DISPATCH                                                  H. Schulzrinne
Internet-Draft                                                       FCC
Intended status: Standards Track                       December 12, 2016
Expires: June 15, 2017

              SIP Call-Info Parameters for Labeling Calls


   Called parties often wish to decide whether to accept, reject or
   redirect calls based on the likely nature of the call.  For example,
   they may want to reject unwanted telemarketing or fraudulent calls,
   but accept emergency alerts from numbers not in their address book.
   This document describes SIP Call-Info parameters and a feature tag
   that allow originating, intermediate and terminating SIP entities to
   label calls as to their type, spam probability and references to
   additional information.

Status of This Memo

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   This Internet-Draft will expire on June 15, 2017.

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   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Normative Language  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview of Operation . . . . . . . . . . . . . . . . . . . .   3
   4.  Parameters  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Call Types  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  SIP Call-Info Header Field Parameters . . . . . . . . . .   6
     8.2.  SIP Global Feature-Capability Indicator . . . . . . . . .   7
     8.3.  SIP Call-Info Type Parameter  . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     11.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   In many countries, an increasing number of calls are unwanted
   [RFC5039], as they might be fraudulent, telemarketing or the
   receiving party does not want to be disturbed by, say, surveys or
   solicitation by charities.  Currently, called parties have to rely
   exclusively on the caller's number or, if provided, caller name, but
   unwanted callers may not provide their true name or use a name that
   misleads, e.g., "Cardholder Services".  On the other hand, many calls
   from unknown numbers may be important to the called party, whether
   this is an emergency alert from their emergency management office or
   a reminder about a doctor's appointment.  Since many subscribers now
   reject all calls from unknown numbers, such calls may also be
   inadvertently be left unanswered.  Users may also install smartphone
   apps that can benefit from additional information in making decisions
   as to whether to ring, reject or redirect a call.

   To allow called parties to make more informed decisions on how to
   handle incoming calls from unknown callers, we describe a new set of
   parameters for the SIP [RFC3261] Call-Info header field for labeling
   the nature of the call.

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   Providers may also find the SIP Priority header (Section 20.26) field
   useful in helping called parties decide how to respond to an incoming

2.  Normative Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14, RFC 2119

3.  Overview of Operation

   This document describes a new set of optional parameters and usage
   for the SIP [RFC3261] Call-Info header field, purpose "info", for
   labeling the nature of the call.  The header field may be inserted by
   the call originator, an intermediate proxy or B2BUA or the
   terminating carrier, based on assertions by the caller, number-
   indexed databases, call analytics or other sources of information.
   The SIP provider serving the called party MUST remove any parameters
   enumerated in this specification that it does not trust.  The Call-
   Info header field MAY be signed using a future "ppt" extension to
   [I-D.ietf-stir-rfc4474bis].  To ensure that an untrusted originating
   caller does not mislead the called party, a new feature tag,
   sip.call-info.spam, indicates whether the terminating carrier will
   remove untrusted information.

   SIP entities MUST add a new Call-Info "info" header field instance,
   rather than add parameters to an existing one.  Thus, there MAY be
   several Call-Info header fields of purpose "info" in one request.

   As defined in [RFC3261], the Call-Info header field contains a URI
   that can provide additional information about the caller or call.
   For example, many call filtering services provide a web page with
   crowd-sourced information about the calling number.  If the entity
   inserting the header field does not have information it wants to link
   to, it MUST use an empty data URL [RFC2397] as a placeholder, as in
   "data:".  (The Call-Info header field syntax makes the URI itself

4.  Parameters

   All of the parameters listed below are optional and may appear in any
   combination and order.  Their ABNF is defined in Section 7.

   spam  The spam parameter carries an estimated probability that the
      call will not be wanted by the called party, expressed as a whole-
      number percentage between 0 and 100, inclusive, with larger

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      numbers indicating higher probability.  The computation of the
      estimate is beyond the scope of this specification.  If not
      specified, the entity inserting the Call-Info information is
      making no claims about the likelihood of being unwanted.  Note
      that call types other than "spam" may have a non-zero spam rating,
      as these calls may also be unwanted by some fraction of the
      recipients, even if they are not illegal in a particular

   type  The type parameter indicates the type of the call or caller.
      It is drawn from an extensible set of values, with the initial set
      listed below.  Gateways to analog phone systems MAY include the
      label in caller name (CNAM) information.  Automated call
      classification systems MAY use this information as one factor in
      deciding how to handle the call.  Calls SHOULD be labeled with
      types that may make it more likely that the caller will answer
      (e.g., for alert and health-related calls) if the entity inserting
      the information is confident that the calling party number is
      valid, e.g., because the request has been signed

   reason  The reason parameter provides free-text information, as a
      string, about the source of the type or spam parameter and is
      meant to be used for debugging, rather than for display to the end
      user.  For example, it may indicate the name of an external
      information source, such as a list of known emergency alerters.

   source  The source parameter identifies the entity, by host name,
      domain or IP address, that inserted the parameters above.  It uses
      the "host" ABNF syntax.

5.  Call Types

   The following initial set of types are defined.  The call types are
   generally based on the caller's telephone number or possibly an
   assertion by a trusted caller, as the content cannot be not known.
   Each call is tagged with at most one type label, i.e., the labels are
   meant to be mutually exclusive.  The definitions are meant to be
   informal and reflect the common understanding of subscribers who are
   not lawyers.  By their very nature, this classification may sometimes
   be erroneous, e.g., if a number has been re-assigned to another
   entity or if crowd-sourced information is wrong, and thus should be
   treated as a hint or estimate.  Each entity inserting type
   information will need to define its own policy as to the level of
   certainty it requires before it inserts type information.

   Other strings may be used; there does not appear to be a need for
   defining vendor-defined strings as the likelihood of confusion

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   between a service-provider-specific usage and a later extension to
   the list appears low.  Additional labels are registered with IANA.

   business  Calls placed by businesses, i.e., an entity or enterprise
      entered into for profit.  This type is used if no other, more
      precise, category fits.

   debt-collection  Calls related to collecting of debt owed or alleged
      to be owed by the called party.

   emergency-alert  Calls that provide the recipient warnings and alerts
      regarding a pending or on-going emergency.  (This call type is
      unrelated to emergency calls placed by individuals using emergency
      numbers such as 9-1-1 or 1-1-2.)

   fraud  The call is considered to be fraudulent.

   government  A call placed by a government entity, if no more specific
      label such as "health" or "debt-collection" is known or applies.

   health  Informational calls by health plans, health care
      clearinghouses or health care provider, where health care means
      care, services, or supplies related to the health of an

   informational  Calls intended to convey information to the called
      party about a transaction such as package delivery, appointment
      reminder, order confirmation.  This call type is only used if the
      calling party believes to have an established business
      relationship with the called party.

   not-for-profit  A call placed by a not-for-profit organization,
      including for soliciting donations or providing information.

   personal  A non-business, person-to-person, call, e.g., from a
      residential line or personal mobile number.

   political  Calls related to elections or other political purposes.

   public-service  Calls that provide the recipient information
      regarding public services, e.g., school closings.

   prison  Calls from jails, prisons and other correctional facilities.

   spam  A call that is likely unwanted, if not otherwise classified.

   spoofed  The calling number for this call has been spoofed.

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   survey  A call that solicits the opinions or data of the called

   telemarketing  Calls placed in order to induce the purchase of a
      product or service to the called party.

   trusted  The call is being placed by a trusted entity and falls
      outside the other categories listed.  This may include call backs,
      e.g., from a conferencing service, or messages from
      telecommunication carriers and utilities.

6.  Example

   "Call-Info: <http://wwww.example.com/5974c8d942f120351143>
   ;source=carrier.example.com ;purpose=info ;spam=85 ;type=fraud
   ;reason="FTC list""

7.  ABNF

                label-info-params = [ci-spam] / [ci-type] / [ci-source] / [ci-reason]
                ci-spam = "spam" EQUAL 1*3DIGIT
                ci-type = "type" EQUAL ("business" / "debt-collection" / "emergency-alert" / "fraud" /
                            "government" / "health" / "informational" / "not-for-profit" /
                            "personal" / "political" / "public-service" / "prison" / "spam" /
                            "spoofed" / "survey" / "telemarketing" / "trusted" /
                ci-source = "source" EQUAL host
                ci-reason = "reason" EQUAL quoted-string

8.  IANA Considerations

8.1.  SIP Call-Info Header Field Parameters

   This document defines the 'spam', 'type', 'reason' and 'source'
   parameters in the Call-Info header in the "Header Field Parameters
   and Parameter Values" registry defined by [RFC3968].

    | Header Field | Parameter Name | Predefined Values | Reference  |
    | Call-Info    | reason         | No                | [this RFC] |
    | Call-Info    | source         | No                | [this RFC] |
    | Call-Info    | spam           | No                | [this RFC] |
    | Call-Info    | type           | Yes               | [this RFC] |

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8.2.  SIP Global Feature-Capability Indicator

   This document defines the feature capability sip.call-info.spam in
   the "Global Feature-Capability Indicator Registration Tree" registry
   defined in [RFC6809].

   Name  sip.call-info.spam

   Description  This feature-capability indicator when used in a
      REGISTER response indicates that the server will add, inspect,
      alter and possibly remove the Call-Info header field parameters
      defined in the reference.

   Reference  [this RFC]

8.3.  SIP Call-Info Type Parameter

   This specification establishes the "Call-Info Type" sub-registry
   under http://www.iana.org/assignments/sip-parameters.  Call-Info
   "type" parameters are used in the "type" parameter in the SIP Call-
   Info header field.  The initial values are listed in Section 5.
   Additional values are allocated by expert review [RFC5226]; only the
   token value, using the ABNF iana-token, and a brief description,
   typically no more than a few sentences, is required.  The ABNF for
   iana-token is defined in [RFC3261].  A specification is not required.

9.  Security Considerations

   The security considerations in [RFC3261] (Section 20.9) apply.  A
   user agent MUST ignore the parameters defined in this document unless
   the SIP REGISTER response contained the sip.call-info.spam feature
   capability.  SIP entities MUST remove any parameters defined here
   that were provided by untrusted third parties.

   The protection offered against rogue SIP entities by the feature
   capability relies on protecting the REGISTER response against man-in-
   the-middle attacks that maliciously add the capability indicator.

10.  Acknowledgements

   Jim Calme and other members of the Robocall Strikeforce helped draft
   the initial list of call types.  Keith Drage and Paul Kyzivat
   provided helpful comments on the document.

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11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2397]  Masinter, L., "The "data" URL scheme", RFC 2397,
              DOI 10.17487/RFC2397, August 1998,

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,

   [RFC3968]  Camarillo, G., "The Internet Assigned Number Authority
              (IANA) Header Field Parameter Registry for the Session
              Initiation Protocol (SIP)", BCP 98, RFC 3968,
              DOI 10.17487/RFC3968, December 2004,

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,

   [RFC6809]  Holmberg, C., Sedlacek, I., and H. Kaplan, "Mechanism to
              Indicate Support of Features and Capabilities in the
              Session Initiation Protocol (SIP)", RFC 6809,
              DOI 10.17487/RFC6809, November 2012,

11.2.  Informative References

              Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-15
              (work in progress), October 2016.

   [RFC5039]  Rosenberg, J. and C. Jennings, "The Session Initiation
              Protocol (SIP) and Spam", RFC 5039, DOI 10.17487/RFC5039,
              January 2008, <http://www.rfc-editor.org/info/rfc5039>.

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Author's Address

   Henning Schulzrinne
   445 12th Street SW
   Washington, DC  20554

   Email: henning.schulzrinne@fcc.gov

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