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Versions: (draft-ietf-sip-info-events) 00 01 02 03 04 05 06 07 08 09 10 RFC 6086

SIPCORE                                                        E. Burger
Internet-Draft                                             NeuStar, Inc.
Obsoletes: RFC 2976                                            H. Kaplan
(if approved)                                                Acme Packet
Expires: April 26, 2010                                      C. Holmberg
                                                                Ericsson
                                                        October 23, 2009


  Session Initiation Protocol (SIP) INFO Method and Package Framework
                   draft-ietf-sipcore-info-events-02

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 26, 2010.

Copyright Notice

   Copyright (c) 2009 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 in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.






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Abstract

   This document defines a new method, INFO, for the Session Initiation
   Protocol (SIP) [RFC3261], and an Info Package mechanism.  The
   document obsoletes [RFC2976].  For backward compatibility the
   document also specifies a "legacy" mode of usage of the INFO method
   that is compatible with the usage previously defined in [RFC2976],
   referred to as "legacy INFO Usage" in this document.

Conventions Used in this Document

   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 RFC 2119 [RFC2119].
   The terminology in this document conforms to the Internet Security
   Glossary [RFC4949].



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Applicability  . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Info Package Support . . . . . . . . . . . . . . . . . . . . .  6
     3.1.   General . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.   User Agent Behavior . . . . . . . . . . . . . . . . . . .  6
     3.3.   Package Versioning  . . . . . . . . . . . . . . . . . . .  7
     3.4.   REGISTER Processing . . . . . . . . . . . . . . . . . . .  7
     3.5.   OPTIONS Processing  . . . . . . . . . . . . . . . . . . .  8
   4.  The INFO Method  . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.   General . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.   INFO Request  . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.   INFO Request Message Body . . . . . . . . . . . . . . . .  9
     4.4.   INFO Response . . . . . . . . . . . . . . . . . . . . . . 10
     4.5.   INFO Response Message Body  . . . . . . . . . . . . . . . 11
     4.6.   Order of Delivery . . . . . . . . . . . . . . . . . . . . 11
   5.  Formal INFO Method Definition  . . . . . . . . . . . . . . . . 11
     5.1.   INFO Method . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  INFO Header Fields . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 13
     6.2.   Info-Package header field . . . . . . . . . . . . . . . . 13
     6.3.   Recv-Info header field  . . . . . . . . . . . . . . . . . 14
   7.  Info Package Considerations  . . . . . . . . . . . . . . . . . 14
     7.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.2.   Appropriateness of Info Package Usage . . . . . . . . . . 14
     7.3.   Dialog Fate Sharing . . . . . . . . . . . . . . . . . . . 14
     7.4.   INFO Request Rate and Volume  . . . . . . . . . . . . . . 14
     7.5.   Alternative Mechanisms  . . . . . . . . . . . . . . . . . 15
       7.5.1.  Alternative SIP signaling plane mechanisms . . . . . . 15
       7.5.2.  Media Plane Mechanisms . . . . . . . . . . . . . . . . 16
       7.5.3.  Non-SIP related mechanisms . . . . . . . . . . . . . . 17
   8.  Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.2.   ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . . 17
   9.  Legacy INFO Usage  . . . . . . . . . . . . . . . . . . . . . . 17
     9.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.2.   Problems  . . . . . . . . . . . . . . . . . . . . . . . . 18
     9.3.   Co-existence with Info Package based INFO usage . . . . . 18
   10. Info Package Requirements  . . . . . . . . . . . . . . . . . . 19
     10.1.  General . . . . . . . . . . . . . . . . . . . . . . . . . 19
     10.2.  Applicability . . . . . . . . . . . . . . . . . . . . . . 19
     10.3.  Info Package Name . . . . . . . . . . . . . . . . . . . . 19
     10.4.  Info Package Parameters . . . . . . . . . . . . . . . . . 20
     10.5.  SIP Option Tags . . . . . . . . . . . . . . . . . . . . . 20
     10.6.  INFO Message Bodies . . . . . . . . . . . . . . . . . . . 20
     10.7.  Info Package Usage Restrictions . . . . . . . . . . . . . 20
     10.8.  Rate of INFO Requests . . . . . . . . . . . . . . . . . . 21



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     10.9.  IANA Registrations  . . . . . . . . . . . . . . . . . . . 21
     10.10. Info Package Security Considerations  . . . . . . . . . . 21
     10.11. Application Procedures  . . . . . . . . . . . . . . . . . 22
     10.12. Examples  . . . . . . . . . . . . . . . . . . . . . . . . 22
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
     11.1.  Update to Registration of SIP INFO Method . . . . . . . . 22
     11.2.  Registration of the Info-Package Header Field . . . . . . 22
     11.3.  Registration of the Recv-Info Header Field  . . . . . . . 23
     11.4.  Creation of the Info Packages Registry  . . . . . . . . . 23
     11.5.  Registration of the Info-Package Content-Disposition  . . 24
     11.6.  SIP Response Code 469 Registration  . . . . . . . . . . . 24
   12. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     12.1.  Indication of which Info Packages UAs are willing to
            receive INFO requests within an invite dialog usage . . . 24
     12.2.  INFO request with information associated with a
            simple Info Package . . . . . . . . . . . . . . . . . . . 25
     12.3.  Multipart INFO Example  . . . . . . . . . . . . . . . . . 25
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 26
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     14.1.  Normative References  . . . . . . . . . . . . . . . . . . 27
     14.2.  Informative References  . . . . . . . . . . . . . . . . . 28
   Appendix A.  Legacy INFO Usages  . . . . . . . . . . . . . . . . . 30
     A.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 30
     A.2.   ISUP  . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     A.3.   QSIG  . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     A.4.   MSCML . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     A.5.   MSML  . . . . . . . . . . . . . . . . . . . . . . . . . . 31
     A.6.   Video Fast Update . . . . . . . . . . . . . . . . . . . . 31
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . . 31
   Appendix C.  Change Log  . . . . . . . . . . . . . . . . . . . . . 31
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33




















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1.  Introduction

   This document defines a new method, INFO, for the Session Initiation
   Protocol (SIP) [RFC3261].

   The purpose of the INFO message is to carry application level
   information between endpoints, using the SIP dialog signaling path.
   Note that the INFO method is not used to update characteristics of a
   SIP dialog or session, but to allow the applications which use the
   SIP session to exchange information (which may update the state of
   those applications).

   This document also defines an Info Package mechanism.  An Info
   Package specification defines the content and semantics of the
   information carried in an INFO message associated with the Info
   Package.  The Info Package mechanism also provides a way for UAs to
   for which Info Packages they are willing to receive INFO requests.
   The document defines how the INFO method is used, new SIP header
   fields for the INFO method, and how to transport payload information
   associated with an Info Package using INFO requests.

   Use of the INFO method does not constitute a separate dialog usage.
   INFO messages are always part of, and share the fate of, an invite
   dialog usage [RFC5057].  INFO messages cannot be sent as part of
   other dialog usages.

   A UA uses the Recv-Info header field, on a per-dialog basis, to
   indicate for which Info Packages it is willing to receive INFO
   requests.  A UA can indicate an initial set of Info Packages during
   dialog establishment and can indicate a new set during the lifetime
   of the invite dialog usage.

   NOTE: A UA can use the Recv-Info header field with a 'nil' value to
   indicate that it is not willing to receive INFO requests for any
   Info-Package, but to inform other UAs that it still supports the Info
   Package mechanism.

   When a UA sends an INFO request, it uses the Info-Package header
   field to indicate which Info Package is associated with the request.
   One particular INFO request can only be associated with a single Info
   Package.

   This document obsoletes [RFC2976].  However, for backward
   compatibility it specifies a "legacy" mode of usage of the INFO
   method that is compatible with the usage previously defined in
   [RFC2976], referred to as "legacy INFO Usage" in this document.





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2.  Applicability

   This document defines a new method, INFO, for the Session Initiation
   Protocol (SIP) [RFC3261], and an Info Package mechanism.  The
   document obsoletes [RFC2976].  For backward compatibility the
   document also specifies a "legacy" mode of usage of the INFO method
   that is compatible with the usage previously defined in [RFC2976],
   referred to as "legacy INFO Usage" in this document.


3.  Info Package Support

3.1.  General

   This section describes how SIP UAs indicate for which Info Packages
   they are willing to receive INFO requests.

3.2.  User Agent Behavior

   A UA which supports the Info Package mechanism MUST indicate, using
   the Revc-Info header field, the set of Info Packages for which it is
   willing to receive INFO request.  A UA can list multiple Info
   Packages in a single Recv-Info header field, and the UA can use
   multiple Recv-Info header fields.

   The indication of Info Packages can take place during the dialog
   establishment, and during a target refresh.  This includes INVITE,
   UPDATE, PRACK, ACK, and their non-failure responses (101-199 and 2xx
   only).  Note that the UAC is not required to indicate its set of Info
   Packages in the initial INVITE request.

   If a UA is not willing to INFO requests for any Info Packages, during
   dialog establishment or later during the invite dialog usage, the UA
   MUST indicate this by including a Recv-Info header field with a 'nil'
   value.  This informs other UAs that the UA still supports the Info
   Package mechanism.

   Example: If a UA has previously indicated Info Packages 'foo' and
   'bar', and the UA during the lifetime of the invite dialog usage
   wants to indicate that it does not want to receive INFO requests for
   any Info Packages anymore, the UA sends a target refresh request with
   a Recv-Info header field with a header value of 'nil'.

   Once a UA has indicated that it is willing to receive INFO requests
   for a specific Info Package, and a dialog has been established, the
   UA MUST be prepared to receive INFO request associated with that Info
   Package.




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   A UA MUST NOT send an INFO request associated with an Info Package
   until it has received an indication that the remote UA is willing to
   receive INFO requests for that Info Package, and a dialog has been
   established with the remote UA.

   If a UA indicates multiple Info Packages, which provide similar
   functionality, it is not possible to indicate a priority order of the
   Info Packages, or that that the UA wishes to only receive INFO
   request for one of the Info Packages.  It is up to the application
   logic associated with the Info Packages, and specific Info Package
   descriptions to describe application behavior in such cases.

   For backward compatibility purpose, even if a UA indicates support of
   the Info Package mechanism, it is still allowed to enable legacy INFO
   usages Section 9.

   This document does not define a SIP option tag [RFC3261] for the Info
   Package mechanism.  However, an Info Package specification can define
   an option-tag associated with the specific Info Package, as described
   in Section 10.5.

   For backward compatibility, if a UA indicates support of the INFO
   method using the Allow header field [RFC3261], it does not implicitly
   indicate support of the Info Package mechanism.  A UA MUST use the
   Recv-Info header field in order to indicate that it supports the Info
   Package mechanism.  Likewise, even if a UA uses the Recv-Info header
   field to indicate that it supports the Info Package mechanism, in
   addition the UA MUST still also explicitly indicate support of the
   INFO method using the Allow header field.

3.3.  Package Versioning

   The Info Package mechanism does not support package versioning.
   Specific Info Package payloads MAY contain version information, which
   is handled by the applications associated with the Info Package, but
   that is outside the scope of the Info Package mechanism.

   NOTE: Even if an Info Package name contains version numbering (e.g.
   foo_v2), the Info Package mechanism does not distinguish a version
   number from the rest of the Info Package name.

3.4.  REGISTER Processing

   This document allows a UA to insert a Recv-Info header field in a
   REGISTER request.  However, a UA SHALL NOT include a header value for
   a specific Info Package unless the specific Info Package
   specification describes how the header field value shall be
   interpreted and used by the registrar, e.g. in order to determine



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   request targets.

   NOTE: Rather than using the Recv-Info header field in order to
   determine request targets, it is recommended to use more appropriate
   mechanisms, e.g. based on [RFC3840].

3.5.  OPTIONS Processing

   If a UA sends an OPTIONS request, or a response, the UA SHALL include
   Recv-Info header field in the message, and list the Info Packages
   that it supports to receive.

   NOTE: As for any other capability and extension, for a specific
   dialog UAs need to indicate which Info Packages they are willing to
   receive within that dialog.


4.  The INFO Method

4.1.  General

   This section describes the UA handling of INFO requests and
   responses, and message bodies carried in INFO messages.

   The INFO method provides additional, application level information
   that can further enhance a SIP application.  Annex A gives more
   details on the types of application for which the usage of INFO is
   seen as appropriate.

4.2.  INFO Request

   When a UA sends an INFO request associated with an Info Package, it
   MUST include an Info-Package header field that indicates which Info
   Package is associated with the request.  A specific INFO request can
   be used only for a single Info Package.  For a specific dialog, a UA
   MUST NOT send INFO requests associated with Info Packages that the
   remote UA has not indicated that it is willing to receive.

   A UA can send an INFO requests associated with a legacy INFO usage
   Section 9.  In such case there is no Info Package associated with the
   usage, and the INFO request does not contain an Info-Package header
   field.  In addition, the UA cannot use the Recv-Info header field to
   indicate whether it is willing to receive INFO requests associated
   with that legacy INFO usage.

   The INFO method MUST NOT be used outside an invite dialog usage.  The
   INFO method has no lifetime beyond its transaction or usage of its
   own.  UAs indicate, per-dialog basis, for which Info Packages they



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   are willing to receive INFO requests.  The set of Info Packages
   cannot automatically be used within other dialogs.

   Due to the possibility of forking, a UAC which, during the early
   dialog phase indicates that it is willing to receive INFO requests
   for one or more Info Packages MUST be prepared to receive INFO
   requests associated with those Info Packages from multiple remote
   UAs.  Note that each remote UA can indicate a different set of Info
   Packages for which they are willing to receive INFO request.

   The construction of the INFO request is the same as any other request
   within an existing invite dialog usage.  A UA can send INFO requests
   both within early and confirmed dialogs.

   The INFO request MUST NOT contain a Recv-Info header field.  The UA
   can only indicate a set of Info Packages for which it is willing to
   receive INFO requests by using the SIP methods (and their responses)
   listed in Section 3.

4.3.  INFO Request Message Body

   The purpose of the INFO request is to carry application level
   information between SIP UAs.  The application data associated with an
   Info Package is carried as payload in the message body of the INFO
   request, using one or more body parts.

   Info Package specifications MUST describe the application level
   information associated with the Info Package.  Each body part MUST
   have a MIME type value, and the syntax and content of the body part,
   defined.

   Each body part, when associated with an Info Package, MUST have a
   Content-Disposition header field with an 'Info-Package' value
   assigned, in order to be able distinguish body parts associated with
   the Info Package from other body parts.

   NOTE: Some SIP functions that are orthogonal to INFO may insert body
   parts unrelated to the Info Package.

   Body parts associated with specific MIME types may sometimes have
   specific Content-Disposition header field values defined for them.
   For example, for body parts with a 'text/plain' MIME a Content-
   Disposition header field with a 'render' value is often assigned.
   However, when a body part in the INFO message is associated with an
   Info Package, it MUST always have a Content-Disposition header field
   with an 'Info-Package' value assigned.  The Info Package
   specification defines how applications process the body part
   contents.



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   If a SIP message body contains multiple body parts, multipart body
   parts [RFC5621] are used to separate them.  If all body parts within
   a multipart body part are associated with the Info Package, the
   multipart body part SHALL have a Content-Disposition header field
   with an 'Info-Package' value assigned to it.  However, each body part
   within the multipart body part MUST still have a Content-Disposition
   header field with an 'Info-Package' value assigned to them, in order
   to avoid that the parser assigns a default Content-Disposition header
   value to the body part.

   NOTE: According to [RFC5621], body parts within a multipart are not
   implicitly assigned the Content-Disposition header field value of the
   multipart body part which they belong to.

   This document does not define Info Package specific rules on how body
   parts associated with Info Packages are to be inserted into multipart
   body parts, and what type of multiparts are used.  If an Info Package
   requires special rules regarding the usage of multipart body parts,
   the specification for that Info Package MUST specify such rules.

   UAs MUST conform to [RFC5621] to support multipart body parts.

   If a UA indicates that it is willing to receive a specific Info
   Package, the UA naturally also supports any associated message body
   part MIME type associated with the Info Package.  However, in
   addition the UA MUST still indicate support of those MIME types in
   the Accept header field, according to the procedures in [RFC3261].

   NOTE: To avoid corner cases with legacy INFO usage, the Info-Package
   header field is used to indicate the Info Package name, rather than
   to use a Content-Disposition header field parameter in order to
   indicate the name.

4.4.  INFO Response

   If a UA receives an INFO request, associated with an Info-Package
   that the UA has indicated willingness to receive, and the INFO
   request contains data associated with that Info-Package, the UA MUST
   send a 200 OK response.

   If a UA receives an INFO request for legacy usage, for which no Info-
   Package is associated (the INFO request does not contain an Info-
   Package header field), the UA MUST send a 200 OK response.

   The UAS MAY send other responses, such as Request Failure (4xx),
   Server Failure (5xx) and Global Failure (6xx) as appropriate for the
   request.




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   If a UA receives an INFO request associated with an Info Package that
   the UA has not indicated willingness to receive, the UA MUST send a
   469 Bad INFO Package response Section 11.6.  In the terminology of
   Multiple Dialog Usages [RFC5057], this represents a Transaction Only
   failure.

   If a UA receives an INFO request that does not match any existing
   invite dialog usage, the UA MUST send a 481 Call Leg/Transaction Does
   Not Exist response.

   If a UA receives an INFO request that carries a message body that the
   UA does not support, and support of the message body is required in
   the Content-Disposition header field, the UA MUST send a 415
   Unsupported Media Type response.  If support of the message body is
   optional, the UA MUST send a 200 OK response even if the UA does not
   support the message body.

4.5.  INFO Response Message Body

   The Info Package mechanism allows a SIP stack to generate a response
   to an INFO request without application interaction.  As a result,
   Info Packages cannot require a message body in INFO responses,
   require different response codes, or otherwise require the response
   to the INFO request to contain application information.  If the
   application needs to send information in the other direction, it can
   send a new INFO request which contains the information.

4.6.  Order of Delivery

   The Info Package mechanism relies on the CSeq header field to detect
   if an INFO request is received out of order.

   If specific applications need additional mechanisms for order of
   delivery, those mechanisms, and related procedures, must be specified
   as part of the associated Info Package, and possible sequence numbers
   etc must be defined as application data.


5.  Formal INFO Method Definition

5.1.  INFO Method

   This document describes one new SIP method: INFO.  This document
   replaces the definition and registrations found in [RFC2976].

   This table expands on Tables 2 and 3 in [RFC3261].

     Header                    Where    INFO



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     ------                    -----    ----
     Accept                      R       o
     Accept-Encoding             R       o
     Accept-Encoding            2xx      o
     Accept-Encoding            415      c
     Accept-Language             R       o
     Accept-Language            2xx      o
     Accept-Language            415      c
     Alert-Info                          -
     Allow                       R       o
     Allow                      200      -
     Allow                      405      o
     Authentication-Info        2xx      o
     Authorization               R       o
     Call-ID                     c       m
     Call-Info                           o
     Contact                             -
     Content-Disposition                 o
     Content-Encoding                    o
     Content-Language                    o
     Content-Length                      o
     Content-Type                        *
     CSeq                        c       m
     Date                                o
     Error-Info               3xx-6xx    o
     Expires                             -
     From                        c       m
     Geolocation                 R       o
     Max-Breadth                 R       -
     Max-Forwards                R       o
     MIME-Version                        o
     Min-Expires                         -
     Organization                        o
     Priority                    R       -
     Privacy                     R       o
     Proxy-Authenticate         407      o
     Proxy-Authorization         R       o
     Proxy-Require               R       o
     Reason                      r       o
     Record-Route                R       o
     Record-Route             2xx,18x    o
     Require                             o
     Retry-After                 R       -
     Retry-After            404,480,486  o
     Retry-After                503      o
     Retry-After              600,603    o
     Route                       R       o
     Security-Client             R       o



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     Security-Server          421,494    o
     Security-Verify             R       o
     Server                      r       o
     Subject                     R       o
     Supported                   R       o
     Supported                  2xx      o
     Timestamp                           o
     To                          c       m  (w/ Tag)
     Unsupported                420      o
     User-Agent                          o
     Via                                 m
     Warning                     r       o
     WWW-Authenticate           401      m
     WWW-Authenticate           407      o

                Figure 1: Table 1: Summary of Header Fields


6.  INFO Header Fields

6.1.  General

   This table expands on tables 2 and 3 in [RFC3261].

Header field where   ACK BYE CAN INV OPT REG PRA INF MSG UPD SUB NOT RFR
------------------------------------------------------------------------
Info-Package   R      -   -   -   -   -   -   -   m*  -   -   -   -   -
Recv-Info      R      o   -   -   o   o   o   o   -   -   o   -   -   -
Recv-Info      2xx    o   -   -   o   o   -   o   -   -   o   -   -   -
Recv-Info      1xx    o   -   -   o   o   -   o   -   -   o   -   -   -
Recv-Info      r      o   -   -   -   o   -   o   -   -   o   -   -   -

   * The Info-Package header field is MANDATORY for INFO requests
   associated with Info Packages.  The Info-Package header field is not
   applicable for legacy usage INFO requests [RFC2976].

                    Table 2: INFO-related Header Fields

6.2.  Info-Package header field

   This document adds Info-Package to the definition of the element
   "message-header" in the SIP message grammar [RFC3261].  Section 4
   describes the Info-Package header field usage.

   For the purposes of matching Info Package types indicated in Recv-
   Info with those in the Info-Package header field value, one compares
   the Info-package-name portion of the Info-package-type portion of the
   Info-Package header field octet-by-octet with that of the Recv-Info



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   header field value.  That is, the Info Package name is case
   sensitive.  Info-package-param is not part of the comparison-checking
   algorithm.

   This document does not define values for Info-Package types.
   Individual Info Package specifications define these values.  Such
   specifications MUST register the values with IANA.  These values are
   Specification Required [RFC5226].

6.3.  Recv-Info header field

   This document adds Recv-Info to the definition of the element
   "message-header" in the SIP message grammar [RFC3261].  Section 3
   describes the Recv-Info header field usage.


7.  Info Package Considerations

7.1.  General

   This section covers considerations to take into account when deciding
   whether the usage of an Info Package is appropriate for transporting
   of application information for a specific use-case.

7.2.  Appropriateness of Info Package Usage

   When designing an Info Package, for application level information
   exchange, it is important to consider: is signaling, using INFO
   requests, within a SIP dialog, an appropriate mechanism for the use-
   case?  Is it because it is the most reasonable and appropriate
   choice, or merely because "it's easy"?  Choosing an inappropriate
   mechanism for a specific use-case can cause negative effects in SIP
   networks where the mechanism is used.

7.3.  Dialog Fate Sharing

   As described in [RFC5057], an INFO request is always part of an
   INVITE dialog usage.

   One needs to consider the fate of the dialog usage of an INFO request
   is rejected.  In some cases it may be acceptable that the whole
   dialog usage is terminated, while in other cases is is desirable to
   maintain the dialog usage.

7.4.  INFO Request Rate and Volume

   There is no default throttling mechanism for INFO requests.  Apart
   from the SIP session establishment, the number of SIP messages



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   exchanged during the lifetime a normal SIP session is rather small.

   Some applications, like sending of DTMF tones, can generate a burst
   of up to 20 messages per second.  Other applications, like constant
   GPS location updates, could generate a high rate of INFO requests
   during the lifetime of the invite dialog usage.

   Furthermore, SIP messages tend to be relatively small, on the order
   of 500 Bytes to 32K Bytes.  SIP is a poor mechanism for direct
   exchange of bulk data beyond these limits, especially if the headers
   plus body exceed the UDP MTU [RFC0768].  Appropriate mechanisms for
   such traffic include HTTP [RFC2616], MSRP [RFC4975], or other user
   plane data transport mechanisms.

7.5.  Alternative Mechanisms

7.5.1.  Alternative SIP signaling plane mechanisms

7.5.1.1.  General

   This subsection describes some alternative mechanisms for
   transporting application information on the SIP signaling plane,
   using SIP messages.

7.5.1.2.  SUBSCRIBE/NOTIFY

   An alternative for application level interaction is to use
   subscription-based events [RFC3265], which uses the SIP SUBSCRIBE and
   NOTIFY methods.  Using that mechanism, a user agent requests state
   information, such as key pad presses from a device to an application
   server or key map images from an application server to a device.

   Event Packages [RFC3265] perform the role of disambiguating the
   context of a message for subscription-based events.  The Info Package
   mechanism provides similar functionality for application information
   exchange using invite dialog usages [RFC5057].

   While an INFO request is always part of, and shares the fate of, an
   existing invite dialog usage, a SUBSCRIBE request creates a new
   session and a subscription dialog usage [RFC5057] which is separate,
   and does not share the fate any other sessions.

   The subscription-based mechanism can be used by SIP entities to
   receive state information about SIP dialogs and sessions, without
   requiring the entities to be part of the route set of those dialogs
   and sessions.

   As SUBSCRIBE/NOTIFY messages traverse through stateful SIP proxies



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   and B2BUAs, the resource impact caused by the subscription sessions
   needs to be considered.  The number of subscription sessions per user
   also needs to be considered.

   As for any other SIP signaling plane based mechanism for transporting
   application information, the SUBSCRIBE/NOTIFY messages can put a
   significant burden on intermediate SIP entities which are part of the
   dialog route set, but do not have any interest in the application
   information transported between the end users.

7.5.1.3.  MESSAGE

   The MESSAGE method [RFC3428] defines one-time instant message
   exchange, typically for sending MIME contents for rendering to the
   ser.

7.5.2.  Media Plane Mechanisms

7.5.2.1.  General

   In SIP, media plane channels associated with SIP dialogs are
   established using SIP signaling, but the data exchanged on the media
   plane channel does not traverse SIP signaling intermediates, so if
   there will be a lot of information exchanged, and there is no need
   for the SIP signaling intermediates routing to examine the
   information, it is recommended to use a media plane mechanism, rather
   than a SIP signaling based.

   A low latency requirement for the exchange of information is one
   strong indicator for using a media channel.  Exchanging information
   through the SIP routing network can introduce hundreds of
   milliseconds of latency.

7.5.2.2.  MRCPv2

   One mechanism for media plane exchange of application data is MRCPv2
   [I-D.ietf-speechsc-mrcpv2], where a media plane connection-oriented
   channel, such as a TCP [RFC0793] or SCTP [RFC4960] stream is
   established.

7.5.2.3.  MRSP

   MSRP [RFC4975] defines session-based instant messaging as well as
   bulk file transfer and other such large-volume uses.







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7.5.3.  Non-SIP related mechanisms

   Another alternative is to use a totally externally signaled channel,
   such as HTTP [RFC2616].  In this model, the user agent knows about a
   rendezvous point to direct HTTP requests to for the transfer of
   information.  Examples include encoding of a prompt to retrieve in
   the SIP Request URI in [RFC4240] or the encoding of a SUBMIT target
   in a VoiceXML [W3C.REC-voicexml21-20070619] script.


8.  Syntax

8.1.  General

   This Section describes the syntax extensions required for the INFO
   method.  The previous sections describe the semantics.  Note the
   formal syntax definitions described in this document use the ABNF
   format used in [RFC3261] and contain references to elements defined
   therein.

8.2.  ABNF

   INFOm               = %x49.4E.46.4F ; INFO in caps
   extension-method    = INFOm / token

   Info-Package        =  "Info-Package" HCOLON Info-package-type
   Recv-Info           =  "Recv-Info" HCOLON Info-package-list
   Info-package-list   =  "nil"
                       / Info-package-type *( COMMA Info-package-type )
   Info-package-type   =  Info-package-name *( ";" Info-package-param)
   Info-package-name   =  token
   Info-package-param  =  generic-param

   NOTE on the Recv-Info production: if the header field value is "nil",
   the header field MUST NOT contain any other Info Packages, and the
   SIP message MUST NOT contain more than one Recv-Info header field.


9.  Legacy INFO Usage

9.1.  General

   A number of applications, standardized and proprietary, make use of
   the INFO method as it was previously defined in [RFC2976], referred
   to as "legacy INFO usage".

   For backward compatibility purpose, this document does not deprecate
   such usages, and does not mandate users to define Info Packages for



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   such usages.  However, any new usage of INFO SHALL use the Info
   Package mechanism defined in this specification.

9.2.  Problems

   While legacy INFO usage has been widely adopted for specific
   application use cases, [RFC2976] did not define a mechanism for SIP
   UAs to indicate for which types of applications and contexts they
   support the INFO method.  In addition, [RFC2976] did not provide a
   mechanism to explicitly indicate the type of application and context
   for which a specific INFO message is associated.

   Example: If the Content-Type is "image/jpeg", the MIME-attached
   content is a JPEG image.  Still, there are many useful ways a UA can
   render an image.  The image could be a caller-id picture, a contact
   icon, a photo for sharing, and so on.  The sender does not know which
   image to send to the receiver if the receiver supports an image
   content type.  Likewise, the receiver does not know the context of an
   image the client is sending if the receiver supports receiving more
   than one image content type.

   Since legacy INFO usages do not have associated Info Packages, it is
   not possible to use the Recv-Info and Info-Package header fields with
   legacy INFO usages.  That is, a UA cannot use the Recv-Info header
   field to indicate for which legacy INFO usages it is willing to
   receive INFO requests, and a UA cannot use the Info-Package header
   field to indicate for which legacy INFO usage an INFO request is
   associated with.

   Due to the problems described above, legacy INFO usages often require
   static configuration about for what type of applications and contexts
   UAs support the INFO method, and the way they handle application
   information transported in INFO messages.  That has caused
   interoperability problems in the industry.  Therefore, a need for a
   well defined and documented description of what the information sent
   in the INFO is used for has been identified.  This situation is
   analogous to the context issue in Internet Mail [RFC3458].

9.3.  Co-existence with Info Package based INFO usage

   As described in Section 4, an INFO request associated with an Info
   Package always contains an Info-Package header field.  A legacy INFO
   request MUST NOT contain an Info-Package header field.

   UAs are allowed to enable both legacy INFO usages and Info Package
   usages as part of the same invite dialog usage.

   See Appendix A for examples of existing legacy INFO usages.



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10.  Info Package Requirements

10.1.  General

   This Section provides guidance on how to define an Info Package, and
   what information needs to be provided.

   If an Info Package extends or modifies the behavior described in this
   document, it MUST be described in the definition for that Info
   Package.  Info Package definitions should not repeat procedures
   defined in this specification, unless needed for clarification or
   emphasis purpose.

   Info Packages MUST NOT weaken any behavior designated with "SHOULD"
   or "MUST" in this specification.  However, Info Packages MAY
   strengthen "SHOULD", "MAY", or "RECOMMENDED" requirements to "MUST"
   strength if applications associated with the Info Package requires
   it.

   Info Package definitions SHALL address the issues defined in the
   following subsections, or document why an issue is not applicable for
   the specific Info Package.

10.2.  Applicability

   The Info Package specification MUST describe why the Info Package
   mechanism, rather than some other mechanism, has been chosen for the
   specific use-case to transfer application information between SIP
   endpoints.  Common reasons can be a requirement for SIP Proxies or
   back-to-back User Agents (B2BUAs) to see the transported application
   information (which would not be the case if the information was
   transported on a media path), or that it is not seen feasible to
   establish separate dialogs (subscription) in order to transport the
   information.

   Annex A provides more information, and describes alternative
   mechanisms which one should consider for solving a specific use-case.

10.3.  Info Package Name

   The Info Package specification MUST define a for Info Package name
   (e.g.  "Info Package for X").

   The specification MUST also define the header field value (e.g.
   "infoX") to be used to indicate support of this package in the Recv-
   Info and Info-Package header fields.  The header field value MUST
   conform to the ABNF defined in Section 8.2.




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   The specification MUST also include the information that appears in
   the IANA registration of the token.  For information on registering
   such types, see Section 9.

10.4.  Info Package Parameters

   The Info Package specification MAY define Info Package parameters
   which can be used in the Recv-Info or Info-Package header fields,
   together with the header field value representing the Info Package.

   The specification MUST describe the syntax and semantics of the
   parameters.  It MUST be specified whether a specific parameter is
   only applicable to the Recv-Info header, the Info-Package header, or
   both.

   Note that Info Package parameters are only applicable for the Info
   Package(s) for which they have been explicitly defined.  They MUST
   NOT be used for other Info Packages.

   NOTE: Info Package parameters defined for specific Info Packages may
   share the name with parameters defined for other Info Packages, but
   the parameter semantics are specific to the Info Package for which
   they are defined.

10.5.  SIP Option Tags

   The Info Package specification MAY define SIP option tags, which can
   be used as described in [RFC3261].

   SIP option tags MUST conform to the SIP Change Process
   [I-D.peterson-rai-rfc3427bis].

10.6.  INFO Message Bodies

   The Info Package specification MUST define what type of message body
   parts are associated with the Info Package, and MUST refer to
   specifications where the syntax, semantics and MIME type of the
   message body parts are described.

   If multiple body parts are used with an Info Package, the Info
   Package specification MUST define whether there are special rules on
   how the body parts are to be inserted in multipart body parts, and
   what types of multipart to use.

10.7.  Info Package Usage Restrictions

   The Info Package specification MUST define whether a UA is allowed to
   send overlapping (outstanding) INFO requests associated with the Info



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   Package, or whether the UA has to wait for the response for a
   previous INFO request associated with the same Info Package.

   The specification MUST define whether there are SIP level
   restrictions in the usage of the Info Package.  For example, an Info
   Package may require support of other SIP extensions (e.g. reliable
   provisional responses).

   The specification MUST define whether there are restrictions on
   indicating support of, or using, the Info Package together with other
   Info Packages.

   As the SIP stack may not be aware of Info Package specific
   restrictions, it cannot be assumed that overlapping requests would be
   rejected.  As defined in Section 4.4, in most cases a 200 OK response
   will be sent for the INFO request.  The application logic associated
   with the Info Package needs to handle situations which can occur due
   to overlapping requests.

10.8.  Rate of INFO Requests

   The Info Package specification MUST specify a maximum rate at which
   INFO requests associated with the specific Info Package can be
   generated by a UA in a dialog.

   The specification MAY define Info Package parameters to be used for
   indicating or negotiating the INFO request rate.  Alternatively the
   rate information can be included in the application information
   associated with the Info Package.

10.9.  IANA Registrations

   The Info Package specification MUST contain an IANA Considerations
   section that includes definitions for the Info Package Name and, if
   needed, supported MIME types.

10.10.  Info Package Security Considerations

   If the application information associated with the Info Package
   requires certain level of security, the Info Package specification
   MUST describe the mechanisms to be used in order to provide the
   required security.

   Otherwise, even if no additional security than what is provided for
   the underlying SIP protocol is needed, this fact SHALL be stated in
   the Info Package specification.

   NOTE: In some cases, it may not be sufficient to mandate TLS in order



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   to secure the Info Package payload, since intermediaries will have
   access to the payload, and beyond the first hop, there is no way to
   assure subsequent hops will not forwards the payload in clear text.
   The best way to ensure secure transport at the application level is
   to have the security at the application level.  One way of achieving
   this is to use end-to-end security techniques such as S/MIME
   [RFC3851].

10.11.  Application Procedures

   The Info Package specification SHOULD contain a description of the
   application procedures associated with the Info Package, or
   alternatively refer to application procedures defined elsewhere.

10.12.  Examples

   It is recommended that Info Package specifications include
   demonstrative message flow diagrams, paired with complete messages
   and message descriptions.

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


11.  IANA Considerations

11.1.  Update to Registration of SIP INFO Method

   Please update the existing registration in the SIP Methods and
   Response Codes registry under the SIP Parameters registry that
   states:

   Method:      INFO
   Reference:   [RFC2976]

   to:

   Method:      INFO
   Reference:   [RFCXXXX]

11.2.  Registration of the Info-Package Header Field

   Please add the following new SIP header field in the Header Fields
   subregistry under the SIP Parameters registry.







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   Header Name:   Info-Package
   Compact Form:  (none)
   Reference:     [RFCXXXX]

11.3.  Registration of the Recv-Info Header Field

   Please add the following new SIP header field in the Header Fields
   subregistry under the SIP Parameters registry.

   Header Name:   Recv-Info
   Compact Form:  (none)
   Reference:     [RFCXXXX]

11.4.  Creation of the Info Packages Registry

   Please create a subregistry in the SIP Parameters registry for Info
   Packages.  This subregistry has a modified First Come First Served
   [RFC5226] policy.

   The following data elements populate the Info Package Registry.
   o  Info Package Name: The Info Package Name is a case-sensitive
      token.  In addition, IANA shall not register multiple Info Package
      names that have identical case-insensitive values.
   o  Info Package Parameters: The Info Package Parameters are case-
      sensitive tokens.  Info Package Parameters are only applicable to
      the Info Package for which they are defined, so the same Info
      Package Parameter Names may exist for different Info Packages.
   o  Info Package Payload MIME Types: A list of zero or more registered
      MIME types from the MIME Type Registry.
   o  Standards Status: Values are "Standards Track" or empty.  See
      below for a discussion and rules on this field.
   o  Reference: If there is a published specification describing the
      Info Package, place a reference to that specification in this
      column.  See below for a discussion on this field.

   If there is a published specification, the registration must include
   a reference to such specification.  The Standards Status field is an
   indicator of the level of community review for the Info Package
   specification.  If the specification meets the requirements for
   Specification Required [RFC5226], the value for the Standards Status
   field is "Standards Track".  Otherwise, the field is empty.

   This document uses the Info Package Name "nil" to represent "no Info
   Package present" and as such, IANA shall not honor a request to
   register the "nil" Info Package.

   The initial population of this table shall be:




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   Name         MIME Type                Standards Status      Reference
   nil                                    Standards Track      [RFCXXXX]

11.5.  Registration of the Info-Package Content-Disposition

   Please add the following new header field value to the Content-
   Disposition registry.
Name: info-package
Description: the body contains information associated with an Info Package
Reference: RFCXXXX

11.6.  SIP Response Code 469 Registration

   Please register the following new response code in the Session
   Initiation Protocol Parameters - Response Codes registry.
   Response Code: 469
   Default Reason Phrase: Bad INFO Package
   Reference: RFCXXXX


12.  Examples

12.1.  Indication of which Info Packages UAs are willing to receive INFO
       requests within an invite dialog usage

   The UAC sends an INVITE request, where the UAC indicates that it is
   willing to receive Info Packages P and R.

   INVITE sip:bob@example.com SIP/2.0
   Via: SIP/2.0/TCP pc33.example.com;branch=z9hG4bK776
   Max-Forwards: 70
   To: Bob <sip:bob@example.com>
   From: Alice <sip:alice@example.com>;tag=1928301774
   Call-ID: a84b4c76e66710@pc33.example.com
   CSeq: 314159 INVITE
   Recv-Info: P, R
   Contact: <sip:alice@pc33.example.com>
   Content-Type: application/sdp
   Content-Length: ...

   ...

   The UAS sends a 200 OK response back to the UAC, where the UAS
   indicates that it is willing to receive Info Packages R and T.







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  SIP/2.0 200 OK
  Via: SIP/2.0/TCP pc33.example.com;branch=z9hG4bK776;received=192.0.2.1
  To: Bob <sip:bob@example.com>;tag=a6c85cf
  From: Alice <sip:alice@example.com>;tag=1928301774
  Call-ID: a84b4c76e66710@pc33.example.com
  CSeq: 314159 INVITE
  Contact: <sip:alice@pc33.example.com>
  Recv-Info: R, T
  Content-Type: application/sdp
  Content-Length: ...

  ...

   The UAC sends ACK.

   ACK sip:ngw1@a.example.com SIP/2.0
   Via: SIP/2.0/TCP pc33.example.com;branch=z9hG4bK754
   Max-Forwards: 70
   To: Bob <sip:bob@example.com>;tag=a6c85cf
   From: Alice <sip:alice@example.com>;tag=1928301774
   Call-ID: a84b4c76e66710@pc33.example.com
   CSeq: 314159 ACK
   Content-Length: 0

12.2.  INFO request with information associated with a simple Info
       Package

   Here Alice sends Bob a simple Info Package payload.

   INFO sip:alice@192.0.2.1 SIP/2.0
   Via: SIP/2.0/UDP 192.0.2.2:5060;branch=z9hG4bKnabcdef
   To: Alice <sip:alice@example.net>;tag=1234567
   From: Bob <sip:bob@example.com>;tag=abcdefg
   Call-Id: 123456mcmxcix
   CSeq: 2 INFO
   Info-Package: foo
   Content-type: application/foo
   Content-Disposition: Info-Package
   Content-length: 24

   I am a foo message type


12.3.  Multipart INFO Example

   Other SIP extensions can sometimes add payload body parts into an
   INFO request, independent of the Info Package.  In this case, the
   Info Package payload gets put into a Multipart MIME body, with a



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   Content-Disposition header field that indicates which body part is
   associated with the Info Package.

   INFO sip:alice@192.0.2.1 SIP/2.0
   Via: SIP/2.0/UDP 192.0.2.2:5060;branch=z9hG4bKnabcdef
   To: Alice <sip:alice@example.net>;tag=1234567
   From: Bob <sip:bob@example.com>;tag=abcdefg
   Call-Id: 123456mcmxcix
   CSeq: 7 INFO
   Info-Package: foo
   mumble-extension: <cid:abcd9999qq>
   Content-Type: multipart/mixed;boundary="theboundary"
   Content-Length: ...

   --theboundary
   Content-Type: application/mumble
   Content-Id: abcd9999qq
   ...

   <mumble stuff>

   --theboundary
   Content-Type: application/foo
   Content-Disposition: Info-Package
   Content-length: 24

   I am a foo message type
   --theboundary--


13.  Security Considerations

   By eliminating multiple usages of INFO messages without adequate
   community review and by eliminating the possibility for rogue SIP UAs
   from confusing another UA by purposely sending unrelated INFO
   requests, we expect this document's clarification of the use of INFO
   to improve the security of the Internet.  Whilst rogue UAs can still
   send unrelated INFO requests, this mechanism provides mechanisms for
   which the UAS and other security devices can filter for approved Info
   Packages.

   If the content of the Info Package payload is private, UAs will need
   to use end-to-end encryption, such as S/MIME, to prevent access to
   the content.  This is particularly important as transport of INFO is
   likely not to be end-to-end, but through SIP proxies and back-to-back
   user agents (B2BUA's), which the user may not trust.

   The INFO request transports application level information.  One



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   implication of this is INFO messages may require a higher level of
   protection than the underlying SIP dialog signaling.  In particular,
   if one does not protect the SIP signaling from eavesdropping or
   authentication and repudiation attacks, for example by using TLS
   transport, then the INFO request and its contents will be vulnerable,
   as well.  Even with SIP/TLS, any SIP hop along the path from UAC to
   UAS can view, modify, or intercept INFO requests, as they can with
   any SIP request.  This means some applications may require end-to-end
   encryption of the INFO payload, beyond, for example, hop-by-hop
   protection of the SIP signaling itself.  Since the application
   dictates the level of security required, individual Info Packages
   have to enumerate these requirements.  In any event, the Info Package
   mechanism described by this document provides the tools for such
   secure, end-to-end transport of application data.

   One interesting property of Info Package use is one can reuse the
   same digest-challenge mechanism used for INVITE based authentication
   for the INFO request.  For example, one could use a quality-of-
   protection (qop) value of authentication with integrity (auth-int),
   to challenge the request and its body, and prevent intermediate
   devices from modifying the body.  However this assumes the device
   which knows the credentials in order to perform the INVITE challenge
   is still in the path for the INFO, or that the far-end UAS knows such
   credentials.


14.  References

14.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [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.

   [RFC5621]  Camarillo, G., "Message Body Handling in the Session
              Initiation Protocol (SIP)", RFC 5621, September 2009.







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14.2.  Informative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, September 1981.

   [RFC2976]  Donovan, S., "The SIP INFO Method", RFC 2976,
              October 2000.

   [RFC4497]  Elwell, J., Derks, F., Mourot, P., and O. Rousseau,
              "Interworking between the Session Initiation Protocol
              (SIP) and QSIG", BCP 117, RFC 4497, May 2006.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              RFC 4949, August 2007.

   [RFC3080]  Rose, M., "The Blocks Extensible Exchange Protocol Core",
              RFC 3080, March 2001.

   [RFC3851]  Ramsdell, B., "Secure/Multipurpose Internet Mail
              Extensions (S/MIME) Version 3.1 Message Specification",
              RFC 3851, July 2004.

   [RFC3725]  Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
              Camarillo, "Best Current Practices for Third Party Call
              Control (3pcc) in the Session Initiation Protocol (SIP)",
              BCP 85, RFC 3725, April 2004.

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

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

   [RFC3372]  Vemuri, A. and J. Peterson, "Session Initiation Protocol
              for Telephones (SIP-T): Context and Architectures",
              BCP 63, RFC 3372, September 2002.

   [RFC3265]  Roach, A., "Session Initiation Protocol (SIP)-Specific
              Event Notification", RFC 3265, June 2002.



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   [RFC3458]  Burger, E., Candell, E., Eliot, C., and G. Klyne, "Message
              Context for Internet Mail", RFC 3458, January 2003.

   [RFC3428]  Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C.,
              and D. Gurle, "Session Initiation Protocol (SIP) Extension
              for Instant Messaging", RFC 3428, December 2002.

   [RFC4028]  Donovan, S. and J. Rosenberg, "Session Timers in the
              Session Initiation Protocol (SIP)", RFC 4028, April 2005.

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              September 2005.

   [RFC4240]  Burger, E., Van Dyke, J., and A. Spitzer, "Basic Network
              Media Services with SIP", RFC 4240, December 2005.

   [RFC4730]  Burger, E. and M. Dolly, "A Session Initiation Protocol
              (SIP) Event Package for Key Press Stimulus (KPML)",
              RFC 4730, November 2006.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [RFC4975]  Campbell, B., Mahy, R., and C. Jennings, "The Message
              Session Relay Protocol (MSRP)", RFC 4975, September 2007.

   [RFC5022]  Van Dyke, J., Burger, E., and A. Spitzer, "Media Server
              Control Markup Language (MSCML) and Protocol", RFC 5022,
              September 2007.

   [RFC5057]  Sparks, R., "Multiple Dialog Usages in the Session
              Initiation Protocol", RFC 5057, November 2007.

   [RFC5168]  Levin, O., Even, R., and P. Hagendorf, "XML Schema for
              Media Control", RFC 5168, March 2008.

   [I-D.peterson-rai-rfc3427bis]
              Peterson, J., Jennings, C., and R. Sparks, "Change Process
              for the Session Initiation Protocol (SIP)",
              draft-peterson-rai-rfc3427bis-03 (work in progress),
              September 2009.

   [W3C.REC-voicexml21-20070619]
              McGlashan, S., Lee, A., Carter, J., Porter, B., Auburn,
              R., Oshry, M., Rehor, K., Bodell, M., Burke, D., Baggia,
              P., Candell, E., and D. Burnett, "Voice Extensible Markup
              Language (VoiceXML) 2.1", World Wide Web Consortium



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              Recommendation REC-voicexml21-20070619, June 2007,
              <http://www.w3.org/TR/2007/REC-voicexml21-20070619>.

   [I-D.ietf-speechsc-mrcpv2]
              Shanmugham, S. and D. Burnett, "Media Resource Control
              Protocol Version 2 (MRCPv2)",
              draft-ietf-speechsc-mrcpv2-20 (work in progress),
              August 2009.

   [I-D.saleem-msml]
              Saleem, A. and G. Sharratt, "Media Server Markup Language
              (MSML)", draft-saleem-msml-09 (work in progress),
              July 2009.

   [Ecma-355]
              "Standard ECMA-355 Corporate Telecommunication Networks -
              Tunnelling of QSIG over SIP", ECMA http://
              www.ecma-international.org/publications/standards/
              Ecma-355.htm, June 2008.


Appendix A.  Legacy INFO Usages

A.1.  General

   This section provides examples of existing legacy INFO usages.  This
   section is not meant to be a comprehensive catalog of legacy INFO
   usages, but it should give the reader a flavor for current legacy
   INFO usages.

A.2.  ISUP

   [RFC3372] specifies the encapsulation of ISUP in SIP message bodies.
   ITU-T and 3GPP have specified similar procedures.

A.3.  QSIG

   [Ecma-355] specifies the encapsulation of QSIG in SIP message bodies.

A.4.  MSCML

   [RFC5022] specifies how INFO is used as a transport mechanism by the
   MSCML protocol.  MSCML uses an option-tag in the Require header field
   to ensure that the receiver understands the INFO content.







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A.5.  MSML

   [I-D.saleem-msml] specifies how INFO us used as a transport mechanism
   by the MSML protocol.

A.6.  Video Fast Update

   Companies have been using INFO messages in order to request fast
   video update.  Currently a standardized mechanism, based on RTCP, has
   been specified in [RFC5168]


Appendix B.  Acknowledgements

   The work on this document was influenced by the "INFO Considered
   Harmful" draft (26 December 2002) written by Jonathan Rosenberg, and
   by the "Packaging and Negotiation of INFO Methods for the Session
   Initiation Protocol" draft (15 January 2003) written by Dean Willis.

   The following individuals have been involved in the work, and have
   provided input and feedback on this document:
      Adam Roach, Anders Kristensen, Andrew Allen, Arun Arunachalam, Ben
      Campbell, Bob Penfield, Bram Verburg, Brian Stucker, Chris
      Boulton, Christian Stredicke, Cullen Jennings, Dale Worley, Dean
      Willis, Eric Rescorla, Frank Miller, Gonzalo Camarillo, Gordon
      Beith, Henry Sinnreich, Inaki Baz Castillo, James Jackson, James
      Rafferty, Jeroen van Bemmel, Joel Halpern, John Elwell, Johnathan
      Rosenberg, Juha Heinanen, Gordon Beith, Keith Drage, Kevin Attard
      Compagno, Manpreet Singh, Martin Dolly, Mary Barnes, Michael
      Procter, Paul Kyzivat, Peili Xu, Peter Blatherwick, Raj Jain,
      Rayees Khan, Robert Sparks, Roland Jesske, Roni Evan Salvatore
      Loreto, Sam Ganesan, Sanjay Sinha, Spencer Dawkins, Steve
      Langstaff, Sumit Garg and Xavier Marjoum.

   John Elwell and Francois Audet helped with QSIG references.  In
   addition, Francois Audet provided text for the revised abstract.
   Keith Drage provided comments and helped immensely with Figure 1.

   John Elwell and Robert Sparks provided valuable feedback during the
   WGLC process, in order to prepare this document for publication.


Appendix C.  Change Log

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

   Changes from draft-ietf-sipcore-info-events-01




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   o  Further changes based on WGLC comments
   o  Appending A moved into the main part of the document
   o  Section name changed from "Modifications to SIP Change Process" to
      "Security Considerations"
   o  "Syntax" section moved further up in the document
   o  Clarification on usage of Info Package related message body parts,
      and the usage of the Content-Disposition header field with those
      body parts
   o  Removed REFER and NOTIFY from the INFO Headers table
   o  Clarified usage of the Recv-Info header field in the REGISTER and
      OPTIONS requests
   o  Major re-write of the Introduction section
   o  Text about legacy INFO and subscription-based events moved from
      the Introduction to the main part of the document
   o  Wording about receiving Info-Packages has been replaced with
      wording about receiving INFO requests for Info-Packages
   o  The text about the usage of message body, and body parts,
      associated with Info Packages, has been clarified

   Changes from draft-ietf-sip-info-events-04
   o  Major re-write of the document, due to problems to implement WGLC
      comments into the existing text structure
   o  Wording allignment
   o  Clarification or roles

   Changes from draft-ietf-sip-info-events-03
   o  Clarified Abstract language
   o  All SIP dialogs are now refered to as sessions
   o  Clarified the image example in the Introduction
   o  Clarified the relationship (none) between SIP Event Packages and
      SIP Info Packages
   o  Really, really clarified the protocol is NOT a negotiation but an
      advertisement
   o  Split Section 3 into UAS and UAC behavior
   o  Moved the example in section 3 into its own sub-section, and used
      full SIP header fields
   o  Clarified forking behavior
   o  Clarified language around when to send a body
   o  Added 469 error response, instead of reusing 489
   o  Clarified overlapping INFO method handling
   o  Fixed table 1 to follow 3261, not 2543
   o  Added REFER to the INFO Headers table
   o  replaced token-nodot with token for Info-Package header field
      values
   o  Clarified end-to-end security considerations
   o  Info Package parameters are semi-colon delimited, not dot
      delimited




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   Changes from -02
   o  Applicability statement explicitly says we're backwards compatible
   o  Explicitly state we work like UPDATE (both early and confirmed
      dialogs)
   o  Agreed text for IANA Considerations package registry

   Changes from -01
   o  One and only one Info Package per INFO
   o  Removed Send-Info header field, greatly simplifying negotiation
   o  Multiple body part identification through Content-Disposition:
      Info-Package
   o  Note that forking INVITEs may result in multiple INFOs coming back
      to INVITE originator
   o  Describe how a UAS can enforce strict adherence to this document
   o  Remove CANCEL INFO faux pas
   o  Better explained overlapping INFO issues and resolutions
   o  Token names are now really case sensitive
   o  Moved Info Package Considerations to an Appendix
   o  Introduced stronger, yet more open, IANA registration process
   o  Took a few more paragraphs from INFO Litmus to cover all bases.
   o  Added RFC 5168 to legacy usages

   Changes from -00
   o  Corrected ABNF.
   o  Enabled sending of legacy INFO messages.  Receiving legacy INFO
      messages was already here.
   o  Negotiation is not Offer/Answer, it is Offer/Offer.
   o  Created the explicit "nil" Info Package to indicate no info
      package.
   o  Fixed CANCEL impacting future transactions.
   o  Added Registrar behavior.
   o  Added OPTIONS processing.
   o  Clarified overlapping INFO method processing.
   o  Described multiple INFO bodies in a single INFO method.
   o  Took out Info-Package as a header field for responses to the INFO
      method.
   o  Expanded on risks of using INFO and filled-in more on the
      alternatives
   o  Moved definitions of INFO into the body of the text and cleaned up
      IANA Considerations section
   o  Added legacy usages descriptions










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Authors' Addresses

   Eric W. Burger
   NeuStar, Inc.
   46000 Center Oak Plaza
   Sterling, VA  20166-6579
   USA

   Email: eburger@standardstrack.com
   URI:   http://www.standardstrack.com


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

   Phone:
   Fax:
   Email: hkaplan@acmepacket.com
   URI:


   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas,   02420
   Finland

   Phone:
   Fax:
   Email: christer.holmberg@ericsson.com
   URI:

















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