





Internet Engineering Task Force (IETF)                       C. Holmberg
Request for Comments: 8262                                   I. Sedlacek
Updates: 5368, 5621, 6442                                       Ericsson
Category: Standards Track                                   October 2017
ISSN: 2070-1721


    Content-ID Header Field in the Session Initiation Protocol (SIP)

Abstract

   This document specifies the Content-ID header field for usage in the
   Session Initiation Protocol (SIP).  This document also updates RFC
   5621, which only allows a Content-ID URL to reference a body part
   that is part of a multipart message-body.  This update enables a
   Content-ID URL to reference a complete message-body and metadata
   provided by some additional SIP header fields.

   This document updates RFC 5368 and RFC 6442 by clarifying their usage
   of the SIP Content-ID header field.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8262.

















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Copyright Notice

   Copyright (c) 2017 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
   (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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Identifying a Body Part . . . . . . . . . . . . . . . . .   3
     1.2.  Referencing a Body Part . . . . . . . . . . . . . . . . .   3
     1.3.  Problem Statement . . . . . . . . . . . . . . . . . . . .   4
     1.4.  Consequences  . . . . . . . . . . . . . . . . . . . . . .   4
       1.4.1.  Example 1: SIP INVITE . . . . . . . . . . . . . . . .   4
       1.4.2.  Example 2: SIP REFER  . . . . . . . . . . . . . . . .   6
     1.5.  Solution  . . . . . . . . . . . . . . . . . . . . . . . .   7
     1.6.  Backward Compatibility  . . . . . . . . . . . . . . . . .   7
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Content-ID Header Field . . . . . . . . . . . . . . . . . . .   8
     3.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.3.  Semantics . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.4.  Procedures  . . . . . . . . . . . . . . . . . . . . . . .   9
       3.4.1.  User Agent (UA) Procedures  . . . . . . . . . . . . .   9
       3.4.2.  Proxy Procedures  . . . . . . . . . . . . . . . . . .   9
       3.4.3.  Example: Referencing the Message-Body of a SIP
               Message . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Update to RFC 5368  . . . . . . . . . . . . . . . . . . . . .  10
   5.  Update to RFC 5621  . . . . . . . . . . . . . . . . . . . . .  11
   6.  Update to RFC 6442  . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Header Field  . . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14





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1.  Introduction

1.1.  Identifying a Body Part

   A SIP message consists of a start-line, one or more header fields, an
   empty line indicating the end of the header fields, and an optional
   message-body as specified in [RFC3261].

   The message-body can be a non-multipart message-body or a multipart
   message-body as specified in [RFC3261].

   [RFC5621] defines generic handling of a multipart message-body in a
   SIP message.

   A multipart message-body contains zero, one, or several body parts
   encoded using the format define in [RFC2045].

   A body part in the multipart message-body is described using header
   fields such as Content-Disposition, Content-Encoding, and Content-
   Type, which provide information on the content of the body part as
   specified in [RFC5621].  A body part in the multipart message-body
   can also contain a Content-ID header field with an ID value uniquely
   identifying the body part as specified in [RFC2045].

1.2.  Referencing a Body Part

   A SIP header field can reference a body part using a Content-ID URL
   as specified in [RFC5621].

   The Content-ID URL is specified in [RFC2392].  [RFC2392] specifies
   how to identify the body part referenced by a Content-ID URL.  The
   Content-ID URL value is included in the Content-ID header field of
   the body part.

   Examples of SIP header fields referencing a body part using a
   Content-ID URL are:

   o  [RFC6442] specifies how a Geolocation header field references a
      body part using a Content-ID URL for providing location
      information.

   o  [RFC5368] specifies how a Refer-To header field references a body
      part using a Content-ID URL to provide a list of targets.








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1.3.  Problem Statement

   How to uniquely identify a complete message-body of a SIP message
   using a Content-ID header field and how to reference a complete
   message-body using a Content-ID URL are not currently specified.

   Note: In [RFC5621], the Content-ID URL references a specific body
   part only.

   Some existing specifications, such as [RFC5368], contain examples
   that show usage of a SIP Content-ID header field referencing a
   complete message-body, even though such usage has never been
   specified.  Many implementors have interpreted these examples to
   indicate that such usage is allowed by the corresponding
   specification, despite the absence of language allowing it.  This
   document updates the normative language in the affected documents to
   explicitly allow such usage.

1.4.  Consequences

   The examples below show the consequences of the problem described
   above.

1.4.1.  Example 1: SIP INVITE

   If a User Agent Client (UAC) sends an INVITE request that conveys
   location by value (as specified in [RFC6442]) and decides not to
   include a Session Description Protocol (SDP) offer, then the UAC
   needs to include only one MIME entity in the INVITE request.  This
   MIME entity can be, for example, of the 'application/pidf+xml' MIME
   type.

   However, due to [RFC6442] requiring inclusion of a Geolocation header
   field referencing the body part with the location information, the
   UAC includes a multipart message-body with a single body part in the
   INVITE request, and includes the location information of
   'application/pidf+xml' MIME type and an associated Content-ID header
   field in the body part.













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     Example message (SIP INVITE):

     INVITE sips:bob@biloxi.example.com SIP/2.0
     Via: SIPS/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf9
     Max-Forwards: 70
     To: Bob <sips:bob@biloxi.example.com>
     From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
     Call-ID: 3848276298220188511@atlanta.example.com
     Geolocation: <cid:target123@atlanta.example.com>
     Geolocation-Routing: no
     Accept: application/sdp, application/pidf+xml
     CSeq: 31862 INVITE
     Contact: <sips:alice@atlanta.example.com>
     Content-Type: multipart/mixed; boundary=boundary1
     Content-Length: ...

     --boundary1
     Content-Type: application/pidf+xml
     Content-ID: <target123@atlanta.example.com>

     <?xml version="1.0" encoding="UTF-8"?>
     <presence
       xmlns="urn:ietf:params:xml:ns:pidf"
       xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
       xmlns:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
       xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
       xmlns:gml="http://www.opengis.net/gml"
       xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
       entity="pres:alice@atlanta.example.com"
       >
       <dm:device id="target123-1">
         <gp:geopriv>
           <gp:location-info>
             <gml:location>
               <gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
                 <gml:pos>32.86726 -97.16054</gml:pos>
               </gml:Point>
             </gml:location>
           </gp:location-info>
           <gp:usage-rules>
             <gbp:retransmission-allowed>no
             </gbp:retransmission-allowed>
             <gbp:retention-expiry>2010-11-14T20:00:00Z
             </gbp:retention-expiry>
           </gp:usage-rules>
           <gp:method>802.11</gp:method>
         </gp:geopriv>




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         <dm:deviceID>mac:1234567890ab</dm:deviceID>
         <dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
       </dm:device>
     </presence>
     --boundary1--

1.4.2.  Example 2: SIP REFER

   If a UAC sends a REFER request including a list of targets as
   specified in [RFC5368], then the UAC needs to include only one MIME
   entity in the REFER request.  This MIME entity is of the
   'application/resource-lists+xml' MIME type.

   However, due to [RFC5368] requiring inclusion of a Refer-To header
   field referencing the body part containing the list of targets, the
   UAC includes a multipart message-body with a single body part in the
   REFER request and includes the list of targets of 'application/
   resource-lists+xml' MIME type and an associated Content-ID header
   field in the body part.

    Example message (SIP REFER):

    REFER sip:conf-123@example.com;gruu;opaque=hha9s8d-999a  SIP/2.0
    Via: SIP/2.0/TCP client.chicago.example.com;branch=z9hG4bKhjhs8ass83
    Max-Forwards: 70
    To: "Conference 123" <sip:conf-123@example.com>
    From: Carol <sip:carol@chicago.example.com>;tag=32331
    Call-ID: d432fa84b4c76e66710
    CSeq: 2 REFER
    Contact: <sip:carol@client.chicago.example.com>
    Refer-To: <cid:cn35t8jf02@example.com>
    Refer-Sub: false
    Require: multiple-refer, norefersub
    Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
    Allow-Events: dialog
    Accept: application/sdp, message/sipfrag
    Content-Type: multipart/mixed; boundary=boundary1
    Content-Length: ...

    --boundary1
    Content-Type: application/resource-lists+xml
    Content-Disposition: recipient-list
    Content-ID: <cn35t8jf02@example.com>








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    <?xml version="1.0" encoding="UTF-8"?>
    <resource-lists
      xmlns="urn:ietf:params:xml:ns:resource-lists"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      >
      <list>
        <entry uri="sip:bill@example.com?method=BYE"/>
        <entry uri="sip:joe@example.org?method=BYE"/>
        <entry uri="sip:ted@example.net?method=BYE"/>
      </list>
    </resource-lists>
    --boundary1--

1.5.  Solution

   In order to solve the problems described above, this document:

   o  Specifies and registers the Content-ID header field as a SIP
      header field.

   o  Specifies that, when used as a SIP header field, the Content-ID
      header field identifies the complete message-body and the metadata
      provided by some additional SIP header fields of the SIP message.

   o  Updates [RFC5621] to enable a Content-ID URL to reference a
      complete message-body and the metadata provided by some additional
      SIP header fields.

   o  Updates [RFC5368] and [RFC6442] by adding text that explicitly
      states that a SIP Content-ID header field can be used.

1.6.  Backward Compatibility

   If an existing specification only defines the usage of a multipart
   message-body to carry a single body part to be referenced by a
   Content-ID URL, implementations MUST NOT carry the MIME entity in a
   non-multipart message-body unless the specification is updated to
   explicitly allow it.

2.  Conventions

   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.  Content-ID Header Field

3.1.  Introduction

   This section defines the usage of the Content-ID header field for
   SIP.

3.2.  Syntax

   The ABNF [RFC5234] for the Content-ID header field is:

    Content-ID = "Content-ID" HCOLON msg-id

    msg-id     = "<" id-left "@" id-right ">"

    Note: id-left and id-right are specified in [RFC5322]. HCOLON is
    defined in [RFC3261].

    Note: When used in a SIP header field, the msg-id syntax has been
    simplified, compared to the syntax in [RFC5322], to disallow the use
    of comments and to adopt to the SIP usage of leading white space.

    The value of the Content-ID header field value must be unique in the
    context of a given SIP message, including any embedded MIME
    Content-ID header field values. Note that the SIP Content-ID header
    field value is not expected to be unique among all SIP messages; it
    has no meaning outside of the message in which it is included.

3.3.  Semantics

   The Content-ID header field included in the header fields of a SIP
   message identifies the message-body of the SIP message and the
   metadata provided by:

   o  A MIME-Version header field, if included in the header fields of
      the SIP message.

   o  Any 'Content-' prefixed header fields (including the Content-ID
      header field itself) included in the header fields of the SIP
      message.

   The Content-ID header field can be included in any SIP message that
   is allowed to contain a message-body.

   Note: The message-body identified by the Content-ID header field can
   be a non-multipart message-body or a multipart message-body.





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3.4.  Procedures

3.4.1.  User Agent (UA) Procedures

   A UA MAY include a Content-ID header field in any SIP message that is
   allowed to contain a message-body.

   A UA MUST NOT include a Content-ID header field in any SIP message
   that is not allowed to contain a message-body.

   A UA MUST set the value of the Content-ID header field to a value
   that is unique in the context of the SIP message.

3.4.2.  Proxy Procedures

   A proxy MUST NOT add a Content-ID header field in a SIP message.

   A proxy MUST NOT modify a Content-ID header field included in a SIP
   message.

   A proxy MUST NOT delete a Content-ID header field from a SIP message.

3.4.3.  Example: Referencing the Message-Body of a SIP Message

   The figure shows an example from [RFC5368], where the SIP Content-ID
   header field is used to reference the message-body (non-multipart) of
   a SIP message.

   REFER sip:conf-123@example.com;gruu;opaque=hha9s8d-999a  SIP/2.0
   Via: SIP/2.0/TCP client.chicago.example.com
           ;branch=z9hG4bKhjhs8ass83
   Max-Forwards: 70
   To: "Conference 123" <sip:conf-123@example.com>
   From: Carol <sip:carol@chicago.example.com>;tag=32331
   Call-ID: d432fa84b4c76e66710
   CSeq: 2 REFER
   Contact: <sip:carol@client.chicago.example.com>
   Refer-To: <cid:cn35t8jf02@example.com>
   Refer-Sub: false
   Require: multiple-refer, norefersub
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
   Allow-Events: dialog
   Accept: application/sdp, message/sipfrag
   Content-Type: application/resource-lists+xml
   Content-Disposition: recipient-list
   Content-Length: 362
   Content-ID: <cn35t8jf02@example.com>




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   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <list>
       <entry uri="sip:bill@example.com?method=BYE" />
       <entry uri="sip:joe@example.org?method=BYE" />
       <entry uri="sip:ted@example.net?method=BYE" />
     </list>
   </resource-lists>

4.  Update to RFC 5368

   This section updates the second paragraph in Section 7 of [RFC5368]
   by allowing usage of either a MIME Content-ID header field or a SIP
   Content-ID header field to label the body part or the message-body
   carrying the URI list.

   OLD TEXT:

      The Refer-To header field of a REFER request with multiple REFER-
      Targets MUST contain a pointer (i.e., a Content-ID Uniform
      Resource Locator (URL) as per RFC 2392 [RFC2392]) that points to
      the body part that carries the URI list.  The REFER-Issuer SHOULD
      NOT include any particular URI more than once in the URI list.

   NEW TEXT:

      The Refer-To header field of a REFER request with multiple REFER-
      Targets MUST contain a pointer (i.e., a Content-ID Uniform
      Resource Locator (URL) as per RFC 2392 [RFC2392]) that points to
      the body part or message-body that carries the URI list.  The
      REFER-Issuer SHOULD NOT include any particular URI more than once
      in the URI list.  The REFER request can use either a MIME Content-
      ID header field [RFC4483] or a SIP Content-ID header field
      [RFC8262] to label the body part or the message-body.
















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5.  Update to RFC 5621

   This section updates Section 9.1 of [RFC5621] by allowing a Content-
   ID URL to reference a message-body and the related metadata
   (Section 3.3) in addition to allowing a reference to a body part.

   OLD TEXT:

      Content-ID URLs allow creating references to body parts.  A given
      Content-ID URL [RFC2392], which can appear in a header field or
      within a body part (e.g., in an SDP attribute), points to a
      particular body part.

   NEW TEXT:

      Content-ID URLs allow the creation of references to body parts or
      message-bodies (and the header fields describing the message-
      bodies).  A given Content-ID URL [RFC2392], which can appear in a
      header field or within a body part (e.g., in an SDP attribute),
      points to a particular body part or the message-body (and the
      header fields describing the message-body).

6.  Update to RFC 6442

   This section updates the second paragraph in Section 3.1 of [RFC6442]
   by allowing usage of either a MIME Content-ID header field or a SIP
   Content-ID header field to label the body part or the message-body
   carrying the location data.

   OLD TEXT:

      In Figure 1, Alice is both the Target and the LS that is conveying
      her location directly to Bob, who acts as an LR.  This conveyance
      is point-to-point: it does not pass through any SIP-layer
      intermediary.  A Location Object appears by-value in the initial
      SIP request as a MIME body, and Bob responds to that SIP request
      as appropriate.  There is a 'Bad Location Information' response
      code introduced within this document to specifically inform Alice
      if she conveys bad location information to Bob (e.g., Bob "cannot
      parse the location provided", or "there is not enough location
      information to determine where Alice is").










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   NEW TEXT:

      In Figure 1, Alice is both the Target and the LS that is conveying
      her location directly to Bob, who acts as an LR.  This conveyance
      is point-to-point: it does not pass through any SIP-layer
      intermediary.  A Location Object appears by-value in the initial
      SIP request as a MIME body, and Bob responds to that SIP request
      as appropriate.  Either a MIME Content-ID header field [RFC4483]
      or the SIP Content-ID header field [RFC8262] MUST be used to label
      the location information.  There is a 'Bad Location Information'
      response code introduced within this document to specifically
      inform Alice if she conveys bad location information to Bob (e.g.,
      Bob "cannot parse the location provided", or "there is not enough
      location information to determine where Alice is").

7.  Security Considerations

   The Content-ID header field value MUST NOT reveal sensitive user
   information.

   If the message-body associated with the Content-ID header field is an
   encrypted body, it MUST NOT be possible to derive a key that can be
   used to decrypt the body from the Content-ID header field value.

8.  IANA Considerations

   This specification registers a new SIP header field according to the
   procedures defined in [RFC3261].

8.1.  Header Field

   The header field described in Section 3 has been registered in the
   "Header Fields" sub-registry of the "Session Initiation Protocol
   (SIP) Parameters" registry by adding a row with these values:

      Header Name: Content-ID

      compact:

      Reference: RFC 8262











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9.  References

9.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
              <https://www.rfc-editor.org/info/rfc2045>.

   [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>.

   [RFC2392]  Levinson, E., "Content-ID and Message-ID Uniform Resource
              Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998,
              <https://www.rfc-editor.org/info/rfc2392>.

   [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>.

   [RFC4483]  Burger, E., Ed., "A Mechanism for Content Indirection in
              Session Initiation Protocol (SIP) Messages", RFC 4483,
              DOI 10.17487/RFC4483, May 2006,
              <https://www.rfc-editor.org/info/rfc4483>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <https://www.rfc-editor.org/info/rfc5322>.

   [RFC5621]  Camarillo, G., "Message Body Handling in the Session
              Initiation Protocol (SIP)", RFC 5621,
              DOI 10.17487/RFC5621, September 2009,
              <https://www.rfc-editor.org/info/rfc5621>.

   [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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9.2.  Informative References

   [RFC5368]  Camarillo, G., Niemi, A., Isomaki, M., Garcia-Martin, M.,
              and H. Khartabil, "Referring to Multiple Resources in the
              Session Initiation Protocol (SIP)", RFC 5368,
              DOI 10.17487/RFC5368, October 2008,
              <https://www.rfc-editor.org/info/rfc5368>.

   [RFC6442]  Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol", RFC 6442,
              DOI 10.17487/RFC6442, December 2011,
              <https://www.rfc-editor.org/info/rfc6442>.

Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com


   Ivo Sedlacek
   Ericsson
   Sokolovska 79
   Praha  18600
   Czech Republic

   Email: ivo.sedlacek@ericsson.com




















Holmberg & Sedlacek          Standards Track                   [Page 14]

