Network Working Group P. Saint-Andre Internet-Draft Cisco Intended status: Informational A. Houri Expires: September 9, 2009 IBM J. Hildebrand Cisco March 8, 2009 Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): Presence draft-saintandre-sip-xmpp-presence-02 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. 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The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 9, 2009. Copyright Notice Saint-Andre, et al. Expires September 9, 2009 [Page 1] Internet-Draft SIP-XMPP Interworking: Presence March 2009 Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document defines a bi-directional protocol mapping for the exchange of presence information between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP). Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Presence Subscriptions . . . . . . . . . . . . . . . . . . . . 3 2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 4 2.3. SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 8 3. Presence Notifications . . . . . . . . . . . . . . . . . . . . 11 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.2. XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 12 3.3. SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 14 4. Content Types . . . . . . . . . . . . . . . . . . . . . . . . 16 5. Security Considerations . . . . . . . . . . . . . . . . . . . 17 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.1. Normative References . . . . . . . . . . . . . . . . . . . 18 6.2. Informative References . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 Saint-Andre, et al. Expires September 9, 2009 [Page 2] Internet-Draft SIP-XMPP Interworking: Presence March 2009 1. Introduction In order to help ensure interworking between presence systems that conform to the requirements of RFC 2779 [IMP-REQS], it is important to clearly define protocol mappings between such systems. Within the IETF, work has proceeded on two presence technologies: o Various extensions to the Session Initiation Protocol ([SIP]) for instant messaging, as developed within the SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE) Working Group; the relevant specification for presence is [SIP-PRES] 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; the relevant specifications are [XMPP] for the XML streaming layer and [XMPP-IM] for basic presence and instant messaging extensions One approach to helping ensure interworking between these protocols is to map each protocol to the abstract semantics described in [CPIM]; that is the approach taken by [SIMPLE-CPIM] and [XMPP-CPIM]. 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). The architectural assumptions underlying such direct mappings are provided in [SIP-XMPP], including mapping of addresses and error condisions. The mappings specified in this document cover basic presence functionality. Mapping of more advanced functionality is out of scope for this document, but other documents in this "series" cover such topics. Note: 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. Presence Subscriptions 2.1. 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 Saint-Andre, et al. Expires September 9, 2009 [Page 3] Internet-Draft SIP-XMPP Interworking: Presence March 2009 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 presence subscription is 3600 seconds, as specified in Section 6.4 of [SIP-PRES]). These differences are addressed below. 2.2. XMPP to SIP 2.2.1. Establishing 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] 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 September 9, 2009 [Page 4] Internet-Draft SIP-XMPP Interworking: Presence March 2009 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: Example: XMPP user subscribes to SIP contact (SIP transformation): | SUBSCRIBE sip:romeo@example.net SIP/2.0 | Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk | From: ;tag=ffd2 | To: | Call-ID: l04th3s1p@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 s2x.example.net;branch=z9hG4bKna998sk | From: ;tag=ffd2 | To: ;tag=j89d | Call-ID: l04th3s1p@example.com | CSeq: 234 SUBSCRIBE | Contact: | Expires: 3600 | Content-Length: 0 In accordance with [SIP-EVENT], the XMPP-SIMPLE gateway should consider the subscription state to be "neutral" until it receives a NOTIFY message. Therefore the SIP user or SIP-XMPP gateway at the SIP user's domain SHOULD immediately send a NOTIFY message containing a "Subscription-State" header whose value contains the string Saint-Andre, et al. Expires September 9, 2009 [Page 5] Internet-Draft SIP-XMPP Interworking: Presence March 2009 "active" (see Section 3). 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=yt66 | To: ;tag=bi54 | Call-ID: l04th3s1p@example.com | Event: presence | Subscription-State: active;expires=499 | Max-Forwards: 70 | CSeq: 8775 NOTIFY | Contact: | Content-Type: application/pidf+xml | Content-Length: 193 | | | | | | open | | | Upon receiving the first NOTIFY with a subscription state of active, the XMPP-SIMPLE gateway MUST generate a presence stanza of type "subscribed": Example: XMPP user receives acknowledgement from SIP contact: | As described under Section 3, the gateway MUST also generate a presence notification to the XMPP user: Example: XMPP user receives presence notification from SIP contact: | Saint-Andre, et al. Expires September 9, 2009 [Page 6] Internet-Draft SIP-XMPP Interworking: Presence March 2009 2.2.2. Refreshing It is the responsibility of the XMPP-SIMPLE gateway to set the value of the "Expires" header and to periodically renew the subscription on the SIMPLE side of the gateway so that the subscription appears to be permanent to the XMPP user (e.g., the XMPP-SIMPLE gateway SHOULD send a new SUBSCRIBE request to the SIP user whenever the XMPP user sends initial presence to its XMPP server, i.e., upon initiating a presence session with the XMPP server). See the Security Considerations (Section 5) of this document for important information and requirements regarding the security implications of this functionality. 2.2.3. Cancelling At any time after subscribing, the XMPP user may unsubscribe from the contact's presence. This is done by sending a presence stanza of 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 s2x.example.net;branch=z9hG4bKna998sk | From: ;tag=j89d | 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: Saint-Andre, et al. Expires September 9, 2009 [Page 7] Internet-Draft SIP-XMPP Interworking: Presence March 2009 Example: XMPP user receives unsubscribed notification: | 2.3. SIP to XMPP 2.3.1. Establishing 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: Example: SIP user subscribes to XMPP contact: | SUBSCRIBE sip:juliet@example.com SIP/2.0 | Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk | From: ;tag=xfg9 | To: ;tag=ur93 | Call-ID: 4wcm0n@example.net | Event: presence | Max-Forwards: 70 | CSeq: 263 SUBSCRIBE | Contact: | Accept: application/pidf+xml | Content-Length: 0 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. 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): | In accordance with [XMPP-IM], the XMPP user's server MUST deliver the presence subscription request to the XMPP user (or, if a subscription already exists in the XMPP user's roster, discard the subscribe request). If the XMPP user approves the subscription request, the XMPP server then MUST return a presence stanza of type "subscribed" from the XMPP user to the SIP user; if a subscription already exists, Saint-Andre, et al. Expires September 9, 2009 [Page 8] Internet-Draft SIP-XMPP Interworking: Presence March 2009 the XMPP server SHOULD auto-reply with a presence stanza of type "subscribed". In any case, if the SIMPLE-XMPP gateway receives a presence stanza of type "subscribed" from the XMPP user, it SHOULD silently discard the stanza. 2.3.2. Refreshing 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 Cancel the subscription (i.e., treat it as temporary) and 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 Maintain the subscription (i.e., treat it as long-lived) and (1) 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", including a Subscription-State of "terminated" and (2) send an XMPP presence stanza of type "unavailable" to the XMPP contact; this violates the letter of the SIP semantic but will seem more natural to the XMPP contact. Which of these options the SIMPLE-XMPP gateway chooses is up to the implementation. If the implementation chooses the first option, the protocol generated would be as follows: Example: SIP subscription expires (treated as temporary by gateway): | If the implementation chooses the second option, the protocol generated would be as follows: Saint-Andre, et al. Expires September 9, 2009 [Page 9] Internet-Draft SIP-XMPP Interworking: Presence March 2009 Example: SIP subscription expires (treated as long-lived by gateway): | NOTIFY sip:192.0.2.2 SIP/2.0 | Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk | From: ;tag=ur93 | To: ;tag=pq72 | Call-ID: j4s0h4vny@example.com | Event: presence | Subscription-State: terminated;reason=timeout | Max-Forwards: 70 | CSeq: 232 NOTIFY | Contact: | Content-Type: application/pidf+xml | Content-Length: 194 | | | | | | closed | | | Example: SIP subscription expires (treated as long-lived by gateway): | 2.3.3. Cancelling At any time, the SIP user may cancel the subscription by sending a SUBSCRIBE message whose "Expires" header is set to a value of zero ("0"): Saint-Andre, et al. Expires September 9, 2009 [Page 10] Internet-Draft SIP-XMPP Interworking: Presence March 2009 Example: SIP user cancels subscription: | SUBSCRIBE sip:192.0.2.1 SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=yt66 | To: ;tag=bi54 | Call-ID: 1tsn1ce@example.net | Event: presence | Max-Forwards: 70 | CSeq: 8775 SUBSCRIBE | Contact: | Expires: 0 | Content-Length: 0 As above, upon receiving such a request, a SIMPLE-XMPP gateway is responsible for doing one of the following: o Cancel the subscription (i.e., treat it as temporary) and send an XMPP presence stanza of type "unsubscribe" to the XMPP contact. o Maintain the subscription (i.e., treat it as long-lived) and (1) 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", (2) send a SIP SUBSCRIBE request to the SIP user with an "Expires" header set to a value of "0" (zero) when it receives XMPP presence of type "unavailable" from the XMPP contact, and (3) send an XMPP presence stanza of type "unavailable" to the XMPP contact. 3. Presence Notifications 3.1. 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. Saint-Andre, et al. Expires September 9, 2009 [Page 11] Internet-Draft SIP-XMPP Interworking: Presence March 2009 [XMPP-IM] defines how XMPP presence stanzas can indicate availability (via absence of a 'type' attribute) or lack of availability (via a 'type' attribute with a value of "unavailable"). SIP presence using a SIP event package for presence is specified in [SIP-PRES]. 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. 3.2. 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 (this is similar to the SIP NOTIFY method). 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] Saint-Andre, et al. Expires September 9, 2009 [Page 12] Internet-Draft SIP-XMPP Interworking: Presence March 2009 lookups. For presence stanzas, the order of lookups recommended by [XMPP-IM] is to first try the "_xmpp-server" service as specified in [XMPP] 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. (Note: The XMPP server may have previously determined that the foreign domain is a SIMPLE server, e.g., when it sent a SIP SUBSCRIBE to the SIP user when Juliet sent initial presence to the XMPP 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 x2s.example.com;branch=z9hG4bKna998sk | From: ;tag=gh19 | To: ;tag=yt66 | 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 | | | Saint-Andre, et al. Expires September 9, 2009 [Page 13] Internet-Draft SIP-XMPP Interworking: Presence March 2009 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 6: Presence syntax mapping from XMPP to SIP +-----------------------------+---------------------------+ | XMPP Element or Attribute | SIP Header or PIDF Data | +-----------------------------+---------------------------+ | stanza | "Event: presence" [1] | | XMPP resource identifer | tuple 'id' attribute | | from | From | | id | Call-ID | | to | To | | type | basic status [2][3] | | xml:lang | Content-Language | | | PIDF priority for tuple | | | (no mapping) | | | note [4] | +-----------------------------+---------------------------+ Note the following regarding these mappings: 1. Only a presence stanza that 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. When the XMPP-SIMPLE gateway receives XMPP presence of type "unavailable" from the XMPP contact, it SHOULD (1) 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" and (2) send a SIP SUBSCRIBE request to the SIP user with an "Expires" header set to a value of "0" (zero). 4. The character data of the XMPP element MAY be mapped to the character data of the PIDF element. 3.3. SIP to XMPP When Romeo changes his presence, his SIP user agent generates a SIP NOTIFY request for any active subscriptions. The syntax of the NOTIFY request is defined in [SIP-PRES]. The following is an example Saint-Andre, et al. Expires September 9, 2009 [Page 14] Internet-Draft SIP-XMPP Interworking: Presence March 2009 of such a request: 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=yt66 | To: ;tag=bi54 | 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 September 9, 2009 [Page 15] Internet-Draft SIP-XMPP Interworking: Presence March 2009 Table 7: 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". 4. Content Types SIP requests of type NOTIFY normally contain presence information encapsulated using the "application/pidf+xml" content type. The recommended procedures for SIMPLE-to-XMPP gateways to use in handling these content types are as follows. The "application/pidf+xml' content type is specified in [PIDF]. The Presence Information Data Format defines a common data format for presence protocols that conform to the Common Profile for Presence ([CPP]), enabling presence information to be transferred across CPP- compliant protocol boundaries without modification, with attendant benefits for end-to-end encryption and performance. Because the syntax for the "application/pidf+xml" content type is Extensible Markup Language ([XML]), it is straightforward to send PIDF data over the Extensible Messaging and Presence Protocol ([XMPP]), since XMPP is simply an XML streaming protocol. In addition to following the syntax mappings specified in Section 3, a SIMPLE-to-XMPP gateway MAY encapsulate PIDF data within an "extended namespace" contained in an XMPP presence stanza. The RECOMMENDED method is to include the PIDF element as a child of the XMPP stanza. Although it may appear that this would be potentially confusing, the inclusion of the 'urn:ietf:params:xml:ns:pidf' namespace ensures that PIDF data is kept separate from XMPP presence data (in accordance with [XML-NAMES]). The following is a simple example of encapsulating Saint-Andre, et al. Expires September 9, 2009 [Page 16] Internet-Draft SIP-XMPP Interworking: Presence March 2009 PIDF data within an "extended namespace" in XMPP: A basic example of PIDF over XMPP: Wooing Juliet open Wooing Juliet 5. Security Considerations Detailed security considerations for presence protocols are given in [IMP-REQS], for SIP-based presence in [SIP-PRES] (see also [SIP]), and for XMPP-based presence in [XMPP-IM] (see also [XMPP]). The mismatch between long-lived XMPP presence subscriptions and short-lived SIP presence subscriptions introduces the possibility of an amplification attack launched from the XMPP network against a SIP presence server. To help prevent such an attack, access to an XMPP- SIMPLE gateway that is hosted on the XMPP network SHOULD be restricted to XMPP users associated with a single domain or trust realm (e.g., a gateway hosted at simple.example.com should allow only users within the example.com domain to access the gateway, not users within example.org, example.net, or any other domain); if a SIP presence server receives communications through an XMPP-SIMPLE gateway from users who are not associated with a domain that is so related to the hostname of the gateway, it MAY (based on local service provisioning) refuse to service such users or refuse to communicate with the gateway. Furthermore, whenever an XMPP-SIMPLE gateway seeks to refresh an XMPP user's long-lived subscription to a SIP user's presence, it MUST first send an XMPP stanza of type "probe" from the address of the gateway to the "bare JID" (user@domain.tld) of the XMPP user, to which the user's XMPP server MUST respond in accordance with [XMPP-IM]; however, the administrator of an XMPP-SIMPLE gateway MAY (based on local service provisioning) exempt "known good" XMPP servers from this check (e.g., the XMPP server associated with the XMPP-SIMPLE gateway as described above). Saint-Andre, et al. Expires September 9, 2009 [Page 17] Internet-Draft SIP-XMPP Interworking: Presence March 2009 6. References 6.1. 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-EVENT] Roach, A., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [SIP-PRES] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", RFC 3856, August 2004. [SIP-XMPP] Saint-Andre, P., Houri, A., and J. Hildebrand, "Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): Core", draft-saintandre-sip-xmpp-core-01 (work in progress), March 2009. [SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [TERMS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [XML] Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F., and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth Edition)", World Wide Web Consortium Recommendation REC- xml-20060816, August 2006, . [XML-NAMES] Bray, T., Hollander, D., and A. Layman, "Namespaces in XML", W3C REC-xml-names, January 1999, . Saint-Andre, et al. Expires September 9, 2009 [Page 18] Internet-Draft SIP-XMPP Interworking: Presence March 2009 [XMPP] 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. 6.2. 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. [IMP-REQS] Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000. [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 Cisco Email: psaintan@cisco.com Avshalom Houri IBM Building 18/D, Kiryat Weizmann Science Park Rehovot 76123 Israel Email: avshalom@il.ibm.com Saint-Andre, et al. Expires September 9, 2009 [Page 19] Internet-Draft SIP-XMPP Interworking: Presence March 2009 Joe Hildebrand Cisco Email: jhildebr@cisco.com Saint-Andre, et al. Expires September 9, 2009 [Page 20]