SALUD L. Liess, Ed.
Internet-Draft R. Jesske
Updates: 3261 (if approved) Deutsche Telekom AG
Intended status: Standards Track A. Johnston
Expires: April 5, 2013 Avaya
D. Worley
Ariadne
P. Kyzivat
Huawei
October 2, 2012
Alert-Info URNs for the Session Initiation Protocol (SIP)
draft-ietf-salud-alert-info-urns-07
Abstract
The Session Initiation Protocol (SIP) supports the capability to
provide a reference to a specific rendering to be used by the UA when
the user is alerted. This is done using the Alert-Info header field.
However, the reference addresses only network resources with specific
rendering properties. There is currently no support for predefined
standard identifiers for describing the semantics of the alerting
situation or the characteristics of the alerting signal, without
being tied to a particular rendering. To overcome this limitation
and support new applications, a new family of URNs for use in SIP
Alert-Info header fields is defined in this specification.
This document normatively updates [RFC3261], the Session Initiation
Protocol (SIP). It changes the usage of the SIP Alert-Info header
field defined in the [RFC3261] by additionally allowing its use in
all provisional responses to INVITE (except the 100 response).
Requirements Language
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 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 5, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Alert-Info Header Field Usage Change . . . . . . . . . . . 6
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. PBX Ring Tones . . . . . . . . . . . . . . . . . . . . . . 9
3.1.1. normal . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1.2. external . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.3. internal . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.4. priority . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.5. short . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.6. delayed . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Service Tones . . . . . . . . . . . . . . . . . . . . . . 10
3.2.1. call-waiting . . . . . . . . . . . . . . . . . . . . . 10
3.2.2. forward . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.3. transfer-recall . . . . . . . . . . . . . . . . . . . 11
3.2.4. auto-callback . . . . . . . . . . . . . . . . . . . . 11
3.2.5. hold-recall . . . . . . . . . . . . . . . . . . . . . 11
3.3. Country-specific ringback tone indications for the
public telephone network . . . . . . . . . . . . . . . . . 11
4. Namespace Registration Template . . . . . . . . . . . . . . . 12
5. Alert-Info URN Values Definitions . . . . . . . . . . . . . . 15
5.1. Alert-category Values Definitions . . . . . . . . . . . . 15
5.2. Alert-indication Values Definitions . . . . . . . . . . . 16
5.2.1. Alert-Info URN Indication Values for the
alert-category 'service' . . . . . . . . . . . . . . . 16
5.2.2. Alert-Info URN Indication Values for the
alert-category 'source' . . . . . . . . . . . . . . . 16
5.2.3. Alert-Info URN Indication Values for the
alert-category 'priority' . . . . . . . . . . . . . . 17
5.2.4. Alert-Info URN Indication Values for the
alert-category 'duration' . . . . . . . . . . . . . . 17
5.2.5. Alert-Info URN Indication Values for the
alert-category 'delay' . . . . . . . . . . . . . . . . 17
5.2.6. Alert-Info URN Indication Values for the
alert-category 'locale' . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
6.1. New alert identifiers . . . . . . . . . . . . . . . . . . 18
6.2. Initial IANA Registration . . . . . . . . . . . . . . . . 19
6.2.1. The "service" alert-category and alert-identifiers . . 19
6.2.2. The "source" alert-category and alert-identifiers . . 19
6.2.3. The "priority" alert-category and alert-identifiers . 20
6.2.4. The "duration" alert-category and alert-identifiers . 20
6.2.5. The "delay" alert-category and alert-identifiers . . 21
6.2.6. The "locale" alert-category and alert-identifiers . . 21
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7. Extensibility Rules . . . . . . . . . . . . . . . . . . . . . 22
7.1. General Extensibility Rules . . . . . . . . . . . . . . . 22
7.2. Extensions Rules for Independent Organizations . . . . . . 22
8. Combinations of Alert-Info URNs . . . . . . . . . . . . . . . 23
8.1. Priority Rules . . . . . . . . . . . . . . . . . . . . . . 23
8.2. Multi-mode signals . . . . . . . . . . . . . . . . . . . . 25
9. Non-normative Algorithm for Handling Combinations of URNs . . 25
9.1. Algorithm Description . . . . . . . . . . . . . . . . . . 25
9.2. Examples of how the algorithm works . . . . . . . . . . . 27
9.2.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . 27
9.2.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . 28
9.2.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . 31
9.2.4. Example 4 . . . . . . . . . . . . . . . . . . . . . . 32
9.2.5. Example 5 . . . . . . . . . . . . . . . . . . . . . . 33
10. User Agent Behaviour . . . . . . . . . . . . . . . . . . . . . 34
11. Proxy Behaviour . . . . . . . . . . . . . . . . . . . . . . . 35
12. Internationalization Considerations . . . . . . . . . . . . . 35
13. Security Considerations . . . . . . . . . . . . . . . . . . . 36
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 36
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
15.1. Normative References . . . . . . . . . . . . . . . . . . . 36
15.2. Informative References . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38
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1. Introduction
1.1. Motivation
The Session Initiation Protocol (SIP) [RFC3261] includes a means to
suggest to a user agent (UA) a particular ringback tone or ring tone
to be used during session establishment. In [RFC3261] this is done
by including a URI in the Alert-Info header field, that specifies the
tone. The URI is most commonly the HTTP URL to the audio file. On
the receipt of the Alert-Info header field the user agent may fetch
the referenced ringback tone or ring tone and play it to the user.
This mechanism hinders interoperability when there is no common
understanding of the meaning of the referenced tone, which might be
country- or vendor-specific. It can lead to problems for the user
trying to interpret the tone and for the UA wanting to substitute its
own tone (e.g., in accordance with user preferences) or provide an
alternative alerting mode (e.g., for hearing-impaired users). If
caller and callee are from different countries, the understanding of
the tones may vary significantly. Hearing impaired users may not
sense the specific tone if it is provided as an audio file. The tone
per se is also not useful for automata.
There are currently interoperability issues around the use of the
Alert-Info header field when not using an external ring file. For
example, consider the PBX special ring tone for an external (to the
PBX) caller. Different vendors use different approaches such as:
Alert-Info: <file://ring.pcm>;alert=normal where ring.pcm is a dummy
file or: Alert-Info: <file://normal.ring.pcm> or: Alert-Info:
<sip:normal-ringtone@example.com>. As a result, Alert-Info currently
only works when the same vendor provides PBX and UA, as only then is
the same "fake" proprietary URI convention used.
Another limitation of the current solution is that the referenced
tones are tied to particular rendering. It is not possible to
provide semantic indications or names for rendering characteristics
that signals the intent and allows the recipient to decide how to
render the received information in an appropriate way.
To solve the described issues, this specification defines the new URN
namespace 'alert' for the Alert-Info header field that allows for
programmatic user interface adaptation and for conversion of
equivalent alerting tones in the Public Switched Telephone Network
(PSTN) when the client is a gateway. The work to standardize an
Alert-Info URN will increase SIP interoperability for this header
field by replacing proprietary conventions used today.
Using the 'alert' namespace provides syntax for several different
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application spaces, e. g.:
o Names for service indications, such as call waiting or automatic
callback, not tied to any particular rendering.
o Names for common ring tones generated by PBX phones for cases such
as an internal enterprise caller, external caller, ringback tone
after a transfer failure or expiration of a hold timer, etc.
o Names for country-specific ringback tones.
o Names for things with specific renderings that aren't purely
audio. They might be static icons, video sequences, text, etc.
Some advantages of a URN rather than a URL of a downloadable
resource:
o Do not need to download it or deal with security issues associated
with dereferencing.
o No formatting or compatibility issues.
o No security risk of rendering something unexpected and
undesirable.
o The tone can be stored locally in whatever format and at whatever
quality level is appropriate, because it is specified "by name"
rather than "by value".
o It is easier to make policy decisions about whether to use it or
not.
o It facilitates translation for the hearing impaired.
The downside is that if the recipient does not understand the URN
then it will only be able to render a default ringback tone or ring
tone.
This document creates a new URN namespace and registry for alert
indications and registers some initial values.
1.2. Alert-Info Header Field Usage Change
This specification changes the usage of the SIP Alert-Info header
field defined in the [RFC3261] by additionally allowing its use in
all provisional responses to INVITE (except the 100 response).
In practice, this specification extends Alert-Info in that it will
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cause the use of a new class of URIs and the use of multiple URIs.
Backward compatibility issues are not expected, as devices that do
not understand an Alert-Info URN should ignore it, and devices should
not malfunction upon receiving multiple Alert-Info alert-params
(which was syntactically permitted before, but rarely used).
1.3. Terminology
This specification uses a number of terms to refer to the roles
involved in the use of alerting indications in SIP. A "specifier"
sends an "alerting indication" (one or more URNs in an Alert-Info
header) to a "renderer" which then "renders" a "signal" or
"rendering" based on the indication to a human user. A "category" is
a characteristic whose "values" can be used to classify indications.
This specification uses the terms "ring tone" and "ringback tone". A
"ring tone" or "calling signal" (terminology used in [E182]) is a
signal generated by the callee's end device, advising the callee
about an incoming call. A "ringback tone" or "ringing tone"
(terminology used in [E182]) is a signal advising the caller that a
connection has been made and that a ring tone is being rendered to
the callee.
2. Requirements
This section discusses the requirements for an alerting indication to
transport the semantics of the alerting situation or the
characteristics of the rendering.
REQ-1: The mechanism will allow user agents (UAs) and proxies to
provide in the Alert-Info header field an alerting indication which
describes the semantics of the signaling situation or the
characteristics of the rendering and allows the recipient to decide
how to render the received information to the user.
REQ-2: The mechanism will allow the alerting indication to be
specified "by name" rather than "by value", to enable local policy
decisions whether to use it or not.
REQ-3: The mechanism will enable alerting indications to represent a
wide variety of signals, which have many largely-orthogonal
characteristics.
REQ-4: has been deleted. To avoid confusion, the number will not be
reused.
REQ-5: The mechanism will enable the set of alerting indications to
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be able to support extensibility by a wide variety of organizations
that are not coordinated with each other. Extensions will be able
to:
- add further values to any existing category
- add further categories that are orthogonal to existing categories
- semantically subdivide the meaning provided by any existing
indication
REQ-6: The mechanism will be flexible, so new alerting indications
can be defined in the future, when SIP-applications evolve. E. g.
Alert-Info URNs could identify specific media by name, such as
"Beethoven's Fifth", and the end device could render some small part
of it as a ring tone.
REQ-7: The mechanism will provide only an indication capability, not
a negotiation capability.
REQ-8: The mechanism will not require an alerting indication to
depend on context provided by a previous alerting indication in
either direction.
REQ-9: The mechanism will allow transmission in the Alert-Info header
field of SIP INVITE requests and provisional 1xx responses excepting
the 100 responses.
REQ-10: The mechanism will be able to accommodate renderers that are
customized with a limited or uncommon set of signals they can render
and renderers that are provided with a set of signals that have
uncommon semantics. (The canonical example is a UA for the hearing-
impaired, customized with an uncomon set of signals, video or text
instead of audio. By REQ-7, the renderer has no way of transmitting
this fact to the specifier.)
REQ-11: The mechanism will allow an alerting indication to reliably
carry all extensions if the specifier and the renderer have designs
that are properly coordinated.
REQ-12: The mechanism will allow a renderer to select a tone that
approximates to that intended by the specifier if the renderer is
unable to provide the precise tone indicated.
REQ-13: The mechanism will support alerting indications relating to
services such as call waiting, forward, transfer-recall, auto-
callback and hold-recall.
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REQ-14: The mechanism will allow rendering common PBX ring tone
types.
REQ-15: The mechanism will allow rendering specific country ringback
tones.
REQ-16: The mechanism will allow rendering tones for emergency
alerts. (Use cases and values definition are not subject of this
specification.)
REQ-17: The mechanism will allow rendering using other means than
tones, e.g. text or images.
REQ-18: The mechanism will allow TDM gateways to map ring/ringback
tones from legacy protocols to SIP at the edge of a network, e.g.
national ring tones as defined in TIA/EIA-41-D and 3GPP2 A.S0014.
(Use cases and values definition are not subject of this
specification.)
REQ-19: The mechanism will ensure that if an UA receives Alert-Info
URNs or portions of an Alert-Info URN it does not understand, it can
ignore them.
REQ-20 The mechanism will allow storage of the actual encoding of the
rendering locally rather than fetching it.
REQ-21: The mechanism must provide a simple way to combine two
alerting indications to produce an alerting indication that requests
a combination of the intentions of the two alerting indications,
where any contradictions or conflicts between the two alerting
indications are resolved in favor of the intention of the first
alerting indication.
3. Use Cases
This section describes some use cases for which the Alert-Info URN
mechanism is needed today.
3.1. PBX Ring Tones
This section defines some commonly encountered ring tones on PBX or
business phones. They are as follows:
3.1.1. normal
This tone indicates that the default or normal ring tone should be
rendered. This is essentially a no-operation Alert-Info URN and
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should be treated by the UA as if no Alert-Info URN is present. This
is most useful when Alert-Info header field parameters are being
used. For example, in [I-D.ietf-bliss-shared-appearances], an Alert-
Info header field needs to be present containing the "appearance"
parameter, but no special ring tone needs to be specified.
3.1.2. external
This tone is used to indicate that the caller is external to the
enterprise or PBX system. This could be a call from the PSTN or from
a SIP trunk.
3.1.3. internal
This tone is used to indicate that the caller is internal to the
enterprise or PBX system. The call could have been originated from
another user on this PBX or on another PBX within the enterprise.
3.1.4. priority
A PBX tone needs to indicate that a priority level alert should be
applied for the type of alerting specified (e.g. internal alerting).
3.1.5. short
In this case the alerting type specified (e.g. internal alerting)
should be rendered shorter than normal. In contact centers, this is
sometimes referred to as "abbreviated ringing" or a "zip tone".
3.1.6. delayed
In this case the alerting type specified should be rendered after a
short delay. In some bridged line/shared line appearance
implementations, this is used so that the bridged line does not ring
at exactly the same time as the main line, but is delayed a few
seconds.
3.2. Service Tones
These tones are used to indicate specific PBX and public network
telephony services.
3.2.1. call-waiting
The Call Waiting Service [TS24.615] permits a callee to be notified
of an incoming call while the callee is engaged in an active or held
call. Subsequently, the callee can either accept, reject, or ignore
the incoming call. There is an interest on the caller side to be
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informed about the call waiting situation on the callee side. Having
this information the caller can decide whether to continue waiting
for callee to pickup or better to call some time later when it is
estimated that the callee could have finished the ongoing
conversation. To provide this information, the callee's UAS ( or
proxy) aware of the call waiting condition can add the call-waiting
indication to the Alert-Info header field in the 180 Ringing
response. As call-waiting information may be subject to the callee's
privacy concerns, the exposure of this information shall be done only
if explicitly required by the callee.
3.2.2. forward
This feature is used in a 180 Ringing response when a call forwarding
feature has been initiated on an INVITE. Many PBX system implement a
forwarding "beep" followed by normal ringing to indicate this. Note
that a 181 response can be used in place of this URN.
3.2.3. transfer-recall
This feature is used when a blind transfer [RFC5589] has been
performed by a server on behalf of the transferor and fails. Instead
of failing the call, the server calls back the transferor, giving
them another chance to transfer or otherwise deal with the call.
This service tone is used to distinguish this INVITE from any other
normal incoming call.
3.2.4. auto-callback
This feature is used when a user has utilized a server to implement
an automatic callback service [I-D.ietf-bliss-call-completion]. When
the user is available, the server calls back the user and utilizes
this service tone to distinguish this from any other normal incoming
call.
3.2.5. hold-recall
This feature is used when a server implements a call hold timer on
behalf of an endpoint. After a certain period of time of being on
hold, the user who placed the call on hold is alerted to either
retrieve the call or otherwise dispose of the call. This service
tone is used to distinguish this case from any other normal incoming
call.
3.3. Country-specific ringback tone indications for the public
telephone network
In the PSTN, different tones are used in different countries. End
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users are accustomed to hear the callee's country ringback tone and
would like to have this feature for SIP.
4. Namespace Registration Template
This section describes the registration template for the 'alert' URN
namespace identifier (NID) according to the [RFC2141] and [RFC3406]
Namespace ID: alert
Registration Information:
Registration version: 1
Registration date: TBD
Declared registrant of the namespace:
Registering organization: IETF
Designated contact: Laura Liess
Designated contact email: l.liess@telekom.de
Declaration of syntactic structure:
The Namespace Specific String (NSS) for the "alert" URNs is called
alert-identifier and has a hierarchical structure. The left-most
<label> is called <alert-category> and is separated from the
right-side of the <alert-identifier>, the <alert-indication> by a
colon. The general form is
urn:alert:{alert-category}:{alert-indication}.
In this specification, following alert-categories identifiers are
described: "service" , "priority" , "source" , "duration", "delay"
and "locale". The <alert-category> set can be extended in the
future.
The categories are orthogonal. Any Alert-Info URN defined in this
specification is syntactically valid for ring and ringback tones
and can be used in INVITE requests or in provisional 1xx responses
excepting the 100 response.
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The<alert-indication>s are hierarchical identifiers. The set of
allowable characters is the same as that for domain names
[RFC1123]. Labels used in <standard-name> MUST comply with the
syntax for Non Reserved LDH-labels [RFC5890]. Labels used in
<private-name> MUST comply with the syntax for Non Reserved LDH-
labels or for A-labels [RFC5890]. Comparisons MUST follow the
comparison rules for the corresponding type of label. Registered
URNs MUST be transmitted as registered. A new name MUST NOT be
registered if it is equal by the comparison rules above to an
already registered name.
The ABNF [RFC5234] for the Alert -Info URNs is shown below:
alert-URN = "urn:alert:" alert-identifier
alert-identifier = alert-category ":" alert-indication
alert-category = name
alert-indication = name *(":" name)
name = standard-name / private-name
standard-name = label
private-name = label "." label *[ "." label ]
label = let-dig [ *let-dig-hyp let-dig ]
let-dig-hyp = let-dig / "-"
let-dig = ALPHA / DIGIT
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
DIGIT = %x30-39 ; 0-9
Note: <private-name> is
Relevant ancillary documentation: None
Community considerations: The alert URN is believed to be relevant
to a large cross-section of Internet users, including both
technical and non-technical users, on a variety of devices and
with a variety of perception capabilities. The 'alert' URN will
allow Internet users to receive more information and enable them
to better make decisions about accepting an offered call, or get
better feedback on the progress of a call they have made. User
interfaces for the perception impaired users can better render the
ringback tone indication based on the Alert-Info URN. The
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assignment of identifiers is described in Section 6. The Alert-
Info URN does not prescribe a particular resolution mechanism, but
any resolution MUST comply with the rules in Section 8.
Namespace considerations: This specification proposes a new URN
namespace "alert" for global names representing the semantic of
signals or renderings. The particular rendering of an "alert" URN
identifier depends on the context in which the rendering is done.
Also the initial scope is the usage in the SIP Alert-Info header,
the new "alert" URN namespace is designed for more general usage.
The URN may appear in any protocols that allow general URIs (e.g.
also in ITU-T protocols) , in web pages or in any end devices
software.
For the reasons described above, the usage of the already existing
namespace "urn:ietf:params" was not considered appropriate. The
URN namespace for Emergency and Other Well-Known Services
[RFC5031], was used as a model.
Note, to be deleted for the final version of this draft: Because
the work on this draft lasts for about fouryears, the new "alert"
URN namespace is already used in already finalized specifications
of other SDOs (3GPP) and there are already existing
implementations in products and large carrier networks.
Also there do not appear to be other URN namespaces that serve the
same need of uniquely identifying the semantic of a signal or
rendering feature. Unlike most other currently registered URN
namespaces, the "alert" URN does not identify documents and
protocol objects (e.g., [RFC3044], [RFC3120], [RFC3187],
[RFC3188], [RFC4179], [RFC4195], [RFC4198] ), types of
telecommunications equipment [RFC4152], people or organizations
[RFC3043].
Identifier uniqueness considerations: An "alert" URN identifies the
semantic or sensory feature of the rendering at the caller's or
callee's end device. The feature identified by a particular
"alert" URN is distinct from the feature identified any other
"alert" URN. For "alert" URN identifiers based on <standard-
name>s this is ensured through the IANA registration of each
"alert" URN (that is, each defined combination of <alert-category>
and <alert-identifier>) as described in Section 6.
"Alert" URN identifiers with a <private-name> part, IANA delegates
the task to act as a registry to the owner of the "reverse FQDN"
in the <private-name>.
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Identifier persistence considerations: The "alert" URN identifiers
based on <standard-name>s for the same indication is expected to
be persistent, as long as it is registered with IANA.
The "alert" For URN identifiers with a <private-name>part, the
owner of the "reverse FQDN" in the <private-name> is responsible
for the correct proper functionality within the private domain.
Process of identifier assignment: The process of identifier
assignment is described in Section 6, which includes the extension
rules for independent organizations described in Section 7.2.
Process for identifier resolution: Alert-Info URNs are statically
resolved according to the IANA registry.
Rules for lexical equivalence: Alert-Info URNs are compared
according to case-insensitive string equality.
Conformance with URN syntax: The BNF in the 'Declaration of
syntactic structure' above constrains the syntax for this URN
scheme.
Validation mechanism: Validation determines whether a given string
is currently a validly-assigned URN [RFC3406]. Static validation
is performed based on the currently registered Alert-Info URNs at
IANA.
Scope: The scope for this URN is public and global.
5. Alert-Info URN Values Definitions
5.1. Alert-category Values Definitions
Following <alert-category> values are defined in this document:
- service
- source
- priority
- duration
- delay
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- locale
5.2. Alert-indication Values Definitions
This section describes the Alert-Info URN indication values for the
alert-categories defined in this document.
For each <alert-category> , a default indication is defined, which is
essentially a no-operation Alert-Info URN and should be treated by
the UA as if no Alert-Info URN for the respective category is
present. Alert-Info URN default indications are most useful when
Alert-Info header field parameters are being used. For example, in
[I-D.ietf-bliss-shared-appearances], an Alert-Info header field needs
to be present containing the "appearance" parameter, but no special
ringtone need be specified.
The "<private-name>" syntax is used for extensions specific to
independent organizations, as described in Section 7.2.
5.2.1. Alert-Info URN Indication Values for the alert-category
'service'
- normal (default)
- call-waiting
- forward
- recall:callback
- recall:hold
- recall:transfer
- <private-name>
Examples: urn:alert:service:call-waiting or
urn:alert:service:recall:transfer.
5.2.2. Alert-Info URN Indication Values for the alert-category 'source'
- unclassified (default)
- internal
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- external
- friend
- family
- <private-name>
Examples: urn:alert:source:external.
5.2.3. Alert-Info URN Indication Values for the alert-category
'priority'
- normal (default)
- low
- high
- <private-name>
Examples: urn:alert:priority:high.
5.2.4. Alert-Info URN Indication Values for the alert-category
'duration'
- normal (default)
- short
- long
- <private-name>
Examples: urn:alert:duration:short.
5.2.5. Alert-Info URN Indication Values for the alert-category 'delay'
- none (default)
- yes
- <private-name>
Examples: urn:alert:delay:yes .
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5.2.6. Alert-Info URN Indication Values for the alert-category 'locale'
- default (default)
- country:<ISO 3166-1 country code>
- <private-name>
The ISO 3166-1 country code [ISO3166-1] is used to inform the UA on
the other side of the call that a country-specific rendering should
be used. For example, to indicate ringback tones from South Africa,
the following URN would be used: <urn:alert:locale:country:za>.
6. IANA Considerations
This section registers a new URN namespace identifier (NID) in
accordance with RFC 3406 with the registration template provided in
Section 4.
6.1. New alert identifiers
Alert URN identifiers are identified by <label>s managed by IANA,
according to the processes outlined in [RFC5226] in a new registry
called "Alert URN Labels". Thus, creating a new Alert-Info URN
identifier requires IANA action. The policy for adding a new alert
category is 'Standards Action'. (This document defines the alert
categories 'service', 'source', 'priority', 'duration', 'delay' and
'locale'. ) The policy for assigning <label>s to <alert-indication>s
and the rules to combine them may differ for each <alert-category>
and MUST be defined by the document describing the corresponding
alert category. The entries in the registration table have the
following format:
<alert-category>/ Reference Description
<alert-identifier>;
---------------------------------------------------------------
foo RFCxyz Description of the 'foo'
<alert-category>;
foo:bar RFCabc Description of the 'foo:bar'
<alert-identifier>
Each <alert-category> or <alert-indication> label MUST NOT exceed 27
characters.
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6.2. Initial IANA Registration
6.2.1. The "service" alert-category and alert-identifiers
The following table contains the initial IANA registration for the
"service" <alert-category> and <alert-identifier>s. The value of
this indicator is set to a value different from "normal" if the
caller or callee is informed that a specific telephony service has
been initiated.
<alert-category>/ Reference Description
<alert-identifier>
-----------------------------------------------------------
service RFC XXXX <alert-category>
for "service"
<alert-identifier>s
service:normal RFC XXXX Normal ring /rinback
rendering (default value)
service:call-waiting RFC XXXX Call waiting was
initiated at the other side
of the call
service:forward RFC XXXX Call has been forwarded
service:recall:calback RFC XXXX Recall due to callback
service:recall:hold RFC XXXX Recall due to call hold
service:recall:transfer RFC XXXX Recall due to callback
service:<private-name> RFC XXXX Reserved for private
extensions
6.2.2. The "source" alert-category and alert-identifiers
The following table contains the initial IANA registration for the
"source" <alert-category> and <alert-identifier>. The value of this
indicator provides information about the user at the other side of
the call.
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<alert-category>/ Reference Description
<alert-identifier>
-----------------------------------------------------------
source RFC XXXX <alert-category>
for "source"
<alert-identifier>s
source:unclassified RFC XXXX Unclassified ring /rinback
rendering (default value)
source:internal RFC XXXX User at the other side of
the call is internal to the
enterprise or PBX system
source:external RFC XXXX User at the other side of
the call is internal to the
enterprise or PBX system
source:friend RFC XXXX User at the other side of
the call is a friend
source:family RFC XXXX User at the other side of
the call is a family member
source:<private-name> RFC XXXX Reserved for private
extensions
6.2.3. The "priority" alert-category and alert-identifiers
The following table contains the initial IANA registration for the
"priority" <alert-category> and <alert-identifier>s. The value of
this indicator provides information about the priority the alerted
user should give to the call.
<alert-category>/ Reference Description
<alert-identifier>
-----------------------------------------------------------
priority RFC XXXX <alert-category> for
"priority" <alert-identifier>s
priority:normal RFC XXXX Normal ring /rinback
rendering (default value)
priority:low RFC XXXX Low priority call.
priority:high RFC XXXX High priority call
priority:<private-name> RFC XXXX Reserved for private
extensions
6.2.4. The "duration" alert-category and alert-identifiers
The following table contains the initial IANA registration for the
"duration" <alert-category> and <alert-identifier>s. The value of
this indicator provides information about the duration of the
alerting signals compared to the default alerting signals.
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<alert-category>/ Reference Description
<alert-identifier>
-----------------------------------------------------------
duration RFC XXXX <alert-category>
for "duration"
<alert-identifier>s
duration:normal RFC XXXX Normal ring /rinback
rendering (default value)
duration:short RFC XXXX Shorter than normal
duration:long RFC XXXX Longer than normal
duration:<private-name> RFC XXXX Reserved for private
extensions.
6.2.5. The "delay" alert-category and alert-identifiers
The following table contains the initial IANA registration for the
"delay" <alert-category> and <alert-identifier>s. The value of this
indicator provides information about the delay of the alerting
signals.
<alert-category>/ Reference Description
<alert-identifier>
-----------------------------------------------------------
delay RFC XXXX <alert-category> for "delay"
<alert-identifier>
delay:none RFC XXXX Immediate alerting
(default value)
delay:yes RFC XXXX Delayed alerting
delay:<private-name> RFC XXXX Reserved for private
extensions
6.2.6. The "locale" alert-category and alert-identifiers
The following table contains the initial IANA registration for the
"locale" <alert-category> and <alert-identifier>s. The value of this
indicator provides information about the location of the user at the
other side of the call.
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<alert-category>/ Reference Description
<alert-identifier>
-----------------------------------------------------------
locale RFC XXXX <alert-category>
for "locale" <alert-identifier>
locale:default RFC XXXX Alerting not location
specific
(default value)
locale:country:<ISO 3166-1 country code>
RFC XXXX Country-specific alerting
locale:<private-name> RFC XXXX Reserved for private
extensions
7. Extensibility Rules
7.1. General Extensibility Rules
The set of Alert-Info URNs is intended to be extensible. An
extension "at the top level" creates an entirely new category (or
characteristic), an extension "at the second level" creates a new
indication value for a category, an extension "at the third level"
creates a subdivision of a indication value, etc. Extensions at
lower levels are preferred over those at upper levels.
URNs allow in principle infinite subdivision of existing indication
values, although most of the standard Alert-Info URNs give only one
level of subdivision and a few give two levels of subdivision.
The process for defining new Alert-Info URNs is described in
Section 6.1. Adding new categories and adding <alert-indication>
values other than via the "private" mechanism described in
Section 7.2 is standards action.
7.2. Extensions Rules for Independent Organizations
The "<private-name>" syntax is for proprietary extensions specific to
independent organizations. The "<private-name>" is used in the form
of a "reverse FQDN" of the entity that defines the extension,
possibly followed by further components. Standard URNs will never
contain a ".", so proprietary extensions need no further marker.
This gives a way of assigning unique names without the need for a new
registry. The namespace for each alert category is independent.
Those assigning new names must ensure they are in a position to
assign names uniquely for the FQDN they choose.
For example, some company SomeCompany.example.org could use
urn:alert:service:call-waiting:org.example.somecompany, which is the
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SomeCompany's private version for call-waiting or it may have several
distinct private versions of call-waiting, e.g.
urn:alert:service:call-waiting:abc.org.example.somecompany and
urn:alert:service:call-waiting:def.org.example.somecompany (which are
siblings in the tree under urn:alert:service:call-waiting). Also it
can subdivide its private version of call-waiting in
urn:alert:service:call-waiting:org.example.somecompany:abc and
urn:alert:service:call-waiting:org.example.somecompany:def (which are
siblings in the tree under service:call- waiting:
org.example.somecompany).
Adding new categories and adding <alert-indication> values via the
"private" mechanism is not a standards action.
8. Combinations of Alert-Info URNs
8.1. Priority Rules
This section describes combination rules for the case when all the
Alert-Info header fields only contain Alert-Info URNs. Combinations
of URNs and URIs in the Alert-Info header fields of the same SIP-
message are not defined in this specification.
In many cases, more than one URNs will be needed to fully define a
particular tone. This is done by including multiple Alert-Info URNs,
in one or more Alert-Info header fields in a request or a response.
For example, an internal, priority call could be indicated by Alert-
Info: <urn:alert:source:internal>, <urn:alert:priority:high>. A
priority call waiting tone could be indicated by Alert-Info:
<urn:alert:service:call-waiting>, <urn:alert:priority:high>.
The sender of the Alert-Info header may include an arbitrary list of
Alert-Info URNs, even if they are redundant or contradictory. An
earlier URN has priority over any later contradictory URN. This
allows any element to modify a list of URNs to require a feature
value (by adding a URN at the beginning of the list) or to suggest a
feature value (by adding a URN at the end of the list).
The receiving UA attempts to match the received Alert-Info URNs
combination with the signal(s) it is able to render.
The implementation is free to ignore any or all parts of the received
Alert-Info URNs. The exact way in which a UA renders a received
combination of Alert-Info URNs is left as an implementation issue.
However, the implementation MUST comply to following rules:
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a. Each alert-info URN has precedence over all URNs that follow
it, and its interpretation is subordinate to all URNs that precede
it.
b. If the UA cannot implement the effect of a URN (because it
does not recognize the URN or the URN's effect is precluded by
preceding URNs), the UA repeatedly removes either
(1) the final <name> of the URN, or
(2) if the final <name> is a <private-name> with three or more
<label>s, the final <label>
until either
(i) the resulting URN is recognized and can be given effect by
some signal (without reducing the degree of expression of any
preceding URN), or
(ii) the resulting URN is reduced to having no <alert-
indication>.
In case (ii), that URN in the series cannot be given effect, so
it is ignored.
c. In case that after processing all the received URNs, the UA
can generate more than one signal that are equally effective at
expressing the URNs (under the preceding rules), one of those
signals is selected. When selecting from the set of equally
effective signals, no signal should be chosen if a less-specific
signal is also in the set. (Specificity is to be judged based on
the defined meanings of the signals to the user.) (E.g., if each
signal is considered to express certain <alert-indication>s of
certain <alert-categories>, one signal is less-specific than a
second signal if the first signal's <alert-indication>s are a
subset or are prefixes of the second signal's <alert-
indication>s.) However, a more-specific signal may be chosen if
the choice is based on information derived from the containing SIP
message. E.g., a signal implying urn:alert-info:priority:high may
be chosen if the SIP message contains the header "Priority:
urgent".
In all situations, the set of signals that can be rendered and their
significances may change based on user preferences and local policy.
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In adidition, they may change based on the status of the UA. E.g.,
if a call is active on the UA, all audible signals may become
unavailable, or audible signals may be available only if
urn:alert-info:priority:high is specified.
8.2. Multi-mode signals
There are cases when the device can render two signal modes (e.g.,
audio and visual, or video or text) at the same time.
Formally, the device must be considered as making its choice from the
set of all combined signals that it can render, and that choice must
conform to the above rules. However, it can be proven that if the
device makes its rendering choice for each of the two modes
independently, with each choice separately conforming to the above
rules, its combined choice conforms to the above rules, when it is
regarded as a choice from among all possible combinations.
In such a situation, it may simplify implementation to make each
choice separately. It is an implementation decision whether to chose
from among combined signals, or to combine choices made from each
signal mode.
9. Non-normative Algorithm for Handling Combinations of URNs
The following text is a non-normative example of an algorithm for
handling combinations of URNs that complies with the requirements in
Section 8. Thus, it demonstrates that requirements in section 7 are
consistent and implementable. (Of course, a device may use any other
algorithm which complies with Section 8.)
9.1. Algorithm Description
For each category (feature), there is a tree of possible values. For
this description, we will name each tree by the category name, and
name each node by the trailing portion of the URN. Each URN thus
corresponds to a node in a category tree. Thus, there is a tree
named "source", whose root node is also named "source", and which has
the children source:internal, source:external, source:friend, and
source:family. For example, urn:alert:source:external is placed at
the node "source:external" in the "source" tree. (Of course, there
are an infinite number of potential additional nodes in the tree for
private values, but we don't have to represent those nodes explicitly
unless the device has a signal representing the private value.)
We assign similar locations to signals, but each signal has a place
in *every* tree. If a signal has a simple meaning, such as "external
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source", its place in the "source" tree is source:external, but its
place in every other feature tree is at the root node, meaning that
it has no particular meaning for that feature.
A signal that has a complex meaning may have non-root positions in
more than one feature tree. For example, an "external, high
priority" signal would be placed at source:external and priority:high
in those trees, but be at the root in all other feature trees.
In order to assure that the algorithm always selects at least one
signal, we assume that there is a "default" signal, whose position in
every feature tree is at the root. The default signal is set up so
that it will never be excluded from the set of acceptable signals for
an indication, but will usually be the least-desirable signal for any
indication.
The algorithm proceeds by considering each URN in the received Alert-
Info header from left to right, while revising a set of signals. The
set of signals starts as the entire set of signals available to the
device. Each URN excludes some signals from the set, and *sorts* the
signals that remain in the set according to how well they represent
the URN. (The details of these operations are described below.) The
first URN is the "major sort", and has the most influence on the
position of a signal in the set. The second URN is a "minor sort",
in that it arranges the orders of the signals that are tied within
the first sort, the third URN arranges the orders of the signals that
are tied within the first two sorts, etc.
At the end of the algorithm, a final, "most minor" sort is done,
which orders the signals which have been tied under all the sorts
driven by the URNs. This final sort places the least specific
signals (within their groups) *first*. (If one signal's position in
each category tree is ancestral or the same as a second signal's
position in that tree, the first signal is "less specific" than the
second signal. Other cases are left to the implementation to
decide.)
Once all the URNs are processed and the sorting is done, the device
selects the first signal in the set.
Here is how a single sort step proceeds, examining a single URN to
modify the set of signals (by excluding some signals and further
sorting the signals that remain):
o The URN specifies a specific node in a specific category tree.
o All signals in the set that are positioned at that node, or at an
ancestor node of the URN, are kept. All other signals are removed
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from the set.
o Within any group of signals that are tied under the previous
sorts, place first those which are at the node of the URN, place
second those which are at the parent node of the URN, etc., and
place last those which are at the root node of the feature tree.
9.2. Examples of how the algorithm works
The following examples show how the algorithm described in the
previous section works:
9.2.1. Example 1
The device has a set of 4 alerting signals. We list their primary
meanings, and the locations that they are placed in the feature
trees:
Signal 1
Meaning: external
Locations:
- source:external
- priority (that is, the root node of the priority tree)
Signal 2
Meaning: internal
Locations:
- source:internal
- priority
Signal 3
Meaning: low
Locations:
- source
- priority:low
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Signal 4
Meaning: high
Locations:
- source
- priority:high
To which we add:
Signal 5
Meaning: default
Locations:
- source
- priority
If the device receives <urn:alert:source:internal>, then the sort is:
Signals at source:internal:
<urn:alert:source:internal>
Signals at source:
<urn:alert:priority:low>
<urn:alert:priority:high>
default
And these signals are excluded from the set:
<urn:alert:source:external>
So in this example, the sorting algorithm properly gives first place
to <urn:alert:source:internal>.
9.2.2. Example 2
Let us add to the set of signals in Example 1 ones that express
combinations like "internal, high priority", but let us specifically
exclude the combination "internal, low priority" so as to set up some
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tricky examples. This enlarges our set of signals:
Signal 1
Meaning: default
Locations:
- source
- priority
Signal 2
Meaning: external
Locations:
- source:external
- priority
Signal 3
Meaning: internal
Locations:
- source:internal
- priority
Signal 4
Meaning: low
Locations:
- source
- priority:low
Signal 5
Meaning: high
Locations:
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- source
- priority:high
Signal 6
Meaning: external high
Locations:
- source:external
- priority:high
Signal 7
Meaning: external low
Locations:
- source:external
- priority:low
Signal 8
Meaning: internal high
Locations:
- source:internal
- priority:high
If the device receives <urn:alert:source:internal>, then the sort is:
Signals at source:internal: (that is, tied for first place)
- internal
-internal high
Signals at source: (tied for second place)
- low
- high
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- default
Signals excluded from the set:
- external
- external low
- external high
Two signals are tied for the first place, but the final sort orders
them:
- internal
- internal high
because it puts the least-specific signal first. So the signal
"internal" is chosen.
9.2.3. Example 3
The same device receives <urn:alert:source:external>,
<urn:alert:priority:low>. The first sort (due to
<urn:alert:source:external>) is:
Signals at source:external:
- external
- external low
- external high
Signals at source:
- low
- high
- default
Signals excluded:
- internal
- internal high
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The second sort (due to <urn:alert:priority:low>) puts signals at
priority:low before signals at priority, and excludes signal at
priority:high:
- external low
- external
- low
- default
Excluded:
- external high
- high
- internal
- internal high
So, we choose "external low".
9.2.4. Example 4
Suppose the same device receives <urn:alert:source:internal>,
<urn:alert:priority:low>. Note that there is no signal that
corresponds to this combination.
The first sort is based on source:internal, and results in this
order:
- internal
- internal high
- low
- high
- default
Excluded:
- external
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- external low
- external high
The second sort is based on priority:low, and results in this order:
- internal
- low
- default
Excluded:
- internal high
- high
- external low
- external
- external high
So we choose the signal "internal".
9.2.5. Example 5
Let us set up a simple set of signals, with three signals giving
priority:
Signal 1
Meaning: default
Locations:
- priority
Signal 2
Meaning: low
Locations:
- priority:low
Signal 3
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Meaning: high
Locations:
- priority:high
Notice that we've used the "default" signal to cover "normal
priority". That is so the signal will cover situations where no
priority URN is present, as well as the ones with
<urn:alert:priority:normal>. So we're deliberately failing to
distinguish "priority:normal" from the default priority.
If the device receives <urn:alert:priority:low>, the sort is:
- low
- default
Excluded:
- high
and signal "low" is chosen.
Similarly, if the device receives <urn:alert:priority:high>, signal
"high" is chosen.
If the device receives <urn:alert:priority:normal>, the sort is:
- default
Excluded:
- low
- high
and signal "default" is chosen.
If no "priority" URN is received, "default" will be put before "low"
and "high" by the final sort, and so it will be chosen.
10. User Agent Behaviour
A SIP UA MAY add a URN or multiple URNs to the Alert-Info header
field in a SIP request or a provisional 1xx response (excepting a 100
response) when it needs to provide additional information about the
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call or about the provided service.
Upon receiving a SIP INVITE request or a SIP provisional response
with an Alert-Info header field that contains a combination of Alert-
Info URNs, the User Agent (UA) attempts to match the received Alert-
Info URNs combination with a signal it can render. The process the
UA uses MUST conform to the rules described in Section 8. (A non-
normative algorithm example for the process is described in
Section 9.)
The User Agent (UA) is responsible for producing a reasonable
rendering regardless of the combination of URIs (of any schemes) in
the Alert-Info header field.
11. Proxy Behaviour
A SIP proxy MAY add a URN or multiple URNs to the Alert-Info header
field in a SIP request or a provisional 1xx response (excepting a 100
response) when it needs to provide additional information about the
call or about the provided service.
Following example shows both the network audio resource referenced by
the HTTP URI and the URN indication for the call-waiting service
transported by the Alert-Info header field in a 180 Ringing
provisional response.
SIP/2.0 180 Ringing
Alert-Info: <http://www.example.com/sound/moo.wav>,
<urn:alert:service:call-waiting>
To: Bob <sip:bob@biloxi.example.com>;tag=a6c85cf
From: Alice <sip:alice@atlanta.example.com>;tag=1928301774
Call-ID: a84b4c76e66710
Contact: <sip:bob@192.0.2.4>
CSeq: 314159 INVITE
Via: SIP/2.0/UDP server10.biloxi.example.com;
branch=z9hG4bK4b43c2ff8.1
Content-Length: 0
12. Internationalization Considerations
The <alert-identifier> labels are protocol elements [RFC6365] and are
not normally seen by users. Thus, the character set for these
elements is restricted, as described in Section 6.
The URNs urn:alert:locale:country:<ISO 3166-1 country code> select
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renderings that are conventional in the specified country.
13. Security Considerations
As an identifier, the alert URN does not appear to raise any
particular security issues. The indications described by the 'alert'
URN are meant to be well-known.
However, the provision of specific indications may raise privacy
issues, e.g. indications about the source of the message or about
services initiated at the other side. Such provision SHALL always be
explicitly authorised by the party (caller or callee) the information
in the Alert-Info URN refers to.
Proxies may choose to suppress undesired indications, e.g. from
untrusted sources, while allowing them from trusted sources.
14. Acknowledgements
The authors wish to thank Denis Alexeitsev, the editor of the initial
draft in BLISS, Anwar Siddiqui for his contributions to the draft,
and Adam Roach, Dean Willis, Martin Huelsemann, Shida Schubert, John
Elwell and Tom Taylor for their comments and suggestions.
15. References
15.1. Normative References
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 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.
[RFC3406] Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
"Uniform Resource Names (URN) Namespace Definition
Mechanisms", BCP 66, RFC 3406, October 2002.
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[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
15.2. Informative References
[E182] "Application of tones and recorded announcements in
telephone services",
http://www.itu.int/rec/T-REC-E.182-199803-I/en .
[I-D.ietf-bliss-call-completion]
Worley, D., Huelsemann, M., Jesske, R., and D. Alexeitsev,
"Call Completion for Session Initiation Protocol (SIP)",
draft-ietf-bliss-call-completion-16 (work in progress),
September 2012.
[I-D.ietf-bliss-shared-appearances]
Johnston, A., Soroushnejad, M., and V. Venkataramanan,
"Shared Appearances of a Session Initiation Protocol (SIP)
Address of Record (AOR)",
draft-ietf-bliss-shared-appearances-13 (work in progress),
July 2012.
[ISO3166-1]
"ISO 3166-1 English country names and code elements", http
://www.iso.org/iso/
english_country_names_and_code_elements .
[RFC3043] Mealling, M., "The Network Solutions Personal Internet
Name (PIN): A URN Namespace for People and Organizations",
RFC 3043, January 2001.
[RFC3044] Rozenfeld, S., "Using The ISSN (International Serial
Standard Number) as URN (Uniform Resource Names) within an
ISSN-URN Namespace", RFC 3044, January 2001.
[RFC3120] Best, K. and N. Walsh, "A URN Namespace for XML.org",
RFC 3120, June 2001.
[RFC3187] Hakala, J. and H. Walravens, "Using International Standard
Book Numbers as Uniform Resource Names", RFC 3187,
October 2001.
[RFC3188] Hakala, J., "Using National Bibliography Numbers as
Uniform Resource Names", RFC 3188, October 2001.
[RFC4152] Tesink, K. and R. Fox, "A Uniform Resource Name (URN)
Namespace for the Common Language Equipment Identifier
(CLEI) Code", RFC 4152, August 2005.
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Internet-Draft Alert-Info URNs October 2012
[RFC4179] Kang, S., "Using Universal Content Identifier (UCI) as
Uniform Resource Names (URN)", RFC 4179, October 2005.
[RFC4195] Kameyama, W., "A Uniform Resource Name (URN) Namespace for
the TV-Anytime Forum", RFC 4195, October 2005.
[RFC4198] Tessman, D., "A Uniform Resource Name (URN) Namespace for
Federated Content", RFC 4198, November 2005.
[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services", RFC 5031,
January 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5589] Sparks, R., Johnston, A., and D. Petrie, "Session
Initiation Protocol (SIP) Call Control - Transfer",
BCP 149, RFC 5589, June 2009.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", BCP 166, RFC 6365,
September 2011.
[TS24.615]
"3GPP TS 24.615 Communication Waiting (CW) using IP
Multimedia (IM) Core Network (CN) subsystem".
Authors' Addresses
Laura Liess (editor)
Deutsche Telekom AG
Heinrich-Hertz Str 3-7
Darmstadt, Hessen 64295
Germany
Phone: +49 6151 5812761
Email: laura.liess.dt@gmail.com
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Roland Jesske
Deutsche Telekom AG
Heinrich-Hertz Str. 3-7
Darmstadt, Hessen 64295
Germany
Phone: +49 6151 5812766
Email: r.jesske@telekom.de
Alan Johnston
Avaya Inc.
St. Louis, MO
United States
Phone:
Email: alan.b.johnston@gmail.com
Dale R. Worley
Ariadne Internet Services, Inc.
738 Main St.
Waltham, MA 02451
US
Phone: +1 781 647 9199
Email: worley@ariadne.com
Paul Kyzivat
Huawei
United States
Email: pkyzivat@alum.mit.edu
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