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SIP Call-Info Parameters for Labeling Calls
draft-ietf-sipcore-callinfo-spam-04

Versions:

Document	Type	Active Internet-Draft (sipcore WG)
	Author	Henning Schulzrinne
	Last updated	2020-03-25 (Latest revision 2019-08-30)
	Replaces	draft-schulzrinne-dispatch-callinfo-spam
	Stream	Internet Engineering Task Force (IETF)
	Intended RFC status	Proposed Standard
	Formats	plain text xml htmlized pdfized bibtex
	Reviews	GENART Last Call review Ready with Nits SECDIR Last Call review Has Nits OPSDIR Last Call review Has Nits
Stream	WG state	Submitted to IESG for Publication
	Document shepherd	Brian Rosen
	Shepherd write-up	Show Last changed 2018-10-23
IESG	IESG state	IESG Evaluation::Revised I-D Needed
	Action Holders	(None)
	Consensus boilerplate	Yes
	Telechat date	(None) Needs a YES. Has 2 DISCUSSes. Needs 6 more YES or NO OBJECTION positions to pass.
	Responsible AD	Murray Kucherawy
	Send notices to	Brian Rosen <br@brianrosen.net>
IANA	IANA review state	IANA OK - Actions Needed

Email authors Email WG IPR References Referenced by Nits

draft-ietf-sipcore-callinfo-spam-04

SIPCORE H. Schulzrinne
Internet-Draft Columbia University
Intended status: Standards Track August 29, 2019
Expires: March 1, 2020

SIP Call-Info Parameters for Labeling Calls
draft-ietf-sipcore-callinfo-spam-04

Abstract

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, confidence and references to additional
information.

Status of This Memo

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

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.

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."

This Internet-Draft will expire on March 1, 2020.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://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

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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 . . . . . . . . . . . . . . . . . . . . 4
4. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Call Types . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. REGISTER Response . . . . . . . . . . . . . . . . . . . . 7
6.2. INVITE Request . . . . . . . . . . . . . . . . . . . . . 7
7. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. SIP Call-Info Header Field Parameters . . . . . . . . . . 8
8.2. SIP Global Feature-Capability Indicator . . . . . . . . . 8
8.3. SIP Call-Info Type Parameter . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11

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 may 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 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
voicemail.

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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This specification assumes that the user agent can trust its SIP
provider to correctly label the nature of calls. This may not always
be the case and not all SIP service providers will label calls, so
users may need to draw on other, third-party, sources of call
information beyond the scope of this specification or may decide to
disregard the call labeling offered by their service provider.
(Service providers may, for example, be reluctant to label calls as
spam.) However, the SIP registrar already occupies a position of
trust by necessity; also, the user agent is typically a customer of
the operator of the registrar or within the same organization, e.g.,
if the registrar is part of a PBX. Thus, the entity inserting the
Call-Info header field and the UAS relying on it SHOULD be part of
the same trust domain [RFC3324]. Conversely, the entity signing the
caller information [RFC8224] is likely either to be the caller itself
or the originating service provider, neither of which is likely to
label the caller as a category unlikely to be answered by the called
party.

The service provider inserting the Call-Info header field may draw on
a wide variety of sources. For example, service providers offering
alerting or notification services (e.g., for packages or health
alerts) may register their phone numbers, after suitable vetting, in
shared databases. Government agencies could publish electronic
directories of official telephone numbers, drawing on the historical
precedent of the "blue pages" found in printed phone directories.
Government regulators for financial services, health care providers
and charitable organizations could provide sources of telephone
numbers and service types belonging to such organizations. Finally,
crowd-sourcing might also be used to populate databases of call
types. In the United States, industry organizations have proposed
variations of such caller databases to prevent accidental blocking of
calls based on their statistics such as frequency or duration alone.

Providers may also find the SIP Priority header ([RFC3261],
Section 20.26) field useful in helping called parties decide how to
respond to an incoming call.

2. Normative Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.

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3. Overview of Operation

This document describes a new set of optional parameters and usage
for the SIP [RFC3261] Call-Info header field, with a 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.

To ensure that an untrusted originating caller does not mislead the
called party, a new feature capability indicator [RFC6809], sip.call-
info.spam, in the REGISTER response signals whether the terminating
carrier supports the feature described in this document and thus will
remove any untrusted 'confidence', 'origin', 'source' and 'type'
Call-Info header field information parameters. It is possible for
the terminating carrier to support this feature by simply removing
all parameters defined in the document, without inserting any of its
own information, although this is likely to be unusual. A user agent
MUST ignore any of the parameters defined in this document unless the
feature capability indicator is present in the response to the
REGISTER request. An example of the REGISTER response is shown in
Section 6.1.

SIP proxies or B2BUAs MUST add a new Call-Info "info" header field
value, rather than add parameters to an existing value. Thus, one
SIP request MAY contain several Call-Info header instances of purpose
"info", either as a single header with a comma-separated list of
header values or separate headers, or some combination.

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
mandatory.) An example is shown in Section 6.2.

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. All
except the 'type' parameter are optional.

confidence The 'confidence' parameter carries an estimated
probability that the call is of the nature indicated in the 'type'

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parameter, expressed as a whole-number percentage between 0 and
100, inclusive, with larger numbers indicating higher probability.
The computation of the estimate is beyond the scope of this
specification. If a 'type' is not specified, this parameter
estimates the likelihood that the call is unwanted spam by the
called party. If the confidence level is not specified, the
sender considers the information reliable enough to act on,
according to its local decision thresholds.

origin The origin parameter provides free-text information, as a
quoted-text (UTF8-encoded) string, about the source of the 'type'
or 'confidence' 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 or a government agency.

source The source parameter identifies the entity, by host name,
domain or IP address, that inserted the 'confidence', 'origin' and
'type' parameters. It uses the "host" ABNF syntax.

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 delivered to user
equipement. 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 [RFC8224].

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.

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

informational Calls intended to convey information to the called
party about a transaction such as package delivery, appointment
reminder, or order confirmation.

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. (For
example, the call has failed STIR validation [RFC8224] within the

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SIP service provider network or the telephone number is not a
valid number or is known not to have been assigned.)

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

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. Examples

6.1. REGISTER Response

The example below shows a partial REGISTER response showing that the
registrar and proxy will remove any untrusted Call-Info header
elements.

SIP/2.0 200 OK
...
From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl
To: Bob <sips:bob@biloxi.example.com>;tag=34095828jh
...
Feature-Caps: *; +sip.call-info.spam

6.2. INVITE Request

INVITE sip:alice@example.com SIP/2.0
...
Call-Info: <http://wwww.example.com/5974c8d942f120351143>
;source=carrier.example.com
;purpose=info ;confidence=85 ;type=fraud
;origin="FTC fraud list"

7. ABNF

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label-info-params = [ci-confidence] / [ci-source] / [ci-origin] / ci-type
ci-confidence = "confidence" EQUAL 1*3DIGIT
ci-origin = "origin" EQUAL quoted-string
ci-source = "source" EQUAL host
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" /
iana-token)

8. IANA Considerations

8.1. SIP Call-Info Header Field Parameters

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

8.2. SIP Global Feature-Capability Indicator

This document defines the feature capability sip.call-info.spam in
the "SIP 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.

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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. B2BUAs or proxies that maintain user registrations MUST
remove any parameters defined in this document that were provided by
untrusted third parties.

The UAS SHOULD only consider Call-Info header field information that
originates from a registrar that is part of the same trust domain
[RFC3324].

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.
Thus, a UAS SHOULD NOT trust the information in the "Call-Info"
header field unless the SIP session between the entity inserting the
header field and the UAS is protected by TLS [RFC8446].

Labeling calls is likely only useful if the caller identity can be
trusted, e.g., by having the call signaling requests signed
[RFC8224], as otherwise spoofed calls would likely be mislabeled and
thus increase the likelihood that the called party is mislead,
answers unwanted calls or is defrauded. Thus, this information MUST
only be added calls with an attestation level of "Full Attestation"
[RFC8588] or for calls where the SIP entity inserting the header
knows to have correct calling number information, e.g., because the
call originated within the same PBX or the same carrier and the
operating entity ensures that caller ID spoofing is highly unlikely
within their realm of responsibility.

10. Acknowledgements

Jim Calme and other members of the Robocall Strikeforce helped draft
the initial list of call types. Tolga Asveren, Ben Campbell, Keith
Drage, Christer Holmberg, Paul Kyzivat and Dale Worley 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,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397,
DOI 10.17487/RFC2397, August 1998,
<https://www.rfc-editor.org/info/rfc2397>.

[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,
<https://www.rfc-editor.org/info/rfc3261>.

[RFC3324] Watson, M., "Short Term Requirements for Network Asserted
Identity", RFC 3324, DOI 10.17487/RFC3324, November 2002,
<https://www.rfc-editor.org/info/rfc3324>.

[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,
<https://www.rfc-editor.org/info/rfc3968>.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.

[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,
<https://www.rfc-editor.org/info/rfc6809>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

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[RFC8224] Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 8224,
DOI 10.17487/RFC8224, February 2018,
<https://www.rfc-editor.org/info/rfc8224>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.

11.2. Informative References

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

[RFC8588] Wendt, C. and M. Barnes, "Personal Assertion Token
(PaSSporT) Extension for Signature-based Handling of
Asserted information using toKENs (SHAKEN)", RFC 8588,
DOI 10.17487/RFC8588, May 2019,
<https://www.rfc-editor.org/info/rfc8588>.

Author's Address

Henning Schulzrinne
Columbia University
450 Computer Science Bldg.
New York, NY 10027
US

Email: hgs@cs.columbia.edu

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SIP Call-Info Parameters for Labeling Calls draft-ietf-sipcore-callinfo-spam-04

SIP Call-Info Parameters for Labeling Calls
draft-ietf-sipcore-callinfo-spam-04