DISPATCH D. Alexeitsev
Internet-Draft L. Liess
Intended status: Standards Track R. Jesske
Expires: August 30, 2010 Deutsche Telekom AG
A. Johnston
A. Siddiqui
Avaya
February 26, 2010
Alert-Info URNs for the Session Initiation Protocol (SIP)
draft-liess-dispatch-alert-info-urns-01
Abstract
The Session Initiation Protocol (SIP) supports the capability to
provide a reference to the alternative ringback tone (RBT) for
caller, or ring tone (RT) for callee using the Alert-Info header.
However, the reference addresses only the network resources with
specific rendering properties. There is currently no support for
predefined standard identifiers for ringback tones or semantic
indications 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.
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 to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
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http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 30, 2010.
Copyright Notice
Copyright (c) 2010 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
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Registration template . . . . . . . . . . . . . . . . . . . . 7
4. Top Level Alert URN Indication Definitions . . . . . . . . . . 10
4.1. PBX Tones . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.1. normal . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.2. external . . . . . . . . . . . . . . . . . . . . . . . 11
4.1.3. internal . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Service Tones . . . . . . . . . . . . . . . . . . . . . . 11
4.2.1. call-waiting . . . . . . . . . . . . . . . . . . . . . 11
4.2.2. forward . . . . . . . . . . . . . . . . . . . . . . . 11
4.2.3. transfer-recall . . . . . . . . . . . . . . . . . . . 11
4.2.4. auto-callback . . . . . . . . . . . . . . . . . . . . 12
4.2.5. hold-recall . . . . . . . . . . . . . . . . . . . . . 12
4.2.6. priority . . . . . . . . . . . . . . . . . . . . . . . 12
4.2.7. zip . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2.8. delayed . . . . . . . . . . . . . . . . . . . . . . . 12
4.3. Country-specific ringback tone indications for the
public telephone network . . . . . . . . . . . . . . . . . 13
4.4. Combinations of URNs . . . . . . . . . . . . . . . . . . . 13
5. User Agent Behavior . . . . . . . . . . . . . . . . . . . . . 13
6. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7.1. New alert-identifiers . . . . . . . . . . . . . . . . . . 14
7.2. Alert-category . . . . . . . . . . . . . . . . . . . . . . 15
7.3. Initial IANA Registration . . . . . . . . . . . . . . . . 15
7.3.1. Indications for PBX-tones . . . . . . . . . . . . . . 15
7.3.2. Additional Indications for PBX-tones . . . . . . . . . 15
7.3.3. Indications for Country-specific Ringback tones in
the public telephone network . . . . . . . . . . . . . 16
7.3.4. Indications for Services . . . . . . . . . . . . . . . 16
7.3.5. Combination Rules for Alert URN Indications . . . . . 16
8. Internationalization Considerations . . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
The Session Initiation Protocol (SIP) [RFC3261] allows for user agent
servers (UAS) and proxies to provide the specific ringback or ring
tone to the user agent (UA). In RFC 3261 this is done by including a
URI reference in the Alert-Info header field, that points to the
tone. The URI reference is most commonly the HTTP URI to the audio
file. On the receipt of the Alert-Info header the user agent may
fetch the referenced ringback or ring tone and play it to the user.
This mechanism does not ensure interoperability when there is no
common understanding of the referenced content (different countries
or vendors, hearing impaired) or when the user wants his own tones
configured in the end device. If caller and callee are from the
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 ringtone 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 proxy 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 a semantic indication 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 that can be understood by
an automaton, would allow for programmatic handling including user
interface adaptation, or conversion to equivalent protocol parameters
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.
Using 'alert' namespace provides syntax for several different
application spaces:
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o Names for services 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 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 URI reference to 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 or ring-tone.
To provide the general awareness about the Alert-Info URNs this
document provides IANA template for registering the URNs and defines
several typical identifiers.
This specification does not change the usage of the SIP Alert-Info-
header defined in the RFC3261. The Alert-Info-header can be used in
INVITE requests and 180 Ringing responses.
2. Requirements
This section discusses the requirements for an identifier to
transport the semantic of a specific ring or ringback tone.
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REQ-1: The mechanism will allow user agents (UAs) and proxies to
provide a semantic indication in the Alert-Info SIP-header that
signals the intent of the rendering and allows the recipient to
decide how to render the received information.
REQ-2: The mechanism will allow interoperability for services as call
waiting, forward, call forwarding, transfer-recall, auto-callback,
hold-recall, crisis.
REQ-3: The mechanism will allow rendering common PBX ring tone types.
REQ-4: The mechanism will allow rendering specific country ringback
tones.
REQ-5: The mechanism will allow rendering tones for emergency alerts.
REQ-6: The mechanism will allow rendering using other means than
tones, e.g. text or images.
REQ-7: The mechanism will allow rendering to be semantic, not biased
towards a particular representation which might not be suitable for
all devices or users. The Alert-Info URN must be semantic whenever
the semantic is known to the sender.
REQ-8: The mechanism will allow non-semantic, rendering-oriented
Alert-Info URNs when the semantic of the rendering is not known by
the sender and the sender can assume that there is a good chance that
for the receiver to know how to render the non-semantic URN. This is
the case, e.g. for:
- ringing tones used in closed in enterprise networks
- ringing tones used in some countries
- when TDM gateways must map ring-/ringback-tones from legacy
protocols to SIP at the edge of a network .
REQ-9: The mechanism must ensure that an UA receiving Alert-Info URNs
or portions of an Alert-Info URN it does not understand, it can
ignore them.
REQ-10: The mechanism will allow storage of the actual encoding
locally rather than fetching it.
REQ-11: The mechanism will allow the identifier to be specified "by
name" rather than "by value", to enable local policy decisions
whether to use it or not.
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REQ-12: The mechanism will allow transmission in the Alert-Info
header of SIP INVITE requests and 180 Ringing responses.
REQ-13: The mechanism will be flexible, so new identifiers 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.
3. Registration template
Below is the registration template for the 'alert' URN scheme
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 right-side
of the alert-identifier, the alert-indication, by a semicolon. In
this specification, three categories of alert-identifiers are
described: the "tone" alert-identifiers, the "ringback" alert-
identifiers and the "service" alert-identifiers.
The "tone" alert-identifier has the general form:
urn:alert:tone:{tone-indication}
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where the tone-indication identifies the semantic or rendering
characteristics of a ring tone. Alert-Info URNs containing the
"tone" alert-identifier can be used in INVITE requests, but not in
180 Ringing responses.
The "ringback" alert-identifier has the general form:
urn:alert:ringback:{ringback-indication}
where the ringback-indication is a unique identifier for a
country-specific ringback tone. Alert-Info URNs containing the
"ringback" alert-identifier can be used in 180 Ringing responses,
but not in INVITE requests.
The "service" alert-identifier has the general form:
urn:alert:service:{service-indication}
where the service-indication is a unique identifier for a service
as call-waiting or transfer-recall. Alert-Info URNs containing
the "service" alert-identifier can be used in both INVITE requests
and 180 Ringing responses.
The tone-indication, the ringback-indication and the service-
indication are hierarchical identifiers, consisting of one label
or a sequence of labels separated by periods. The left-most label
is the most significant one and is called 'top-level indication' ,
while names to the right are called 'sub-indication'. The set of
allowable characters is the same as that for domain names
[RFC1123]. Labels are case-insensitive, but MUST be specified in
all lower-case.
Labels can be removed right-to-left excepting the left-most label;
the resulting tone-indication or service-indication is still
valid, referring to a more generic tone-indication, ringback-
indication or service-indication. In other words, if a tone
'x.y.z' exists, the tones 'x' and 'x.y' are also valid tones.
Each alert indication identifier SHALL explicitly define it's
validity respective the sub-indications.
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The ABNF [RFC5234] for the "tone" and "service" alert URNs is
shown below:
alert-URN = "URN:alert:" alert-identifier
alert-identifier= alert-category ":" alert-indication
alert-category = "tone"/ "ringback"/ "service"
alert-indication= top-level *("." sub-indication)
top-level = let-dig [ *25let-dig-hyp let-dig ]
sub-indication = 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
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 indication based on the 'alert' URN. The assignment of
identifiers is described in Section 7. The 'alert' URN does not
prescribe a particular resolution mechanism, but it is assumed
that a number of different entities could operate and offer such
mechanisms.
Namespace considerations: There do not appear to be other URN
namespaces that serve the same need of uniquely identifying
'alert' communication and information services.
Identifier uniqueness considerations: An 'alert' URN identifies a
logical service or tone, specified in the 'alert' indication
registration (see Section 7). Resolution of the registered URN
will return a particular instance of the alert identifier. Alert
identifier URNs MUST be unique for each unique indication; this is
guaranteed through the registration of each alert indication
within this namespace, described in Section 7.
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Identifier persistence considerations: The 'alert' URN for the same
indication is expected to be persistent, as long as it is
registered with IANA.
Process of identifier assignment: The process of identifier
assignment is described in Section 7.
Process for identifier resolution: 'alert' URNs are statically
resolved according to the IANA registry.
Rules for lexical equivalence: 'alert' 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' URNs at
IANA.
Scope: The scope for this URN is public and global.
4. Top Level Alert URN Indication Definitions
This section describes the use cases that are supported by the
'alert' URNs.
4.1. PBX Tones
This section defines some commonly encountered ring-tones on PBX or
business phones. They are as follows:
4.1.1. normal
This tone indicates that the default or normal ring-tone should be
rendered. This is essentially a no-operation Alert-Info URN and
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 ringtone need be specified. If no special
alerting is to be used, urn:alert:tone:normal should be used.
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4.1.2. 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. For this case, urn:alert:tone:external should be used.
4.1.3. 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.
For this case, the urn:alert:tone:internal should be used.
4.2. Service Tones
These tones are used to indicate specific PBX and telephony services.
4.2.1. call-waiting
The call waiting Service [TS24.615] permits a callee to be notified
of an incoming call whilst the media resources are not available for
the incoming call and 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
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 URN to the Alert-Info header. 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 user.
The urn:alert:service:call-waiting should be used for this case.
4.2.2. 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. The
urn:alert:service:forward should be used for this case. Note that a
181 response can be used in place of this URN.
4.2.3. 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
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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. The urn:alert:service:transfer-recall should
be used for this case.
4.2.4. auto-callback
This feature is used when a user has utilized a server to implement
an automatic callback service. 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. The
urn:alert:service:auto-callback should be used for this case.
4.2.5. 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. The urn:alert:service:hold-recall should be used for this
case.
4.2.6. priority
This sub-level is used to indicate that a priority level alert should
be applied for the type of alerting specified. For example,
urn:alert:tone:priority would be used to generate priority alerting.
4.2.7. zip
This sub-level is used to indicate that the alert type specified
should be rendered shorter than normal. In contact centers, this is
sometimes referred to as "abbreviated ringing" or a "zip tone". For
example, urn:alert:tone:zip would generate a shorter than normal
ring-tone.
4.2.8. delayed
This sub-level is used to indicate that the alerting type specified
show 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. For example, urn:alert:tone:delayed would
generate a normal ring-tone, delayed by a few seconds.
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4.3. Country-specific ringback tone indications for the public
telephone network
In the PSTN, different tones are used in different countries. End
users are accustomed to hear the callee's country ringback tone.
The ISO 3166-1 country code [ISO 3166-1] is used as a top-level
indication to infor the UAC about the country-specific tone which
should be rendered to the caller. For example, to indicate ringback
tones from South Africa, the following URN would be used:
<urn:alert:ringback:za>.
4.4. Combinations of URNs
In some cases, more than one URN will need to be specified to fully
define a particular tone. This is done by including multiple URNs.
For example, an internal, priority call could be indicated by Alert-
Info: <urn:alert:tone:internal>, <urn:alert:tone:priority>. A
priority call waiting tone could be indicated by Alert-Info:
<urn:alert:service:call-waiting>, <urn:alert:tone:priority>.
5. User Agent Behavior
Upon receiving a SIP INVITE request or a SIP 180-Ringing response
with an Alert-Info header that contains a single or multiple 'alert'
URNs, the User Agent (UA) attempts to match the received Alert-Info
URNs with the known indications or indication combinations. The User
Agent (UA) ignores the Alert-Info URNs for which no match is found
and proceeds with the normal operation. If one or multiple URNs
match(es) a known indication or a known indication combination, the
User Agent (UA) renders the indication or the indication combination
to the user accordingly. The User Agent (UA) is responsible for the
non disturbing rendering if multiple indications and network
resources are to be rendered simultaneously.
6. Proxy Behavior
A SIP proxy MAY add a URN or multiple URNs to the Alert-Info header
in a SIP request or a 180 Ringing provisional response when it needs
to provide additional information about the call or about the
provided service. A SIP Proxy SHOULD NOT add a mixture of 'alert'
URNs and URIs to the Alert-Info header that may cause disturbing
rendering interference at the recipient's User Agent (UA).
Following example shows both the network audio resource referenced by
the HTTP URI and the URN indication for the call-waiting service
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transported by the Alert-Info header in a 180 Ringing provisional
response.
Alert-Info: <http://www.example.com/sound/moo.wav>,
<urn:alert:service:call-waiting>
7. IANA Considerations
This section registers a new URN scheme with the registration
template provided in section Registration Template.
Below, the section 7.1 details how to register new alert-identifiers.
Descriptions of alert-indications for the first three alert-
identifiers described in this document , 'service', 'tone' and
'ringback', are given in Section 7.2 and Section 7.3, respectively.
Finally, Section 7.4 contains the initial registration table.
7.1. New alert-identifiers
Alert URNs are identified by labels managed by IANA, according to the
processes outlined in [RFC5226] in a new registry called "Alert URN
Labels". Thus, creating a new alert-identifier requires IANA action.
The policy for adding a new alert-identifier category is 'Standards
Action'. (This document defines the alert-identifier categories
'service' , 'tone' and 'ringback'.) The policy for assigning labels
to alert top-level indications or sub-indications and the rules to
combine top-level indications and sub-indications may differ for each
alert-identifier category and MUST be defined by the document
describing the corresponding alert indications. The entries in the
registration table have the following format:
Category/ Reference Description
Top-Indication/
Sub-Indication
------------------------------------------------------------
foo RFC XXXX Description of the 'foo'
alert-category
bar RFC YYYY Description of the 'bar'
alert-indication of the foo
alert-category
Each alert-category or alert-indication label MUST NOT exceed 27
characters.
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7.2. Alert-category
This section defines the alert-identifier registration within the
IANA registry defined in Section 7.1, using the alert-category labels
'service', 'tone' and 'ringback'.
The 'tone' alert-category label provides information about ringing
tones rendered by a UAS to the callee. The 'tone' alert-category
label may be generated by a UAC or a proxy and transmitted in a
INVITE request to the UAS.
The 'ringback' alert-category label provides information about
ringback tone rendered by a UAC to the caller. The 'ringback' alert-
category label may be generated by a UAS or a proxy and transmitted
in a 180 Ringing response.
The 'service' alert-category label describes special tones rendered
by a UAC or the UAS to the caller or the callee. The 'service'
alert-category label may be generated by a UAC, a UAS or a proxy and
transmitted in a INVITE request or a 180 Ringing response.
The normal rendering is audio, however there can be other renderings
applicable if needed by the user interface specifics.
7.3. Initial IANA Registration
7.3.1. Indications for PBX-tones
The following table contains the initial IANA registration for "tone"
top-level alert URN indications for PBX-tones.
Top-level Reference Description
Indication
-----------------------------------------------------------
normal RFC XXXX Normal ring-tone
internal RFC XXXX Internal PBX caller PBX ring-tone
external RFC XXXX External PBX caller PBX ring-tone
7.3.2. Additional Indications for PBX-tones
The following table contains the initial IANA registration for "tone"
top-level alert URN indications for PBX-tones.
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Top-level Reference Description
Indication
------------------------------------------------
priority RFC XXXX Priority ring-tone
zip RFC XXXX zip ring-tone
delayed RFC XXXX Delayed ring-tone
7.3.3. Indications for Country-specific Ringback tones in the public
telephone network
For the alert-category "ringback", the alert-indication contains the
ISO 3166-1 country code [ISO 3166-1]. For example, to indicate the
Romanian ringback tone, the country-code "ro" is used and the Alert-
Info URN will be <urn:alert:ringback:ro>.
7.3.4. Indications for Services
The following table contains the initial IANA registration for
"service" alert-indications.
Top-level Reference Description
Indication
--------------------------------------------------------
call-waiting RFC XXXX Call waiting service indication
forward RFC XXXX Call forwarding service
indication
transfer-recall RFC XXXX Transfer Recall service
indication
auto-callback RFC XXXX Auto Callback service indication
hold-recall RFC XXXX Hold Recall service indication
crisis RFC XXXX Crisis alerting indication
Editor's Note: RFC XXXX should be replaced with this specification.
7.3.5. Combination Rules for Alert URN Indications
Senders may insert one or more Alert-Info URNs. Following rules
apply:
- Senders should not insert two different URNs from one of the groups
described above.
- Any indication for PBX-tones can be combined with any additional
indication for PBX-tones.
- Indications and additional indications for PBX-tones can not be
combined with indication for country specific ringback (they are sent
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in diferent messages).
-Indications and additional indications for PBX-tones as well as
indication for country specific ringback can be combind with
indications for services which can be sent in the same SIP message
(INVITE or 180 Ringing).
- For stand-alone additional indication for PBX-tones, the receiver
should assume the "normal" indication for PBX-tones.
UAs may have rules how to render specific combinations of Alert-Info
URNs. An UA receiving a combination of Alert-Info URN which it does
not know how to render, it may choose to render a subset of it or to
ignore the content of the Alert-Info URN Header.
8. Internationalization Considerations
The alert-identifier labels are protocol elements [RFC3536] and are
not normally seen by users. Thus, the character set for these
elements is restricted, as described in Section 6.
9. 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, so privacy considerations do not
apply to the URN.
Provision of the specific indications from callee to caller may raise
privacy issues. Such provision SHALL always be explicitly authorised
by the callee.
10. Acknowledgements
The draft is based on the ideas expressed by Paul Kyzivat on the
BLISS WG mailing list. The authors wish to thank Paul Kyzivat, Adam
Roach, Dean Willis, Martin Huelsemann, Shida Schubert, John Elwell
and Tom Taylor for their comments and suggestions.
11. References
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11.1. 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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
11.2. Informative References
[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-04 (work in progress),
October 2009.
[ISO 3166-1]
"ISO 3166-1 English country names and code elements", http
://www.iso.org/iso/
english_country_names_and_code_elements .
[RFC3536] Hoffman, P., "Terminology Used in Internationalization in
the IETF", RFC 3536, May 2003.
[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.
[TS24.615]
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"3GPP TS 24.615 Communication Waiting (CW) using IP
Multimedia (IM) Core Network (CN) subsystem".
Authors' Addresses
Denis Alexeitsev
Deutsche Telekom AG
Friedrich-Ebert-Allee
Bonn 53113
Germany
Phone: +49-228-18112010
Email: d.alexeitsev@telekom.de
Laura Liess
Deutsche Telekom AG
Heinrich-Hertz Str 3-7
Darmstadt, Hessen 64295
Germany
Phone: +49-6151-6282761
Email: laura.liess.dt@gmail.com
Roland Jesske
Deutsche Telekom AG
Heinrich-Hertz Str 3-7
Darmstadt, Hessen 64295
Germany
Phone: +49-6151-6282766
Email: r.jesske@telekom.de
Alan Johnston
Avaya
St. Louis, MO
United States
Phone:
Email: alan.b.johnston@gmail.com
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Anwar Siddiqui
Avaya
Milpitas, CA
United States
Phone:
Email: anwars@avaya.com
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