Network Working Group P. Saint-Andre Internet-Draft Cisco Systems, Inc. Intended status: Standards Track A. Houri Expires: April 3, 2014 IBM J. Hildebrand Cisco Systems, Inc. September 30, 2013 Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): Presence draft-ietf-stox-presence-05 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). Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on April 3, 2014. Copyright Notice Copyright (c) 2013 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must Saint-Andre, et al. Expires April 3, 2014 [Page 1] Internet-Draft SIP-XMPP Interworking: Presence September 2013 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Subscriptions . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 4 3.2.1. Establishing . . . . . . . . . . . . . . . . . . . . . 4 3.2.2. Refreshing . . . . . . . . . . . . . . . . . . . . . . 7 3.2.3. Cancelling . . . . . . . . . . . . . . . . . . . . . . 7 3.3. SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 8 3.3.1. Establishing . . . . . . . . . . . . . . . . . . . . . 8 3.3.2. Refreshing . . . . . . . . . . . . . . . . . . . . . . 10 3.3.3. Cancelling . . . . . . . . . . . . . . . . . . . . . . 12 4. Notifications . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2. XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 13 4.3. SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 16 5. Requests . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.1. XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 18 5.2. SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 19 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 8.1. Normative References . . . . . . . . . . . . . . . . . . . 21 8.2. Informative References . . . . . . . . . . . . . . . . . . 21 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22 Saint-Andre, et al. Expires April 3, 2014 [Page 2] Internet-Draft SIP-XMPP Interworking: Presence September 2013 1. Introduction In order to help ensure interworking between presence systems that conform to the instant message / presence requirements [RFC2779], 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 ([RFC3261]) for instant messaging, as developed within the SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE) Working Group; the relevant specification for presence is [RFC3856] 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 [RFC6120] for the XML streaming layer and [RFC6121] 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 [RFC3860]; that is the approach taken by both [RFC3922] and [I-D.ietf-simple-cpim-mapping]. 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 [I-D.ietf-stox-core], including mapping of addresses and error conditions. The mappings specified in this document cover basic presence functionality. Mapping of more advanced functionality (e.g., so-called "rich presence") is out of scope for this document. SIP and XMPP differ significantly in their presence subscription models, since SIP subscriptions are short-lived (requiring relatively frequent refreshes even during a presence session) whereas XMPP subscriptions last across presence sessions until they are explicitly cancelled. This document provides suggestions for bridging the gap between these very different models. The discussion venue for this document is the mailing list of the STOX WG; visit https://www.ietf.org/mailman/listinfo/stox for subscription information and discussion archives. 2. Terminology A number of terms used here are explained in [RFC3261], [RFC3856], [RFC6120], and [RFC6121]. Saint-Andre, et al. Expires April 3, 2014 [Page 3] Internet-Draft SIP-XMPP Interworking: Presence September 2013 The 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 [RFC2119]. 3. Subscriptions 3.1. 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 [RFC6121]. Presence subscriptions using a SIP event package for presence are specified in [RFC3856]. As described in [RFC6121], 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 [RFC3856], 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 a Presence URI of the form but who might 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 [RFC3856]). These differences are addressed below. 3.2. XMPP to SIP 3.2.1. Establishing An XMPP user (e.g., juliet@example.com) initiates a subscription by sending a subscription request to another entity (e.g., romeo@example.net), and the other entity (conventionally called a "contact") either accepts or declines the request. 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) Saint-Andre, et al. Expires April 3, 2014 [Page 4] Internet-Draft SIP-XMPP Interworking: Presence September 2013 the contact cancels the subscription. The subscription request is encapsulated in a presence stanza of type "subscribe": Example 1: XMPP user subscribes to SIP contact: | Upon receiving such a presence stanza, the XMPP server to which Juliet has connected needs to determine the identity of the domainpart in the 'to' address, which it does by following the procedures discussed in [I-D.ietf-stox-core]. Here we assume that the XMPP server has determined the domain is serviced by a SIMPLE server, that it contains or has available to it an XMPP-SIMPLE gateway or connection manager (which enables it to speak natively to SIMPLE servers), and that it hands off 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 2: 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 | 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: Saint-Andre, et al. Expires April 3, 2014 [Page 5] Internet-Draft SIP-XMPP Interworking: Presence September 2013 Example 3: 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 [RFC6665], 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 "active" (see Section 4). Example 4: 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 | away | | | In response, the SIMPLE-XMPP gateway would send a 200 OK (not shown here since it is not translated into an XMPP stanza). Saint-Andre, et al. Expires April 3, 2014 [Page 6] Internet-Draft SIP-XMPP Interworking: Presence September 2013 Upon receiving the first NOTIFY with a subscription state of active, the XMPP-SIMPLE gateway MUST generate a presence stanza of type "subscribed": Example 5: XMPP user receives acknowledgement from SIP contact: | As described under Section 4, the gateway MUST also generate a presence notification to the XMPP user: Example 6: XMPP user receives presence notification from SIP contact: | 3.2.2. 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 7) of this document for important information and requirements regarding the security implications of this functionality. 3.2.3. Cancelling At any time after subscribing, the XMPP user can unsubscribe from the contact's presence. This is done by sending a presence stanza of type "unsubscribe": Example 7: 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: Saint-Andre, et al. Expires April 3, 2014 [Page 7] Internet-Draft SIP-XMPP Interworking: Presence September 2013 Example 8: 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 | 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 send a presence stanza of type "unsubscribed" to the XMPP user: Example 9: XMPP user receives unsubscribed notification: | 3.3. SIP to XMPP 3.3.1. 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 10: 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 | 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 Saint-Andre, et al. Expires April 3, 2014 [Page 8] Internet-Draft SIP-XMPP Interworking: Presence September 2013 seconds = 1 hour) applies. Upon receiving the SUBSCRIBE, the SIP server needs to determine the identity of the domain portion of the Request-URI or To header, which it does by following the procedures discussed in [I-D.ietf-stox-core]. Here we assume that the SIP server has determined that the domain is serviced by an XMPP server, that it contains or has available to it a SIP-to-XMPP gateway or connection manager (which enables it to speak natively to XMPP servers), and that it hands off the message to the gateway. The SIP-to-XMPP gateway is then responsible for translating the SUBSCRIBE into an XMPP subscription request from the SIP user to the XMPP user: Example 11: SIP user subscribes to XMPP contact (XMPP transformation): | In accordance with [RFC6121], 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, 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. If the XMPP user declines the subscription request, the XMPP server then MUST return a presence stanza of type "unsubscribed" from the XMPP user to the SIP user and the XMPP-SIMPLE gateway MUST transform that stanza into an empty SIP NOTIFY message with a Subscription- State of "terminated" and a reason of "rejected": Saint-Andre, et al. Expires April 3, 2014 [Page 9] Internet-Draft SIP-XMPP Interworking: Presence September 2013 Example 12: SIP subscription request rejected: | 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: 4wcm0n@example.net | Event: presence | Subscription-State: terminated;reason=rejected | Max-Forwards: 70 | CSeq: 232 NOTIFY | Contact: | Content-Type: application/pidf+xml | Content-Length: 0 3.3.2. Refreshing For as long as a SIP user is online and interested in receiving presence notifications from the XMPP users, the user's SIP user agent is responsible for periodically refreshing the subscription by sending an updated SUBSCRIBE request with an appropriate value for the Expires header. In response, the SIMPLE-XMPP gateway MUST send a SIP NOTIFY to the user agent (per [RFC6665]; if the gateway has meaningful information about the availability state of the XMPP user then the NOTIFY MUST communicate that information (e.g., by including a PIDF body [RFC3863] with the relevant data), whereas if the gateway does not have meaningful information about the availability state of the XMPP user then the NOTIFY MUST be empty as allowed by [RFC6665]. Once the SIP user goes offline at the end of a presence session, 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" with a reason of "timeout" 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. Saint-Andre, et al. Expires April 3, 2014 [Page 10] Internet-Draft SIP-XMPP Interworking: Presence September 2013 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 13: SIP subscription expires (treated as temporary by gateway): | If the implementation chooses the second option, the protocol generated would be as follows: Example 14: 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 15: SIP subscription expires (treated as long-lived by gateway): | Saint-Andre, et al. Expires April 3, 2014 [Page 11] Internet-Draft SIP-XMPP Interworking: Presence September 2013 3.3.3. Cancelling At any time, the SIP user can cancel the subscription by sending a SUBSCRIBE message whose "Expires" header is set to a value of zero ("0"): Example 16: SIP user cancels subscription: | SUBSCRIBE sip:juliet@example.com SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=yt66 | 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. 4. Notifications 4.1. 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 Saint-Andre, et al. Expires April 3, 2014 [Page 12] Internet-Draft SIP-XMPP Interworking: Presence September 2013 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 might address broader notions of presence, including extended presence. [RFC6121] 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 [RFC3856]. As described in [RFC6121], 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 [RFC3856], 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 Presence URI of the form but who might 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. This document addresses basic presence or network availability only, not the various extensions to SIP and XMPP for "rich presence", such as [RFC4480], [XEP-0107], and [XEP-0108]. 4.2. 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 [RFC6121]. The following is an example of such a stanza: Example 17: 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 Saint-Andre, et al. Expires April 3, 2014 [Page 13] Internet-Draft SIP-XMPP Interworking: Presence September 2013 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. Thus the XMPP server needs to determine the identity of the domainpart in the 'to' address, which it does by following the procedures discussed in [I-D.ietf-stox-core]. Here we assume that the XMPP server has determined the domain is serviced by a SIMPLE server, that it contains or has available to it an XMPP-SIMPLE gateway or connection manager (which enables it to speak natively to SIMPLE servers), and that it hands off 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 18: 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 | Contact: ;gr=balcony | 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 | away | | | The mapping of XMPP syntax elements to SIP syntax elements SHOULD be as shown in the following table. (Mappings for elements not Saint-Andre, et al. Expires April 3, 2014 [Page 14] Internet-Draft SIP-XMPP Interworking: Presence September 2013 mentioned are undefined.) Table 1: 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 (2) | | from | From | | id | CSeq (3) | | to | To | | type | basic status (4) (5) | | xml:lang | Content-Language | | | priority for tuple (6) | | | no mapping (7) | | | | +-----------------------------+---------------------------+ 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. The PIDF schema defines the tuple 'id' attribute as having a datatype of "xs:ID"; because this datatype is more restrictive than the "xs:string" datatype for XMPP resourceparts (in particular, a number is not allowed as the first character of an ID), it is RECOMMENDED to prepend the resourcepart with "ID-" or some other alphabetic string when mapping from XMPP to SIP. 3. This mapping is OPTIONAL. 4. 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 communications, the gateway SHOULD map that information to a PIDF status of "closed". 5. 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). 6. The value of the XMPP element is an integer between -128 and +127, whereas the the value of the PIDF element's 'priority' attribute is a decimal number from zero to one inclusive, with a maximum of three decimal places. If the Saint-Andre, et al. Expires April 3, 2014 [Page 15] Internet-Draft SIP-XMPP Interworking: Presence September 2013 value of the XMPP element is negative, an XMPP-SIMPLE gateway MUST NOT map the value. If an XMPP-SIMPLE gateway maps positive values, it SHOULD treat XMPP priority 0 as PIDF priority 0 and XMPP priority 127 as PIDF priority 1, mapping intermediate values appropriately so that they are unique (e.g., XMPP priority 1 to PIDF priority 0.007, XMPP priority 2 to PIDF priority 0.015, and so on up through mapping XMPP priority 126 to PIDF priority 0.992; note that this is an example only, and that the exact mapping is up to the implementation). 7. Some implementations support custom extensions to encapsulate this information; however, there is no need to standardize a PIDF extension for this purpose, since PIDF is already extensible and thus the element can be included directly, qualified by the 'jabber:client' namespace in the PIDF XML. The examples in this document illustrate this usage, which is RECOMMENDED. The most useful values are likely "away" and "dnd", although note that the latter value merely means "busy" and does not imply that a server or client ought to block incoming traffic while the user is in that state. 8. Some implementations support custom extensions to encapsulate detailed information about availability; however, there is no need to standardize a PIDF extension for this purpose, since PIDF is already extensible and thus the element (qualified by the 'jabber:client' namespace) can be included directly in the PIDF XML. The examples in this document illustrate this usage, which is RECOMMENDED. The most useful values are likely "away" and "dnd", although note that the latter value merely means "busy" and does not imply that a server or client ought to block incoming traffic while the user is in that state. Naturally, a gateway can choose to translate a custom extension into an established value of the element [RFC6121], or translate a element into a custom extension that the gateway knows is supported by the user agent of the intended recipient. Unfortunately, this behavior does not guarantee that information will not be lost; to help prevent information loss, a gateway ought to include both the element and the custom extension if the gateway cannot suitably translate the custom value into a value. 4.3. 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 [RFC3856]. The following is an example of such a request: Saint-Andre, et al. Expires April 3, 2014 [Page 16] Internet-Draft SIP-XMPP Interworking: Presence September 2013 Example 19: 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 | Contact: ;gr=orchard | 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 the NOTIFY, the SIP server needs to determine the identity of the domain portion of the Request-URI or To header, which it does by following the procedures discussed in [I-D.ietf-stox-core]. Here we assume that the SIP server has determined that the domain is serviced by an XMPP server, that it contains or has available to it a SIP-to-XMPP gateway or connection manager (which enables it to speak natively to XMPP servers), and that it hands off the message to the gateway. The SIP-to-XMPP gateway is then responsible for translating the NOTIFU into an XMPP presence stanza from the SIP user to the XMPP user: Example 20: 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 Saint-Andre, et al. Expires April 3, 2014 [Page 17] Internet-Draft SIP-XMPP Interworking: Presence September 2013 mentioned are undefined.) Table 2: 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 (2) | | From | from | | priority for tuple | (3) | | To | to | | | | | | (4) | +---------------------------+-----------------------------+ 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". 2. This mapping is OPTIONAL. 3. See the notes following Table 1 of this document regarding mapping of presence priority. 4. If a SIP implementation supports the element (qualified by the 'jabber:client' namespace) as a PIDF extension for availability status as described in the notes following Table 1 of this document, the SIP-to-XMPP gateway is responsible for including that element in the XMPP presence notification. 5. Requests Both SIP and XMPP provide methods for requesting presence information about another entity. 5.1. XMPP to SIP In XMPP, a request for presence information is completed by sending a presence stanza of type "probe": Example 21: XMPP server sends presence probe on behalf of XMPP user: | Saint-Andre, et al. Expires April 3, 2014 [Page 18] Internet-Draft SIP-XMPP Interworking: Presence September 2013 Note: As described in [RFC6121], presence probes are used by XMPP servers to request presence on behalf of XMPP users; XMPP clients are discouraged from sending presence probes since retrieving presence is a service that servers provide. An XMPP-SIMPLE gateway would transform the presence probe into its SIP equivalent, which is a SUBSCRIBE request with an Expires header value of zero: Example 22: Presence probe (SIP transformation): | SUBSCRIBE sip:romeo@example.net SIP/2.0 | Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk | From: ;tag=ffd2 | Call-ID: l04th3s1p@example.com | Event: presence | Max-Forwards: 70 | CSeq: 123 SUBSCRIBE | Contact: | Accept: application/pidf+xml | Expires: 0 | Content-Length: 0 As described in [RFC3856], this cancels any subscription but causes a NOTIFY to be sent to the subscriber, just as a presence probe does (the transformation rules for presence notifications have been previously described in this document). 5.2. SIP to XMPP In SIP, a request for presence information is effectively completed by sending a SUBSCRIBE with an Expires header value of zero: Example 23: SIP user sends presence request: | SUBSCRIBE sip:juliet@example.com SIP/2.0 | Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk | From: ;tag=yt66 | Call-ID: 1tsn1ce@example.net | Event: presence | Max-Forwards: 70 | CSeq: 8775 SUBSCRIBE | Contact: | Expires: 0 | Content-Length: 0 When honoring the long-lived semantics of an XMPP presence subscription, a SIMPLE-XMPP gateway SHOULD translate such a SIP Saint-Andre, et al. Expires April 3, 2014 [Page 19] Internet-Draft SIP-XMPP Interworking: Presence September 2013 request into a presence stanza of type 'probe' if it does not already have presence information about the subscribee: Example 24: SIP user requests XMPP presence (XMPP transformation): | 6. IANA Considerations This document makes no requests of IANA. 7. Security Considerations Detailed security considerations for presence protocols are given in [RFC2779], for SIP-based presence in [RFC3856] (see also [RFC3261]), and for XMPP-based presence in [RFC6121] (see also [RFC6120]). 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 ought to 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 [RFC6121]; 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). 8. References Saint-Andre, et al. Expires April 3, 2014 [Page 20] Internet-Draft SIP-XMPP Interworking: Presence September 2013 8.1. Normative References [I-D.ietf-stox-core] 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-ietf-stox-core-06 (work in progress), September 2013. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3261] 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. [RFC3856] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", RFC 3856, August 2004. [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 6120, March 2011. [RFC6121] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence", RFC 6121, March 2011. [RFC6665] Roach, A., "SIP-Specific Event Notification", RFC 6665, July 2012. 8.2. Informative References [I-D.ietf-simple-cpim-mapping] Rosenberg, J. and B. Campbell, "CPIM Mapping of SIMPLE Presence and Instant Messaging", draft-ietf-simple-cpim-mapping-01 (work in progress), June 2002. [RFC2779] Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000. [RFC3860] Peterson, J., "Common Profile for Instant Messaging (CPIM)", RFC 3860, August 2004. [RFC3863] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, "Presence Information Data Format (PIDF)", RFC 3863, August 2004. Saint-Andre, et al. Expires April 3, 2014 [Page 21] Internet-Draft SIP-XMPP Interworking: Presence September 2013 [RFC3922] Saint-Andre, P., "Mapping the Extensible Messaging and Presence Protocol (XMPP) to Common Presence and Instant Messaging (CPIM)", RFC 3922, October 2004. [RFC4480] Schulzrinne, H., Gurbani, V., Kyzivat, P., and J. Rosenberg, "RPID: Rich Presence Extensions to the Presence Information Data Format (PIDF)", RFC 4480, July 2006. [XEP-0107] Saint-Andre, P. and R. Meijer, "User Mood", XSF XEP 0107, October 2008. [XEP-0108] Meijer, R. and P. Saint-Andre, "User Activity", XSF XEP 0108, October 2008. Appendix A. Acknowledgements The authors wish to thank the following individuals for their feedback: Chris Christou, Fabio Forno, Adrian Georgescu, Philipp Hancke, Saul Ibarra Corretge, Markus Isomaki, Paul Kyzivat, Salvatore Loreto, Michael Lundberg, Daniel-Constantin Mierla, and Tory Patnoe. Some text in this document was borrowed from [RFC3922]. Authors' Addresses Peter Saint-Andre Cisco Systems, Inc. 1899 Wynkoop Street, Suite 600 Denver, CO 80202 USA Phone: +1-303-308-3282 Email: psaintan@cisco.com Avshalom Houri IBM Rorberg Building, Pekris 3 Rehovot 76123 Israel Email: avshalom@il.ibm.com Saint-Andre, et al. Expires April 3, 2014 [Page 22] Internet-Draft SIP-XMPP Interworking: Presence September 2013 Joe Hildebrand Cisco Systems, Inc. 1899 Wynkoop Street, Suite 600 Denver, CO 80202 USA Email: jhildebr@cisco.com Saint-Andre, et al. Expires April 3, 2014 [Page 23]