BLISS D. Alexeitsev
Internet-Draft L. Liess
Intended status: Standards Track R. Jesske
Expires: January 14, 2010 M. Huelsemann
Deutsche Telekom AG
A. Johnston
Avaya
July 13, 2009
Alert-Info URNs for the Session Initiation Protocol (SIP)
draft-alexeitsev-bliss-alert-info-urns-02
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Copyright Notice
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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 tied rendering. To overcome this limitations and
support new applications a family of the URNs 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].
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Registration template . . . . . . . . . . . . . . . . . . . . 5
3. Top Level Alert URN Indication Definitions . . . . . . . . . . 8
3.1. PBX Tones . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.1. normal . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.2. external . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.3. internal . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Service Tones . . . . . . . . . . . . . . . . . . . . . . 8
3.2.1. call-waiting . . . . . . . . . . . . . . . . . . . . . 9
3.2.2. forward . . . . . . . . . . . . . . . . . . . . . . . 9
3.2.3. transfer-recall . . . . . . . . . . . . . . . . . . . 9
3.2.4. auto-callback . . . . . . . . . . . . . . . . . . . . 9
3.2.5. hold-recall . . . . . . . . . . . . . . . . . . . . . 9
3.2.6. crisis . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Alert Level URN Sub-Indications Definitions . . . . . . . . . 10
4.1. priority . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. short . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. delayed . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. User Agent Behavior . . . . . . . . . . . . . . . . . . . . . 10
6. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7.1. New alert-identifiers . . . . . . . . . . . . . . . . . . 11
7.2. Alert-category . . . . . . . . . . . . . . . . . . . . . . 12
7.3. Initial IANA Registration . . . . . . . . . . . . . . . . 12
8. Internationalization Considerations . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. An Appendix . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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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.
Current solution is sufficient for human users that share the same
understanding of the tones. However 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. 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 and support new applications 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.
Using 'alert' namespace provides syntax for several different
application spaces:
o Names for common ring-tones generated by PBX phone 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 services such as call waiting or automatic callback, not
tied to any particular rendering.
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.
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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.
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.
2. Registration template
Below is the registration template for the 'alert' URN scheme
according to the RFC 3406 [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:
Namespace Specific String (NSS) in the 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, two categories of alert-
identifiers are described: the "tone" alert-identifiers and the
"service" alert-identifiers.
The "tone" alert-identifier has the general form:
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urn:alert:tone:{tone-indication}
where the tone-indication identifies the semantic of a tone.
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.
The tone-indication and 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 or service-
indication. In other words, if a tone 'x.y.z' exists, the tone
'x' and 'x.y' are also valid tone. Each alert indication
identifier SHALL explicitly define it's validity respective the
sub-indications.
The ABNF [RFC4234] 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"/"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
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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 the IANA Considerations (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 IANA Considerations (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).
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 the IANA Considerations (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.
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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.
3. Top Level Alert URN Indication Definitions
This section describes the use cases that are supported by the
'alert' URNs.
3.1. PBX 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 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.
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. For this case, urn:alert:tone:external should be used.
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.
For this case, the urn:alert:tone:internal should be used.
3.2. Service Tones
These tones are used to indicate specific PBX and telephony services.
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3.2.1. 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.
3.2.2. forward
This feature is used in a 180 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.
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. The urn:alert:service:transfer-recall should
be used for this case.
3.2.4. 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.
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
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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.
3.2.6. crisis
This feature is used for emergency announcements sent over PBX
systems such as building evacuations, alarms, etc. This service tone
is used to distinguish this case from any other normal incoming call.
The urn:alert:service:crisis should be used for this case.
4. Alert Level URN Sub-Indications Definitions
These sub-indications can be applied to any of the Top Level Alert
Indications defined in the previous sections.
4.1. 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:internal.priority would be used to generate alerting
for a priority internal PBX call.
4.2. short
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:normal.short would generate a shorter than
normal ring-tone.
4.3. 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:external.delayed
would generate an external ring-tone, delayed by a few seconds.
5. User Agent Behavior
Upon receiving a SIP request or a SIP 180 Ringing response with an
Alert-Info header that contains a single or multiple 'alert' URNs,
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the User Agent (UA) attempts to match the received URNs with the
known indications. If no match is found, the User Agent (UA) ignores
the received 'alert' URNs and proceeds with the normal operation. If
the one or multiple URNs matches a known indication, the User Agent
(UA) renders the indication(s) to the user according to the tone or
service identifier in the received alert URN. 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 the
'alert' URNs and URIs to the Alert-Info header that may cause
disturbing rendering interference at the recepient'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
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 two alert-identifiers
described in this document , service and tone, 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 identifiers and alert-indications are identified by labels
managed by IANA, according to the processes outlined in [RFC2434] 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' and 'tone'.) The
policy for assigning labels to alert-indications may differ for each
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alert-identifier category and MUST be defined by the document
describing the coresponding alert-identifier.
Entries in the registration table have the following format:
Category/Indication Reference Description
--------------------------------------------------------------------
foo RFC XXXX Description of the 'foo' alert-category
bar RFC YYYY Description of the 'bar' alert-indication
of the foo alert-category
bar.moo RFC ZZZZ Description of the 'bar.moo'
alert-indication of the foo alert-category
Each alert-category or alert-indication label MUST NOT exceed 27
characters.
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' and 'tone'.
The 'tone' alert-category label provides information about ringing
tones generated by a UAS and rendered to the callee in response to an
INVITE.
The 'service' alert-category label describes tones that should be
generated by the UAC or UAS and rendered to the caller or calee upon
receipt of a 180 response or a request. The normal rendering is
audio, however there can be other renderings applicable if needed by
the user interface specifics.
7.3. Initial IANA Registration
The following table contains the initial IANA registration for "tone"
alert-indications.
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Alert-Indication Reference Description
--------------------------------------------------------
normal RFC XXXX Normal ring-tone
normal.priority RFC XXXX Priority normal ring-tone
normal.short RFC XXXX Short normal ring-tone
normal.delayed RFC XXXX Delayed normal ring-tone
internal RFC XXXX Internal PBX caller PBX ring-tone
internal.priority RFC XXXX Priority internal PBX caller PBX ring-tone
internal.short RFC XXXX Short internal PBX caller PBX ring-tone
internal.delayed RFC XXXX Delayed internal PBX caller PBX ring-tone
external RFC XXXX External PBX caller PBX ring-tone
external.priority RFC XXXX Priority external PBX caller PBX ring-tone
external.short RFC XXXX Short external PBX caller PBX ring-tone
external.delayed RFC XXXX Delayed external PBX caller PBX ring-tone
The following table contains the initial IANA registration for
"service" alert-indications.
Alert-Indication Reference Description
--------------------------------------------------------
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.
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.
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10. Acknowledgements
The draft is based on the ideas expressed by Paul Kyzivat on the
BLISS WG mailing list.
11. References
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.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
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-02 (work in progress),
March 2009.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC3536] Hoffman, P., "Terminology Used in Internationalization in
the IETF", RFC 3536, May 2003.
[RFC5589] Sparks, R., Johnston, A., and D. Petrie, "Session
Initiation Protocol (SIP) Call Control - Transfer",
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BCP 149, RFC 5589, June 2009.
[TS24.615]
"3GPP TS 24.615 Communication Waiting (CW) using IP
Multimedia (IM) Core Network (CN) subsystem".
Appendix A. An Appendix
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: l.liess@telekom.de
Roland Jesske
Deutsche Telekom AG
Heinrich-Hertz Str 3-7
Darmstadt, Hessen 64295
Germany
Phone: +49-6151-6282766
Email: r.jesske@telekom.de
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Martin Huelsemann
Deutsche Telekom AG
Heinrich-Hertz Str 3-7
Darmstadt, Hessen 64295
Germany
Phone: +49-6151-6282765
Email: martin.huelsemann@telekom.de
Alan Johnston
Avaya
St. Louis, MO 63124
United States
Phone:
Email: alan@sipstation.com
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