| Network Working Group | P. Saint-Andre |
| Internet-Draft | &yet |
| Obsoletes: 7248 (if approved) | June 11, 2015 |
| Intended status: Standards Track | |
| Expires: December 13, 2015 |
Interworking between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP): Presence
draft-ietf-stox-7248bis-02
This document defines a bidirectional protocol mapping for the exchange of presence information between the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP). This document obsoletes RFC 7248.
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/.
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This Internet-Draft will expire on December 13, 2015.
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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:
One approach to helping ensure interworking between these protocols is to map each protocol to the abstract semantics described in [RFC3860]; however, apparently that approach has never been implemented. The approach taken in this document is to directly map semantics from one protocol to another (i.e., from SIP/SIMPLE (SIP for Instant Messaging and Presence Leveraging Extensions) to XMPP and vice versa), since that is how existing systems solve the interworking problem.
The architectural assumptions underlying such direct mappings are provided in [RFC7247], 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.
This document obsoletes RFC 7248.
The documents in this series are intended for use by software developers who have an existing system based on one of these technologies (e.g., SIP) and would like to enable communication from that existing system to systems based on the other technology (e.g., XMPP). We assume that readers are familiar with the core specifications for both SIP [RFC3261] and XMPP [RFC6120], with the base document for this series [RFC7247], and with the following presence-related specifications:
A number of terms used here (user, contact, subscription, notification, etc.) are explained in [RFC3261], [RFC3856], [RFC6120], and [RFC6121]. This document uses some, but not all, of the terms defined in the Model for Presence and Instant Messaging [RFC2778].
In flow diagrams, SIP traffic is shown using arrows such as "***>", whereas XMPP traffic is shown using arrows such as "...>".
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].
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:
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 <pres:user@domain> but who might be referenced by a SIP or SIPS ((Session Initiation Protocol Secure) URI of the form <sip:user@domain> or <sips:user@domain>. In practice, 'pres' URIs are rarely used, which is why the examples in this document use 'sip' URIs.
The subscription models underlying XMPP and SIP differ mainly in the fact that XMPP presence subscriptions are long-lived (indeed permanent if not explicitly cancelled, so that a subscription need never be refreshed during any given presence "session"), 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], so that a subscription needs to be explicitly refreshed if it will have the appearance of being permanent or even of lasting as long as the duration of a presence "session"). This disparity has implications for the handling of subscription cancellations in either direction and, from the SIP side, subscription refreshes.
The following diagram illustrates the protocol flow for establishing a presence subscription from an XMPP user to a SIP user, as further explained in the text and examples after the diagram.
XMPP XMPP SIP SIP
User Server Server User
| + X2S GW | |
| | | |
| (F1) XMPP | | |
| subscribe | | |
|...........>| | |
| | (F2) SIP | |
| | SUBSCRIBE | |
| |***********>| |
| | | (F3) SIP |
| | | SUBSCRIBE |
| | |***********>|
| | | (F4) SIP |
| | | 200 OK |
| | |<***********|
| | (F5) SIP | |
| | 200 OK | |
| |<***********| |
| | | (F6) SIP |
| | | NOTIFY |
| | |<***********|
| | | (F7) SIP |
| | | 200 OK |
| | |***********>|
| | (F8) SIP | |
| | NOTIFY | |
| |<***********| |
| (F9) XMPP | | |
| subscribed | | |
|<...........| | |
| (F10) XMPP | | |
| presence | | |
|<...........| | |
| | | |
An XMPP user (e.g., juliet@example.com) initiates a subscription by sending a subscription request to a contact (e.g., romeo@example.net), and the 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) 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 (F1)
| <presence from='juliet@example.com'
| to='romeo@example.net'
| type='subscribe'/>
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 explained in Section 5 of [RFC7247]. If the domain is a SIP domain, the XMPP server will hand off the <presence/> stanza to an associated XMPP-to-SIP gateway or connection manager that natively communicates with presence-aware SIP servers.
The XMPP-to-SIP gateway is then responsible for translating the XMPP subscription request into a SIP SUBSCRIBE request addressed from the XMPP user to the SIP user:
Example 2: SIP Transformation of XMPP Subscription Request (F2)
| SUBSCRIBE sip:romeo@example.net SIP/2.0
| Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
| To: <sip:romeo@example.com>;tag=ffd2
| From: <sip:juliet@example.com>;tag=j89d
| Call-ID: 5BCF940D-793D-43F8-8972-218F7F4EAA8C
| Event: presence
| Max-Forwards: 70
| CSeq: 1 SUBSCRIBE
| Contact: <sip:x2s.example.com;transport=tcp>
| Accept: application/pidf+xml
| Expires: 3600
| Content-Length: 0
Once the SIP-to-XMPP gateway has passed the SIP SUBSCRIBE off to the SIP server and the SIP server has delivered the SIP SUBSCRIBE to the SIP user (F3, no example shown), the SIP user then would send a response indicating acceptance of the subscription request:
Example 3: SIP User Accepts Subscription Request (F4)
| SIP/2.0 200 OK
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| From: <sip:romeo@example.net>;tag=ffd2
| To: <sip:juliet@example.com>;tag=j89d
| Call-ID: 5BCF940D-793D-43F8-8972-218F7F4EAA8C
| CSeq: 1 SUBSCRIBE
| Contact: <sip:simple.example.net;transport=tcp>
| Expires: 3600
| Content-Length: 0
In accordance with [RFC6665], the XMPP-to-SIP gateway SHOULD consider the subscription state to be "neutral" until it receives a NOTIFY message. Therefore, the SIP user or SIP-to-XMPP gateway at the SIP user's domain SHOULD immediately send a NOTIFY message containing a Subscription-State header [RFC6665] whose value contains the string "active" (see Section 5 below).
Example 4: SIP User Sends Presence Notification (F6)
| NOTIFY sip:192.0.2.1 SIP/2.0
| Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
| From: <sip:romeo@example.net>;tag=ffd2
| To: <sip:juliet@example.com>;tag=j89d
| Call-ID: 5BCF940D-793D-43F8-8972-218F7F4EAA8C
| Event: presence
| Subscription-State: active;expires=499
| Max-Forwards: 70
| CSeq: 2 NOTIFY
| Contact: <sip:simple.example.net;transport=tcp>
| Content-Type: application/pidf+xml
| Content-Length: 193
|
| <?xml version='1.0' encoding='UTF-8'?>
| <presence xmlns='urn:ietf:params:xml:ns:pidf'
| entity='pres:romeo@example.net'>
| <tuple id='ID-dr4hcr0st3lup4c'>
| <status>
| <basic>open</basic>
| <show xmlns='jabber:client'>away</show>
| </status>
| </tuple>
| </presence>
In response, the presence-aware SIP-to-XMPP gateway would send a 200 OK to the SIP user (not shown here, since it is not translated into an XMPP stanza).
Upon receiving the first NOTIFY with a subscription state of active, the XMPP-to-SIP gateway MUST generate a <presence/> stanza of type "subscribed":
Example 5: XMPP User Receives Acknowledgement from SIP Contact (F9)
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='subscribed'/>
As described in Section 5, the gateway MUST also generate a presence notification addressed to the XMPP user:
Example 6: XMPP User Receives Presence Notification from SIP Contact (F10)
| <presence from='romeo@example.net/dr4hcr0st3lup4c'
| to='juliet@example.com'/>
It is the responsibility of the XMPP-to-SIP 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. For example, the XMPP-to-SIP gateway SHOULD send a new SUBSCRIBE request to the SIP user whenever the XMPP user initiates a presence session with the XMPP server by sending initial presence to its XMPP server. The XMPP-to-SIP gateway also SHOULD send a new SUBSCRIBE request to the SIP user whenever the SIP presence subscription is scheduled to expire during the XMPP user's active presence session.
The rules regarding SIP SUBSCRIBE requests for the purpose of establishing and refreshing a presence subscription are provided in [RFC6665]. Those rules also apply to XMPP-to-SIP gateways. Furthermore, an XMPP-to-SIP gateway MUST consider the XMPP subscription to be permanently cancelled (and so inform the XMPP user) if it receives a SIP response of 403, 489, or 603. By contrast, it is appropriate to consider a SIP response of 423 or 481 to be a transient error and to maintain the long-lived XMPP presence subscription. [RFC6665] explains more detailed considerations about the handling of SIP responses in relation to subscription requests and refreshes.
Finally, see the security considerations section (Section 8) of this document for important information and requirements regarding the security implications of subscription refreshes.
The following diagram illustrates the protocol flow for cancelling an XMPP user's presence subscription to a SIP user, as further explained in the text and examples after the diagram.
XMPP XMPP SIP SIP
User Server Server User
| + X2S GW | |
| | | |
| (F11) XMPP | | |
|unsubscribe | | |
|...........>| | |
| | (F12) SIP | |
| | SUBSCRIBE | |
| | Expires: 0 | |
| |***********>| |
| | | (F13) SIP |
| | | SUBSCRIBE |
| | | Expires: 0 |
| | |***********>|
| | | (F14) SIP |
| | | 200 OK |
| | |<***********|
| | (F15) SIP | |
| | 200 OK | |
| |<***********| |
| (F16) XMPP | | |
| unsub'd | | |
|<...........| | |
| | | |
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 (F11)
| <presence from='juliet@example.com'
| to='romeo@example.net'
| type='unsubscribe'/>
The XMPP-to-SIP gateway is responsible for translating the unsubscribe command into a SIP SUBSCRIBE request with the Expires header set to a value of zero:
Example 8: SIP Transformation of XMPP Unsubscribe (F12)
| SUBSCRIBE sip:romeo@example.net SIP/2.0
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| To: <sip:romeo@example.com>;tag=ffd2
| From: <sip:juliet@example.com>;tag=j89d
| Call-ID: 5BCF940D-793D-43F8-8972-218F7F4EAA8C
| Event: presence
| Max-Forwards: 70
| CSeq: 42 SUBSCRIBE
| Contact: <sip:x2s.example.com;transport=tcp>
| Accept: application/pidf+xml
| Expires: 0
| Content-Length: 0
Upon receiving the SIP 200 OK acknowleding the unsubscribe, the XMPP-to-SIP gateway SHOULD send a <presence/> stanza of type "unsubscribed" addressed to the XMPP user:
Example 9: XMPP User Receives Unsubscribed Notification (F16)
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='unsubscribed'/>
The following diagram illustrates the protocol flow for establishing a presence subscription from a SIP user to an XMPP user, as further explained in the text and examples after the diagram.
SIP SIP XMPP XMPP
User Server Server User
| + S2X GW | |
| | | |
| (F17) SIP | | |
| SUBSCRIBE | | |
|**********>| | |
| | (F18) XMPP | |
| | subscribe | |
| |...........>| |
| | | (F19) XMPP|
| | | subscribe |
| | |..........>|
| | | (F20) XMPP|
| | | subscribed|
| | |<..........|
| | (F21) XMPP | |
| | subscribed | |
| |<...........| |
| (F22) SIP | | |
| 200 OK | | |
|<**********| | |
| | | |
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 (F17)
| SUBSCRIBE sip:juliet@example.com SIP/2.0
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| To: <sip:juliet@example.net>;tag=ur93
| From: <sip:romeo@example.net>;tag=xfg9
| Call-ID: AA5A8BE5-CBB7-42B9-8181-6230012B1E11
| Event: presence
| Max-Forwards: 70
| CSeq: 1 SUBSCRIBE
| Contact: <sip:simple.example.net;transport=tcp>
| 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 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 explained in Section 5 of [RFC7247]. If the domain is an XMPP domain, the SIP server will hand off the SUBSCRIBE to an associated SIP-to-XMPP gateway or connection manager that natively communicates with XMPP servers.
The SIP-to-XMPP gateway is then responsible for translating the SUBSCRIBE into an XMPP subscription request addressed from the SIP user to the XMPP user:
Example 11: XMPP Transformation of SIP SUBSCRIBE (F18)
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='subscribe'/>
In accordance with [RFC6121], once it receives the stanza from the XMPP-to-SIP gateway, 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, the XMPP server SHOULD auto-reply with a <presence/> stanza of type 'subscribed').
If the XMPP user approves the subscription request, the XMPP server then MUST return a <presence/> stanza of type "subscribed" addressed from the XMPP user to the SIP user. The XMPP-to-SIP gateway is responsible for translating the <presence/> stanza of type "subscribed" into a SIP 200 OK response.
If the XMPP user declines the subscription request, the XMPP server then MUST return a <presence/> stanza of type "unsubscribed" addressed from the XMPP user to the SIP user and the XMPP-to-SIP gateway MUST transform that stanza into an empty SIP NOTIFY message with a Subscription-State header [RFC6665] of "terminated" and a reason of "rejected":
Example 12: Subscription Request Rejected
| NOTIFY sip:192.0.2.2 SIP/2.0
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=ur93
| To: <sip:romeo@example.net>;tag=xfg9
| Call-ID: AA5A8BE5-CBB7-42B9-8181-6230012B1E11
| Event: presence
| Subscription-State: terminated;reason=rejected
| Max-Forwards: 70
| CSeq: 2 NOTIFY
| Contact: <sip:x2s.example.com;transport=tcp>
| Content-Type: application/pidf+xml
| Content-Length: 0
For as long as a SIP user is online and interested in receiving presence notifications from the XMPP contact, 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 presence-aware SIP-to-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 (e.g., obtained from the core presence session in the XMPP server) 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 ends its presence session, it is the responsibility of the presence-aware SIP-to-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:
Which of these options a presence-aware SIP-to-XMPP gateway chooses is up to the implementation.
If the implementation chooses the first option, the protocol generated would be as follows:
Example 13: XMPP Handling of Temporary Subscription Expiry
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='unsubscribe'/>
If the implementation chooses the second option, the protocol generated would be as follows:
Example 14: SIP Handling of Long-Lived Subscription Expiry
| NOTIFY sip:192.0.2.2 SIP/2.0
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=ur93
| To: <sip:romeo@example.net>;tag=xfg9
| Call-ID: AA5A8BE5-CBB7-42B9-8181-6230012B1E11
| Event: presence
| Subscription-State: terminated;reason=timeout
| Max-Forwards: 70
| CSeq: 6 NOTIFY
| Contact: <sip:x2s.example.com;transport=tcp>
| Content-Type: application/pidf+xml
| Content-Length: 194
|
| <?xml version='1.0' encoding='UTF-8'?>
| <presence xmlns='urn:ietf:params:xml:ns:pidf'
| entity='pres:juliet@example.com'>
| <tuple id='ID-yn0cl4bnw0yr3vym'>
| <status>
| <basic>closed</basic>
| </status>
| </tuple>
| </presence>
Example 15: XMPP Handling of Long-Lived Subscription Expiry
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='unavailable'/>
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
| To: <sip:juliet@example.com>;tag=ur93
| From: <sip:romeo@example.net>;tag=xfg9
| Call-ID: AA5A8BE5-CBB7-42B9-8181-6230012B1E11
| Event: presence
| Max-Forwards: 70
| CSeq: 66 SUBSCRIBE
| Contact: <sip:simple.example.net;transport=tcp>
| Expires: 0
| Content-Length: 0
As above, upon receiving such a request, a presence-aware SIP-to-XMPP gateway is responsible for doing one of the following:
Both XMPP and presence-aware SIP systems enable entities (often, but not necessarily, human users) to send presence notifications to other entities. At its most basic, the term "presence" refers to information about an entity's "on/off" availability for communication on a network. Often, this basic concept is supplemented by information that further specifies the entity's context or status while available for communication; these availability states commonly include "away" and "do not disturb". Some systems and protocols extend the concepts of presence and availability 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). This document focuses on the "least common denominator" of network availability only, although future documents might address broader notions of presence, including availability states and 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], XMPP presence information about an entity is communicated by means of an XML <presence/> stanza sent over an XML stream. This document assumes 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. In general, XMPP presence is sent by the user to the user's server and then broadcast 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 a Presence URI of the form <pres:user@domain> but who might be referenced by a SIP or SIPS URI of the form <sip:user@domain> or <sips:user@domain>.
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].
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 <presence/> stanza. The syntax of the <presence/> 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
| <presence from='juliet@example.com/yn0cl4bnw0yr3vym'/>
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. 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 [RFC7247]. If the domain is a SIP domain, the XMPP server will hand off the <presence/> stanza to an associated XMPP-to-SIP gateway or connection manager that natively communicates with presence-aware SIP servers (no example shown).
The XMPP-to-SIP 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: SIP Transformation of XMPP Presence Notification
| NOTIFY sip:192.0.2.2 SIP/2.0
| Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=gh19
| To: <sip:romeo@example.net>;tag=yt66
| Contact: <sip:juliet@example.com>;gr=yn0cl4bnw0yr3vym
| Call-ID: 2B44E147-3B53-45E4-9D48-C051F3216D14
| Event: presence
| Subscription-State: active;expires=599
| Max-Forwards: 70
| CSeq: 2 NOTIFY
| Contact: <sip:x2s.example.com;transport=tcp>
| Content-Type: application/pidf+xml
| Content-Length: 192
|
| <?xml version='1.0' encoding='UTF-8'?>
| <presence xmlns='urn:ietf:params:xml:ns:pidf'
| entity='pres:juliet@example.com'>
| <tuple id='ID-yn0cl4bnw0yr3vym'>
| <status>
| <basic>open</basic>
| <show xmlns='jabber:client'>away</show>
| </status>
| </tuple>
| </presence>
The mapping of XMPP syntax elements to SIP syntax elements MUST be as shown in the following table. (Mappings for elements not mentioned are undefined.)
+-----------------------------+---------------------------+
| XMPP Element or Attribute | SIP Header or PIDF Data |
+-----------------------------+---------------------------+
| <presence/> 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/> | priority for tuple (6) |
+-----------------------------+---------------------------+
| <show/> | no mapping (7) |
+-----------------------------+---------------------------+
| <status/> | <note/> |
+-----------------------------+---------------------------+
Table 1: Presence Syntax Mapping from XMPP to SIP
Note the following regarding these mappings:
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:
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: <sip:romeo@example.net>;tag=yt66
| To: <sip:juliet@example.com>;tag=bi54
| Contact: <sip:romeo@example.net>;gr=dr4hcr0st3lup4c
| Call-ID: C33C6C9D-0F4A-42F9-B95C-7CE86B526B5B
| Event: presence
| Subscription-State: active;expires=499
| Max-Forwards: 70
| CSeq: 8 NOTIFY
| Contact: <sip:simple.example.net;transport=tcp>
| Content-Type: application/pidf+xml
| Content-Length: 193
|
| <?xml version='1.0' encoding='UTF-8'?>
| <presence xmlns='urn:ietf:params:xml:ns:pidf'
| entity='pres:romeo@example.net'>
| <tuple id='ID-dr4hcr0st3lup4c'>
| <status>
| <basic>closed</basic>
| </status>
| </tuple>
| </presence>
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 [RFC7247]. If the domain is an XMPP domain, the SIP server will hand off the NOTIFY to an associated SIP-to-XMPP gateway or connection manager that natively communicates with XMPP servers.
The SIP-to-XMPP gateway is then responsible for translating the NOTIFY into an XMPP <presence/> stanza addressed from the SIP user to the XMPP user:
Example 20: XMPP Transformation of SIP Presence Notification
| <presence from='romeo@example.net'
| to='juliet@example.com/yn0cl4bnw0yr3vym'
| type='unavailable'/>
The mapping of SIP syntax elements to XMPP syntax elements MUST be as shown in the following table. (Mappings for elements not mentioned are undefined.)
+---------------------------+-----------------------------+
| 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 | <priority/> (3) |
+---------------------------+-----------------------------+
| To | to |
+---------------------------+-----------------------------+
| <note/> | <status/> |
+---------------------------+-----------------------------+
| <show/> | <show/> (4) |
+---------------------------+-----------------------------+
Table 2: Presence Syntax Mapping from SIP to XMPP
Note the following regarding these mappings:
Both SIP and XMPP provide methods for requesting presence information about another entity.
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
| <presence from='juliet@example.com/chamber'
| to='romeo@example.net'
| type='probe'/>
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-to-SIP gateway would transform the presence probe into its SIP equivalent, which is a SUBSCRIBE request with an Expires header value of zero:
Example 22: SIP Transformation of XMPP Presence Probe
| SUBSCRIBE sip:romeo@example.net SIP/2.0
| Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=j89d
| Call-ID: 5BCF940D-793D-43F8-8972-218F7F4EAA8C
| Event: presence
| Max-Forwards: 70
| CSeq: 1 SUBSCRIBE
| Contact: <sip:x2s.example.com;transport=tcp>
| 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 Section 5.2 of this document).
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: <sip:romeo@example.net>;tag=yt66
| Call-ID: 717B1B84-F080-4F12-9F44-0EC1ADE767B9
| Event: presence
| Max-Forwards: 70
| CSeq: 1 SUBSCRIBE
| Contact: <sip:simple.example.net;transport=tcp>
| Expires: 0
| Content-Length: 0
When honoring the long-lived semantics of an XMPP presence subscription, a presence-aware SIP-to-XMPP gateway MUST translate such a SIP request into a <presence/> stanza of type "probe" if it does not already have presence information about the contact:
Example 24: XMPP Transformation of SIP Presence Request
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='probe'/>
This document makes no requests of IANA.
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 (since each long-lived XMPP presence subscription would typically result in multiple subscription refresh requests on the SIP side of a gateway). Therefore, access to an XMPP-to-SIP gateway SHOULD be restricted in various ways; among other things, only an XMPP service that carefully controls account provisioning and provides effective methods for the administrators to control the behavior of registered users ought to host such a gateway (e.g., not a service that offers open account registration) and a gateway ought to be associated only 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-to-SIP gateway from users who are not associated with a domain that is so related to the hostname of the gateway, it SHOULD (based on local service provisioning) refuse to service such users or refuse to receive traffic from with the gateway. As a futher check, whenever an XMPP-to-SIP gateway seeks to refresh an XMPP user's long-lived subscription to a SIP user's presence, it MUST first send an XMPP <presence/> 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]; this puts an equal burden on the XMPP server and the SIP server.
| [RFC2778] | Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. |
| [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. |
| [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. |
Thanks to the authors, contributors, and other individuals acknowledged in RFC 7248.
Thanks to Saul Ibarra Corretge for his review during Working Group Last Call.
Special thanks to Ben Campbell for identifying the underlying discrepancy that resulted in the need to obsolete RFC 7248.
Thanks also to Markus Isomaki and Yana Stamcheva as the working group chairs and Alissa Cooper as the sponsoring Area Director.