One document matched: draft-saintandre-sip-xmpp-presence-00.txt
Network Working Group P. Saint-Andre
Internet-Draft XMPP Standards Foundation
Intended status: Informational A. Houri
Expires: July 7, 2008 IBM
J. Hildebrand
Jabber, Inc.
January 4, 2008
Interworking between the Session Initiation Protocol (SIP) and the
Extensible Messaging and Presence Protocol (XMPP): Presence
draft-saintandre-sip-xmpp-presence-00
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Copyright Notice
Copyright (C) The IETF Trust (2008).
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).
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Presence Subscriptions . . . . . . . . . . . . . . . . . . . . 3
2.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 8
3. Presence Notifications . . . . . . . . . . . . . . . . . . . . 10
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. XMPP to SIP . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. SIP to XMPP . . . . . . . . . . . . . . . . . . . . . . . 14
4. Content Types . . . . . . . . . . . . . . . . . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.1. Normative References . . . . . . . . . . . . . . . . . . . 18
6.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . . . 21
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1. Introduction
In order to help ensure interworking between presence systems that
conform to the requirements of RFC 2779 [IMP-REQS], it is important
to clearly define protocol mappings between such systems. Within the
IETF, work has proceeded on two presence technologies:
o Various extensions to the Session Initiation Protocol ([SIP]) for
instant messaging, as developed within the SIP for Instant
Messaging and Presence Leveraging Extensions (SIMPLE) Working
Group; the relevant specification for presence is [SIP-PRES]
o The Extensible Messaging and Presence Protocol (XMPP), which
consists of a formalization of the core XML streaming protocols
developed originally by the Jabber open-source community; the
relevant specifications are [XMPP] for the XML streaming layer and
[XMPP-IM] for basic presence and instant messaging extensions
One approach to helping ensure interworking between these protocols
is to map each protocol to the abstract semantics described in
[CPIM]; that is the approach taken by [SIMPLE-CPIM] and [XMPP-CPIM].
The approach taken in this document is to directly map semantics from
one protocol to another (i.e., from SIP/SIMPLE to XMPP and vice-
versa).
The architectural assumptions underlying such direct mappings are
provided in [SIP-XMPP], including mapping of addresses and error
condisions. The mappings specified in this document cover basic
presence functionality. Mapping of more advanced functionality is
out of scope for this document, but other documents in this "series"
cover such topics.
Note: The capitalized key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in RFC 2119 [TERMS].
2. Presence Subscriptions
2.1. Overview
Both XMPP and presence-aware SIP systems enable entities (often but
not necessarily human users) to subscribe to the presence of other
entities. XMPP presence subscriptions are specified in [XMPP-IM].
Presence subscriptions using a SIP event package for presence are
specified in [SIP-PRES].
As described in [XMPP-IM], XMPP presence subscriptions are managed
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using XMPP presence stanzas of type "subscribe", "subscribed",
"unsubscribe", and "unsubscribed". The main subscription states are
"none" (neither the user nor the contact is subscribed to the other's
presence information), "from" (the user has a subscription from the
contact), "to" (the user has a subscription to the contact's presence
information), and "both" (both user and contact are subscribed to
each other's presence information).
As described in [SIP-PRES], SIP presence subscriptions are managed
through the use of SIP SUBSCRIBE events sent from a SIP user agent to
an intended recipient who is most generally referenced by an Instant
Message URI of the form <pres:user@domain> but who may be referenced
by a SIP or SIPS URI of the form <sip:user@domain> or
<sips:user@domain>.
The subscription models underlying XMPP and SIP are quite different.
For instance, XMPP presence subscriptions are long-lived (indeed
permanent if not explicitly cancelled), whereas SIP presence
subscriptions are short-lived (the default time to live of a SIP
presence subscription is 3600 seconds, as specified in Section 6.4 of
[SIP-PRES]). These differences are addressed below.
2.2. XMPP to SIP
2.2.1. Establishing
An XMPP user initiates a subscription by sending a subscription
request to another entity (conventionally called a "contact"), which
request the contact either accepts or declines. If the contact
accepts the request, the user will have a subscription to the
contact's presence information until (1) the user unsubscribes or (2)
the contact cancels the subscription. The subscription request is
encapsulated in a presence stanza of type "subscribe":
Example: XMPP user subscribes to SIP contact:
| <presence from='juliet@example.com'
| to='romeo@example.net'
| type='subscribe'/>
Upon receiving such a stanza, the XMPP server to which Juliet has
connected needs to determine the identity of the foreign domain,
which it does by performing one or more [SRV] lookups. For presence
stanzas, the order of lookups recommended by [XMPP-IM] is to first
try the "_xmpp-server" service as specified in [XMPP] and to then try
the "_pres" service as specified in [IMP-SRV]. Here we assume that
the first lookup will fail but that the second lookup will succeed
and return a resolution "_pres._simple.example.net.", since we have
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already assumed that the example.net hostname is running a SIP
presence service.
Once the XMPP server has determined that the foreign domain is
serviced by a SIMPLE server, it must determine how to proceed. We
here assume that the XMPP server contains or has available to it an
XMPP-SIMPLE gateway. The XMPP server would then deliver the presence
stanza to the XMPP-SIMPLE gateway.
The XMPP-SIMPLE gateway is then responsible for translating the XMPP
subscription request into a SIP SUBSCRIBE request from the XMPP user
to the SIP user:
Example: XMPP user subscribes to SIP contact (SIP transformation):
| SUBSCRIBE sip:romeo@example.net SIP/2.0
| Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=ffd2
| To: <sip:romeo@example.net>
| Call-ID: l04th3s1p@example.com
| Event: presence
| Max-Forwards: 70
| CSeq: 123 SUBSCRIBE
| Contact: <sip:sipgate.example.com;transport=tcp>
| Accept: application/pidf+xml
| Expires: 3600
| Content-Length: 0
The SIP user then SHOULD send a response indicating acceptance of the
subscription request:
Example: SIP accepts subscription request:
| SIP/2.0 200 OK
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| From: <sip:romeo@example.net>;tag=ffd2
| To: <sip:juliet@example.com>;tag=j89d
| Call-ID: l04th3s1p@example.com
| CSeq: 234 SUBSCRIBE
| Contact: <sip:simple.example.net;transport=tcp>
| Expires: 3600
| Content-Length: 0
In accordance with [SIP-EVENT], the XMPP-SIMPLE gateway should
consider the subscription state to be "neutral" until it receives a
NOTIFY message. Therefore the SIP user or SIP-XMPP gateway at the
SIP user's domain SHOULD immediately send a NOTIFY message containing
a "Subscription-State" header whose value contains the string
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"active" (see Section 3).
Example: SIP user sends presence notification:
| NOTIFY sip:192.0.2.1 SIP/2.0
| Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
| From: <sip:romeo@example.net>;tag=yt66
| To: <sip:juliet@example.com>;tag=bi54
| Call-ID: l04th3s1p@example.com
| 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='orchard'>
| <status>
| <basic>open</basic>
| </status>
| </tuple>
| </presence>
Upon receiving the first NOTIFY with a subscription state of active,
the XMPP-SIMPLE gateway MUST generate a presence stanza of type
"subscribed":
Example: XMPP user receives acknowledgement from SIP contact:
| <presence to='romeo@example.net'
| from='juliet@example.com'
| type='subscribed'/>
For information about handling of the NOTIFY message, see Section 3.
2.2.2. Refreshing
It is the responsibility of the XMPP-SIMPLE gateway to set the value
of the "Expires" header and to periodically renew the subscription on
the SIMPLE side of the gateway so that the subscription appears to be
permanent to the XMPP user (e.g., the XMPP-SIMPLE gateway SHOULD send
a new SUBSCRIBE request to the SIP user whenever the XMPP user sends
initial presence to its XMPP server, i.e., upon initiating a presence
session with the XMPP server). See the Security Considerations
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(Section 5) of this document for important information and
requirements regarding the security implications of this
functionality.
2.2.3. Cancelling
At any time after subscribing, the XMPP user may unsubscribe from the
contact's presence. This is done by sending a presence stanza of
type "unsubscribe":
Example: XMPP user unsubscribes from SIP contact:
| <presence from='juliet@example.com'
| to='romeo@example.net'
| type='unsubscribe'/>
The XMPP-SIMPLE gateway is responsible for translating the
unsubscribe command into a SIP SUBSCRIBE request with the "Expires"
header set to a value of zero:
Example: XMPP user unsubscribes from SIP contact (SIP
transformation):
| SUBSCRIBE sip:romeo@example.net SIP/2.0
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=j89d
| To: <sip:romeo@example.net>;tag=xfg9
| Call-ID: 1ckm32@example.com
| 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-SIMPLE gateway
SHOULD a presence stanza of type "unsubscribed" to the XMPP user:
Example: XMPP user receives unsubscribed notification:
| <presence to='romeo@example.net'
| from='juliet@example.com'
| type='unsubscribed'/>
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2.3. SIP to XMPP
2.3.1. Establishing
A SIP user initiates a subscription to a contact's presence
information by sending a SIP SUBSCRIBE request to the contact. The
following is an example of such a request:
Example: SIP user subscribes to XMPP contact:
| SUBSCRIBE sip:juliet@example.com SIP/2.0
| Via: SIP/2.0/TCP s2x.example.net;branch=z9hG4bKna998sk
| From: <sip:romeo@example.net>;tag=xfg9
| To: <sip:juliet@example.com>;tag=ur93
| Call-ID: 4wcm0n@example.net
| Event: presence
| Max-Forwards: 70
| CSeq: 263 SUBSCRIBE
| Contact: <sip:simple.example.net;transport=tcp>
| Accept: application/pidf+xml
| Content-Length: 0
Upon receiving such a request, a SIMPLE-XMPP gateway is responsible
for translating it into an XMPP subscription request from the SIP
user to the XMPP user:
Example: SIP user subscribes to XMPP contact (XMPP transformation):
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='subscribe'/>
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.
2.3.2. Refreshing
It is the responsibility of the SIMPLE-XMPP gateway to properly
handle the difference between short-lived SIP presence subscriptions
and long-lived XMPP presence subscriptions. The gateway has two
options when the SIP user's subscription expires:
o Cancel the subscription (i.e., treat it as temporary) and send an
XMPP presence stanza of type "unsubscribe" to the XMPP contact;
this honors the SIP semantic but will seem rather odd to the XMPP
contact.
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o Maintain the subscription (i.e., treat it as long-lived) and (1)
send a SIP NOTIFY request to the SIP user containing a PIDF
document specifying that the XMPP contact now has a basic status
of "closed", including a Subscription-State of "terminated" and
(2) send an XMPP presence stanza of type "unavailable" to the XMPP
contact; this violates the letter of the SIP semantic but will
seem more natural to the XMPP contact.
Which of these options the SIMPLE-XMPP gateway chooses is up to the
implementation.
If the implementation chooses the first option, the protocol
generated would be as follows:
Example: SIP subscription expires (treated as temporary by gateway):
| <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: 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: <sip:juliet@example.com>;tag=ur93
| To: <sip:romeo@example.net>;tag=pq72
| Call-ID: j4s0h4vny@example.com
| Event: presence
| Subscription-State: terminated;reason=timeout
| Max-Forwards: 70
| CSeq: 232 NOTIFY
| Contact: <sip:sipgate.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='balcony'>
| <status>
| <basic>closed</basic>
| </status>
| </tuple>
| </presence>
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Example: SIP subscription expires (treated as long-lived by gateway):
| <presence from='romeo@example.net'
| to='juliet@example.com'
| type='unavailable'/>
2.3.3. Cancelling
At any time, the SIP user may cancel the subscription by sending a
SUBSCRIBE message whose "Expires" header is set to a value of zero
("0"):
Example: SIP user cancels subscription:
| SUBSCRIBE sip:192.0.2.1 SIP/2.0
| Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
| From: <sip:romeo@example.net>;tag=yt66
| To: <sip:juliet@example.com>;tag=bi54
| Call-ID: 1tsn1ce@example.net
| 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 SIMPLE-XMPP gateway is
responsible for doing one of the following:
o Cancel the subscription (i.e., treat it as temporary) and send an
XMPP presence stanza of type "unsubscribe" to the XMPP contact.
o Maintain the subscription (i.e., treat it as long-lived) and (1)
send a SIP NOTIFY request to the SIP user containing a PIDF
document specifying that the XMPP contact now has a basic status
of "closed", (2) send a SIP SUBSCRIBE request to the SIP user with
an "Expires" header set to a value of "0" (zero) when it receives
XMPP presence of type "unavailable" from the XMPP contact, and (3)
send an XMPP presence stanza of type "unavailable" to the XMPP
contact.
3. Presence Notifications
3.1. Overview
Both XMPP and presence-aware SIP systems enable entities (often but
not necessarily human users) to send presence notifications to other
entities. At a minimum, the term "presence" refers to information
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about an entity's availability for communication on a network (on/
off), often supplemented by information that further specifies the
entity's communications context (e.g., "do not disturb"). Some
systems and protocols extend this notion even further and refer to
any relatively ephemeral information about an entity as a kind of
presence; categories of such "extended presence" include geographical
location (e.g., GPS coordinates), user mood (e.g., grumpy), user
activity (e.g., walking), and ambient environment (e.g., noisy). In
this document, we focus on the "least common denominator" of network
availability only, although future documents may address broader
notions of presence, including extended presence.
Presence using XMPP presence stanzas of type "available" or
"unavailable" is specified in [XMPP-IM]. SIP presence using a SIP
event package for presence is specified in [SIP-PRES].
As described in [XMPP-IM], 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 (again, this is a simplifying assumption
introduced for explanatory purposes only). In general, XMPP presence
is sent by the user to the user's server and then broadcasted to all
entities who are subscribed to the user's presence information.
As described in [SIP-PRES], presence information about an entity is
communicated by means of a SIP NOTIFY event sent from a SIP user
agent to an intended recipient who is most generally referenced by an
Instant Message URI of the form <pres:user@domain> but who may be
referenced by a SIP or SIPS URI of the form <sip:user@domain> or
<sips:user@domain>. Here again we introduce the simplifying
assumption that the user agent is controlled by a human user.
3.2. XMPP to SIP
When Juliet interacts with her XMPP client to modify her presence
information (or when her client automatically updates her presence
information, e.g. via an "auto-away" feature), her client generates
an XMPP <presence/> stanza. The syntax of the <presence/> stanza,
including required and optional elements and attributes, is defined
in [XMPP-IM]. The following is an example of such a stanza:
Example: XMPP user sends presence notification:
| <presence from='juliet@example.com/balcony'/>
Upon receiving such a stanza, the XMPP server to which Juliet has
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connected broadcasts it to all subscribers who are authorized to
receive presence notifications from Juliet (this is similar to the
SIP NOTIFY method). For each subscriber, broadcasting the presence
notification involves either delivering it to a local recipient (if
the hostname in the subscriber's address matches one of the hostnames
serviced by the XMPP server) or attempting to route it to the foreign
domain that services the hostname in the subscriber's address.
Naturally, in this document we assume that the hostname is a SIP
presence service hosted by a separate server. As specified in
[XMPP-IM], the XMPP server needs to determine the identity of the
foreign domain, which it does by performing one or more [SRV]
lookups. For presence stanzas, the order of lookups recommended by
[XMPP-IM] is to first try the "_xmpp-server" service as specified in
[XMPP] and to then try the "_pres" service as specified in [IMP-SRV].
Here we assume that the first lookup will fail but that the second
lookup will succeed and return a resolution
"_pres._simple.example.net.", since we have already assumed that the
example.net hostname is running a SIP presence service. (Note: The
XMPP server may have previously determined that the foreign domain is
a SIMPLE server, e.g., when it sent a SIP SUBSCRIBE to the SIP user
when Juliet sent initial presence to the XMPP server, in which case
it would not need to perform the SRV lookups; the caching of such
information is a matter of implementation and local service policy,
and is therefore out of scope for this document.)
Once the XMPP server has determined that the foreign domain is
serviced by a SIMPLE server, it must determine how to proceed. We
here assume that the XMPP server contains or has available to it an
XMPP-SIMPLE gateway. The XMPP server would then deliver the presence
stanza to the XMPP-SIMPLE gateway.
The XMPP-SIMPLE gateway is then responsible for translating the XMPP
presence stanza into a SIP NOTIFY request and included PIDF document
from the XMPP user to the SIP user.
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Example: XMPP user sends presence notification (SIP transformation):
| NOTIFY sip:192.0.2.2 SIP/2.0
| Via: SIP/2.0/TCP x2s.example.com;branch=z9hG4bKna998sk
| From: <sip:juliet@example.com>;tag=gh19
| To: <sip:romeo@example.net>;tag=yt66
| Call-ID: j4s0h4vny@example.com
| Event: presence
| Subscription-State: active;expires=599
| Max-Forwards: 70
| CSeq: 157 NOTIFY
| Contact: <sip:sipgate.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='balcony'>
| <status>
| <basic>open</basic>
| </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.)
Table 6: Presence syntax mapping from XMPP to SIP
+-----------------------------+---------------------------+
| XMPP Element or Attribute | SIP Header or PIDF Data |
+-----------------------------+---------------------------+
| <presence/> stanza | "Event: presence" [1] |
| XMPP resource identifer | tuple 'id' attribute |
| from | From |
| id | Call-ID |
| to | To |
| type | basic status [2][3] |
| xml:lang | Content-Language |
| <priority/> | PIDF priority for tuple |
| <show/> | (no mapping) |
| <status/> | note [4] |
+-----------------------------+---------------------------+
Note the following regarding these mappings:
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1. Only a presence stanza that lacks a 'type' attribute or whose
'type' attribute has a value of "unavailable" should be mapped by
an XMPP-SIMPLE gateway to a SIP NOTIFY request, since those are
the only presence stanzas that represent notifications.
2. Because the lack of a 'type' attribute indicates that an XMPP
entity is available for communications, the gateway SHOULD map
that information to a PIDF <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".
3. When the XMPP-SIMPLE gateway receives XMPP presence of type
"unavailable" from the XMPP contact, it SHOULD (1) send a SIP
NOTIFY request to the SIP user containing a PIDF document
specifying that the XMPP contact now has a basic status of
"closed" and (2) send a SIP SUBSCRIBE request to the SIP user
with an "Expires" header set to a value of "0" (zero).
4. The character data of the XMPP <status/> element MAY be mapped to
the character data of the PIDF <note/> element.
3.3. SIP to XMPP
When Romeo changes his presence, his SIP user agent generates a SIP
NOTIFY request for any active subscriptions. The syntax of the
NOTIFY request is defined in [SIP-PRES]. The following is an example
of such a request:
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Example: SIP user sends presence notification:
| NOTIFY sip:192.0.2.1 SIP/2.0
| Via: SIP/2.0/TCP simple.example.net;branch=z9hG4bKna998sk
| From: <sip:romeo@example.net>;tag=yt66
| To: <sip:juliet@example.com>;tag=bi54
| Call-ID: j0sj4sv1m@example.net
| 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='orchard'>
| <status>
| <basic>open</basic>
| </status>
| </tuple>
| </presence>
Upon receiving such a request, a SIMPLE-XMPP gateway is responsible
for translating it into an XMPP presence stanza from the SIP user to
the XMPP user:
Example: SIP user sends presence notification (XMPP transformation):
| <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.)
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Table 7: Presence syntax mapping from SIP to XMPP
+---------------------------+-----------------------------+
| SIP Header or PIDF Data | XMPP Element or Attribute |
+---------------------------+-----------------------------+
| basic status | type [1] |
| Content-Language | xml:lang |
| CSeq | id (OPTIONAL) |
| From | from |
| priority for tuple | <priority/> |
| To | to |
| body of MESSAGE | <body/> |
+---------------------------+-----------------------------+
Note the following regarding these mappings:
1. A PIDF basic status of "open" SHOULD be mapped to no 'type'
attribute, and a PIDF basic status of "closed" SHOULD be mapped
to a 'type' attribute whose value is "unavailable".
4. Content Types
SIP requests of type NOTIFY normally contain presence information
encapsulated using the "application/pidf+xml" content type. The
recommended procedures for SIMPLE-to-XMPP gateways to use in handling
these content types are as follows.
The "application/pidf+xml' content type is specified in [PIDF]. The
Presence Information Data Format defines a common data format for
presence protocols that conform to the Common Profile for Presence
([CPP]), enabling presence information to be transferred across CPP-
compliant protocol boundaries without modification, with attendant
benefits for end-to-end encryption and performance. Because the
syntax for the "application/pidf+xml" content type is Extensible
Markup Language ([XML]), it is straightforward to send PIDF data over
the Extensible Messaging and Presence Protocol ([XMPP]), since XMPP
is simply an XML streaming protocol.
In addition to following the syntax mappings specified in Section 3,
a SIMPLE-to-XMPP gateway MAY encapsulate PIDF data within an
"extended namespace" contained in an XMPP presence stanza. The
RECOMMENDED method is to include the PIDF <presence/> element as a
child of the XMPP <presence/> stanza. Although it may appear that
this would be potentially confusing, the inclusion of the
'urn:ietf:params:xml:ns:pidf' namespace ensures that PIDF data is
kept separate from XMPP presence data (in accordance with
[XML-NAMES]). The following is a simple example of encapsulating
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PIDF data within an "extended namespace" in XMPP:
A basic example of PIDF over XMPP:
<presence from='romeo@example.net/orchard' xml:lang='en'>
<show>dnd</show>
<status>Wooing Juliet</status>
<presence xmlns='urn:ietf:params:xml:ns:pidf'
entity='pres:romeo@example.net'>
<tuple id='orchard'>
<status>
<basic>open</basic>
</status>
</tuple>
</presence>
</presence>
5. Security Considerations
Detailed security considerations for presence protocols are given in
[IMP-REQS], for SIP-based presence in [SIP-PRES] (see also [SIP]),
and for XMPP-based presence in [XMPP-IM] (see also [XMPP]).
The mismatch between long-lived XMPP presence subscriptions and
short-lived SIP presence subscriptions introduces the possibility of
an amplification attack launched from the XMPP network against a SIP
presence server. To help prevent such an attack, access to an XMPP-
SIMPLE gateway that is hosted on the XMPP network SHOULD be
restricted to XMPP users associated with a single domain or trust
realm (e.g., a gateway hosted at simple.example.com should allow only
users within the example.com domain to access the gateway, not users
within example.org, example.net, or any other domain); if a SIP
presence server receives communications through an XMPP-SIMPLE
gateway from users who are not associated with a domain that is so
related to the hostname of the gateway, it MAY (based on local
service provisioning) refuse to service such users or refuse to
communicate with the gateway. Furthermore, whenever an XMPP-SIMPLE
gateway seeks to refresh an XMPP user's long-lived subscription to a
SIP user's presence, it MUST first send an XMPP <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 [XMPP-IM]; however, the administrator
of an XMPP-SIMPLE gateway MAY (based on local service provisioning)
exempt "known good" XMPP servers from this check (e.g., the XMPP
server associated with the XMPP-SIMPLE gateway as described above).
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6. References
6.1. Normative References
[IMP-SRV] Peterson, J., "Address Resolution for Instant Messaging
and Presence", RFC 3861, August 2004.
[PIDF] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr,
W., and J. Peterson, "Presence Information Data Format
(PIDF)", RFC 3863, August 2004.
[SIP] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[SIP-EVENT]
Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[SIP-PRES]
Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.
[SIP-XMPP]
Saint-Andre, P., Houri, A., and J. Hildebrand,
"Interworking between the Session Initiation Protocol
(SIP) and the Extensible Messaging and Presence Protocol
(XMPP): Core", draft-saintandre-sip-xmpp-core-00 (work in
progress), January 2008.
[SRV] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-
xml, October 2000, <http://www.w3.org/TR/REC-xml>.
[XML-NAMES]
Bray, T., Hollander, D., and A. Layman, "Namespaces in
XML", W3C REC-xml-names, January 1999,
<http://www.w3.org/TR/REC-xml-names>.
[XMPP] Saint-Andre, P., "Extensible Messaging and Presence
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Protocol (XMPP): Core", RFC 3920, October 2004.
[XMPP-IM] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 3921, October 2004.
6.2. Informative References
[CPIM] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.
[CPP] Peterson, J., "Common Profile for Presence (CPP)",
RFC 3859, August 2004.
[IMP-REQS]
Day, M., Aggarwal, S., and J. Vincent, "Instant Messaging
/ Presence Protocol Requirements", RFC 2779,
February 2000.
[SIMPLE-CPIM]
Rosenberg, J. and B. Campbell, "CPIM Mapping of SIMPLE
Presence and Instant Messaging",
draft-ietf-simple-cpim-mapping-01 (work in progress),
June 2002.
[XMPP-CPIM]
Saint-Andre, P., "Mapping the Extensible Messaging and
Presence Protocol (XMPP) to Common Presence and Instant
Messaging (CPIM)", RFC 3922, October 2004.
Authors' Addresses
Peter Saint-Andre
XMPP Standards Foundation
P.O. Box 1641
Denver, CO 80201
USA
Email: stpeter@jabber.org
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Avshalom Houri
IBM
Building 18/D, Kiryat Weizmann Science Park
Rehovot 76123
Israel
Email: avshalom@il.ibm.com
Joe Hildebrand
Jabber, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
Email: jhildebrand@jabber.com
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