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Versions: (draft-veillette-core-yang-cbor-mapping) 00 01 02 03 04 05

Internet Engineering Task Force                        M. Veillette, Ed.
Internet-Draft                                   Trilliant Networks Inc.
Intended status: Standards Track                           A. Pelov, Ed.
Expires: February 9, 2018                                         Acklio
                                                             A. Somaraju
                                                   Tridonic GmbH & Co KG
                                                               R. Turner
                                                              Landis+Gyr
                                                             A. Minaburo
                                                                  Acklio
                                                         August 08, 2017


                CBOR Encoding of Data Modeled with YANG
                      draft-ietf-core-yang-cbor-05

Abstract

   This document defines encoding rules for serializing configuration
   data, state data, RPC input and RPC output, Action input, Action
   output and notifications defined within YANG modules using the
   Concise Binary Object Representation (CBOR) [RFC7049].

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 http://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 February 9, 2018.

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
   (http://trustee.ietf.org/license-info) in effect on the date of



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   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
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   3
     2.1.  YANG Schema Item iDentifier (SID) . . . . . . . . . . . .   4
     2.2.  CBOR diagnostic notation  . . . . . . . . . . . . . . . .   5
   3.  Properties of the CBOR Encoding . . . . . . . . . . . . . . .   6
   4.  Encoding of YANG Data Node Instances  . . . . . . . . . . . .   7
     4.1.  The 'leaf' Data Node  . . . . . . . . . . . . . . . . . .   7
     4.2.  The 'container' Data Node . . . . . . . . . . . . . . . .   7
       4.2.1.  SIDs as keys  . . . . . . . . . . . . . . . . . . . .   8
       4.2.2.  Member names as keys  . . . . . . . . . . . . . . . .  10
     4.3.  The 'leaf-list' Data Node . . . . . . . . . . . . . . . .  10
     4.4.  The 'list' Data Node  . . . . . . . . . . . . . . . . . .  11
       4.4.1.  SIDs as keys  . . . . . . . . . . . . . . . . . . . .  11
       4.4.2.  Member names as keys  . . . . . . . . . . . . . . . .  14
     4.5.  The 'anydata' Data Node . . . . . . . . . . . . . . . . .  15
     4.6.  The 'anyxml' Data Node  . . . . . . . . . . . . . . . . .  17
   5.  Representing YANG Data Types in CBOR  . . . . . . . . . . . .  17
     5.1.  The unsigned integer Types  . . . . . . . . . . . . . . .  17
     5.2.  The integer Types . . . . . . . . . . . . . . . . . . . .  18
     5.3.  The 'decimal64' Type  . . . . . . . . . . . . . . . . . .  18
     5.4.  The 'string' Type . . . . . . . . . . . . . . . . . . . .  18
     5.5.  The 'boolean' Type  . . . . . . . . . . . . . . . . . . .  19
     5.6.  The 'enumeration' Type  . . . . . . . . . . . . . . . . .  19
     5.7.  The 'bits' Type . . . . . . . . . . . . . . . . . . . . .  20
     5.8.  The 'binary' Type . . . . . . . . . . . . . . . . . . . .  21
     5.9.  The 'leafref' Type  . . . . . . . . . . . . . . . . . . .  21
     5.10. The 'identityref' Type  . . . . . . . . . . . . . . . . .  22
       5.10.1.  SIDs as identityref  . . . . . . . . . . . . . . . .  22
       5.10.2.  Name as identityref  . . . . . . . . . . . . . . . .  23
     5.11. The 'empty' Type  . . . . . . . . . . . . . . . . . . . .  23
     5.12. The 'union' Type  . . . . . . . . . . . . . . . . . . . .  24
     5.13. The 'instance-identifier' Type  . . . . . . . . . . . . .  25
       5.13.1.  SIDs as instance-identifier  . . . . . . . . . . . .  25
       5.13.2.  Names as instance-identifier . . . . . . . . . . . .  28
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  29
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
     7.1.  Tags Registry . . . . . . . . . . . . . . . . . . . . . .  29
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  29
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  30



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     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  30
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   The specification of the YANG 1.1 data modelling language [RFC7950]
   defines an XML encoding for data instances, i.e. contents of
   configuration datastores, state data, RPC inputs and outputs, action
   inputs and outputs, and event notifications.

   A new set of encoding rules has been defined to allow the use of the
   same data models in environments based on the JavaScript Object
   Notation (JSON) Data Interchange Format [RFC7159].  This is
   accomplished in the JSON Encoding of Data Modeled with YANG
   specification [RFC7951].

   The aim of this document is to define a set of encoding rules for the
   Concise Binary Object Representation (CBOR) [RFC7049].  The resulting
   encoding is more compact compared to XML and JSON and more suitable
   for Constrained Nodes and/or Constrained Networks as defined by
   [RFC7228].

2.  Terminology and Notation

   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 [RFC2119].

   The following terms are defined in [RFC7950]:

   o  action

   o  anydata

   o  anyxml

   o  data node

   o  data tree

   o  feature

   o  identity

   o  module

   o  notification



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   o  RPC

   o  schema node

   o  schema tree

   o  submodule

   The following terms are defined in [RFC7951]:

   o  member name

   o  name of an identity

   o  namespace-qualified

   This specification also makes use of the following terminology:

   o  child: A schema node defined within a collection such as a
      container, a list, a case, a notification, an RPC input, an RPC
      output, an action input, an action output.

   o  delta: Difference between the current SID and a reference SID.  A
      reference SID is defined for each context for which deltas are
      used.

   o  item: A schema node, an identity, a module, a submodule or a
      feature defined using the YANG modeling language.

   o  parent: The collection in which a schema node is defined.

   o  YANG Schema Item iDentifier (SID): Unsigned integer used to
      identify different YANG items.

2.1.  YANG Schema Item iDentifier (SID)

   Some of the items defined in YANG [RFC7950] require the use of a
   unique identifier.  In both NETCONF [RFC6241] and RESTCONF [RFC8040],
   these identifiers are implemented using names.  To allow the
   implementation of data models defined in YANG in constrained devices
   and constrained networks, a more compact method to identify YANG
   items is required.  This compact identifier, called YANG Schema Item
   iDentifier (SID), is encoded using an unsigned integer.  The
   following items are identified using SIDs:

   o  identities

   o  data nodes



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   o  RPCs and associated input(s) and output(s)

   o  actions and associated input(s) and output(s)

   o  notifications and associated information

   o  YANG modules, submodules and features

   To minimize its size, in certain positions, SIDs are represented
   using a (signed) delta from a reference SID and the current SID.
   Conversion from SIDs to deltas and back to SIDs are stateless
   processes solely based on the data serialized or deserialized.

   Mechanisms and processes used to assign SIDs to YANG items and to
   guarantee their uniqueness is outside the scope of the present
   specification.  If SIDs are to be used, the present specification is
   used in conjunction with a specification defining this management.
   One example for such a specification is under development as
   [I-D.ietf-core-sid].

2.2.  CBOR diagnostic notation

   Within this document, CBOR binary contents are represented using an
   equivalent textual form called CBOR diagnostic notation as defined in
   [RFC7049] section 6.  This notation is used strictly for
   documentation purposes and is never used in the data serialization.
   Table 1 below provides a summary of this notation.
























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   +----------+------+--------------------------+-----------+----------+
   | CBOR     | CBOR | Diagnostic notation      | Example   | CBOR     |
   | content  | type |                          |           | encoding |
   +----------+------+--------------------------+-----------+----------+
   | Unsigned | 0    | Decimal digits           | 123       | 18 7b    |
   | integer  |      |                          |           |          |
   | Negative | 1    | Decimal digits prefixed  | -123      | 38 7a    |
   | integer  |      | by a minus sign          |           |          |
   | Byte     | 2    | Hexadecimal value        | h'f15c'   | 42 f15c  |
   | string   |      | enclosed between single  |           |          |
   |          |      | quotes and prefixed by   |           |          |
   |          |      | an 'h'                   |           |          |
   | Text     | 3    | String of Unicode        | "txt"     | 63       |
   | string   |      | characters enclosed      |           | 747874   |
   |          |      | between double quotes    |           |          |
   | Array    | 4    | Comma-separated list of  | [ 1, 2 ]  | 82 01 02 |
   |          |      | values within square     |           |          |
   |          |      | brackets                 |           |          |
   | Map      | 5    | Comma-separated list of  | { 1: 123, | a2       |
   |          |      | key : value pairs within | 2: 456 }  | 01187b   |
   |          |      | curly braces             |           | 021901c8 |
   | Boolean  | 7/20 | false                    | false     | f4       |
   |          | 7/21 | true                     | true      | f5       |
   | Null     | 7/22 | null                     | null      | f6       |
   | Not      | 7/23 | undefined                | undefined | f7       |
   | assigned |      |                          |           |          |
   +----------+------+--------------------------+-----------+----------+

                 Table 1: CBOR diagnostic notation summary

   The following extensions to the CBOR diagnostic notation are
   supported:

   o  Any text within and including a pair of slashes is considered a
      comment.

   o  Deltas are visualized as numbers preceded by a '+' or '-' sign.
      The use of the '+' sign for positive deltas represents an
      extension to the CBOR diagnostic notation as defined by [RFC7049]
      section 6.

3.  Properties of the CBOR Encoding

   This document defines CBOR encoding rules for YANG schema trees and
   their subtrees.

   Basic schema nodes such as leaf, leaf-list, list, anydata and anyxml
   can be encoded standalone.  In this case, only the value of this



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   schema node is encoded in CBOR.  Identification of this value needs
   to be provided by some external means when required.

   A collection such as container, list instance, notification, RPC
   input, RPC output, action input and action output is serialized using
   a CBOR map in which each child schema node is encoded using a key and
   a value.  This specification supports two type of CBOR keys; YANG
   Schema Item iDentifier (SID) as defined in Section 2.1 and member
   names as defined in [RFC7951].  Each of these key types is encoded
   using a specific CBOR type which allows their interpretation during
   the deserialization process.  The end user of this mapping
   specification (e.g.  RESTCONF [RFC8040], CoMI [I-D.ietf-core-comi])
   can mandate the use of a specific key type.

   In order to minimize the size of the encoded data, the proposed
   mapping avoids any unnecessary meta-information beyond those natively
   supported by CBOR.  For instance, CBOR tags are used solely in the
   case of anyxml data nodes and the union datatype to distinguish
   explicitly the use of different YANG datatypes encoded using the same
   CBOR major type.

4.  Encoding of YANG Data Node Instances

   Schema node instances defined using the YANG modeling language are
   encoded using CBOR [RFC7049] based on the rules defined in this
   section.  We assume that the reader is already familiar with both
   YANG [RFC7950] and CBOR [RFC7049].

4.1.  The 'leaf' Data Node

   Leafs MUST be encoded based on the encoding rules specified in
   Section 5.

4.2.  The 'container' Data Node

   Collections such as containers, list instances, notifications, RPC
   inputs, RPC outputs, action inputs and action outputs MUST be encoded
   using a CBOR map data item (major type 5).  A map is comprised of
   pairs of data items, with each data item consisting of a key and a
   value.  Each key within the CBOR map is set to a data node
   identifier, each value is set to the value of this data node instance
   according to the instance datatype.

   This specification supports two type of CBOR keys; SID as defined in
   Section 2.1 encoded as deltas and member names as defined in
   [RFC7951] encoded using CBOR text strings.  The use of CBOR byte
   strings for keys is reserved for future extensions.




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4.2.1.  SIDs as keys

   Keys implemented using SIDs MUST be encoded using a CBOR unsigned
   integer (major type 0) or CBOR negative integer (major type 1),
   depending on the actual value.  Keys are represented as the delta of
   the associated SID, delta values are computed as follows:

   o  The delta value is equal to the SID of the current schema node
      minus the SID of the parent schema node.  When no parent exists in
      the context of use of this container, the delta is set to the SID
      of the current schema node (i.e., a parent with SID equal to zero
      is assumed).

   o  Delta values may result in a negative number, clients and servers
      MUST support both unsigned and negative deltas.

   The following example shows the encoding of a 'system-state'
   container instance with a single child, a clock container.  The clock
   container container has two children, a 'current-datetime' leaf and a
   'boot-datetime' leaf.

   Definition example from [RFC7317]:

   typedef date-and-time {
     type string {
       pattern '\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[\+\-]
                \d{2}:\d{2})';
     }
   }

   container system-state {

     container clock {
       leaf current-datetime {
         type date-and-time;
       }

       leaf boot-datetime {
         type date-and-time;
       }
     }
   }

   For this first representation, we assume that parent SID of the root
   container (i.e. 'system-state') is not available to the serializer.
   In this case, root data nodes are encoded using absolute SIDs.

   CBOR diagnostic notation:



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   {
     1717 : {                             / clock  (SID 1717) /
       +2 : "2015-10-02T14:47:24Z-05:00", / current-datetime (SID 1719)/
       +1 : "2015-09-15T09:12:58Z-05:00"  / boot-datetime (SID 1718) /
     }
   }

   CBOR encoding:

   a1                                     # map(1)
      19 06b5                             # unsigned(1717)
      a2                                  # map(2)
         02                               # unsigned(2)
         78 1a                            # text(26)
         323031352d31302d30325431343a34373a32345a2d30353a3030
         01                               # unsigned(1)
         78 1a                            # text(26)
         323031352d30392d31355430393a31323a35385a2d30353a3030

   On the other hand, if the serializer is aware of the parent SID, 1716
   in the case 'system-state' container, root data nodes are encoded
   using deltas.

   CBOR diagnostic notation:

   {
     +1 : {                               / clock  (SID 1717) /
       +2 : "2015-10-02T14:47:24Z-05:00", / current-datetime (SID 1719)/
       +1 : "2015-09-15T09:12:58Z-05:00"  / boot-datetime (SID 1718) /
     }
   }

   CBOR encoding:

   a1                                     # map(1)
      01                                   # unsigned(1)
      a2                                  # map(2)
         02                               # unsigned(2)
         78 1a                            # text(26)
         323031352d31302d30325431343a34373a32345a2d30353a3030
         01                               # unsigned(1)
         78 1a                            # text(26)
         323031352d30392d31355430393a31323a35385a2d30353a3030








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4.2.2.  Member names as keys

   Keys implemented using member names MUST be encoded using a CBOR text
   string data item (major type 3).  A namespace-qualified member name
   MUST be used for all members of a top-level collection, and then also
   whenever the namespaces of the schema node and its parent are
   different.  In all other cases, the simple form of the member name
   MUST be used.  Names and namespaces are defined in [RFC7951] section
   4.

   The following example shows the encoding of a 'system' container
   instance using names.  This example is described in Section 4.2.1.

   CBOR diagnostic notation:

   {
     "ietf-system:clock" : {
       "current-datetime" : "2015-10-02T14:47:24Z-05:00",
       "boot-datetime" : "2015-09-15T09:12:58Z-05:00"
     }
   }

   CBOR encoding:

   a1                                          # map(1)
      71                                       # text(17)
         696574662d73797374656d3a636c6f636b    # "ietf-system:clock"
      a2                                       # map(2)
         70                                    # text(16)
            63757272656e742d6461746574696d65   # "current-datetime"
         78 1a                                 # text(26)
            323031352d31302d30325431343a34373a32345a2d30353a3030
         6d                                    # text(13)
            626f6f742d6461746574696d65         # "boot-datetime"
         78 1a                                 # text(26)
            323031352d30392d31355430393a31323a35385a2d30353a3030

4.3.  The 'leaf-list' Data Node

   A leaf-list MUST be encoded using a CBOR array data item (major type
   4).  Each entry of this array MUST be encoded using the rules defined
   by the YANG type specified.

   The following example shows the encoding a 'search' leaf-list
   instance containing the two entries, "ietf.org" and "ieee.org".

   Definition example [RFC7317]:




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   typedef domain-name {
     type string {
       length "1..253";
       pattern '((([a-zA-Z0-9_]([a-zA-Z0-9\-_]){0,61})?[a-zA-Z0-9].)
                *([a-zA-Z0-9_]([a-zA-Z0-9\-_]){0,61})?[a-zA-Z0-9]\.?
                )|\.';
     }
   }

   leaf-list search {
     type domain-name;
     ordered-by user;
   }

   CBOR diagnostic notation: [ "ietf.org", "ieee.org" ]

   CBOR encoding: 82 68 696574662e6f7267 68 696565652e6f7267

4.4.  The 'list' Data Node

   A list MUST be encoded using a CBOR array data item (major type 4).
   Each list instance within this CBOR array is encoded using a CBOR map
   data item (major type 5) based on the same rules as a YANG container
   as defined in Section 4.2.

4.4.1.  SIDs as keys

   The following example show the encoding of a 'server' list instance
   using SIDs.  It is important to note that the protocol or method
   using this mapping may carry a parent SID or may have the knowledge
   of this parent SID based on its context.  In these cases, delta
   encoding can be performed based on this parent SID which minimizes
   the size of the encoded data.

   Definition example from [RFC7317]:
















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   list server {
     key name;

     leaf name {
       type string;
     }
     choice transport {
       case udp {
         container udp {
           leaf address {
             type host;
             mandatory true;
           }
           leaf port {
             type port-number;
           }
         }
       }
     }
     leaf association-type {
       type enumeration {
         enum server;
         enum peer;
         enum pool;
       }
       default server;
     }
     leaf iburst {
       type boolean;
       default false;
     }
     leaf prefer {
       type boolean;
       default false;
     }
   }

   CBOR diagnostic notation:













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   [
     {
       1755 : "NRC TIC server",          / name (SID 1755) /
       1757 : {                          / udp (SID 1757) /
         +1 : "tic.nrc.ca",              / address (SID 1758) /
         +2 : 123                        / port (SID 1759) /
       },
       1753 : 0,                         / association-type (SID 1753) /
       1754 : false,                     / iburst (SID 1754) /
       1756 : true                       / prefer (SID 1756) /
     },
     {
       1755 : "NRC TAC server",          / name (SID 1755) /
       1757 : {                          / udp (SID 1757) /
         +1 : "tac.nrc.ca"               / address (SID 1758) /
       }
     }
   ]

   CBOR encoding:

   82                                    # array(2)
      a5                                 # map(5)
         19 06db                         # unsigned(1755)
         6e                              # text(14)
            4e52432054494320736572766572 # "NRC TIC server"
         19 06dd                         # unsigned(1757)
         a2                              # map(2)
            01                           # unsigned(1)
            6a                           # text(10)
               7469632e6e72632e6361      # "tic.nrc.ca"
            02                           # unsigned(2)
            18 7b                        # unsigned(123)
         19 06d9                         # unsigned(1753)
         00                              # unsigned(0)
         19 06da                         # unsigned(1754)
         f4                              # primitive(20)
         19 06dc                         # unsigned(1756)
         f5                              # primitive(21)
      a2                                 # map(2)
         19 06db                         # unsigned(1755)
         6e                              # text(14)
            4e52432054414320736572766572 # "NRC TAC server"
         19 06dd                         # unsigned(1757)
         a1                              # map(1)
            01                           # unsigned(1)
            6a                           # text(10)
               7461632e6e72632e6361      # "tac.nrc.ca"



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4.4.2.  Member names as keys

   The following example shows the encoding of a 'server' list instance
   using names.  This example is described in Section 4.4.1.

   CBOR diagnostic notation:

   [
     {
       "ietf-system:name" : "NRC TIC server",
       "ietf-system:udp" : {
         "address" : "tic.nrc.ca",
         "port" : 123
       },
       "ietf-system:association-type" : 0,
       "ietf-system:iburst" : false,
       "ietf-system:prefer" : true
     },
     {
       "ietf-system:name" : "NRC TAC server",
       "ietf-system:udp" : {
         "address" : "tac.nrc.ca"
       }
     }
   ]

   CBOR encoding:
























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   82                                            # array(2)
      a5                                         # map(5)
         70                                      # text(16)
            696574662d73797374656d3a6e616d65     # "ietf-system:name"
         6e                                      # text(14)
            4e52432054494320736572766572         # "NRC TIC server"
         6f                                      # text(15)
            696574662d73797374656d3a756470       # "ietf-system:udp"
         a2                                      # map(2)
            67                                   # text(7)
               61646472657373                    # "address"
            6a                                   # text(10)
               7469632e6e72632e6361              # "tic.nrc.ca"
            64                                   # text(4)
               706f7274                          # "port"
            18 7b                                # unsigned(123)
         78 1c                                   # text(28)
            696574662d73797374656d3a6173736f63696174696f6e2d74797065
         00                                      # unsigned(0)
         72                                      # text(18)
            696574662d73797374656d3a696275727374 # "ietf-system:iburst"
         f4                                      # primitive(20)
         72                                      # text(18)
            696574662d73797374656d3a707265666572 # "ietf-system:prefer"
         f5                                      # primitive(21)
      a2                                         # map(2)
         70                                      # text(16)
            696574662d73797374656d3a6e616d65     # "ietf-system:name"
         6e                                      # text(14)
            4e52432054414320736572766572         # "NRC TAC server"
         6f                                      # text(15)
            696574662d73797374656d3a756470       # "ietf-system:udp"
         a1                                      # map(1)
            67                                   # text(7)
               61646472657373                    # "address"
            6a                                   # text(10)
               7461632e6e72632e6361              # "tac.nrc.ca"

4.5.  The 'anydata' Data Node

   An anydata serves as a container for an arbitrary set of schema nodes
   that otherwise appear as normal YANG-modeled data.  An anydata
   instance is encoded using the same rules as a container, i.e., CBOR
   map.  The requirement that anydata content can be modeled by YANG
   implies the following:

   o  Keys of any inner data nodes MUST be set to valid deltas or member
      names.



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   o  The CBOR array MUST contain either unique scalar values (as a
      leaf-list, see Section 4.3), or maps (as a list, see Section 4.4).

   o  Values MUST follow the encoding rules of one of the datatypes
      listed in Section 5.

   The following example shows a possible use of anydata.  In this
   example, an anydata is used to define a data node containing a
   notification event, this data node can be part of a YANG list to
   create an event logger.

   Definition example:

   anydata event;

   This example also assumes the assistance of the following
   notification.

   module example-port {
     ...

     notification example-port-fault {  # SID 2600
       leaf port-name {                 # SID 2601
         type string;
       }
       leaf port-fault {                # SID 2601
         type string;
       }
     }
   }

   CBOR diagnostic notation:

   {
     2601 : "0/4/21",       / port-name /
     2602 : "Open pin 2"    / port-fault /
   }

   CBOR encoding:

   a2                         # map(2)
      19 0a29                 # unsigned(2601)
      66                      # text(6)
         302f342f3231         # "0/4/21"
      19 0a2a                 # unsigned(2602)
      6a                      # text(10)
         4f70656e2070696e2032 # "Open pin 2"




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4.6.  The 'anyxml' Data Node

   An anyxml schema node is used to serialize an arbitrary CBOR content,
   i.e., its value can be any CBOR binary object. anyxml value may
   contain CBOR data items tagged with one of the tag listed in
   Section 7.1, these tags shall be supported.

   The following example shows a valid CBOR encoded instance.

   Definition example from [RFC7951]:

   anyxml bar;

   CBOR diagnostic notation: [true, null, true]

   CBOR encoding: 83 f5 f6 f5

5.  Representing YANG Data Types in CBOR

   The CBOR encoding of an instance of a leaf or leaf-list data node
   depends on the built-in type of that data node.  The following sub-
   section defined the CBOR encoding of each built-in type supported by
   YANG as listed in [RFC7950] section 4.2.4.  Each subsection shows an
   example value assigned to a data node instance of the discussed
   built-in type.

5.1.  The unsigned integer Types

   Leafs of type uint8, uint16, uint32 and uint64 MUST be encoded using
   a CBOR unsigned integer data item (major type 0).

   The following example shows the encoding of a 'mtu' leaf instance set
   to 1280 bytes.

   Definition example from [RFC7277]:

   leaf mtu {
     type uint16 {
       range "68..max";
     }
   }

   CBOR diagnostic notation: 1280

   CBOR encoding: 19 0500






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5.2.  The integer Types

   Leafs of type int8, int16, int32 and int64 MUST be encoded using
   either CBOR unsigned integer (major type 0) or CBOR negative integer
   (major type 1), depending on the actual value.

   The following example shows the encoding of a 'timezone-utc-offset'
   leaf instance set to -300 minutes.

   Definition example from [RFC7317]:

   leaf timezone-utc-offset {
     type int16 {
       range "-1500 .. 1500";
     }
   }

   CBOR diagnostic notation: -300

   CBOR encoding: 39 012b

5.3.  The 'decimal64' Type

   Leafs of type decimal64 MUST be encoded using a decimal fraction as
   defined in [RFC7049] section 2.4.3.

   The following example shows the encoding of a 'my-decimal' leaf
   instance set to 2.57.

   Definition example from [RFC7317]:

   leaf my-decimal {
     type decimal64 {
       fraction-digits 2;
       range "1 .. 3.14 | 10 | 20..max";
     }
   }

   CBOR diagnostic notation: 4([-2, 257])

   CBOR encoding: c4 82 21 19 0101

5.4.  The 'string' Type

   Leafs of type string MUST be encoded using a CBOR text string data
   item (major type 3).





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   The following example shows the encoding of a 'name' leaf instance
   set to "eth0".

   Definition example from [RFC7223]:

   leaf name {
     type string;
   }

   CBOR diagnostic notation: "eth0"

   CBOR encoding: 64 65746830

5.5.  The 'boolean' Type

   Leafs of type boolean MUST be encoded using a CBOR true (major type
   7, additional information 21) or false data item (major type 7,
   additional information 20).

   The following example shows the encoding of an 'enabled' leaf
   instance set to 'true'.

   Definition example from [RFC7317]:

   leaf enabled {
     type boolean;
   }

   CBOR diagnostic notation: true

   CBOR encoding: f5

5.6.  The 'enumeration' Type

   Leafs of type enumeration MUST be encoded using a CBOR unsigned
   integer (major type 0) or CBOR negative integer (major type 1),
   depending on the actual value.  Enumeration values are either
   explicitly assigned using the YANG statement 'value' or automatically
   assigned based on the algorithm defined in [RFC7950] section 9.6.4.2.

   The following example shows the encoding of an 'oper-status' leaf
   instance set to 'testing'.

   Definition example from [RFC7317]:







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   leaf oper-status {
     type enumeration {
       enum up { value 1; }
       enum down { value 2; }
       enum testing { value 3; }
       enum unknown { value 4; }
       enum dormant { value 5; }
       enum not-present { value 6; }
       enum lower-layer-down { value 7; }
     }
   }

   CBOR diagnostic notation: 3

   CBOR encoding: 03

5.7.  The 'bits' Type

   Leafs of type bits MUST be encoded using a CBOR byte string data item
   (major type 2).  Bits position are either explicitly assigned using
   the YANG statement 'position' or automatically assigned based on the
   algorithm defined in [RFC7950] section 9.7.4.2.

   Bits position 0 to 7 are assigned to the first byte within the byte
   string, bits 8 to 15 to the second byte, and subsequent bytes are
   assigned similarly.  Within each byte, bits are assigned from least
   to most significant.

   The following example shows the encoding of a 'mybits' leaf instance
   with the 'disable-nagle' and '10-Mb-only' flags set.

   Definition example from [RFC7950]:

   leaf mybits {
     type bits {
       bit disable-nagle {
         position 0;
       }
       bit auto-sense-speed {
         position 1;
       }
       bit 10-Mb-only {
         position 2;
       }
     }
   }

   CBOR diagnostic notation: h'05'



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   CBOR encoding: 41 05

5.8.  The 'binary' Type

   Leafs of type binary MUST be encoded using a CBOR byte string data
   item (major type 2).

   The following example shows the encoding of an 'aes128-key' leaf
   instance set to 0x1f1ce6a3f42660d888d92a4d8030476e.

   Definition example:

   leaf aes128-key {
     type binary {
       length 16;
     }
   }

   CBOR diagnostic notation: h'1f1ce6a3f42660d888d92a4d8030476e'

   CBOR encoding: 50 1f1ce6a3f42660d888d92a4d8030476e

5.9.  The 'leafref' Type

   Leafs of type leafref MUST be encoded using the rules of the schema
   node referenced by the 'path' YANG statement.

   The following example shows the encoding of an 'interface-state-ref'
   leaf instance set to "eth1".

   Definition example from [RFC7223]:




















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   typedef interface-state-ref {
     type leafref {
       path "/interfaces-state/interface/name";
     }
   }

   container interfaces-state {
     list interface {
       key "name";
       leaf name {
         type string;
       }
       leaf-list higher-layer-if {
         type interface-state-ref;
       }
     }
   }

   CBOR diagnostic notation: "eth1"

   CBOR encoding: 64 65746831

5.10.  The 'identityref' Type

   This specification supports two approaches for encoding identityref,
   a YANG Schema Item iDentifier (SID) as defined in Section 2.1 or a
   name as defined in [RFC7951] section 6.8.

5.10.1.  SIDs as identityref

   When schema nodes of type identityref are implemented using SIDs,
   they MUST be encoded using a CBOR unsigned integer data item (major
   type 0).  (Note that no delta mechanism is employed for SIDs as
   identityref.)

   The following example shows the encoding of a 'type' leaf instance
   set to the value 'iana-if-type:ethernetCsmacd' (SID 1180).

   Definition example from [RFC7317]:












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   identity interface-type {
   }

   identity iana-interface-type {
     base interface-type;
   }

   identity ethernetCsmacd {
     base iana-interface-type;
   }

   leaf type {
     type identityref {
       base interface-type;
     }
   }

   CBOR diagnostic notation: 1180

   CBOR encoding: 19 049c

5.10.2.  Name as identityref

   Alternatively, an identityref may be encoded using a name as defined
   in [RFC7951] section 6.8.  When names are used, identityref MUST be
   encoded using a CBOR text string data item (major type 3).  If the
   identity is defined in another module than the leaf node containing
   the identityref value, the namespace-qualified form MUST be used.
   Otherwise, both the simple and namespace-qualified forms are
   permitted.  Names and namespaces are defined in [RFC7951] section 4.

   The following example shows the encoding of the identity 'iana-if-
   type:ethernetCsmacd' using its name.  This example is described in
   Section 5.10.1.

   CBOR diagnostic notation: "iana-if-type:ethernetCsmacd"

   CBOR encoding: 78 1b
   69616e612d69662d747970653a65746865726e657443736d616364

5.11.  The 'empty' Type

   Leafs of type empty MUST be encoded using the CBOR null value (major
   type 7, additional information 22).

   The following example shows the encoding of a 'is-router' leaf
   instance when present.




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   Definition example from [RFC7277]:

   leaf is-router {
     type empty;
   }

   CBOR diagnostic notation: null

   CBOR encoding: f6

5.12.  The 'union' Type

   Leafs of type union MUST be encoded using the rules associated with
   one of the types listed.  When used in a union, the following YANG
   datatypes are prefixed by CBOR tag to avoid confusion between
   different YANG datatypes encoded using the same CBOR major type.

   o  bits

   o  enumeration

   o  identityref

   o  instance-identifier

   See Section 7.1 for more information about these CBOR tags.

   The following example shows the encoding of an 'ip-address' leaf
   instance when set to "2001:db8:a0b:12f0::1".

   Definition example from [RFC7317]:




















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   typedef ipv4-address {
     type string {
     pattern '(([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\.){3}
              ([0-9][1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])(%[\p{N}
              \p{L}]+)?';
     }
   }

   typedef ipv6-address {
     type string {
       pattern '((:|[0-9a-fA-F]{0,4}):)([0-9a-fA-F]{0,4}:){0,5}((([0-9a
                -fA-F]{0,4}:)?(:|[0-9a-fA-F]{0,4}))|(((25[0-5]|2[0-4][0
                -9]|[01]?[0-9]?[0-9])\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0
                -9]?[0-9])))(%[\p{N}\p{L}]+)?';
       pattern '(([^:]+:){6}(([^:]+:[^:]+)|(.*\..*)))|((([^:]+:)*[^:]+)
                ?::(([^:]+:)*[^:]+)?)(%.+)?';
     }
   }

   typedef ip-address {
     type union {
       type ipv4-address;
       type ipv6-address;
     }
   }

   leaf address {
     type inet:ip-address;
   }

   CBOR diagnostic notation: "2001:db8:a0b:12f0::1"

   CBOR encoding: 74 323030313a6462383a6130623a313266303a3a31

5.13.  The 'instance-identifier' Type

   This specification supports two approaches for encoding an instance-
   identifier, one based on YANG Schema Item iDentifier (SID) as defined
   in Section 2.1 and one based on names as defined in [RFC7951] section
   6.11.

5.13.1.  SIDs as instance-identifier

   SIDs uniquely identify a data node.  In the case of a single instance
   data node, a data node defined at the root of a YANG module or
   submodule or data nodes defined within a container, the SID is
   sufficient to identify this instance.




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   In the case of a data node member of a YANG list, a SID is combined
   with the list key(s) to identify each instance within the YANG
   list(s).

   Single instance data nodes MUST be encoded using a CBOR unsigned
   integer data item (major type 0) and set to the targeted data node
   SID.

   Data nodes member of a YANG list MUST be encoded using a CBOR array
   data item (major type 4) containing the following entries:

   o  The first entry MUST be encoded as a CBOR unsigned integer data
      item (major type 0) and set to the targeted data node SID.

   o  The following entries MUST contain the value of each key required
      to identify the instance of the targeted data node.  These keys
      MUST be ordered as defined in the 'key' YANG statement, starting
      from top level list, and follow by each of the subordinate
      list(s).

   *First example:*

   The following example shows the encoding of a leaf instance of type
   instance-identifier which identifies the data node "/system/contact"
   (SID 1737).

   Definition example from [RFC7317]:

   container system {

     leaf contact {
       type string;
     }

     leaf hostname {
       type inet:domain-name;
     }
   }

   CBOR diagnostic notation: 1737

   CBOR encoding: 19 06c9

   *Second example:*

   The following example shows the encoding of a leaf instance of type
   instance-identifier which identify the data node instance




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   "/system/authentication/user/authorized-key/key-data" (SID 1730) for
   user name "bob" and authorized-key "admin".

   Definition example from [RFC7317]:

   list user {
     key name;

     leaf name {
       type string;
     }
     leaf password {
       type ianach:crypt-hash;
     }

     list authorized-key {
       key name;

       leaf name {
         type string;
       }
       leaf algorithm {
         type string;
       }
       leaf key-data {
         type binary;
     }
   }

   CBOR diagnostic notation: [1730, "bob", "admin"]

   CBOR encoding:

   83                      # array(3)
      19 06c2              # unsigned(1730)
      63                   # text(3)
         626f62            # "bob"
      65                   # text(5)
         61646d696e        # "admin"

   *Third example:*

   The following example shows the encoding of a leaf instance of type
   instance-identifier which identify the list instance
   "/system/authentication/user" (SID 1726) corresponding to the user
   name "jack".

   CBOR diagnostic notation: [1726, "jack"]



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   CBOR encoding:

   82                      # array(2)
      19 06be              # unsigned(1726)
      64                   # text(4)
         6a61636b          # "jack"

5.13.2.  Names as instance-identifier

   The use of names as instance-identifier is defined in [RFC7951]
   section 6.11.  The resulting xpath MUST be encoded using a CBOR text
   string data item (major type 3).

   *First example:*

   This example is described in Section 5.13.1.

   CBOR diagnostic notation: "/ietf-system:system/contact"

   CBOR encoding:

   78 1c 2f20696574662d73797374656d3a73797374656d2f636f6e74616374

   *Second example:*

   This example is described in Section 5.13.1.

   CBOR diagnostic notation:

   "/ietf-system:system/authentication/user[name='bob']/authorized-key
   [name='admin']/key-data"

   CBOR encoding:

   78 59
      2f696574662d73797374656d3a73797374656d2f61757468656e74696361
      74696f6e2f757365725b6e616d653d27626f62275d2f617574686f72697a
      65642d6b65795b6e616d653d2761646d696e275d2f6b65792d64617461

   *Third example:*

   This example is described in Section 5.13.1.

   CBOR diagnostic notation:

   "/ietf-system:system/authentication/user[name='bob']"

   CBOR encoding:



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   78 33
      2f696574662d73797374656d3a73797374656d2f61757468656e74696361
      74696f6e2f757365725b6e616d653d27626f62275d

6.  Security Considerations

   The security considerations of [RFC7049] and [RFC7950] apply.

   This document defines an alternative encoding for data modeled in the
   YANG data modeling language.  As such, this encoding does not
   contribute any new security issues in addition of those identified
   for the specific protocol or context for which it is used.

   To minimize security risks, software on the receiving side SHOULD
   reject all messages that do not comply to the rules of this document
   and reply with an appropriate error message to the sender.

7.  IANA Considerations

7.1.  Tags Registry

   This specification requires the assignment of CBOR tags for the
   following YANG datatypes.  These tags are added to the Tags Registry
   as defined in section 7.2 of [RFC7049].

   +-----+---------------------+---------------------------+-----------+
   | Tag | Data Item           | Semantics                 | Reference |
   +-----+---------------------+---------------------------+-----------+
   | 40  | bits                | YANG bits datatype        | RFC XXXX  |
   | 41  | enumeration         | YANG enumeration datatype | RFC XXXX  |
   | 42  | identityref         | YANG identityref datatype | RFC XXXX  |
   | 43  | instance-identifier | YANG instance-identifier  | RFC XXXX  |
   |     |                     | datatype                  |           |
   +-----+---------------------+---------------------------+-----------+

   // RFC Ed.: update Tag values using allocated tags if needed and
   remove this note // RFC Ed.: replace XXXX with RFC number and remove
   this note

8.  Acknowledgments

   This document has been largely inspired by the extensive works done
   by Andy Bierman and Peter van der Stok on [I-D.ietf-core-comi].
   [RFC7951] has also been a critical input to this work.  The authors
   would like to thank the authors and contributors to these two drafts.

   The authors would also like to acknowledge the review, feedback, and
   comments from Ladislav Lhotka and Juergen Schoenwaelder.



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9.  References

9.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
              October 2013, <http://www.rfc-editor.org/info/rfc7049>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <http://www.rfc-editor.org/info/rfc7950>.

9.2.  Informative References

   [I-D.ietf-core-comi]
              Veillette, M., Stok, P., Pelov, A., and A. Bierman, "CoAP
              Management Interface", draft-ietf-core-comi-01 (work in
              progress), July 2017.

   [I-D.ietf-core-sid]
              Veillette, M., Pelov, A., Turner, R., Minaburo, A., and A.
              Somaraju, "YANG Schema Item iDentifier (SID)", draft-ietf-
              core-sid-01 (work in progress), May 2017.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <http://www.rfc-editor.org/info/rfc7159>.

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
              <http://www.rfc-editor.org/info/rfc7223>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <http://www.rfc-editor.org/info/rfc7228>.





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   [RFC7277]  Bjorklund, M., "A YANG Data Model for IP Management",
              RFC 7277, DOI 10.17487/RFC7277, June 2014,
              <http://www.rfc-editor.org/info/rfc7277>.

   [RFC7317]  Bierman, A. and M. Bjorklund, "A YANG Data Model for
              System Management", RFC 7317, DOI 10.17487/RFC7317, August
              2014, <http://www.rfc-editor.org/info/rfc7317>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <http://www.rfc-editor.org/info/rfc7951>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <http://www.rfc-editor.org/info/rfc8040>.

Authors' Addresses

   Michel Veillette (editor)
   Trilliant Networks Inc.
   610 Rue du Luxembourg
   Granby, Quebec  J2J 2V2
   Canada

   Phone: +14503750556
   Email: michel.veillette@trilliantinc.com


   Alexander Pelov (editor)
   Acklio
   2bis rue de la Chataigneraie
   Cesson-Sevigne, Bretagne  35510
   France

   Email: a@ackl.io


   Abhinav Somaraju
   Tridonic GmbH & Co KG
   Farbergasse 15
   Dornbirn, Vorarlberg  6850
   Austria

   Phone: +43664808926169
   Email: abhinav.somaraju@tridonic.com






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Internet-Draft   CBOR Encoding of Data Modeled with YANG     August 2017


   Randy Turner
   Landis+Gyr
   30000 Mill Creek Ave
   Suite 100
   Alpharetta, GA  30022
   US

   Phone: ++16782581292
   Email: randy.turner@landisgyr.com
   URI:   http://www.landisgyr.com/


   Ana Minaburo
   Acklio
   2bis rue de la chataigneraie
   Cesson-Sevigne, Bretagne  35510
   France

   Email: ana@ackl.io
































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