[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-liess-dispatch-alert-info-urns) 00 01 02 03 04 05 06 07 08 09 10 11 12 13

SALUD                                                      L. Liess, Ed.
Internet-Draft                                                 R. Jesske
Updates: 3261 (if approved)                          Deutsche Telekom AG
Intended status: Standards Track                             A. Johnston
Expires: October 7, 2012                                       D. Worley
                                                                   Avaya
                                                              P. Kyzivat
                                                           April 5, 2012


       Alert-Info URNs for the Session Initiation Protocol (SIP)
                  draft-ietf-salud-alert-info-urns-06

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/.

   Internet-Drafts are draft documents valid for a maximum of six months



Liess, et al.            Expires October 7, 2012                [Page 1]

Internet-Draft               Alert-Info URNs                  April 2012


   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 October 7, 2012.

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.































Liess, et al.            Expires October 7, 2012                [Page 2]

Internet-Draft               Alert-Info URNs                  April 2012


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  . . . . . . . . . . . . . . 14
     5.1.  Alert-category Values Definitions  . . . . . . . . . . . . 14
     5.2.  Alert-indication Values Definitions  . . . . . . . . . . . 15
       5.2.1.  Alert-Info URN Indication Values for the
               alert-category 'service' . . . . . . . . . . . . . . . 15
       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'  . . . . . . . . . . . . . . 16
       5.2.4.  Alert-Info URN Indication  Values for the
               alert-category 'duration'  . . . . . . . . . . . . . . 16
       5.2.5.  Alert-Info URN Indication Values for the
               alert-category 'delay' . . . . . . . . . . . . . . . . 16
       5.2.6.  Alert-Info URN Indication Values for the
               alert-category 'locale'  . . . . . . . . . . . . . . . 17
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
     6.1.  New alert identifiers  . . . . . . . . . . . . . . . . . . 17
     6.2.  Initial IANA Registration  . . . . . . . . . . . . . . . . 18
       6.2.1.  The "service" alert-category and alert-identifiers . . 18
       6.2.2.  The "source" alert-category and alert-identifiers  . . 18
       6.2.3.  The "priority" alert-category and alert-identifiers  . 19
       6.2.4.  The "duration" alert-category and alert-identifiers  . 19
       6.2.5.  The "delay"  alert-category and alert-identifiers  . . 20
       6.2.6.  The "locale"  alert-category and alert-identifiers . . 20



Liess, et al.            Expires October 7, 2012                [Page 3]

Internet-Draft               Alert-Info URNs                  April 2012


   7.  Extensibility Rules  . . . . . . . . . . . . . . . . . . . . . 21
     7.1.  General Extensibility Rules  . . . . . . . . . . . . . . . 21
     7.2.  Extensions Rules for Independent Organizations . . . . . . 21
   8.  Combinations of Alert-Info URNs  . . . . . . . . . . . . . . . 22
     8.1.  Priority Rules . . . . . . . . . . . . . . . . . . . . . . 22
     8.2.  Multi-mode signals . . . . . . . . . . . . . . . . . . . . 23
   9.  Non-normative Algorithm for Handling Combinations of URNs  . . 24
     9.1.  Algorithm Description  . . . . . . . . . . . . . . . . . . 24
     9.2.  Examples of how the algorithm works  . . . . . . . . . . . 25
       9.2.1.  Example 1  . . . . . . . . . . . . . . . . . . . . . . 26
       9.2.2.  Example 2  . . . . . . . . . . . . . . . . . . . . . . 27
       9.2.3.  Example 3  . . . . . . . . . . . . . . . . . . . . . . 30
       9.2.4.  Example 4  . . . . . . . . . . . . . . . . . . . . . . 31
       9.2.5.  Example 5  . . . . . . . . . . . . . . . . . . . . . . 32
   10. User Agent Behaviour . . . . . . . . . . . . . . . . . . . . . 33
   11. Proxy Behaviour  . . . . . . . . . . . . . . . . . . . . . . . 34
   12. Internationalization Considerations  . . . . . . . . . . . . . 34
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 34
   14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 35
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 35
     15.2. Informative References . . . . . . . . . . . . . . . . . . 35
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36




























Liess, et al.            Expires October 7, 2012                [Page 4]

Internet-Draft               Alert-Info URNs                  April 2012


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



Liess, et al.            Expires October 7, 2012                [Page 5]

Internet-Draft               Alert-Info URNs                  April 2012


   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



Liess, et al.            Expires October 7, 2012                [Page 6]

Internet-Draft               Alert-Info URNs                  April 2012


   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



Liess, et al.            Expires October 7, 2012                [Page 7]

Internet-Draft               Alert-Info URNs                  April 2012


   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.




Liess, et al.            Expires October 7, 2012                [Page 8]

Internet-Draft               Alert-Info URNs                  April 2012


   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



Liess, et al.            Expires October 7, 2012                [Page 9]

Internet-Draft               Alert-Info URNs                  April 2012


   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



Liess, et al.            Expires October 7, 2012               [Page 10]

Internet-Draft               Alert-Info URNs                  April 2012


   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



Liess, et al.            Expires October 7, 2012               [Page 11]

Internet-Draft               Alert-Info URNs                  April 2012


   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.





Liess, et al.            Expires October 7, 2012               [Page 12]

Internet-Draft               Alert-Info URNs                  April 2012


      The alert-indications are hierarchical identifiers.  The set of
      allowable characters is the same as that for domain names
      [RFC1123].  Labels are case-insensitive.  Comparisons MUST be
      case-insensitive.  Registered URNs SHOULD be transmitted as
      registered.  A new name MUST NOT be registered if it is equal by
      case-insensitive comparison 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




      Throughout this document, "<private-name>" is used as a syntactic
      variable for any string conformant to the "private-name" ABNF
      above.

   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
      assignment of identifiers is described in Section 6.  The Alert-
      Info URN does not prescribe a particular resolution mechanism, but



Liess, et al.            Expires October 7, 2012               [Page 13]

Internet-Draft               Alert-Info URNs                  April 2012


      any resolution MUST comply with the rules in Section 8.

   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-Info URN identifies a
      semantic or sensory feature of alert rendering at the caller's or
      callee's end device.  The feature identified by a particular
      Alert-Info URN is persistent and distinct from the feature
      identified any other Alert-Info URN through the IANA registration
      of each Alert-Info URN (that is, each defined combination of
      alert-category and alert-identifier) as described in Section 6.

   Identifier persistence considerations:  The Alert-Info 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 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:






Liess, et al.            Expires October 7, 2012               [Page 14]

Internet-Draft               Alert-Info URNs                  April 2012


   - service

   - source

   - priority

   - duration

   - delay

   - 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.



Liess, et al.            Expires October 7, 2012               [Page 15]

Internet-Draft               Alert-Info URNs                  April 2012


5.2.2.  Alert-Info URN Indication Values for the alert-category 'source'

   - unclassified (default)

   - internal

   - 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'








Liess, et al.            Expires October 7, 2012               [Page 16]

Internet-Draft               Alert-Info URNs                  April 2012


   - none (default)

   - yes

   - <private-name>

   Examples: urn:alert:delay:yes .

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 labels 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 labels to alert-indications 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:










Liess, et al.            Expires October 7, 2012               [Page 17]

Internet-Draft               Alert-Info URNs                  April 2012


      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.

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-identifiers.  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-identifiers
   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-identifiers.  The value of this
   indicator provides information about the user at the other side of
   the call.






Liess, et al.            Expires October 7, 2012               [Page 18]

Internet-Draft               Alert-Info URNs                  April 2012


   alert-category/              Reference  Description
   alert-identifier
   -----------------------------------------------------------
   source                        RFC XXXX  Alert-category for "source"
                                           alert-identifiers
   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-identifiers.  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-
                                             identifiers
   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-identifiers.  The value of this
   indicator provides information about the duration of the alerting
   signals compared to the default alerting signals.





Liess, et al.            Expires October 7, 2012               [Page 19]

Internet-Draft               Alert-Info URNs                  April 2012


 alert-category/                 Reference  Description
 alert-identifier
 -----------------------------------------------------------
 duration                        RFC XXXX  Alert-category for "duration"
                                           alert-identifiers
 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-identifiers.  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-identifiers
   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-identifiers.  The value of this
   indicator provides information about the location of the user at the
   other side of the call.

   alert-category/               Reference  Description
   alert-identifier
   -----------------------------------------------------------
   locale                        RFC XXXX  Alert-category for "locale"
                                           alert-identifiers
   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



Liess, et al.            Expires October 7, 2012               [Page 20]

Internet-Draft               Alert-Info URNs                  April 2012


                                           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
   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).




Liess, et al.            Expires October 7, 2012               [Page 21]

Internet-Draft               Alert-Info URNs                  April 2012


   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:

      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




Liess, et al.            Expires October 7, 2012               [Page 22]

Internet-Draft               Alert-Info URNs                  April 2012


         (2) if the final name is a private-name with three or more
         labels, 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-indications of
      certain alert-categories, one signal is less-specific than a
      second signal if the first signal's alert-indications are a subset
      or are prefixes of the second signal's alert-indications.)
      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.
   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



Liess, et al.            Expires October 7, 2012               [Page 23]

Internet-Draft               Alert-Info URNs                  April 2012


   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
   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



Liess, et al.            Expires October 7, 2012               [Page 24]

Internet-Draft               Alert-Info URNs                  April 2012


   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
      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:





Liess, et al.            Expires October 7, 2012               [Page 25]

Internet-Draft               Alert-Info URNs                  April 2012


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

   Signal 4

      Meaning: high

      Locations:

      - source

      - priority:high

   To which we add:




Liess, et al.            Expires October 7, 2012               [Page 26]

Internet-Draft               Alert-Info URNs                  April 2012


   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
   tricky examples.  This enlarges our set of signals:

   Signal 1

      Meaning: default

      Locations:

      - source

      - priority




Liess, et al.            Expires October 7, 2012               [Page 27]

Internet-Draft               Alert-Info URNs                  April 2012


   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:

      - source

      - priority:high

   Signal 6

      Meaning: external high

      Locations:

      - source:external




Liess, et al.            Expires October 7, 2012               [Page 28]

Internet-Draft               Alert-Info URNs                  April 2012


      - 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

      - 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:



Liess, et al.            Expires October 7, 2012               [Page 29]

Internet-Draft               Alert-Info URNs                  April 2012


      - 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

   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:



Liess, et al.            Expires October 7, 2012               [Page 30]

Internet-Draft               Alert-Info URNs                  April 2012


      - 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

      - external low

      - external high

   The second sort is based on priority:low, and results in this order:

      - internal

      - low

      - default

   Excluded:





Liess, et al.            Expires October 7, 2012               [Page 31]

Internet-Draft               Alert-Info URNs                  April 2012


      - 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

      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:



Liess, et al.            Expires October 7, 2012               [Page 32]

Internet-Draft               Alert-Info URNs                  April 2012


      - 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
   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.




Liess, et al.            Expires October 7, 2012               [Page 33]

Internet-Draft               Alert-Info URNs                  April 2012


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
   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.




Liess, et al.            Expires October 7, 2012               [Page 34]

Internet-Draft               Alert-Info URNs                  April 2012


   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.

   [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]
              Huelsemann, M., Jesske, R., Worley, D., and D. Alexeitsev,
              "Call Completion for Session Initiation Protocol (SIP)",
              draft-ietf-bliss-call-completion-14 (work in progress),
              November 2011.




Liess, et al.            Expires October 7, 2012               [Page 35]

Internet-Draft               Alert-Info URNs                  April 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-09 (work in progress),
              December 2011.

   [ISO3166-1]
              "ISO 3166-1 English country names and code elements", http
              ://www.iso.org/iso/
              english_country_names_and_code_elements .

   [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.

   [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 6282761
   Email: laura.liess.dt@gmail.com












Liess, et al.            Expires October 7, 2012               [Page 36]

Internet-Draft               Alert-Info URNs                  April 2012


   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 Inc.
   St. Louis, MO
   United States

   Phone:
   Email: alan.b.johnston@gmail.com


   Dale R. Worley
   Avaya Inc.
   600 Technology Park Dr.
   Billerica, MA  01821
   US

   Phone: +1 978 288 5505
   Email: dworley@avaya.com
   URI:   http://www.avaya.com


   Paul Kyzivat
   United States

   Email: pkyzivat@alum.mit.edu

















Liess, et al.            Expires October 7, 2012               [Page 37]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/