's subscription expires: o Send an XMPP presence stanza of type "unsubscribe" to the XMPP contact; this honors the SIP semantic but will seem rather odd to the XMPP contact. o Send a SIP NOTIFY request to the SIP user containing a PIDF document specifying that the XMPP contact now has a basic status of closed; this violates the letter of the SIP semantic but will seem more natural to the XMPP contact. Which of these the SIMPLE-XMPP gateway chooses is up to the implementation. At any time, the SIP user may cancel the subscription by sending a SUBSCRIBE request whose Expires header is set to a value of zero: Saint-Andre, et al. Expires December 11, 2005 [Page 15] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Example: SIP user cancels subscription: | SUBSCRIBE sip:juliet@example.com SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=ffd2 | To: ;tag=xfg9 | Call-ID: 1tsn1ce@example.net | Event: presence | Max-Forwards: 70 | CSeq: 987 SUBSCRIBE | Contact: | Expires: 0 | Accept: application/pidf+xml | Content-Length: 0 Upon receiving such a request, a SIMPLE-XMPP gateway is responsible for translating it into an XMPP presence stanza of type "unsubscribe" from the SIP user to the XMPP user: Example: SIP user cancels subscription (XMPP transformation): | 5. Presence Notifications 5.1 Overview Both XMPP and presence-aware SIP systems enable entities (often but not necessarily human users) to send presence notifications to other entities. At a minimum, the term "presence" refers to information about an entity's availability for communication on a network (on/ off), often supplemented by information that further specifies the entity's communications context (e.g., "do not disturb"). Some systems and protocols extend this notion even further and refer to any relatively ephemeral information about an entity as a kind of presence; categories of such "extended presence" include geographical location (e.g., GPS coordinates), user mood (e.g., grumpy), user activity (e.g., walking), and ambient environment (e.g., noisy). In this document, we focus on the "least common denominator" of network availability only, although future documents may address broader notions of presence, including "extended presence". Presence using XMPP presence stanzas of type "available" or "unavailable" is specified in [XMPP-IM]. SIP presence using a SIP event package for presence is specified in [SIP-PRES]. Saint-Andre, et al. Expires December 11, 2005 [Page 16] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 As described in [XMPP-IM], presence information about an entity is communicated by means of an XML stanza sent over an XML stream. In this document we will assume that such a presence stanza is sent from an XMPP client to an XMPP server over an XML stream negotiated between the client and the server, and that the client is controlled by a human user (again, this is a simplifying assumption introduced for explanatory purposes only). In general, XMPP presence is sent by the user to the user's server and then broadcasted to all entities who are subscribed to the user's presence information. As described in [SIP-PRES], presence information about an entity is communicated by means of a SIP NOTIFY event sent from a SIP user agent to an intended recipient who is most generally referenced by an Instant Message URI of the form but who may be referenced by a SIP or SIPS URI of the form or . Here again we introduce the simplifying assumption that the user agent is controlled by a human user. 5.2 XMPP to SIP When Juliet interacts with her XMPP client to modify her presence information (or when her client automatically updates her presence information, e.g. via an "auto-away" feature), her client generates an XMPP stanza. The syntax of the stanza, including required and optional elements and attributes, is defined in [XMPP-IM]. The following is an example of such a stanza: Example: XMPP user sends presence notification: | Upon receiving such a stanza, the XMPP server to which Juliet has connected broadcasts it to all subscribers who are authorized to receive presence notifications from Juliet. For each subscriber, broadcasting the presence notification involves either delivering it to a local recipient (if the hostname in the subscriber's address matches one of the hostnames serviced by the XMPP server) or attempting to route it to the foreign domain that services the hostname in the subscriber's address. Naturally, in this document we assume that the hostname is a SIP presence service hosted by a separate server. As specified in [XMPP-IM], the XMPP server needs to determine the identity of the foreign domain, which it does by performing one or more [SRV] lookups. For presence stanzas, the order of lookups recommended by [XMPP-IM] is to first try the "_xmpp- server" service as specified in [XMPP-CORE] and to then try the "_pres" service as specified in [IMP-SRV]. Here we assume that the first lookup will fail but that the second lookup will succeed and return a resolution "_pres._simple.example.net.", since we have Saint-Andre, et al. Expires December 11, 2005 [Page 17] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 already assumed that the example.net hostname is running a SIP presence service. (Note: The XMPP server may have previously determined that the foreign domain is a SIMPLE server, in which case it would not need to perform the SRV lookups; the caching of such information is a matter of implementation and local service policy, and is therefore out of scope for this document.) Once the XMPP server has determined that the foreign domain is serviced by a SIMPLE server, it must determine how to proceed. We here assume that the XMPP server contains or has available to it an XMPP-SIMPLE gateway. The XMPP server would then deliver the presence stanza to the XMPP-SIMPLE gateway. The XMPP-SIMPLE gateway is then responsible for translating the XMPP presence stanza into a SIP NOTIFY request and included PIDF document from the XMPP user to the SIP user: Example: XMPP user sends presence notification (SIP transformation): | NOTIFY sip:192.0.2.2 SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=ffd2 | To: ;tag=xfg9 | Call-ID: j4s0h4vny@example.com | Event: presence | Subscription-State: active;expires=599 | Max-Forwards: 70 | CSeq: 157 NOTIFY | Contact: | Content-Type: application/pidf+xml | Content-Length: 192 | | | | | | open | | | The mapping of XMPP syntax elements to SIP syntax elements SHOULD be as shown in the following table. (Mappings for elements not mentioned are undefined.) Saint-Andre, et al. Expires December 11, 2005 [Page 18] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Table 5: Presence syntax mapping from XMPP to SIP +-----------------------------+---------------------------+ | XMPP Element or Attribute | SIP Header or PIDF Data | +-----------------------------+---------------------------+ | stanza | "Event: presence" [1] | | from | From | | id | (no mapping) | | to | To | | type | basic status [2] | | xml:lang | Content-Language | | | PIDF priority for tuple | | | (no mapping) | | | note [3] | +-----------------------------+---------------------------+ Note the following regarding these mappings: 1. Only a presence stanza which lacks a 'type' attribute or whose 'type' attribute has a value of "unavailable" should be mapped by an XMPP-SIMPLE gateway to a SIP NOTIFY request, since those are the only presence stanzas that represent notifications. 2. Because the lack of a 'type' attribute indicates that an XMPP entity is available for communications, the gateway SHOULD map that information to a PIDF status of "open". Because a 'type' attribute with a value of "unavailable" indicates that an XMPP entity is not available for communications, the gateway SHOULD map that information to a PIDF status of "closed". 3. The character data of the XMPP element MAY be mapped to the character data of the PIDF element. 5.3 SIP to XMPP When Romeo changes his presence, his SIP user agent generates a SIP NOTIFY request. The syntax of the NOTIFY request is defined in [SIP- PRES]. The following is an example of such a request: Saint-Andre, et al. Expires December 11, 2005 [Page 19] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Example: SIP user sends presence notification: | NOTIFY sip:192.0.2.1 SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=ffd2 | To: ;tag=xfg9 | Call-ID: j0sj4sv1m@example.net | Event: presence | Subscription-State: active;expires=499 | Max-Forwards: 70 | CSeq: 8775 NOTIFY | Contact: | Content-Type: application/pidf+xml | Content-Length: 193 | | | | | | closed | | | Upon receiving such a request, a SIMPLE-XMPP gateway is responsible for translating it into an XMPP presence stanza from the SIP user to the XMPP user: Example: SIP user sends presence notification (XMPP transformation): | The mapping of SIP syntax elements to XMPP syntax elements SHOULD be as shown in the following table. (Mappings for elements not mentioned are undefined.) Saint-Andre, et al. Expires December 11, 2005 [Page 20] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Table 6: Presence syntax mapping from SIP to XMPP +---------------------------+-----------------------------+ | SIP Header or PIDF Data | XMPP Element or Attribute | +---------------------------+-----------------------------+ | basic status | type [1] | | Content-Language | xml:lang | | CSeq | id (OPTIONAL) | | From | from | | priority for tuple | | | To | to | | body of MESSAGE | | +---------------------------+-----------------------------+ Note the following regarding these mappings: 1. A PIDF basic status of "open" SHOULD be mapped to no 'type' attribute, and a PIDF basic status of "closed" SHOULD be mapped to a 'type' attribute whose value is "unavailable". 6. IANA Considerations This document requires no action on the part of the IANA. 7. Security Considerations Detailed security considerations for instant messaging and presence protocols are given in [IMP-REQS], specifically in Sections 5.1 through 5.4. Detailed security considerations for XMPP are given in XMPP Core [XMPP-CORE]. Detailed security considerations for SIP- based messaging are given in [SIP-IM] and for SIP-based presence are given in [SIP-PRES] (see also the security considerations for the Session Initiation Protocol given in [SIP]). This document specifies methods for exchanging instant messages and presence information through a gateway that translates between SIP and XMPP. Such a gateway MUST be compliant with the minimum security requirements of the instant messaging and presence protocols for which it translates (i.e., SIP and XMPP). The introduction of gateways to the security model of instant messaging and presence specified in [IMP-REQS] introduces some new risks. In particular, end-to-end security properties (especially confidentiality and integrity) between instant messaging and presence user agents that interface through a SIMPLE-XMPP gateway can be provided only if common formats are supported. Specification of those common formats is out of scope for this document, although it is recommended to use [MSGFMT] for instant messages and [PIDF] for presence. Saint-Andre, et al. Expires December 11, 2005 [Page 21] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 [IMP-REQS] requires that conformant technologies shall include methods for blocking communications from unwanted addresses. Such blocking is the responsibility of conformant technology (e.g., XMPP or SIP) and is out of scope for this memo. 8. Acknowledgements The authors wish to thank Nathaniel Borenstein and Rohan Mahy for suggestions and encouragement, Daniel-Constantin Mierla for earlier work on SIMPLE-XMPP interworking, and Sandeep Sharma for feedback based on implementation experience. 9. References 9.1 Normative References [IMP-SRV] Peterson, J., "Address Resolution for Instant Messaging and Presence", RFC 3861, August 2004. [PIDF] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, "Presence Information Data Format (PIDF)", RFC 3863, August 2004. [SIP] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [SIP-IM] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C., and D. Gurle, "Session Initiation Protocol (SIP) Extension for Instant Messaging", RFC 3428, December 2002. [SIP-PRES] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", RFC 3856, August 2004. [SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ("STRINGPREP")", RFC 3454, December 2002. [TERMS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Saint-Andre, et al. Expires December 11, 2005 [Page 22] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 [URL-GUIDE] Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke, "Guidelines for new URL Schemes", RFC 2718, November 1999. [XMPP-CORE] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 3920, October 2004. [XMPP-IM] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence", RFC 3921, October 2004. 9.2 Informative References [CPIM] Peterson, J., "Common Profile for Instant Messaging (CPIM)", RFC 3860, August 2004. [CPP] Peterson, J., "Common Profile for Presence (CPP)", RFC 3859, August 2004. [DRAFT-UMPP] Mahy, R., "A Unified Proposal for Server-to-Server Presence and Instant Messaging", draft-mahy-impp-unified-proposal-00 (work in progress), February 2004. [IDNA] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003. [IMP-MODEL] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [IMP-REQS] Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000. [IRC] Oikarinen, J. and D. Reed, "Internet Relay Chat Protocol", RFC 1459, May 1993. [JEP-0106] Saint-Andre, P. and J. Hildebrand, "JID Escaping", JSF JEP 0106, May 2005. [MSGFMT] Klyne, G. and D. Atkins, "Common Presence and Instant Messaging (CPIM): Message Format", RFC 3862, August 2004. Saint-Andre, et al. Expires December 11, 2005 [Page 23] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 [MSRP] Campbell, B., Mahy, R., and C. Jennings, "The Message Session Relay Protocol", draft-ietf-simple-message-sessions-10 (work in progress), February 2005. [SIMPLE-CPIM] Rosenberg, J. and B. Campbell, "CPIM Mapping of SIMPLE Presence and Instant Messaging", draft-ietf-simple-cpim-mapping-01 (work in progress), June 2002. [XMPP-CPIM] Saint-Andre, P., "Mapping the Extensible Messaging and Presence Protocol (XMPP) to Common Presence and Instant Messaging (CPIM)", RFC 3922, October 2004. Authors' Addresses Peter Saint-Andre Jabber Software Foundation Avshalom Houri IBM Joe Hildebrand Jabber, Inc. Saint-Andre, et al. Expires December 11, 2005 [Page 24] Internet-Draft Basic XMPP-SIMPLE Interop June 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Saint-Andre, et al. Expires December 11, 2005 [Page 25]