wdiff rfc6809.original rfc6809.txt

SIPCORE Working Group
Internet Engineering Task Force (IETF) C. Holmberg
Internet-Draft
Request for Comments: 6809 I. Sedlacek
Intended status:
Category: Standards Track Ericsson
Expires: April 22, 2013
ISSN: 2070-1721 H. Kaplan
Acme Packet
October 19,
November 2012

Mechanism to indicate support Indicate Support of features Features and capabilities Capabilities in the
Session Initiation Protocol (SIP)
draft-ietf-sipcore-proxy-feature-12.txt

Abstract

This specification defines a new SIP header field, Feature-Caps. The
Feature-Caps header field conveys feature capability feature-capability indicators that
are used to indicate support of features and capabilities for SIP
entities that are not represented by the Uniform Resource Identifier
(URI) of the Contact header field.

SIP entities that are represented by the URI of the SIP Contact
header field can convey media feature tags in the Contact header
field to indicate support of features and capabilities.

This specification also defines feature capability indicators, feature-capability indicators and
creates a new IANA registry, "Proxy-Feature Feature Capability Feature-Capability
Indicator Trees", for registering feature capability feature-capability indicators.

Status of this This Memo

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This Internet-Draft will expire on April 22, 2013.
http://www.rfc-editor.org/info/rfc6809.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 ....................................................3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 .....................................................4
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 .....................................................4
4. Feature-Caps Header Field . . . . . . . . . . . . . . . . . . 5 .......................................4
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 5 ...............................................4
4.2. User Agent and Proxy Behavior . . . . . . . . . . . . . . 5 ..............................4
4.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 5 .............................................4
4.2.2. B2BUA Behavior . . . . . . . . . . . . . . . . . . . . 6 ......................................5
4.2.3. Registrar Behavior . . . . . . . . . . . . . . . . . . 6 ..................................6
4.2.4. Proxy behavior . . . . . . . . . . . . . . . . . . . . 7 Behavior ......................................6
4.3. SIP Message Type and Response Code Semantics . . . . . . . 7 ...............7
4.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 7 .............................................7
4.3.2. SIP Dialog . . . . . . . . . . . . . . . . . . . . . . 7 ..........................................7
4.3.3. SIP Registration (REGISTER) . . . . . . . . . . . . . 8 .........................7
4.3.4. SIP Stand-Alone Standalone Transactions . . . . . . . . . . . . . 8 .........................8
5. Feature Capability Feature-Capability Indicators . . . . . . . . . . . . . . . . 9 ...................................8
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 9 ...............................................8
5.2. Registration Trees . . . . . . . . . . . . . . . . . . . . 9 .........................................9
5.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 9 .............................................9
5.2.2. Global Tree . . . . . . . . . . . . . . . . . . . . . 9 .........................................9
5.2.3. SIP Tree . . . . . . . . . . . . . . . . . . . . . . . 10 ............................................9
5.3. Feature Capability Feature-Capability Indicator Specification Requirements . 10 ...10
5.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 10 ............................................10
5.3.2. Overall Description . . . . . . . . . . . . . . . . . 10 ................................10
5.3.3. Feature Capability Feature-Capability Indicator Values . . . . . . . . . 11 ................10
5.3.4. Usage Restrictions . . . . . . . . . . . . . . . . . . 11 .................................11
5.3.5. Interoperability Considerations . . . . . . . . . . . 11 ....................11
5.3.6. Security Considerations . . . . . . . . . . . . . . . 12 ............................11
5.3.7. Examples . . . . . . . . . . . . . . . . . . . . . . . 12 ...........................................12
5.3.8. Other Information . . . . . . . . . . . . . . . . . . 12 ..................................12
6. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 .........................................................12
6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 12 ...................................................12
6.2. Syntax: Feature-Caps header field . . . . . . . . . . . . 12 Header Field .........................12
6.2.1. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . 12 ...............................................12
6.3. Syntax: feature capability indicator . . . . . . . . . . . 13 Feature-Capability Indicator ......................12
6.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 13 ............................................12
6.3.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . 13 ...............................................13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 ............................................13
7.1. Registration of the Feature-Caps header field . . . . . . 13 Header Field .............13
7.2. Registration of the Feature-Caps header field parameter . 13 Header Field Parameter ...13
7.3. Proxy-Feature Feature Capability Feature-Capability Indicator Trees . . . . . 14 ..........14
7.3.1. Introduction . . . . . . . . . . . . . . . . . . . . . 14 .......................................14
7.3.2. Global Feature Capability Feature-Capability Indicator
Registration Tree . . . . . . . . . . . . . . . . . . . . . . . . . 15 ..................................14
7.3.3. SIP Feature Capability Feature-Capability Indicator
Registration Tree . . 15 ..................................15
8. Feature Capability Feature-Capability Indicator Registration Template . . . . . . 16 .............16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17 ........................................17
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 ..............................................17
11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. ....................................................18
11.1. Normative References . . . . . . . . . . . . . . . . . . . 20
12.2. .....................................18
11.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 ...................................18

1. Introduction

The Session Initiation Protocol (SIP) [RFC3261] "Caller Preferences"
extension, extension for
indicating User Agent (UA) capabilities, defined in RFC 3840
[RFC3840], provides a mechanism that allows a SIP message to convey
information relating to the originator's features and capabilities,
using the Contact header field.

o - The SIP entity acts as a SIP proxy.

o - The SIP entity acts as a SIP registrar.

o - The SIP entity acts as a Back-to-Back User Agent (B2BUA)
[RFC3261], where the Contact header field URI represents another
SIP entity.

SIP entities that are represented by the URI of the SIP Contact
header field can convey media feature tags in the Contact header
field to indicate support of features and capabilities.

Unlike media feature tags, feature capability feature-capability indicators are intended
to only be used with the SIP protocol. SIP.

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].

3. Definitions

Downstream SIP entity: SIP entity in the direction towards which a
SIP request is sent.

Upstream SIP entity: SIP entity in the direction from which a SIP
request is received.

4. Feature-Caps Header Field

4.1. Introduction

The Feature-Caps header field is used by SIP entities to convey
support of features and capabilities, by setting feature capability feature-capability
indicators. A feature capability feature-capability indicator conveyed in a Feature-
Caps
Feature-Caps header field indicates that a SIP entity in the SIP
message
signalling signaling path supports the associated feature and
capability.

4.2. User Agent and Proxy Behavior

4.2.1. General

If the URI in a Contact header field of a request or response
represents a SIP entity, the entity MUST NOT indicate supported
features and capabilities using a Feature-Caps header field within
that request or response.

When a SIP entity receives a SIP request, or response, that contains
one or more Feature-Caps header fields, the feature capability feature-capability
indicators in the header field inform the entity about the features
and capabilities supported by entities in the SIP message signalling signaling
path. The procedure by which features and capabilities are invoked
are outside the scope of this specification, specification and MUST be described by
individual feature capability feature-capability indicator specifications.

A Feature-Caps header field value cannot convey the address of the
SIP entity that inserted the Feature-Caps header field. If
additional data about a supported feature needs to be conveyed, such
as the address of the SIP entity that indicated support of the
feature, then the feature definition needs to define a way to convey
that information as a value of the associated feature capability feature-capability
indicator.

When a SIP entity adds a Feature-Caps header field to a SIP message,
it MUST place the header field before any existing Feature-Caps
header field in the message to be forwarded, so that the added header
field becomes the top-most one. Then, when another SIP entity
receives a SIP request or the response, the SIP feature capability feature-capability
indicators in the top-most Feature-Caps header field will represent
the supported features and capabilities "closest", from a SIP
signaling point of view, to the entity.

Based on features and policies, a SIP entity MAY remove a Feature-
Caps
Feature-Caps header field from a SIP message. Also, a SIP entity MAY
remove a feature capability feature-capability indicator from a Feature-Caps header
field within a SIP message. A SIP entity SHOULD NOT re-order the Feature-
Caps
Feature-Caps header fields within a SIP message.

For a given fc-value, as defined in section Section 6.2.1, the order in which
feature capability
feature-capability indicators are listed has no significance. For
example, "foo;bar" and "bar;foo" have the same meaning (i.e. (i.e., that
the SIP entity that inserted the feature capability feature-capability indicator
supports the features and capabilities associated with the "foo" and
"bar"
feature capability indicators. feature-capability indicators).

4.2.2. B2BUA Behavior

The procedures in this Section section apply to User Agents (UAs) [RFC3261]
that are part of B2BUAs that are referenced in the message by a
Record-Route header field rather than by the URI of the Contact
header field.

When such a UA sends a SIP request, if the UA wants to indicate
support of features and capabilities towards its downstream SIP
entities, it inserts a Feature-Caps header field to in the request,
containing one or more feature capability feature-capability indicators associated with
the supported features and capabilities, before it forwards the
request.

If the SIP request is triggered by another SIP request that the B2BUA
has received, the UA MAY forward received Feature-Caps header fields
by copying them to the outgoing SIP request, similar to a SIP proxy,
before it inserts its own Feature-Caps header field to in the SIP
request.

When such a UA receives a SIP response, if the UA wants to indicate
support of features and capabilities towards its upstream SIP
entities, it inserts a Feature-Caps header field to in the response,
containing one or more feature capability feature-capability indicators associated with
the supported features and capabilities, before it forwards the
response.

If the SIP response is triggered by another SIP response that the
B2BUA has received, the UA MAY forward received Feature-Caps header
field
fields by copying them to the outgoing SIP response, similar to a SIP
proxy, before it inserts its own Feature-Caps header field to in the SIP
response.

4.2.3. Registrar Behavior

If a SIP registrar wants to indicate support of features and
capabilities towards its upstream SIP entities, it inserts a Feature-
Caps
Feature-Caps header field, containing one or more feature capability feature-capability
indicators associated with the supported features and capabilities,
to
in a REGISTER response.

4.2.4. Proxy behavior Behavior

When a SIP proxy receives a SIP request, if the proxy wants to
indicate support of features and capabilities towards its downstream
SIP entities, it inserts a Feature-Caps header field to in the request,
containing one or more SIP feature capability feature-capability indicators associated
with the supported features and capabilities, before it forwards the
request.

When a proxy receives a SIP response, if the proxy wants to indicate
support of features and capabilities towards its upstream SIP
entities, it inserts a Feature-Caps header field to in the response,
containing one or more SIP feature capability feature-capability indicators associated
with the supported features and capabilities, before it forwards the
response.

4.3. SIP Message Type and Response Code Semantics

4.3.1. General

This Section section describes the general usage and semantics of the
Feature-Caps header field for different SIP message types and
response codes.

Section 6.2.1 defines the Feature-Caps header field ABNF.

4.3.2. SIP Dialog

The Feature-Caps header field can be used within an initial SIP
request for a dialog, within a target refresh SIP request, and within
any 18x or 2xx response associated with such requests.

If a feature capability feature-capability indicator is inserted in a Feature-Caps
header field of an initial request for a dialog, or within a response
of such a request, it indicates to the receivers of the request (or
response) that the feature associated with the feature capability feature-capability
indicator is supported for the duration of the dialog, until a target
refresh request is sent for the dialog, or until the dialog is
terminated.

Unless a feature capability feature-capability indicator is inserted in a Feature-Caps
header field of a target refresh request, or within a response of
such a request, it indicates to the receivers of the request (or
response) that the feature is no longer supported for the dialog.

For a given dialog dialog, a SIP entity MUST insert the same feature feature-
capability indicators in all 18x and 2xx responses associated with a
given transaction.

As it cannot be guaranteed that 2xx responses associated with SIP
SUBSCRIBE requests will reach the User Agent Client (UAC) [RFC3261],
due to forking of the request, entities need to indicate supported
features and capabilities in the SIP NOTIFY request that will be sent
for each of the created subscription dialogs.

4.3.3. SIP Registration (REGISTER)

The Feature-Caps header field can be used within a SIP REGISTER
request,
request and within the 200 (OK) response associated with such a
request.

If a feature capability feature-capability indicator is conveyed in a Feature-Caps
header field of a REGISTER request, or within an associated response,
it indicates to the receivers of the message that the feature
associated with the feature capability feature-capability indicator is supported for the
registration, until the registration of the contact that was
explicitly conveyed in the REGISTER request expires, or until the
registered contact is explicitly refreshed and the refresh REGISTER
request does not contain the feature capability feature-capability indicator associated
with the feature.

While a REGISTER response can contain contacts that have been
registered as part of other registration transactions, support of any
indicated feature only applies to requests sent to the contact(s)
that were explicitly conveyed in the associated REGISTER request.

This specification does not define any semantics for usage of the
Feature-Caps header field in pure registration binding fetching
messages (see Section 10.2.3 of RFC 3261), where the REGISTER request
does not contain a Contact header field. Unless such semantics is are
defined in a future extension, fetching messages will not have any
impact on previously indicated support of features and capabilities,
and SIP entities MUST NOT insert a Feature-Caps header field to in such
messages.

If SIP Outbound outbound [RFC5626] is used, the rules above apply. However,
supported features and capabilities only apply for the registration
flow on which support has been explicitly indicated.

4.3.4. SIP Stand-Alone Standalone Transactions

The Feature-Caps header field can be used within a standalone SIP
request,
request and within any 2xx response associated with such a request.

If a feature capability feature-capability indicator is inserted in a Feature-Caps
header field of a standalone request, or within a response of such a
request, it indicates to the receivers of the request (or response)
that the feature associated with the feature capability feature-capability indicator is
supported for the duration of the standalone transaction.

5. Feature Capability Feature-Capability Indicators

5.1. Introduction

Feature capability

Feature-capability indicators are used by SIP entities not
represented by the URI of the Contact header field to indicate
support of features and capabilities, where media feature tags cannot
be used to indicate the such support.

A value, or a list of values, that provides additional information
about the supported feature or capability, capability can be associated with a
feature capability
feature-capability indicator.

5.2. Registration Trees

5.2.1. General

The following subsections define registration trees, distinguished
by the use of faceted names (e.g., names of the form "tree.feature-
name").
"tree.feature-name"). The registration trees are defined in the IANA "Proxy-
Feature Feature Capability
"Proxy-Feature Feature-Capability Indicator Trees" registry.

The trees defined herein are similar to the global tree and sip SIP tree
defined for media feature tags, in RFC RFCs 2506 [RFC2506] and RFC 3840. 3840
[RFC3840]. Other registration trees are outside the scope of this
specification.

In contrast to RFC RFCs 2506 and RFC 3840, this specification only defines a
global tree and a sip SIP tree, as they are the only trees defined in
those RFCs that have been used for defining SIP-specific media
feature tags.

When a feature capability feature-capability indicator is registered in any registration
tree, no leading "+" is used in the registration.

5.2.2. Global Tree

The global feature capability feature-capability indicator tree is similar to the media
feature tag global tree defined in RFC 2506 [RFC2506].

A feature capability feature-capability indicator in the global tree will be
distinguished by the leading facet "g.". An organization can propose
either a designation indicative of the feature, feature (e.g., "g.blinktags")
or a faceted designation including the organization name (e.g.,
"g.organization.blinktags").

5.2.3. SIP Tree

The sip feature capability SIP feature-capability indicator tree is similar to the media
feature tag sip SIP tree defined in RFC 3840.

A feature capability feature-capability indicator in the sip SIP tree will be distinguished
by the leading facet "sip.".

5.3. Feature Capability Feature-Capability Indicator Specification Requirements

5.3.1. General

A feature capability feature-capability indicator specification MUST address the issues
defined in the following subsections, subsections or document why an issue is not
applicable for the specific feature capability feature-capability indicator. A
reference to the specification MUST be provided when the feature feature-
capability indicator is registered with IANA (see Section 8).

It is bad practice for feature capability feature-capability indicator specifications to
repeat procedures (e.g. (e.g., general procedures on the usage of the
Feature-Caps header field and feature capability feature-capability indicators) defined
in this specification, unless needed for clarification or emphasis
purpose.
purposes. A feature capability feature-capability indicator specification MUST NOT
modify the Feature-Caps header field rules and semantics defined in
Section 4.

A feature capability feature-capability indicator specification MUST NOT weaken any
behavior designated with "SHOULD" or "MUST" in this specification.
However, a specification MAY strengthen "SHOULD", "MAY", or
"RECOMMENDED" requirements to "MUST" strength if features and
capabilities associated with the feature capability feature-capability indicator
require it.

5.3.2. Overall Description

The feature capability feature-capability indicator specification MUST contain an
overall description of the feature capability feature-capability indicator: how it is
used to indicate support of a feature, a description of the feature
associated with the feature capability feature-capability indicator, a description of
any additional information (conveyed using one or more feature feature-
capability indicator values) that can be conveyed together with the
feature capability
feature-capability indicator, and a description of how the associated
feature MAY be exercised/invoked.

5.3.3. Feature Capability Feature-Capability Indicator Values

A feature capability feature-capability indicator can have an associated value, or a
list of values. The feature capability feature-capability indicator specification MUST
define the syntax and semantics of any value defined for the feature feature-
capability indicator, including possible restrictions related to the
usage of a specific value. The feature capability feature-capability indicator
specification MUST define the value(s) in accordance with the ABNF
defined in Section 6.3.2. The feature capability feature-capability indicator
specification MUST define whether the feature capability feature-capability indicator
has a default value.

If no values are defined for the feature capability feature-capability indicator, it
MUST be indicated in the feature capability feature-capability indicator specification.

A feature capability feature-capability indicator value is only applicable for the
feature capability
feature-capability indicator for which it has been defined. For
other feature capability feature-capability indicators, the value has to be defined
explicitly, even if the semantics are identical.

It is strongly RECOMMENDED to not re-use a value that already has
been defined for another feature capability feature-capability indicator, unless the
semantics of the values are the same.

5.3.4. Usage Restrictions

If there are restrictions on how SIP entities can insert a feature feature-
capability indicator, the feature capability feature-capability indicator specification
MUST document such restrictions.

There might be restrictions related to whether or not entities

o are allowed to insert a feature capability feature-capability indicator in registration related
registration-related messages, standalone transaction messages, dialog related or
dialog-related messages,
whether entities

o are allowed to insert a feature capability feature-capability indicator in requests
or responses, whether entities

o also need to support other features and capabilities in order to
insert a feature capability feature-capability indicator, and whether entities

o are allowed to indicate support of a feature in conjunction with
another feature.

5.3.5. Interoperability Considerations

The feature capability feature-capability indicator specification MUST document any
specific interoperability considerations that apply to the feature feature-
capability indicator.

Interoperability considerations can e.g. can, e.g., include procedures related
to cases where an expected feature capability feature-capability indicator is not
present,
present or where it contains an unexpected value.

5.3.6. Security Considerations

The feature capability feature-capability indicator specification MUST document any
specific security considerations that apply to the feature capability feature-capability
indicator.

5.3.7. Examples

It is recommended that the feature capability feature-capability indicator specification
provide demonstrative message flow diagrams, paired with complete
messages and message descriptions.

Note that example message flows are by definition informative, informative and do
not replace normative text.

5.3.8. Other Information

If there is additional information about the feature capability feature-capability
indicator, it is recommended to describe such information. It can
include e.g.
include, for example, names of related feature capability feature-capability indicators.

6. Syntax

6.1. General

This Section section defines the ABNF for the Feature-Caps header field, field and
for the feature capability feature-capability indicators. The ABNF defined in this
specification is conformant to RFC 5234 [RFC5234]." [RFC5234].

6.2. Syntax: Feature-Caps header field Header Field

6.2.1. ABNF

The ABNF for the Feature-Caps header fields is:

Feature-Caps = "Feature-Caps" HCOLON fc-value
*(COMMA fc-value)
fc-value = "*" *(SEMI feature-cap)

NOTE: The "*" value is present in order to follow the guidelines for
syntax in RFC 4485 [RFC4485] and to maintain a consistent format with
RFC
RFCs 3840 [RFC3840] and RFC 3841 [RFC3841].

6.3. Syntax: feature capability indicator Feature-Capability Indicator

6.3.1. General

In a feature capability feature-capability indicator name (ABNF: fcap-name), dots can be
used to implement a feature capability feature-capability indicator tree hierarchy (e.g.
(e.g., tree.feature.subfeature). The description of usage of such a
tree hierarchy must be described when registered.

6.3.2. ABNF

The ABNF for the feature capability indicator: feature-capability indicator is:

feature-cap = "+" fcap-name [EQUAL LDQUOT (fcap-value-list
/ fcap-string-value ) RDQUOT]
fcap-name = ftag-name
fcap-value-list = tag-value-list
fcap-string-value = string-value
;; ftag-name, tag-value-list, string-value defined in RFC 3840

NOTE: In comparison with media feature tags, the "+" sign in front of
the feature capability feature-capability indicator name is mandatory.

7. IANA Considerations

7.1. Registration of the Feature-Caps header field Header Field

This specification registers a new SIP header field, Feature-Caps,
according to the process of defined in RFC 3261 [RFC3261].

The following is the registration for the Feature-Caps header field: in the "Header
Fields" registry:

RFC Number: RFC XXXX 6809

Header Field Name: Feature-Caps

7.2. Registration of the Feature-Caps header field parameter Header Field Parameter

This specification adds the Feature-Caps header field to the IANA
"Header Field Parameters and Parameter Values" registry, according to
the process of described in RFC 3968 [RFC3968].

Predefined
Header Field Parameter Name Values Reference
------------------------------------------------------------------
--------------------------------------------------------------------

Feature-Caps +<fcap-name> * No [RFC XXXX] [RFC6809]

* <fcap-name> denotes parameter names conforming to the
syntax <fcap-name> defined in RFC XXXX. 6809. Valid
feature capability
feature-capability indicators are registered in [IANA:
insert reference to the new
Proxy-Feature Feature
Capability Feature-Capability Indicator Trees registry].

(IANA: please sort the "Feature-Caps" line into the table and place
the remainder of the above as a footnote to the table.) registry.

7.3. Proxy-Feature Feature Capability Feature-Capability Indicator Trees

7.3.1. Introduction

This specification creates a new sub registry sub-registry to the IANA "Session
Initiation Protocol (SIP) Parameters" Protocol Registry, registry, according to the
process of defined in RFC 5226. The name of the sub registry sub-registry is "Proxy-
Feature Feature Capability
"Proxy-Feature Feature-Capability Indicator Trees".

Feature capability

Feature-capability indicators are categorized by the "leading facet"
of their name. The leading facet is a prefix of the name consisting
of all characters up to and including the first ".". Feature Feature-
capability indicator names that contain no "." characters are
considered to have an empty ("") leading facet.

The "Proxy-Feature Feature Capability Feature-Capability Indicator Trees" registry
contains sub registries sub-registries for subsets (called 'trees') of feature feature-
capability indicators sharing the same leading facet. Each feature feature-
capability indicator is registered within the tree that matches its
leading facet. If no tree matches its leading facet facet, then the feature
capability
feature-capability indicator can not cannot be registered.

New feature capability feature-capability indicator sub registries sub-registries (trees) can be
registered. The registration must meet the "Standards Action"
policies defined in RFC 5226 [RFC5226]. A new name, unique leading
facet, and registration policies (as defined in RFC 5226) for feature
capability
feature-capability indicators within this tree need to be provided.

This document defines the first two feature capability feature-capability indicator
trees ("g." and "sip."). It does not define a tree for the empty
leading facet.

7.3.2. Global Feature Capability Feature-Capability Indicator Registration Tree

This specification creates a new feature capability feature-capability indicator tree in
the IANA "Proxy-Feature Feature Capability Feature-Capability Indicator Trees" registry.
The name of the tree is "Global Feature Capability Feature-Capability Indicator
Registration Tree", and its leading facet is "g.". It is used for
the registration of feature capability feature-capability indicators.

When a feature capability feature-capability indicator is registered in the global tree,
it needs to meet the "Specification Required" policies defined in
RFC 5226. A designated area expert will review the proposed feature feature-
capability indicator, indicator and consult with members of related mailing
lists. The information required in the registration is defined in
Section 5.3 of RFC XXXX. this document.

Note that all feature capability feature-capability indicators registered in the global
tree will have names with a leading facet "g.". No leading "+" is
used in the registrations in any of the feature capability feature-capability indicator
registration trees.

The format of the global tree is as described below:

Name Description Reference
------------------------------

Name - contains the Feature Capability Feature-Capability Indicator Name, provided in
the registration feature capability feature-capability indication registration template.

Description,

Description - provided in the registration feature capability feature-capability
indication registration template.

Reference - contains the Feature Capability Feature-Capability Indicator Specification
Reference, specification
reference provided in the registration feature capability feature-capability indication
registration template.

No initial values are registered in the global tree.

7.3.3. SIP Feature Capability Feature-Capability Indicator Registration Tree

This specification creates a new feature capability feature-capability indicator tree in
the IANA "Proxy-Feature Feature Capability Feature-Capability Indicator Trees" registry.
The name of the tree is "SIP Feature Capability Feature-Capability Indicator
Registration Tree", and its leading facet is "sip.". It is used for
the registration of feature capability feature-capability indicators.

When a feature capability feature-capability indicator is registered in the sip SIP tree, it
needs to meet the "IETF Review" policies defined in RFC 5226. The
information required in the registration is defined in Section 5.3 of
RFC XXXX.
this document.

Note that all feature capability feature-capability indicators registered in the SIP
tree will have names with a leading facet "sip.". No leading "+" is
used in the registrations in any of the feature capability feature-capability indicator
registration trees.

The format of the SIP tree is as described below:

Name Description Reference
------------------------------

Name - contains the Feature Capability Feature-Capability Indicator Name, provided in
the registration feature capability feature-capability indication registration template.

Description,

Description - provided in the registration feature capability feature-capability
indication registration template.

No initial values are registered in the SIP tree.

8. Feature Capability Feature-Capability Indicator Registration Template

Registration requests for the global tree are submitted by e-mail email to
iana@iana.org.

Registration requests for the sip SIP tree requires submitting an
Internet-Draft to the IESG.

| Instructions are preceded by '|'. All fields are mandatory.

Feature capability

Feature-capability indicator name:

Description:

| The description should be no longer than 4 lines. More
| detailed information can be provided in the feature
| capability indicator specification.

Feature capability indicator name:

| The referenced specification must contain the information
| listed in Section 5.3 of RFC XXXX.

Feature capability

Feature-capability indicator specification reference:

| The referenced specification must contain the information
| listed in Section 5.3 of RFC XXXX. 6809.

Contact:

| Name(s) & email address(es) of person(s) to
| contact for further information."

(IANA: Please replace XXXX with the assigned RFC number) information.

9. Security Considerations

The security issues for feature capability feature-capability indicators are similar to
the ones defined in RFC 3840 for media feature tags. Media feature
tags can reveal information about end-users end users and end-user equipment,
which can be used for industrial espionage. The knowledge about end-
user equipment capabilities can also be used to influence application
behavior. As feature capability feature-capability indicators are not intended to
convey capability information of end-user devices, such end-user
security aspects of RFC 3840 do not apply to feature capability feature-capability
indicators.

In addition, the RFC 3840 security issue discussed in RFC 3840 regarding an
attacker using the SIP caller preferences extension [RFC3841] in
order to affect routing decisions does not apply, as the mechanism is
not defined to be used with feature capability feature-capability indicators.

Feature capability

Feature-capability indicators can, however, provide capability and
characteristics information about the SIP entity, some of which might
be sensitive. Malicious elements viewing the indicators may be able
to discern application deployment details or identify elements with
exploitable feature implementation weaknesses. The Feature-Caps
header field does not convey address information about SIP entities.
However, individual feature capability feature-capability indicators might provide
address information as feature capability feature-capability indicator values.
Therefore, if the feature capability feature-capability indicators provide information
that requires data integrity or origin authentication, mechanisms for
providing those MUST be provided. If confidentiality is required required,
then the specification MUST call for the use of Transport Layer
Security (TLS) [RFC5246] at all hops. Since there are no
satisfactory middle-
to-end middle-to-end or middle-to-middle SIP confidentiality
mechanisms, TLS is as good as it gets gets, and specifications SHOULD NOT
define feature
capability feature-capability indicators that need confidentiality that
is better than the hop-by-hop confidentiality provided by TLS.

10. Acknowledgements

The authors wish to thank everyone in the SIP community that provided
input and feedback on the work of this specification.

11. Change Log

[RFC EDITOR NOTE: Please remove this Section when publishing]

Changes from draft-holmberg-sipcore-proxy-feature-11
o IANA: Indicating that no initial values are registered in the
trees.
o IESG: Editorial changes based on comments from Barry Leiba.
o IESG: Reference to RFC 5234 added based on comments from Adrian
Farrel.
o IESG: Editorial changes and Security Consideration modification
based on comments from Stephen Farrell.
o IESG: Editorial changes based on comments from Pete Resnick.

Changes from draft-holmberg-sipcore-proxy-feature-10
o Editorial changes.

o 'IETF Consensus' changed to 'IETF Review' (section 7.3.3)

Changes from draft-holmberg-sipcore-proxy-feature-09
o Editorial changes based on SECDIR comments from Radia Perlman.
o Editorial changes based on Gen-Art comments from Brian E
Carpenter.
o Editorial changes based on OPSDIR comments from Jouni Korhonen.
o Change in security considerations indicating that, if sensitive
information is conveyed, mechanisms for guaranteeing
confidentiality and authenticity must be provided.

Changes from draft-holmberg-sipcore-proxy-feature-08
o Comments from Atle Mondrad.

Changes from draft-holmberg-sipcore-proxy-feature-06
o Editorial changes.

Changes from draft-holmberg-sipcore-proxy-feature-05
o AD comments from Robert Sparks
o Additional text added to the Security Considerations section.
o IANA registration template modified.
o IANA registration procedures clarified.
o Feature Capability Indicator specification requirements modified.
o Note regarding SUBSCRIBE 200 responses added.
o Editorial modifications.

Changes from draft-holmberg-sipcore-proxy-feature-04
o WGLC comments from Keith Drage
o 'feature cap' name changed to 'feature capability indicator'.
o Feature-Caps header field added to IANA Header Field Parameters
and Parameter Values registry.
o Editorial modifications.

Changes from draft-ietf-sipcore-proxy-feature-03
o Additional Security Considerations text added.
o IANA Considerations modified.
o Editorial corrections.

Changes from draft-ietf-sipcore-proxy-feature-02
o Changes based on WGLC comments from Shida Schubert.
o - Document title changed
o - Terminology alignment
o - Note text clarifications
o Changes based on WGLC comments from Lili Yang.

Changes from draft-ietf-sipcore-proxy-feature-01
o Changes based on comments from Paul Kyzivat.
o IANA Considerations text added.

Changes from draft-holmberg-sipcore-proxy-feature-04/
draft-ietf-sipcore-proxy-feature-00
o Media feature tags replaced with feature caps, based on SIPCORE
consensus at IETF#83 (Paris).
o Editorial corrections and modifications.

Changes from draft-holmberg-sipcore-proxy-feature-03
o Hadriel Kaplan added as co-author.
o Terminology change: instead of talking of proxies, talk about
entities which are not represented by the URI in a Contact header
field (http://www.ietf.org/mail-archive/web/sipcore/current/
msg04449.html).
o Clarification regarding the usage of the header field in 18x/2xx
responses (http://www.ietf.org/mail-archive/web/sipcore/current/
msg04449.html).
o Specifying that feature support can also be indicated in target
refresh requests (http://www.ietf.org/mail-archive/web/sipcore/
current/msg04454.html).
o Feature Cap specification registration information added.

Changes from draft-holmberg-sipcore-proxy-feature-02
o Definition, and usage of, a new header field, instead of Path,
Record-Route, Route and Service-Route.

Changes from draft-holmberg-sipcore-proxy-feature-01
o Requirement section added
o Use-cases and examples updated based on work in 3GPP

Changes from draft-holmberg-sipcore-proxy-feature-00
o Additional use-cases added
o Direction section added

12. References

12.1.

11.1. 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.

[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.

12.2.

11.2. Informative References

[RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506, March 1999.

[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004.

[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.

[RFC3968] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Header Field Parameter Registry for the Session
Initiation Protocol (SIP)", BCP 98, RFC 3968,
December 2004.

[RFC4485] Rosenberg, J. and H. Schulzrinne, "Guidelines for Authors
of Extensions to the Session Initiation Protocol (SIP)",
RFC 4485, May 2006.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.

[RFC5626] Jennings, C., Mahy, R., and F. Audet, "Managing Client-
Initiated Connections in the Session Initiation Protocol
(SIP)", RFC 5626, October 2009.

[3GPP.23.237]
3GPP, "IP Multimedia Subsystem (IMS) Service Continuity;
Stage 2", 3GPP TS 23.237 10.9.0, March 2012.

[3GPP.24.837]
3GPP, "IP Multimedia (IM) Core Network (CN) subsystem
inter-UE transfer enhancements; Stage 3", 3GPP TR 24.837
10.0.0, April 2011.

Authors' Addresses

Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland

Email:

EMail: christer.holmberg@ericsson.com

Ivo Sedlacek
Ericsson
Scheelevaegen 19C
Lund 22363
Sweden

Email:

EMail: ivo.sedlacek@ericsson.com

Hadriel Kaplan
Acme Packet
71 Third Ave.
Burlington, MA 01803
USA

Email:

EMail: hkaplan@acmepacket.com