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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: June 5, 2010                                        C. Holmberg
                                                                Ericsson
                                                        December 2, 2009


  Session Initiation Protocol (SIP) INFO Method and Package Framework
                   draft-ietf-sipcore-info-events-03

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].

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at



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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on June 5, 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
   (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 BSD License.

































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Applicability  . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  The INFO Method  . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.   General . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.   INFO Request  . . . . . . . . . . . . . . . . . . . . . .  6
       3.2.1.  INFO Request Sender  . . . . . . . . . . . . . . . . .  6
       3.2.2.  INFO Request Receiver  . . . . . . . . . . . . . . . .  7
     3.3.   INFO Message Body . . . . . . . . . . . . . . . . . . . .  8
       3.3.1.  INFO Request Message Body  . . . . . . . . . . . . . .  8
       3.3.2.  INFO Response Message Body . . . . . . . . . . . . . .  8
     3.4.   Order of Delivery . . . . . . . . . . . . . . . . . . . .  8
   4.  Info Packages  . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.   General . . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.2.   User Agent Behavior . . . . . . . . . . . . . . . . . . .  9
       4.2.1.  General  . . . . . . . . . . . . . . . . . . . . . . .  9
       4.2.2.  UA Procedures  . . . . . . . . . . . . . . . . . . . .  9
       4.2.3.  Recv-Info header field rules . . . . . . . . . . . . . 11
       4.2.4.  Info Package fallback rules  . . . . . . . . . . . . . 11
     4.3.   REGISTER Processing . . . . . . . . . . . . . . . . . . . 12
     4.4.   OPTIONS Processing  . . . . . . . . . . . . . . . . . . . 12
   5.  Formal INFO Method Definition  . . . . . . . . . . . . . . . . 12
     5.1.   INFO Method . . . . . . . . . . . . . . . . . . . . . . . 12
   6.  INFO Header Fields . . . . . . . . . . . . . . . . . . . . . . 14
     6.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 14
     6.2.   Info-Package header field . . . . . . . . . . . . . . . . 14
     6.3.   Recv-Info header field  . . . . . . . . . . . . . . . . . 15
   7.  Info Package Considerations  . . . . . . . . . . . . . . . . . 15
     7.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.2.   Appropriateness of Info Package Usage . . . . . . . . . . 15
     7.3.   INFO Request Rate and Volume  . . . . . . . . . . . . . . 15
     7.4.   Alternative Mechanisms  . . . . . . . . . . . . . . . . . 16
       7.4.1.  Alternative SIP signaling plane mechanisms . . . . . . 16
       7.4.2.  Media Plane Mechanisms . . . . . . . . . . . . . . . . 17
       7.4.3.  Non-SIP related mechanisms . . . . . . . . . . . . . . 17
   8.  Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 18
     8.2.   ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . . 18
   9.  Legacy INFO Usage  . . . . . . . . . . . . . . . . . . . . . . 18
     9.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 18
     9.2.   Problems  . . . . . . . . . . . . . . . . . . . . . . . . 18
     9.3.   Co-existence with Info Package based INFO usage . . . . . 19
   10. Info Package Requirements  . . . . . . . . . . . . . . . . . . 19
     10.1.  General . . . . . . . . . . . . . . . . . . . . . . . . . 19
     10.2.  Overal Description  . . . . . . . . . . . . . . . . . . . 20
     10.3.  Applicability . . . . . . . . . . . . . . . . . . . . . . 20
     10.4.  Info Package Name . . . . . . . . . . . . . . . . . . . . 20



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     10.5.  Info Package Parameters . . . . . . . . . . . . . . . . . 21
     10.6.  SIP Option Tags . . . . . . . . . . . . . . . . . . . . . 21
     10.7.  INFO Message Body Parts . . . . . . . . . . . . . . . . . 21
     10.8.  Info Package Usage Restrictions . . . . . . . . . . . . . 22
     10.9.  Rate of INFO Requests . . . . . . . . . . . . . . . . . . 22
     10.10. Info Package Security Considerations  . . . . . . . . . . 22
     10.11. Implementation Details  . . . . . . . . . . . . . . . . . 23
     10.12. Examples  . . . . . . . . . . . . . . . . . . . . . . . . 23
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
     11.1.  Update to Registration of SIP INFO Method . . . . . . . . 23
     11.2.  Registration of the Info-Package Header Field . . . . . . 24
     11.3.  Registration of the Recv-Info Header Field  . . . . . . . 24
     11.4.  Creation of the Info Packages Registry  . . . . . . . . . 24
     11.5.  Registration of the Info-Package Content-Disposition  . . 25
     11.6.  SIP Response Code 469 Registration  . . . . . . . . . . . 25
   12. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     12.1.  Indication for which Info Packages UAs are willing to
            receive INFO requests . . . . . . . . . . . . . . . . . . 25
       12.1.1. Initial INVITE request . . . . . . . . . . . . . . . . 25
       12.1.2. Target refresh . . . . . . . . . . . . . . . . . . . . 26
     12.2.  INFO request associated with Info Package . . . . . . . . 27
       12.2.1. Single payload . . . . . . . . . . . . . . . . . . . . 27
       12.2.2. Multipart INFO . . . . . . . . . . . . . . . . . . . . 27
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 30
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
     14.1.  Normative References  . . . . . . . . . . . . . . . . . . 31
     14.2.  Informative References  . . . . . . . . . . . . . . . . . 31
   Appendix A.  Legacy INFO Usage . . . . . . . . . . . . . . . . . . 34
     A.1.   General . . . . . . . . . . . . . . . . . . . . . . . . . 34
     A.2.   ISUP  . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     A.3.   QSIG  . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     A.4.   MSCML . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     A.5.   MSML  . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     A.6.   Video Fast Update . . . . . . . . . . . . . . . . . . . . 34
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . . 34
   Appendix C.  Change Log  . . . . . . . . . . . . . . . . . . . . . 35
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37














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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 might update the state of
   those applications).

   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, or outside an existing dialog.

   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
   indicate for which Info Packages they are willing to receive INFO
   requests, and which Info Package a specific INFO request is
   associated with.

   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 an empty Recv-Info header field (a header field
   without a 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.  The INFO Method

3.1.  General

   The INFO method provides a mechanism for transporting application
   level information that can further enhance a SIP application.  Annex
   A gives more details on the types of applications for which the use
   of INFO is appropriate.

   This section describes how a UA handles INFO requests and responses,
   as well as the message bodies included in INFO messages.

3.2.  INFO Request

3.2.1.  INFO Request Sender

   An INFO request can be associated with an Info Package (see X), or
   associated with a legacy INFO usage (see Y).

   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.

   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.

   When a UA sends an INFO request associated with an legacy INFO usage
   there is no Info Package associated with the request, and the UA MUST
   NOT include an Info-Package header field in the request.

   The INFO request MUST NOT contain a Recv-Info header field.  A 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 4.

   A UA MUST NOT use the INFO method outside an invite dialog usage.



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   UAs indicate, per-dialog basis, for which Info Packages they are
   willing to receive INFO requests.  The set of Info Packages cannot
   automatically be used within other dialogs.

   If a UA receives a 469 (Bad INFO Package) response to an INFO
   request, based on [RFC5057] the response represents a Transaction
   Only failure, and the UA MUST NOT terminate the invite dialog usage.

   Due to the possibility of forking, the UA whichs sends the initial
   INVITE reqest MUST be prepared to receive INFO requests from multiple
   remote UAs during the early dialog phase.  In addition, the UA MUST
   be prepared to receive different Recv-Info header field values from
   different remote UAs.

   NOTE: If the UAS (receiver of the initial INVITE request) sends an
   INFO request just after it has sent the response which creates the
   dialog, the UAS needs to be prepared that the INFO request can reach
   the UAC before the dialog creating response, and might therefore be
   rejected by the UAC.  In addition, an INFO request might be rejected
   due to a race condition, if a UA sends the INFO request at the same
   time as the remote UA sends a new set of Info Packages for which it
   is willing to receive INFO requests.

3.2.2.  INFO Request Receiver

   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 (see Section 11.6).  In the
   terminology of Multiple Dialog Usages [RFC5057], this represents a
   Transaction Only failure, and does not terminate the invite dialog
   usage.

   If a UA receives an INFO request associated with an Info Package, and
   the message body part associated with the Info Package contains a
   message body MIME type that the UA support, but which usage is not
   defined for the specific Info Package, it is RECOMMENDED that the UA
   sends a 415 (Unsupported Media Type) response.

   The UA MAY send other error responses, such as Request Failure (4xx),
   Server Failure (5xx) and Global Failure (6xx), in accordance with the
   error handling procedures in [RFC3261].

   Otherwise, if the INFO request is syntactically correct and well
   structured, the UA MUST send a 200 (OK) response.

   NOTE: If the application needs to reject the information which it
   received in an INFO request, that needs to be done on the application
   level.  Ie the application needs to trigger a new INFO request, which



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   contains information that the previously received application data
   was not accepted.  Individual Info Package specifications need to
   describe the details for such procedures.

3.3.  INFO Message Body

3.3.1.  INFO Request Message Body

   The purpose of the INFO request is to carry application level
   information between SIP UAs.  The application information data is
   carried in the payload of the message body of the INFO request.

   NOTE: An INFO request assocated with an Info Package can also include
   information associated with the Info Package using Info-Package
   header field parameters.

   If an INFO request associated with an Info Package contains a message
   body part, the body part is identified by a Content-Disposition
   header field 'Info-Package' value.  The body part can contain a
   single MIME type, or it can be a multipart [RFC5621] which contains
   other body parts associated with the Info Package.

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

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

   When a UA supports a specific Info-Package, the UA also support all
   message body MIME types associated with that Info-Package.  However,
   in accordance with [RFC3261] the UA still indicates the supported
   MIME types using the Accept header.

3.3.2.  INFO Response Message Body

   A UA MUST NOT include a message body associated with an Info Package
   in an INFO response.  Message bodies associated with Info Packages
   MUST only be sent in INFO requests.

   A UA MAY include a message body which is not associated with an Info
   Package in an INFO response.

3.4.  Order of Delivery

   The Info Package mechanism does not define a delivery order
   mechanism.  Info Packages can rely 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



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   delivery, those mechanisms, and related procedures, are specified as
   part of the associated Info Package, and possible sequence numbers
   etc must be defined as application data.


4.  Info Packages

4.1.  General

   An Info Package specification defines the content and semantics of
   the information carried in an INFO message associated with an Info
   Package.  The Info Package mechanism provides a way for UAs to
   indicate for which Info Packages they are willing to receive INFO
   requests, and which Info Package a specific INFO request is
   associated with.

4.2.  User Agent Behavior

4.2.1.  General

   This section describes how a UA handles Info Packages, how a UA uses
   the Recv-Info header field, and how the UA acts in re-INVITE rollback
   situations.

4.2.2.  UA Procedures

   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 requests.  A UA can list multiple Info
   Packages in a single Recv-Info header field, and the UA can use
   multiple Recv-Info header fields.  A UA can an empty Recv-Info header
   field, ie a header field without any header field values.

   A UA provides its set of Info Packages for which it is willing to
   receive INFO requests during the dialog establishment.  A UA can
   update the set of Info Packages during the invite dialog usage.

   If a UA is not willing to receive INFO requests for any Info
   Packages, during dialog establishment or later during the invite
   dialog usage, the UA MUST indicate this by including an empty Recv-
   Info header field.  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' in a Recv-Info header field, 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
   message with an empty Recv-Info header field.



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   Once a UA has sent a set of Info Packages, the set is valid until the
   UA sends a new set, or an empty Recv-Info header field.

   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 until the UA indicates that it is no longer willing to
   receive INFO requests associated with that Info Package.

   For a specific dialog usage, 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, or after the UA has received an indication that the remote
   UA is no longer willing to receive INFO requests associated with that
   Info Package.

   NOTE: When a UA sends a message which contains a Recv-Info header
   field with a new set of Info Packages for which the UA is willing to
   receive INFO requests the remote UA might, before it receives the
   message, send an INFO request based on the old set of Info Packages.
   In this case the receiver of the INFO requests rejects, and sends a
   469 (Bad INFO Package) response to, the INFO request.

   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
   specifications, 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 Appendix A.  In addition, 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 still indicates support of the INFO
   method using the Allow header.

   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 10.6.






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4.2.3.  Recv-Info header field rules

   The text below defines rules on when a UA is required to include a
   Recv-Info header field in SIP messages.  Section 6.1 lists the SIP
   methods, for which a UA can insert a Recv-Info header field in
   requests and responses.

   - The sender of an initial INVITE request MUST include a Recv-Info
   header field in the initial INVITE request, even if the sender is not
   willing to receive INFO requests asscoiated with any Info Package.

   - The receiver of a request which contains a Recv-Info header field
   MUST include a Recv-Info header field in a reliable 18x/2xx response
   to the request, even if the request contains an empty Recv-Info
   header field, and even if the header field value of the receiver has
   not changed since the previous time it sent a Recv-Info header field.

   - A UA MUST NOT include a Recv-Info header field in a response if the
   associated request did not contain a Recv-Info header field.

   NOTE: Different from the rules for generating SDP answers, the
   receiver of a request which contains a set of Info Packages is not
   restricted to generate its own set of Info Packages as a subset of
   the Info Package set received in the Info Package header field of the
   request.

   NOTE: Similar to SDP answers, the receiver can include the same Recv-
   Info header field value in multiple responses (18x/2xx) for the same
   INVITE/re-INVITE transaction, but the receiver is not allowed to
   include a Recv-Info header field value which is different from a
   value that the receiver has already included in a response for the
   same transaction.

4.2.4.  Info Package fallback rules

   If the receiver of a request which contains a Recv-Info header field
   rejects the request, both the sender and receiver of the request MUST
   roll back to the set of Info Packages which was used before the
   request was sent.  This also applies to the case where the receiver
   of an INVITE/re-INVITE request has included a Recv-Info header field
   in a provisional response, but later rejects the request.

   NOTE: The dialog state rollback rules for Info Packages might differ
   from the rules for other types of dialog state information (SDP,
   target, etc).






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4.3.  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
   request targets.

   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].  However, this document does not
   define a feature tag for the Info Package mechanism, or a mechanism
   to define feature tags for specific Info Packages.

4.4.  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.


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
     ------                    -----    ----
     Accept                      R       o
     Accept                     415      o
     Accept-Encoding             R       o
     Accept-Encoding            2xx      o
     Accept-Encoding            415      c
     Accept-Language             R       o
     Accept-Language            2xx      o
     Accept-Language            415      o
     Accept-Resource-Priority 2xx,417    o
     Alert-Info                          -
     Allow                       R       o



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     Allow                      405      m
     Allow                       r       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
     Geolocation-Error           r       o
     Max-Breadth                 R       -
     Max-Forwards                R       o
     MIME-Version                        o
     Min-Expires                         -
     Organization                        -
     Priority                    R       -
     Privacy                             o
     Proxy-Authenticate         401      m
     Proxy-Authenticate         407      o
     Proxy-Authorization         R       o
     Proxy-Require               R       o
     Reason                      R       o
     Record-Route                R       o
     Record-Route             2xx,18x    o
     Referred-By                 R       o
     Request-Disposition         R       o
     Require                             o
     Resource-Priority                   o
     Retry-After                 R       -
     Retry-After         404,413,480,486 o
     Retry-After              500,503    o
     Retry-After              600,603    o
     Route                       R       o
     Security-Client             R       o
     Security-Server          421,494    o
     Security-Verify             R       o
     Server                      r       o
     Subject                     R       o
     Supported                   R       o



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     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*  -   -   -   -   -
Info-Package   469    -   -   -   -   -   -   -   m*  -   -   -   -   -
Recv-Info      R      -   -   -   m   m   o   o   -   -   o   -   -   -
Recv-Info      2xx    -   -   -   o** m   -   o***-   -   o***-   -   -
Recv-Info      1xx    -   -   -   o** -   -   -   -   -   -   -   -   -
Recv-Info      r      -   -   -   o   o   -   o   -   -   o   -   -   -

   The support and usage of the Info-Package and Recv-Info header fields
   is not applicalbe to UAs that only support legacy INFO usages. * Not
   applicalbe to INFO requests and responses associated with legacy INFO
   usages. ** Mandatory in at least one reliable 18x/2xx response, if
   sent, to the INVITE request, if the associated INVITE request
   contained a Recv-Info header field. *** Mandatory if the associated
   request contained a Recv-Info header field.

                    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 3
   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.

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 4
   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.  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
   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



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   plane data transport mechanisms.

7.4.  Alternative Mechanisms

7.4.1.  Alternative SIP signaling plane mechanisms

7.4.1.1.  General

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

7.4.1.2.  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 UA 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 separate
   dialog usage [RFC5057], and is normally sent outside an existing
   dialog usage.

   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
   and B2BUAs, the resource impact caused by the subscription dialogs
   needs to be considered.  The number of subscription dialogs 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.






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7.4.1.3.  MESSAGE

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

7.4.2.  Media Plane Mechanisms

7.4.2.1.  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.

7.4.2.2.  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.

7.4.2.3.  MRSP

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

7.4.3.  Non-SIP related mechanisms

   Another alternative is to use a totally externally signaled channel,
   such as HTTP [RFC2616].  In this model, the UA 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





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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   =  Info-package-type *( COMMA Info-package-type )
   Info-package-type   =  Info-package-name *( SEMI Info-package-param)
   Info-package-name   =  token
   Info-package-param  =  generic-param


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
   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



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   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 3, an INFO request associated with an Info
   Package always contains an Info-Package header field.  A UA MUST NOT
   insert an Info-Package header field in a legacy INFO request.

   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.


10.  Info Package Requirements

10.1.  General

   This section provides guidance on how to define an Info Package, and
   what information needs to exist in an Info Package specification.

   If, for an Info Package, there is a need to extend or modify the
   behavior described in this document, that behaviour MUST be described
   in the Info Package specification.  It is bad practice for Info
   Package specifications to repeat procedures defined in this document,
   unless needed for clarification or emphasis purpose.

   Info Package specifications MUST NOT weaken any behavior designated
   with "SHOULD" or "MUST" in this specification.  However, Info



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   Packages specifications MAY strengthen "SHOULD", "MAY", or
   "RECOMMENDED" requirements to "MUST" strength if applications
   associated with the Info Package requires it.

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

   Section 7.4 describes alternative mechanisms, which should be
   considered as part of the process for solving a specific use-case,
   when for transporting application information.

10.2.  Overal Description

   The Info Package specification MUST contain an overlap description of
   the Info Package: what type of information are carried in INFO
   requests associated with the Info Package, and for what type of
   applications and functionalities UAs can use the Info Package.

   If the Info Package is defined for a specific application, the Info
   Package specification MUST state which application UAs can use the
   Info Package with.

10.3.  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.

10.4.  Info Package Name

   The Info Package specification MUST define an Info Package name,
   which UAs use as a header field value (e.g. "infoX") to be identify
   the Info Package in the Recv-Info and Info-Package header fields.
   The header field value MUST conform to the ABNF defined in
   Section 8.2.

   The Info Package mechanism does not support package versioning.
   Specific Info Package message body payloads can contain version



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   information, which is handled by the applications associated with the
   Info Package.  However, such feature is outside the scope of the
   generic 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.

   The IANA registration requirements for Info Package names are defined
   in Section 10.5.

10.5.  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 which indicates the Info Package
   name (see Section 10.4.

   The Info Package specification MUST define the syntax and semantics
   of the defined parameters.  In addition, the specification MUST
   define whether a specific parameter is only applicable to the Recv-
   Info header field, the Info-Package header field, or both.

   By default, an Info Package parameter is only applicable for the Info
   Package for which the parameter has been explicitly defined.

   NOTE: Info Package parameters defined for specific Info Packages can
   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.

10.6.  SIP Option Tags

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

   The registration requirements for option tags are defined in
   [I-D.peterson-rai-rfc3427bis].

10.7.  INFO Message Body Parts

   The Info Package specification MUST define which message body part
   MIME types are associated with the Info Package.  The specification
   MUST either define those body parts, which include the syntax,
   semantics and MIME type of the each body part, or refer to other
   documents which define the body parts.

   If multiple message body part MIME types are associated with an Info



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   Package, the Info Package specification MUST define whether UAs need
   to use multipart body parts in order to include multiple body parts
   in a single INFO request.

10.8.  Info Package Usage Restrictions

   If there are restrictions on how UAs can use an Info Package, the
   Info Package specification MUST document such restrictions.

   There can be restrictions related to whether UAs are allowed to send
   overlapping (outstanding) INFO requests associated with the Info
   Package, or whether the UA has to wait for the response for a
   previous INFO request associated with the same Info Package.

   There can also be restrictions related to whether UAs need to support
   and use other SIP extensions and capabilities when they use the Info
   Package, and if there are restrictions related to how UAs can use the
   Info-Package together with other Info Packages.

   As the SIP stack might not be aware of Info Package specific
   restrictions, it cannot be assumed that overlapping requests would be
   rejected.  As defined in Section 3.2.2, UAs will normally send a 200
   (OK) response to an INFO request.  The application logic associated
   with the Info Package needs to handle situations where UAs do not
   follow restrictions associated with the Info Package.

10.9.  Rate of INFO Requests

   If there is a maximum or minumum rate at which UAs can send INFO
   requests associated with the Info Package within a dialog, the Info
   Package specification MUST document the rate values.

   If the rates can vary, the Info Package specification MAY define Info
   Package parameters that UAs can use to indicate or negotiate the
   rates.  Alternatively the rate information can be part of the
   application data information associated with the Info Package.

10.10.  Info Package Security Considerations

   If the application information carried in INFO requests associated
   with the Info Package requires certain level of security, the Info
   Package specification MUST describe the mechanisms that UAs need to
   use in order to provide the required security.

   If the Info Package specification does not require any additional
   security, other than what the underlying SIP protocol provides, it
   MUST be stated in the Info Package specification.




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

   It is strongly RECOMMENDED that the Info Package specification
   defines the procedure how implementors shall implement and use the
   Info Package, or refer to other locations where implementors can find
   that information.

   NOTE: Sometimes Info Package designer might choose to not reveal the
   details of an Info Package.  However, in order to allow multiple
   implementations to support the Info Package, Info Package designers
   are stronly encouraged to provide the implementation details.

10.12.  Examples

   It is RECOMMENDED that the Info Package specification provides
   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:








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   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.

   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.

   Based on [RFC5226], IANA assigns an expert in order to review an Info
   Package which is to be registered.  The Info Package specification is
   provided to the reviewer, who ensures that the Info Package is
   described in a proper way.

   The reviewer does not consider the applicability of the Info Package
   for the usage for which it is defined.

   The following data elements populate the Info Package Registry.
   o  Info Package Name: The Info Package Name is a case insensitive
      token.  In addition, IANA shall not register multiple Info Package
      names that have identical case-insensitive values.
   o  Reference: A reference to a specification which describes the Info
      Package.

   The initial population of this table shall be:

   Name         Reference







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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 for which Info Packages UAs are willing to receive
       INFO requests

12.1.1.  Initial INVITE request

   The UAC sends an initial INVITE request, where the UAC indicates that
   it is willing to receive INFO requests for 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 requests for 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:bob@pc33.example.com>
  Recv-Info: R, T
  Content-Type: application/sdp
  Content-Length: ...

  ...

   The UAC sends an ACK request.

   ACK sip:bob@pc33.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

12.1.2.  Target refresh

   The UAC sends an UPDATE request within the invite dialog usage, where
   the UAC indicates (using an empty Recv-Info header field) that it is
   not willing to receive INFO requests for any Info Packages.

   UPDATE sip:bob@pc33.example.com SIP/2.0
   Via: SIP/2.0/TCP pc33.example.com;branch=z9hG4bK776
   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: 314163 UPDATE
   Recv-Info:
   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 requests for Info
   Packages R.




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  SIP/2.0 200 OK
  Via: SIP/2.0/TCP pc33.example.com;branch=z9hG4bK893;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: 314163 INVITE
  Contact: <sip:alice@pc33.example.com>
  Recv-Info: R, T
  Content-Type: application/sdp
  Content-Length: ...

  ...

12.2.  INFO request associated with Info Package

12.2.1.  Single payload

   The UA sends an INFO request associated with Info Package foo.

   INFO sip:alice@pc33.example.com SIP/2.0
   Via: SIP/2.0/UDP 192.0.2.2:5060;branch=z9hG4bKnabcdef
   To: Bob <sip:bob@example.com>;tag=a6c85cf
   From: Alice <sip:alice@example.com>;tag=1928301774
   Call-Id: a84b4c76e66710@pc33.example.com
   CSeq: 314333 INFO
   Info-Package: foo
   Content-type: application/foo
   Content-Disposition: Info-Package
   Content-length: 24

   I am a foo message type


12.2.2.  Multipart INFO

12.2.2.1.  Non-Info Package body part

   SIP extensions can sometimes add body part payloads 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 Content-
   Disposition header field that indicates which body part is associated
   with the Info Package.









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   INFO sip:alice@pc33.example.com 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: a84b4c76e66710@pc33.example.com
   CSeq: 314400 INFO
   Info-Package: foo
   Content-Type: multipart/mixed;boundary="theboundary"
   Content-Length: ...

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

   <mumble stuff>

   --theboundary
   Content-Type: application/foo-x
   Content-Disposition: Info-Package
   Content-length: 59

   I am a foo-x message type, and I belong to Info Package foo
   --theboundary--

12.2.2.2.  Info Package with multiple body parts inside multipart body
           part

   Multiple body part payloads can be associated with a single Info
   Package.  In this case, the body parts are put into a Multipart MIME
   body, with a Content-Disposition header field that indicates which
   body part is associated with the Info Package.




















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   INFO sip:alice@pc33.example.com 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: a84b4c76e66710@pc33.example.com
   CSeq: 314423 INFO
   Info-Package: foo
   Content-Type: multipart/mixed;boundary="theboundary"
   Content-Disposition: Info-Package
   Content-Length: ...

   --theboundary
   Content-Type: application/foo-x
   Content-length: 59

   I am a foo-x message type, and I belong to Info Package foo

   <mumble stuff>

   --theboundary
   Content-Type: application/foo-y
   Content-length: 59

   I am a foo-y message type, and I belong to Info Package foo
   --theboundary--

12.2.2.3.  Info Package with single body part inside multipart body part

   The body part payload associated with the Info Package can have a
   Content-Disposition header field value other than "Info-Package".  In
   this case, the body part is put into a Multipart MIME body, with a
   Content-Disposition header field that indicates which body part is
   associated with the Info Package.


















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   INFO sip:alice@pc33.example.com 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: a84b4c76e66710@pc33.example.com
   CSeq: 314423 INFO
   Info-Package: foo
   Content-Type: multipart/mixed;boundary="theboundary"
   Content-Disposition: Info-Package
   Content-Length: ...

   --theboundary
   Content-Type: application/foo-x
   Content-Disposition: icon
   Content-length: 59

   I am a foo-x message type, and I belong to Info Package foo
   --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
   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



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   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.

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.

   [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,



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              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.

   [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.



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   [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) and the Real-
              time Applications and Infrastructure Area",
              draft-peterson-rai-rfc3427bis-04 (work in progress),
              October 2009.

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



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


Appendix A.  Legacy INFO Usage

A.1.  General

   This section provides examples of existing legacy INFO usages.  The
   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.

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.




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   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.

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

   Adam Roach, Dean Willis, John Elwell and Paul Kyzivat provided
   valuable input in order to sort out the message body part usage for
   Info Packages.


Appendix C.  Change Log

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

   Changes from draft-ietf-sipcore-info-events-02
   o  Further changes based on WGLC comments
   o  Allignment with "specification" and "definition" terminology
   o  Location switch of sections 3 and 4
   o  Corrections in header table
   o  IANA Info Package registration input changed
   o  Clarifiaction regarding which SIP messages can contain the Recv-
      Info header field
   o  Recv-Info 'nil' value removed
   o  Rules on usage of Recv-Info header clarified
   o  Recv-Info fallback rules added
   o  Additional examples added

   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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