One document matched: draft-saintandre-xmpp-feature-set-00.txt
Network Working Group P. Saint-Andre
Internet-Draft XMPP Standards Foundation
Intended status: Informational October 31, 2007
Expires: May 3, 2008
A Feature Set for the Extensible Messaging and Presence Protocol (XMPP)
draft-saintandre-xmpp-feature-set-00
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines a protocol feature set for the Extensible
Messaging and Presence Protocol (XMPP), in accordance with the
concepts and formats proposed by Larry Masinter within the NEWTRK
Working Group.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Domain Identifier . . . . . . . . . . . . . . . . . . . . 4
2.2. Node Identifier . . . . . . . . . . . . . . . . . . . . . 4
2.3. Resource Identifier . . . . . . . . . . . . . . . . . . . 4
3. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. TCP Binding . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Namespaces . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3.1. Initial Stream . . . . . . . . . . . . . . . . . . . . 6
3.3.2. Response Stream . . . . . . . . . . . . . . . . . . . 6
3.4. Stream Features . . . . . . . . . . . . . . . . . . . . . 7
3.5. Closing Streams . . . . . . . . . . . . . . . . . . . . . 7
3.6. Stream Errors . . . . . . . . . . . . . . . . . . . . . . 7
4. STARTTLS Negotiation . . . . . . . . . . . . . . . . . . . . . 8
5. SASL Negotiation . . . . . . . . . . . . . . . . . . . . . . . 8
6. Mandatory TLS and SASL Technologies . . . . . . . . . . . . . 9
7. Resource Binding . . . . . . . . . . . . . . . . . . . . . . . 9
8. Server Dialback . . . . . . . . . . . . . . . . . . . . . . . 9
9. XML Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 10
10.2. Message Stanzas . . . . . . . . . . . . . . . . . . . . . 11
10.3. Presence Stanzas . . . . . . . . . . . . . . . . . . . . . 11
10.4. IQ Stanzas . . . . . . . . . . . . . . . . . . . . . . . . 12
10.5. Stanza Errors . . . . . . . . . . . . . . . . . . . . . . 12
10.6. Extended Content . . . . . . . . . . . . . . . . . . . . . 13
10.7. Stanza Handling . . . . . . . . . . . . . . . . . . . . . 13
11. Rosters . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
12. Presence Subscriptions . . . . . . . . . . . . . . . . . . . . 14
13. Presence Exchange . . . . . . . . . . . . . . . . . . . . . . 14
14. Security Considerations . . . . . . . . . . . . . . . . . . . 15
15. Informative References . . . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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1. Introduction
The Extensible Messaging and Presence Protocol (XMPP) is an
application profile of the Extensible Markup Language [XML] for
streaming XML data in close to real time between any two (or more)
network-aware entities. XMPP is typically used to exchange messages,
share presence information, and engage in structured request-response
interactions. The basic syntax and semantics of XMPP were developed
originally within the Jabber open-source community, mainly in 1999.
In late 2002, the XMPP Working Group was chartered with developing an
adaptation of the core Jabber protocol that would be suitable as an
IETF instant messaging (IM) and presence technology. As a result of
work by the XMPP WG, [RFC3920] and [RFC3921] were published in
October 2004, representing the most complete definition of XMPP at
that time.
The XMPP developer community has garnered extensive implementation
and deployment experience with XMPP since 2004. In addition, formal
interoperability testing has been carried out under the auspices of
the XMPP Standards Foundation (XSF). As a result, [rfc3920bis] and
[rfc3921bis] are currently being refined to capture the consensus of
the XMPP developer community regarding the features of XMPP.
This document defines a protocol feature set for XMPP. The feature
set attempts to adhere to the concepts and formats proposed by Larry
Masinter within the IETF's NEWTRK Working Group in 2005 (see
[INTEROP]). Therefore this document describes the set of
specifications and the features defined therein that constitute the
Extensible Messaging and Presence Protocol for the purpose of
interoperability testing.
The specifications considered to define XMPP are rfc3920bis and
rfc3921bis. Although the core XML streaming layer specified in
rfc3920bis is not necessarily tied to the instant messaging and
presence semantics specified in rfc3921bis, this interoperability
report treats them as a single protocol, since to date they usually
have been implemented and deployed as such. Where appropriate, this
interoperability report discusses the relevant feature as specified
in RFC3920 or RFC3921, experience and testing results related to that
feature, and modifications to the feature as specified in rfc3920bis
or rfc3921bis.
The remaining sections of this document specify the particular
features of XMPP. Because XMPP uses a client-server architecture,
each feature is labelled as applying to the client role, the server
role, or both. In addition, each feature is labelled as REQUIRED,
RECOMMENDED, or OPTIONAL, where those terms are to be understood as
described in [RFC2119].
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Note: This document contains brief descriptions of XMPP features.
Exact definitions of these features are contained in the relevant
specifications. In case the brief description for any feature as
provided in this document is inconsistent with the exact definition
as provided in the relevant specification, the exact definition shall
rule. This document does not specify the features of XMPP, it only
refers to them.
2. Addresses
XMPP addresses are of the form [node@]domain[/resource]. Rules for
each portion of the address are specified in Section 3 of rfc3920bis.
The following features apply.
2.1. Domain Identifier
As specified in Section 3.2 of rfc3920bis:
1. The domain identifier portion of an XMPP address must conform to
the Nameprep profile of Stringprep. Conformance with this
feature is REQUIRED for servers and RECOMMENDED for clients.
2. The domain identifier portion of an XMPP address must not be more
than 1023 bytes in length. Conformance with this feature is
REQUIRED for clients and for servers.
2.2. Node Identifier
As specified in Section 3.3 of rfc3920bis:
1. The node identifier portion of an XMPP address must conform to
the Nodeprep profile of Stringprep. Conformance with this
feature is REQUIRED for servers and RECOMMENDED for clients.
2. The node identifier portion of an XMPP address must not be more
than 1023 bytes in length. Conformance with this feature is
REQUIRED for clients and for servers.
2.3. Resource Identifier
As specified in Section 3.4 of rfc3920bis:
1. The resource identifier portion of an XMPP address must conform
to the Resourceprep profile of Stringprep. Conformance with this
feature is REQUIRED for servers and RECOMMENDED for clients.
2. The resource identifier portion of an XMPP address must not be
more than 1023 bytes in length. Conformance with this feature is
REQUIRED for clients and for servers.
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3. XML Streams
At root, XMPP is a technology for streaming XML data between a client
and a server or between two servers. Thus the management of XML
streams is a core aspect of XMPP. The following features apply.
3.1. TCP Binding
As specified in Section 4 of rfc3920bis:
1. XML streams are communicated over a TCP connection. Conformance
with this feature is REQUIRED for clients and for servers.
2. Before opening a TCP connection and XML stream to an XMPP server,
an entity must resolve the hostname of the server. Conformance
with this feature is REQUIRED for clients and for servers.
3. If an existing connection is unexpectedly terminated (e.g.,
because of a software or hardware failure), an entity should
follow the guidelines in section 5.7 of rfc3920bis regarding
hostname resolution and the time between reconnection attempts.
Conformance with this feature is RECOMMENDED for clients and for
servers.
3.2. Namespaces
As specified in Section 5.4 and Section 12.2 of rfc3920bis:
1. An XML stream must be qualified by a streams namespace of
'http://etherx.jabber.org/streams'. Conformance with this
feature is REQUIRED for clients and for servers.
2. All elements within the streams namespace must be prefixed with a
namespace prefix. Conformance with this feature is REQUIRED for
clients and for servers.
3. The streams namespace prefix should be "stream:". Conformance
with this feature is RECOMMENDED for clients and for servers.
4. An XML stream must have a default namespace other than the
streams namespace. Conformance with this feature is REQUIRED for
clients and for servers.
5. An implementation must support 'jabber:client' as a default
namespace. Conformance with this feature is REQUIRED for clients
and for servers.
6. An implementation must support 'jabber:server' as a default
namespace. Conformance with this feature is REQUIRED for servers
(the feature does not apply to clients).
3.3. Attributes
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3.3.1. Initial Stream
As specified in Section 5.3 of rfc3920bis:
1. An initiating entity should include a 'from' attribute in the
initial stream header it sends to a receiving entity.
Conformance with this feature is RECOMMENDED for clients and for
servers. (Note: This feature was modified in rfc3920bis as
compared to RFC3920, since implementation and deployment
experience has shown that including the 'from' attribute makes
stream establishment more efficient.)
2. An initiating entity should include a 'to' attribute in the
initial stream header it sends to a receiving entity.
Conformance with this feature is RECOMMENDED for clients and for
servers.
3. An initiating entity should include an 'xml:lang' attribute in
the initial stream headers that it generates. Conformance with
this feature is RECOMMENDED for clients and for servers.
4. An initiating entity must include a 'version' attribute whose
value is "1.0" (for XMPP 1.0 support) in the initial stream
headers it generates. Conformance with this feature is REQUIRED
for clients and for servers.
3.3.2. Response Stream
As specified in Section 5.3 of rfc3920bis:
1. A receiving entity must include a 'from' attribute in the
response stream header it sends to an initiating entity.
Conformance with this feature is REQUIRED for servers (the
feature does not apply to clients).
2. A receiving entity should include a 'to' attribute in the
response stream header it sends to an initiating entity.
Conformance with this feature is RECOMMENDED for servers (the
feature does not apply to clients). (Note: This feature was
modified in rfc3920bis as compared to RFC3920, since
implementation and deployment experience has shown that including
the 'to' attribute makes stream establishment more efficient.)
3. A receiving entity must include an 'id' attribute in the response
stream header it sends to an initiating entity. Conformance with
this feature is REQUIRED for servers (the feature does not apply
to clients).
4. The value of the 'id' attribute included in the response stream
header must be unique within the receiving entity. Conformance
with this feature is REQUIRED for servers (the feature does not
apply to clients).
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5. If the stream header that a receiving entity receives from an
initiating entity includes a 'version' attribute whose value is
"1.0", the receiving entity must include a 'version' attribute
whose value is "1.0" in the response stream headers it generates.
Conformance with this feature is REQUIRED for servers.
3.4. Stream Features
As specified in Section 5.5 of rfc3920bis:
1. A receiving entity must advertise the stream-related features it
supports after sending a response stream header. Conformance
with this feature is REQUIRED for servers (the feature does not
apply to clients).
2. A receiving entity should include an empty <required/> element if
a feature must be negotiated in order to successfully complete
stream negotiation or other subsequent tasks before XML stanzas
may be sent (e.g., resource binding for client-to-server
streams).
3.5. Closing Streams
As specified in Section 5.5 of rfc3920bis:
1. A stream is closed by sending a closing stream tag </stream:
stream> to the other party. Conformance with this feature is
REQUIRED for clients and for servers.
2. The entity that sends a closing stream tag should wait for the
other party to also send a closing stream tag before terminating
the underlying TCP connection; however, the entity MAY consider
both streams to be void if the other entity does not send its
closing stream tag within a reasonable amount of time.
Conformance with this feature is RECOMMENDED for clients and for
servers.
3. After an entity sends a closing stream tag, it MUST NOT send
further data over that stream. Conformance with this feature is
REQUIRED for clients and for servers.
4. After the entity that sent the first closing stream tag receives
a reciprocal closing stream tag from the other party (or if it
considers the stream to be void after a reasonable amount of
time), it MUST terminate the underlying TCP connection or
connections. Conformance with this feature is REQUIRED for
clients and for servers.
3.6. Stream Errors
As specified in Section 5.8 of rfc3920bis:
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1. An entity must generate a stream error (followed by a closing
stream tag and termination of the TCP connection) when it detects
a stream-related error condition. Conformance with this feature
is REQUIRED for clients and for servers.
2. The syntax for stream errors must follow the definition in
Section 4.7.2 of rfc3920bis. Conformance with this feature is
REQUIRED for clients and for servers.
4. STARTTLS Negotiation
As specified in Section 6 of rfc3920bis:
1. An implementation must support Transport Layer Security (TLS) for
channel encryption of XML streams. Conformance with this feature
is REQUIRED for clients and for servers.
2. There must be no whitespace between XML elements sent during TLS
negotiation. Conformance with this feature is REQUIRED for
clients and for servers.
3. Certificate validation must follow the rules in Section 14.2 of
rfc3920bis. Conformance with this feature is REQUIRED for
clients and for servers.
4. Upon successful TLS negotiation, the initiating entity must send
a new initial stream header to the receiving entity. Conformance
with this feature is REQUIRED for clients and for servers.
5. SASL Negotiation
As specified in Section 7 of rfc3920bis:
1. An implementation must support the Simple Authentication and
Security Layer (SASL) for authentication of XML streams.
Conformance with this feature is REQUIRED for clients and for
servers.
2. There must be no whitespace between XML elements sent during SASL
negotiation. Conformance with this feature is REQUIRED for
clients and for servers.
3. Upon successful SASL negotiation, the initiating entity must send
a new initial stream header to the receiving entity. Conformance
with this feature is REQUIRED for clients and for servers.
4. An implementation must support the SASL error conditions
specified in Section 6.4 of rfc3920bis. Conformance with this
feature is REQUIRED for clients and for servers.
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6. Mandatory TLS and SASL Technologies
As specified in Section 15.7 of rfc3920bis:
1. An implementation must support the TLS_RSA_WITH_3DES_EDE_CBC_SHA
cipher. Conformance with this feature is REQUIRED for clients
and for servers.
2. An implementation must support TLS plus SASL PLAIN for client-to-
server streams. Conformance with this feature is REQUIRED for
clients and for servers. (Note: This feature was added in
rfc3920bis as compared to RFC3920, since implementation of SASL
EXTERNAL is uncommon in XMPP clients, in part because underlying
security features such as X.509 certificates are not yet widely
deployed.)
3. An implementation must support TLS plus SASL EXTERNAL for server-
to-server connections. Conformance with this feature is REQUIRED
for servers.
4. For backward-compatibility, an implementation should support SASL
DIGEST-MD5 for server-to-server connections. Conformance with
this feature is RECOMMENDED for servers and clients.
7. Resource Binding
As specified in Section 8 of rfc3920bis:
1. An implementation must support resource binding for client-to-
server connections. Conformance with this feature is REQUIRED
for clients and for servers.
2. A client implementation must be able to request generation of a
resource (rather than providing it). Conformance with this
feature is RECOMMENDED for clients (the feature does not apply to
servers).
3. A server implementation must be able to generate a resource on
request. Conformance with this feature is REQUIRED for servers
(the feature does not apply to clients).
4. An implementation should be able to bind multiple resources to an
XML stream as specified in Section 8.5 of rfc3920bis.
Conformance with this feature is RECOMMENDED for servers and
OPTIONAL for clients.
8. Server Dialback
For backward-compatiblity, an implementation should support server
dialback for server-to-server connections. Conformance with this
feature is RECOMMENDED for servers (the feature does not apply to
clients). Server dialback was specified in Section 8 of RFC 3920 and
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is now canonically documented in [XEP-0220].
9. XML Usage
1. As specified in Section 12 of rfc3920bis, an implementation must
not inject XML comments, processing instructions, internal or
external DTD subsets, internal or external entity references
other than the predefined XML entities, or XML character data or
attribute values containing unescaped characters that map to the
predefined entities. Conformance with this feature is REQUIRED
for clients and for servers.
2. As specified in Section 12.1 of rfc3920bis, an implementation
must return a <restricted-xml/> stream error if it receives XML
comments, processing instructions, internal or external DTD
subsets, internal or external entity references other than the
predefined XML entities, or XML character data or attribute
values containing unescaped characters that map to the predefined
entities. Conformance with this feature is REQUIRED for clients
and for servers. (Note: This feature was modified in rfc3920bis
as compared to RFC3920, since ignoring such data rather than
returning an error is inconsistent with the stream error handling
recommendations in Section 5.8 of rfc3920bis.)
10. XML Stanzas
An implementation must handle the <presence/>, <message/>, and <iq/>
stanza types. Conformance with this feature is REQUIRED for clients
and for servers.
10.1. Attributes
As specified in Section 9.1 of rfc3920bis:
1. An implementation must support the 'to' attribute on all stanza
types to encapsulate the intended recipient's address, as
specified in Section 9.1.1 of rfc3920bis. Conformance with this
feature is REQUIRED for clients and servers.
2. An implementation must support the 'from' attribute on all stanza
types to encapsulate the sender's address, as specified in
Section 9.1.2 of rfc3920bis. Conformance with this feature is
REQUIRED for clients and servers.
3. In streams qualified by the 'jabber:client' namespace, the
receiving entity must validate the address of the sender by
verifying that it is that of a connected resource for the sending
entity or by stamping the 'from' value itself, as specified in
Section 9.1.2 of rfc3920bis. Conformance with this feature is
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REQUIRED for servers (the feature does not apply to clients).
4. In streams qualified by the 'jabber:server' namespace, the
sending entity must ensure that every stanza it sends possesses a
'from' attribute and that the domain identifier portion of the
encapsulated JID value matches a hostname of the server, as
specified in Section 9.1.2 of rfc3920bis. Conformance with this
feature is REQUIRED for servers (the feature does not apply to
clients).
5. In streams qualified by the 'jabber:server' namespace, the
receiving entity must ensure that every stanza it receives
possesses a 'from' attribute and that the domain identifier
portion of the encapsulated JID value matches a hostname of the
sending entity, as specified in Section 9.1.2 of rfc3920bis.
Conformance with this feature is REQUIRED for servers (the
feature does not apply to clients).
6. An XML stanza should possess an 'xml:lang' attribute, as
specified in section 9.1.5 of rfc3920bis. Conformance with this
feature is RECOMMENDED for clients and for servers.
10.2. Message Stanzas
As specified in Section 5 of rfc3921bis:
1. An implementation must differentiate between messages of type
"normal", "chat", "groupchat", "headline", and "error".
Conformance with this feature is REQUIRED for clients (the
feature does not apply to servers).
2. An implementation must support the <body/> child element of the
<message/> stanza. Conformance with this feature is REQUIRED for
clients (the feature does not apply to servers).
3. An implementation should support the <subject/> and <thread/>
child elements of the <message/> stanza. Conformance with this
feature is RECOMMENDED for clients (the feature does not apply to
servers).
10.3. Presence Stanzas
As specified in Section 6 of rfc3921bis:
1. An implementation must support <presence/> stanzas with no 'type'
attribute to signal availability and of type "unavailable" to
signal lack of availability. Conformance with this feature is
REQUIRED for clients and for servers.
2. An implementation must support <presence/> stanzas of type
"subscribe", "unsubscribe", "subscribed", and "unsubscribed" to
manage presence subscriptions. Conformance with this feature is
REQUIRED for clients and for servers.
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3. An implementation must support <presence/> stanzas of type
"probe" to discover the presence of subscribed entities.
Conformance with this feature is REQUIRED for servers (the
feature does not apply to clients).
10.4. IQ Stanzas
As specified in Section 9.2.3 of rfc3920bis:
1. An <iq/> stanza must possess an 'id' attribute. Conformance with
this feature is REQUIRED for clients and for servers.
2. The 'type' attribute of an <iq/> stanza must be present and it
must have a value of "get", "set", "result", or "error".
Conformance with this feature is REQUIRED for clients and for
servers.
3. The response to an <iq/> stanza of type "get" or "set" must be an
<iq/> stanza of type "result" or "error". Conformance with this
feature is REQUIRED for clients and for servers.
4. An <iq/> stanza of type "get" or "set" must contain only one
child element. Conformance with this feature is REQUIRED for
clients and for servers.
5. An <iq/> stanza of type "result" must contain zero child elements
or one child element. Conformance with this feature is REQUIRED
for clients and for servers.
6. An <iq/> stanza of type "error" should contain the child element
received in the corresponding <iq/> stanza of type "get" or
"set". Conformance with this feature is RECOMMENDED for clients
and for servers.
10.5. Stanza Errors
As specified in Section 9.3 of rfc3920bis:
1. A <message/>, <presence/>, or <iq/> stanza whose type is "error"
must contain an <error/> child element whose syntax adheres to
the definition specified in Section 9.3.2 of rfc3920bis.
Conformance with this feature is REQUIRED for clients and for
servers.
2. An implementation must not return an error stanza in response to
a <message/>, <presence/>, or <iq/> stanza whose type is "error".
Conformance with this feature is REQUIRED for clients and for
servers.
3. An implementation must support the stanza error conditions
specified in Section 9.3.3 of rfc3920bis. Conformance with this
feature is REQUIRED for clients and for servers.
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10.6. Extended Content
As specified in Section 9.4 of rfc3920bis:
1. An implementation must not process XML data qualified by XML
namespaces it does not understand. Conformance with this feature
is REQUIRED for clients and for servers.
10.7. Stanza Handling
As specified in Section 11 of rfc3920bis and Section 8 of rfc3921bis:
1. A server must properly handle an XML stanza with no 'to' address,
as specified in Section 11.1 of rfc3920bis. Conformance with
this feature is REQUIRED for servers (the feature does not apply
to clients).
2. A server must properly handle an XML stanza with a 'to' address
whose domain identifier does not match one of the configured
hostnames of the server, as specified in Section 11.3 of
rfc3920bis and Section 8.4 of rfc3921bis. Conformance with this
feature is REQUIRED for servers (the feature does not apply to
clients).
3. A server must properly handle an XML stanza with a 'to' address
whose domain identifier exactly matches one of the configured
hostnames of the server (or such a hostname appended by an XMPP
resource identifier, as specified in Section 11.2 of rfc3920bis.
Conformance with this feature is REQUIRED for servers (the
feature does not apply to clients).
4. A server must properly handle an XML stanza with a 'to' address
of the form <node@domain> or <node@domain/resource> whose
domain identifier matches one of the configured hostnames of the
server, as specified in Section 11.2.3 of rfc3920bis and Sections
8.1, 8.2, and 8.3 of rfc3921bis. Conformance with this feature
is REQUIRED for servers (the feature does not apply to clients).
11. Rosters
As specified in Section 2 of rfc3921bis:
1. An implementation must use <iq/> stanzas containing <query/>
elements qualified by the 'jabber:iq:roster' namespace in order
to manage contact lists (in XMPP, "rosters"). Conformance with
this feature is REQUIRED for clients and for servers.
2. A client implementation should retrieve its roster before sending
initial presence. Conformance with this feature is RECOMMENDED
for clients (the feature does not apply to servers).
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3. A server implementation must send a roster push to each
interested resource whenever one of the client's resources adds,
updates, or deletes a roster item. Conformance with this feature
is REQUIRED for severs (the feature does not apply to clients).
12. Presence Subscriptions
As specified in Section 3 of rfc3921bis:
1. In order to request a subscription to another entity's presence,
a client implementation must send a presence stanza of type
"subscribe". Conformance with this feature is REQUIRED for
clients (the feature does not apply to servers).
2. In order to approve a subscription request received from another
entity, a client implementation must send a presence stanza of
type "subscribed". Conformance with this feature is REQUIRED for
clients (the feature does not apply to servers).
3. In order to deny a subscription request received from another
entity, a client implementation must send a presence stanza of
type "unsubscribed". Conformance with this feature is REQUIRED
for clients (the feature does not apply to servers).
4. In order to cancel a previously-requested subscription to another
entity's presence, a client implementation must send a presence
stanza of type "unsubscribe". Conformance with this feature is
REQUIRED for clients (the feature does not apply to servers).
5. A server implementation must not auto-approve subscription
requests it receives on behalf of a local account. Conformance
with this feature is REQUIRED for servers (the feature does not
apply to clients).
6. A server implementation that receives a subscription request for
a local account must deliver the request to the account's
interested resources until the account owner either approves or
denies the subscription request. Conformance with this feature
is REQUIRED for servers (the feature does not apply to clients).
13. Presence Exchange
As specified in Section 4 of rfc3921bis:
1. In order to advertise its network availability (presence), a
client implementation shall send a presence stanza with no 'to'
attribute and no 'type' attribute. Conformance with this feature
is REQUIRED for clients (the feature does not apply to servers).
2. In order to advertise the fact that it is not available for
communication over the network, a client implementation shall
send a presence stanza with no 'to' attribute and a 'type'
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Internet-Draft XMPP Feature Set October 2007
attribute whose value is "unavailable". Conformance with this
feature is REQUIRED for clients (the feature does not apply to
servers).
3. When it receives a presence stanza with no 'to' attribute and
either no 'type' attribute or a 'type' attribute whose value is
"unavailable", a server implementation shall broadcast that
presence information to all subscribed entities (as fully
explained and qualified in Sections 4.2, 4.4, and 4.5 of
rfc3921bis). Conformance with this feature is REQUIRED for
servers (the feature does not apply to clients)
4. When it receives a presence stanza with a 'to' attribute and
either no 'type' attribute or a 'type' attribute whose value is
"unavailable", a server implementation shall route or deliver
that directed presence information to the intended recipient only
(as fully explained and qualified in Section 4.6 of rfc3921bis).
Conformance with this feature is REQUIRED for servers (the
feature does not apply to clients)
5. When it receives an initial presence stanza from a connected
client, a server implementation should send presence probes to
all of the entities to which the local account is subscribed (as
fully explained and qualified in Section 4.3 of rfc3921bis).
Conformance with this feature is REQUIRED for servers (the
feature does not apply to clients).
14. Security Considerations
This document does not directly discuss security issues, since they
are discussed in the relevant sections of RFC3920, RFC3921,
rfc3920bis, and rfc3921bis.
RFC3921 requires client implementations to use the technology
specified in [RFC3923] for end-to-end signing and object encryption
of XML stanzas in the context of instant messaging and presence
applications. Unfortunately, there exist no implementations of the
protocol specified in RFC 3923; as a result, no implementation and
deployment experience exists and no interoperability testing could be
performed.
15. Informative References
[INTEROP] Masinter, L., "Formalizing IETF Interoperability
Reporting", draft-ietf-newtrk-interop-reports-00 (work in
progress), October 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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Internet-Draft XMPP Feature Set October 2007
[RFC3920] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[rfc3920bis]
Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", draft-saintandre-rfc3920bis-04
(work in progress), October 2007.
[RFC3921] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 3921, October 2004.
[rfc3921bis]
Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
draft-saintandre-rfc3921bis-04 (work in progress),
October 2007.
[RFC3923] Saint-Andre, P., "End-to-End Signing and Object Encryption
for the Extensible Messaging and Presence Protocol
(XMPP)", RFC 3923, October 2004.
[XEP-0220]
Saint-Andre, P. and J. Miller, "Server Dialback", XSF
XEP 0220, July 2007.
[XML] Paoli, J., Maler, E., Sperberg-McQueen, C., Yergeau, F.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
Author's Address
Peter Saint-Andre
XMPP Standards Foundation
P.O. Box 1641
Denver, CO 80201
US
Email: stpeter@jabber.org
URI: xmpp:stpeter@jabber.org
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Internet-Draft XMPP Feature Set October 2007
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