Internet Engineering Task Force (IETF) P. Saint-Andre
Request for Comments: 7248 &yet
Category: Standards Track A. Houri
ISSN: 2070-1721 IBM
J. Hildebrand
Cisco Systems, Inc.
May 2014
Interworking between the Session Initiation Protocol (SIP) and the
Extensible Messaging and Presence Protocol (XMPP): Presence
Abstract
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).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7248.
Copyright Notice
Copyright (c) 2014 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
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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 ....................................................2
2. Intended Audience ...............................................3
3. Terminology .....................................................3
4. Subscriptions to Presence Information ...........................4
4.1. Overview ...................................................4
4.2. XMPP to SIP ................................................5
4.2.1. Establishing a Presence Subscription ................5
4.2.2. Refreshing a Presence Subscription ..................9
4.2.3. Cancelling a Presence Subscription .................10
4.3. SIP to XMPP ...............................................12
4.3.1. Establishing a Presence Subscription ...............12
4.3.2. Refreshing a Presence Subscription .................14
4.3.3. Cancelling a Presence Subscription .................17
5. Notifications of Presence Information ..........................17
5.1. Overview ..................................................17
5.2. XMPP to SIP ...............................................19
5.3. SIP to XMPP ...............................................22
6. Requests for Presence Information ..............................24
6.1. XMPP to SIP ...............................................24
6.2. SIP to XMPP ...............................................25
7. Security Considerations ........................................26
8. References .....................................................27
8.1. Normative References ......................................27
8.2. Informative References ....................................27
Appendix A. Acknowledgements ......................................29
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 presence, in particular [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]; although that is the approach taken by both [RFC3922] and
[SIMPLE-CPIM-MAPPING], to the best of our knowledge 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.
2. Intended Audience
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:
o "A Presence Event Package for the Session Initiation Protocol
(SIP)" [RFC3856]
o "Presence Information Data Format (PIDF)" [RFC3863]
o "Extensible Messaging and Presence Protocol (XMPP): Instant
Messaging and Presence" [RFC6121]
o "SIP-Specific Event Notification" [RFC6665]
3. Terminology
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].
4. Subscriptions to Presence Information
4.1. Overview
Both XMPP and presence-aware SIP systems enable entities (often, but
not necessarily, human users) to subscribe to the presence of other
entities. XMPP presence subscriptions are specified in [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:
o "none" (neither the user nor the contact is subscribed to the
other's presence information)
o "from" (the user has a subscription from the contact)
o "to" (the user has a subscription to the contact's presence
information)
o "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 <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.
4.2. XMPP to SIP
4.2.1. Establishing a Presence Subscription
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 XMPP-to-SIP SIP-to-XMPP SIP SIP
User Server Gateway Gateway Server User
| | | | | |
| (F1) XMPP | | | | |
| subscribe | | | | |
|..........>| | | | |
| | (F2) XMPP | | | |
| | subscribe | | | |
| |...........>| | | |
| | | (F3) SIP SUBSCRIBE | |
| | |**************************>| |
| | | | | (F4) SIP |
| | | | | SUBSCRIBE |
| | | | |**********>|
| | | | | (F5) SIP |
| | | | | 200 OK |
| | | | (F6) SIP |<**********|
| | | | 200 OK | (F7) SIP |
| | | |<***********| NOTIFY |
| | | | |<**********|
| | | | (F8) SIP | |
| | | | NOTIFY | |
| | | |<***********| |
| | | | (F9) SIP | |
| | | | 200 OK | |
| | | |***********>| |
| | | | | (F10) SIP |
| | (F11) XMPP subscribed | | 200 OK |
| |<..........................| |**********>|
| | (F12) XMPP presence | | |
| |<..........................| | |
| (F13) XMPP| | | | |
| subscribed| | | | |
|<..........| | | | |
| (F14) 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 (F3)
| SUBSCRIBE sip:romeo@example.net SIP/2.0
| Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=ffd2
| Call-ID: 5BCF940D-793D-43F8-8972-218F7F4EAA8C
| Event: presence
| Max-Forwards: 70
| CSeq: 123 SUBSCRIBE
| Contact: <sip:x2s.example.com;transport=tcp>
| Accept: application/pidf+xml
| Expires: 3600
| Content-Length: 0
Once the XMPP-to-SIP gateway has passed the SIP SUBSCRIBE off to the
SIP server (via the SIP-to-XMPP gateway) and the SIP server has
delivered the SIP SUBSCRIBE to the SIP user (F3 and F4; no example
shown for F4), the SIP user would then send a response indicating
acceptance of the subscription request:
Example 3: SIP Accepts Subscription Request (F6)
| 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: 234 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 whose value contains the string "active"
(see Section 5).
Example 4: SIP User Sends Presence Notification (F7)
| 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
| Call-ID: 5BCF940D-793D-43F8-8972-218F7F4EAA8C
| Event: presence
| Subscription-State: active;expires=499
| Max-Forwards: 70
| CSeq: 8775 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-orchard'>
| <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 (F13)
| <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
(F14)
| <presence from='romeo@example.net/orchard'
| to='juliet@example.com'/>
4.2.2. Refreshing a Presence Subscription
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 SIP 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 7) of this
document for important information and requirements regarding the
security implications of subscription refreshes.
4.2.3. Cancelling a Presence Subscription
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 XMPP-to-SIP SIP-to-XMPP SIP SIP
User Server Gateway Gateway Server User
| | | | | |
| (F15) XMPP| | | | |
|unsubscribe| | | | |
|..........>| | | | |
| | (F16) XMPP | | | |
| | unsubscribe| | | |
| |...........>| | | |
| | | (F17) SIP SUBSCRIBE | |
| | | Expires: 0 | | |
| | |**************************>| |
| | | | | (F18) SIP |
| | | | | SUBSCRIBE |
| | | | | Expires: 0|
| | | | |**********>|
| | | | | (F19) SIP |
| | | | | 200 OK |
| | | | |<**********|
| | | | (F20) SIP | |
| | | | 200 OK | |
| | | |<***********| |
| | (F21) XMPP unsubscribed | | |
| |<..........................| | |
| (F22) XMPP| | | | |
| unsubscribed | | | |
|<..........| | | | |
| | | | | |
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 (F15)
| <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 (F17)
| SUBSCRIBE sip:romeo@example.net SIP/2.0
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=j89d
| Call-ID: 9D9F00DF-FCA9-4E7E-B970-80B638D5218A
| Event: presence
| Max-Forwards: 70
| CSeq: 789 SUBSCRIBE
| Contact: <sip:x2s.example.com;transport=tcp>
| Accept: application/pidf+xml
| Expires: 0
| Content-Length: 0
Upon sending the transformed 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 (F22)
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='unsubscribed'/>
4.3. SIP to XMPP
4.3.1. Establishing a Presence Subscription
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 SIP-to-XMPP XMPP-to-SIP XMPP XMPP
User Server Gateway Gateway Server User
| | | | | |
| (F23) SIP | | | | |
| SUBSCRIBE | | | | |
|**********>| | | | |
| | (F24) SIP | | | |
| | SUBSCRIBE | | | |
| |***********>| | | |
| | | (F25) XMPP subscribe | |
| | |..........................>| |
| | | | | (F26) XMPP|
| | | | | subscribe |
| | | | |..........>|
| | | | | (F27) XMPP|
| | | | | subscribed|
| | | | |<..........|
| | | | (F28) XMPP | |
| | | | subscribed | |
| | | |<...........| |
| | (F29) SIP 200 OK | | |
| |<**************************| | |
| (F30) 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 (F23)
| SUBSCRIBE sip:juliet@example.com SIP/2.0
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| From: <sip:romeo@example.net>;tag=xfg9
| Call-ID: AA5A8BE5-CBB7-42B9-8181-6230012B1E11
| Event: presence
| Max-Forwards: 70
| CSeq: 263 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 (F25)
| <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 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=pq72
| Call-ID: AA5A8BE5-CBB7-42B9-8181-6230012B1E11
| Event: presence
| Subscription-State: terminated;reason=rejected
| Max-Forwards: 70
| CSeq: 232 NOTIFY
| Contact: <sip:x2s.example.com;transport=tcp>
| Content-Type: application/pidf+xml
| Content-Length: 0
4.3.2. Refreshing a Presence Subscription
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:
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 strange to the XMPP
contact (since it will appear that the SIP user has cancelled a
long-lived subscription).
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"
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 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=pq72
| Call-ID: 2B44E147-3B53-45E4-9D48-C051F3216D14
| Event: presence
| Subscription-State: terminated;reason=timeout
| Max-Forwards: 70
| CSeq: 232 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-balcony'>
| <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'/>
4.3.3. Cancelling a Presence Subscription
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: <sip:romeo@example.net>;tag=yt66
| Call-ID: 717B1B84-F080-4F12-9F44-0EC1ADE767B9
| Event: presence
| Max-Forwards: 70
| CSeq: 8775 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:
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
3. send an XMPP <presence/> stanza of type "unavailable" to the
XMPP contact
5. Notifications of Presence Information
5.1. Overview
Both XMPP and presence-aware SIP systems enable entities (often, but
not necessarily, human users) to send presence notifications to other
entities. At 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). In this document, we focus 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. 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. 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].
5.2. XMPP to SIP
When Juliet interacts with her XMPP client to modify her presence
information (or when her client automatically updates her presence
information, e.g., via an "auto-away" feature), her client generates
an XMPP <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/balcony'/>
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=balcony
| Call-ID: 2B44E147-3B53-45E4-9D48-C051F3216D14
| Event: presence
| Subscription-State: active;expires=599
| Max-Forwards: 70
| CSeq: 157 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-balcony'>
| <status>
| <basic>open</basic>
| <show xmlns='jabber:client'>away</show>
| </status>
| </tuple>
| </presence>
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.)
+-----------------------------+---------------------------+
| XMPP Element or Attribute | SIP Header or PIDF Data |
+-----------------------------+---------------------------+
| <presence/> stanza | "Event: presence" (1) |
+-----------------------------+---------------------------+
| XMPP resource identifier | 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:
(1) Only an XMPP <presence/> stanza that lacks a 'type' attribute or
whose 'type' attribute has a value of "unavailable" SHOULD be
mapped by an XMPP-to-SIP 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), prepending the resourcepart with "ID-" or some other
alphabetic string when mapping from XMPP to SIP is RECOMMENDED.
(3) In practice, XMPP <presence/> stanzas often do not include the
'id' attribute.
(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 basic 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 basic status of "closed".
(5) When the XMPP-to-SIP gateway receives XMPP presence of type
"unavailable" from the XMPP contact, it SHOULD (a) 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 (b) 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 <priority/> element is an integer between
-128 and +127, whereas the value of the PIDF <contact/>
element's 'priority' attribute is a decimal number from zero to
one inclusive, with a maximum of three decimal places. If the
value of the XMPP <priority/> element is negative, an XMPP-to-
SIP gateway MUST NOT map the value. If an XMPP-to-SIP 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
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 <show/> 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 <show/>
element [RFC6121] or translate a <show/> 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 <show/>
element and the custom extension if the gateway cannot suitably
translate the custom value into a <show/> value.
5.3. 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:
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=orchard
| Call-ID: C33C6C9D-0F4A-42F9-B95C-7CE86B526B5B
| Event: presence
| Subscription-State: active;expires=499
| Max-Forwards: 70
| CSeq: 8775 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-orchard'>
| <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/balcony'
| type='unavailable'/>
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.)
+---------------------------+-----------------------------+
| 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:
(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 <show/> 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.
6. Requests for Presence Information
Both SIP and XMPP provide methods for requesting presence information
about another entity.
6.1. 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
| <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=ffd2
| Call-ID: 5BCF940D-793D-43F8-8972-218F7F4EAA8C
| Event: presence
| Max-Forwards: 70
| CSeq: 123 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).
6.2. 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: <sip:romeo@example.net>;tag=yt66
| Call-ID: 717B1B84-F080-4F12-9F44-0EC1ADE767B9
| Event: presence
| Max-Forwards: 70
| CSeq: 8775 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 SHOULD 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'/>
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 (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 the gateway. As a further 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
Jabber ID (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.
8. References
8.1. Normative References
[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.
[RFC3863] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr,
W., and J. Peterson, "Presence Information Data Format
(PIDF)", RFC 3863, 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.
[RFC7247] Saint-Andre, P., Houri, A., and J. Hildebrand,
"Interworking between the Session Initiation Protocol
(SIP) and the Extensible Messaging and Presence Protocol
(XMPP): Architecture, Addresses, and Error Handling",
RFC 7247, May 2014.
8.2. Informative References
[RFC2778] Day, M., Rosenberg, J., and H. Sugano, "A Model for
Presence and Instant Messaging", RFC 2778, February 2000.
[RFC2779] Day, M., Aggarwal, S., Mohr, G., 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.
[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.
[SIMPLE-CPIM-MAPPING]
Campbell, B. and J. Rosenberg, "CPIM Mapping of SIMPLE
Presence and Instant Messaging", Work in Progress,
June 2002.
[XEP-0107] Saint-Andre, P. and R. Meijer, "User Mood", XSF XEP 0107,
October 2008, <http://xmpp.org/extensions/xep-0107.html>.
[XEP-0108] Meijer, R. and P. Saint-Andre, "User Activity",
XSF XEP 0108, October 2008,
<http://xmpp.org/extensions/xep-0108.html>.
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, Olle Johansson, Paul
Kyzivat, Salvatore Loreto, Michael Lundberg, Daniel-Constantin
Mierla, and Tory Patnoe.
Dave Crocker provided helpful and detailed feedback on behalf of the
Applications Area Directorate.
Ben Laurie performed a review on behalf of the Security Directorate,
resulting in improvements to the security considerations.
During IESG review, Pete Resnick caught several oversights in the
document with regard to interoperability.
The authors gratefully acknowledge the assistance of Markus Isomaki
and Yana Stamcheva as the working group chairs and Gonzalo Camarillo
as the sponsoring Area Director.
Some text in this document was borrowed from [RFC3922].
Peter Saint-Andre wishes to acknowledge Cisco Systems, Inc., for
employing him during his work on earlier versions of this document.
Authors' Addresses
Peter Saint-Andre
&yet
EMail: ietf@stpeter.im
Avshalom Houri
IBM
Rorberg Building, Pekris 3
Rehovot 76123
Israel
EMail: avshalom@il.ibm.com
Joe Hildebrand
Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
EMail: jhildebr@cisco.com
|
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