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CoRE                                                     P. van der Stok
Internet-Draft                                                consultant
Intended status: Standards Track                              A. Bierman
Expires: July 22, 2017                                         YumaWorks
                                                            M. Veillette
                                                 Trilliant Networks Inc.
                                                                A. Pelov
                                                                  Acklio
                                                        January 18, 2017


                       CoAP Management Interface
                     draft-vanderstok-core-comi-11

Abstract

   This document describes a network management interface for
   constrained devices and networks, called CoAP Management Interface
   (CoMI).  The Constrained Application Protocol (CoAP) is used to
   access data resources specified in YANG, or SMIv2 converted to YANG.
   CoMI uses the YANG to CBOR mapping and converts YANG identifier
   strings to numeric identifiers for payload size reduction.  CoMI
   extends the set of YANG based protocols, NETCONF and RESTCONF, with
   the capability to manage constrained devices and networks.

Note

   Discussion and suggestions for improvement are requested, and should
   be sent to core@ietf.org.

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 July 22, 2017.





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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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  CoMI Architecture . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Major differences between RESTCONF and CoMI . . . . . . .   7
     2.2.  Compression of YANG identifiers . . . . . . . . . . . . .   7
   3.  Example syntax  . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  CoAP Interface  . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  /c Function Set . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Using the 'k' query parameter . . . . . . . . . . . . . .  10
     5.2.  Data Retrieval  . . . . . . . . . . . . . . . . . . . . .  11
       5.2.1.  Using the 'c' query parameter . . . . . . . . . . . .  12
       5.2.2.  Using the 'd' query parameter . . . . . . . . . . . .  12
       5.2.3.  GET . . . . . . . . . . . . . . . . . . . . . . . . .  13
       5.2.4.  FETCH . . . . . . . . . . . . . . . . . . . . . . . .  15
     5.3.  Data Editing  . . . . . . . . . . . . . . . . . . . . . .  16
       5.3.1.  Data Ordering . . . . . . . . . . . . . . . . . . . .  16
       5.3.2.  POST  . . . . . . . . . . . . . . . . . . . . . . . .  16
       5.3.3.  PUT . . . . . . . . . . . . . . . . . . . . . . . . .  17
       5.3.4.  iPATCH  . . . . . . . . . . . . . . . . . . . . . . .  18
       5.3.5.  DELETE  . . . . . . . . . . . . . . . . . . . . . . .  19
     5.4.  Full Data Store access  . . . . . . . . . . . . . . . . .  19
       5.4.1.  Full Data Store examples  . . . . . . . . . . . . . .  20
     5.5.  Notify functions  . . . . . . . . . . . . . . . . . . . .  21
       5.5.1.  Notify Examples . . . . . . . . . . . . . . . . . . .  22
     5.6.  RPC statements  . . . . . . . . . . . . . . . . . . . . .  22
       5.6.1.  RPC Example . . . . . . . . . . . . . . . . . . . . .  23
   6.  Access to MIB Data  . . . . . . . . . . . . . . . . . . . . .  23
   7.  Use of Block  . . . . . . . . . . . . . . . . . . . . . . . .  25
   8.  Resource Discovery  . . . . . . . . . . . . . . . . . . . . .  25
   9.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .  27
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  28



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   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  29
   13. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .  30
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  33
     14.2.  Informative References . . . . . . . . . . . . . . . . .  35
   Appendix A.  YANG example specifications  . . . . . . . . . . . .  37
     A.1.  ietf-system . . . . . . . . . . . . . . . . . . . . . . .  37
     A.2.  server list . . . . . . . . . . . . . . . . . . . . . . .  38
     A.3.  interfaces  . . . . . . . . . . . . . . . . . . . . . . .  39
     A.4.  Example-port  . . . . . . . . . . . . . . . . . . . . . .  40
     A.5.  IP-MIB  . . . . . . . . . . . . . . . . . . . . . . . . .  41
   Appendix B.  Comparison with LWM2M  . . . . . . . . . . . . . . .  43
     B.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .  43
     B.2.  Defining Management Resources . . . . . . . . . . . . . .  44
     B.3.  Identifying Management Resources  . . . . . . . . . . . .  44
     B.4.  Encoding of Management Resources  . . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45

1.  Introduction

   The Constrained Application Protocol (CoAP) [RFC7252] is designed for
   Machine to Machine (M2M) applications such as smart energy and
   building control.  Constrained devices need to be managed in an
   automatic fashion to handle the large quantities of devices that are
   expected in future installations.  The messages between devices need
   to be as small and infrequent as possible.  The implementation
   complexity and runtime resources need to be as small as possible.

   This draft describes the CoAP Management Interface which uses CoAP
   methods to access structured data defined in YANG [RFC7950].  This
   draft is complementary to the draft [I-D.ietf-netconf-restconf] which
   describes a REST-like interface called RESTCONF, which uses HTTP
   methods to access structured data defined in YANG.

   The use of standardized data sets, specified in a standardized
   language such as YANG, promotes interoperability between devices and
   applications from different manufacturers.  A large amount of
   Management Information Base (MIB) [mibreg] specifications already
   exists for monitoring purposes.  This data can be accessed in
   RESTCONF or CoMI if the server converts the SMIv2 modules to YANG,
   using the mapping rules defined in [RFC6643].

   CoMI and RESTCONF are intended to work in a stateless client-server
   fashion.  They use a single round-trip to complete a single editing
   transaction, where NETCONF needs up to 10 round trips.





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   To promote small packets, CoMI uses a YANG to CBOR mapping
   [I-D.ietf-core-yang-cbor] and numeric identifiers [I-D.ietf-core-sid]
   to minimize CBOR payloads and URI length.

1.1.  Terminology

   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].

   Readers of this specification should be familiar with all the terms
   and concepts discussed in [RFC3410], [RFC3416], and [RFC2578].

   The following terms are defined in the NETCONF protocol [RFC6241]:
   client, configuration data, datastore, and server.

   The following terms are defined in the YANG data modelling language
   [RFC7950]: anydata, anyxml, container, data node, key, key leaf,
   leaf, leaf-list, and list.

   The following terms are defined in RESTCONF protocol
   [I-D.ietf-netconf-restconf]: data resource, datastore resource, edit
   operation, query parameter, and target resource.

   The following terms are defined in this document:

   data node instance:  An instance of a data node specified in a YANG
      module present in the server.  The instance is stored in the
      memory of the server.

   Notification instance:  An instance of a schema node of type
      notification, specified in a YANG module present in the server.
      The instance is generated in the server at the occurrence of the
      corresponding event and appended to a stream.

   YANG schema item identifier:  Numeric identifier which replaces the
      name identifying a YANG item (see section 6.2 of [RFC7950])
      (anydata, anyxml, data node, RPC, Action, Notification, Identity,
      Module name, Submodule name, Feature).

   list instance identifier:  Handle used to identify a YANG data node
      that is an instance of a YANG "list" specified with the values of
      the key leaves of the list.

   single instance identifier:  Handle used to identify a specific data
      node which can be instantiated only once.  This includes data
      nodes defined at the root of a YANG module or submodule and data




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      nodes defined within a container.  This excludes data nodes
      defined within a list or any children of these data nodes.

   instance identifier:  List instance identifier or single instance
      identifier.

   data node value:  Value assigned to a data node instance.  Data node
      values are encoded based on the rules defined in section 4 of
      [I-D.ietf-core-yang-cbor].

   set of data node instances:  Represents the payload of CoAP methods
      when a collection is sent or returned.  There are two
      possibilities, dependent on Request context:

      1.  CBOR array of pair(s) <instance identifier, data node value >

      2.  CBOR map of pair(s) <instance identifier, data node value >

      TODO: Reduce to one, if possible

   The following list contains the abbreviations used in this document.

   SID:  YANG Schema Item iDentifier.

2.  CoMI Architecture

   This section describes the CoMI architecture to use CoAP for the
   reading and modifying the content of a datastore used for the
   management of the instrumented node.






















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   +--------------------------------------------------------------+
   |                    SMIv2  specification (2)                  |
   +--------------------------------------------------------------+
                                 \/
   +--------------------------------------------------------------+
   |                    YANG  specification  (1)                  |
   +---------*-----------------------------------------*----------+
             | compilation                             | compilation
             |              security (7)               |
   client   \|/      [===========================]    \|/    Server
   +--------------------+                       +------------------+
   |                    |                       |                  |
   | Request generation +--> CoAP request(3) -->| Request retrieval|
   | answer retrieval   |<-- CoAP response(3)<--| answer generation|
   |       (4)          |                       |       (4)        |
   +--------------------+                       | +---------------+|
                                                | | datastore (5) ||
                                                | +---------------+|
                                                |                  |
                                                |      Variable    |
                                                |Instrumentation(6)|
                                                +------------------+


                   Figure 1: Abstract CoMI architecture

   Figure 1 is a high level representation of the main elements of the
   CoAP management architecture.  A client sends requests as payload in
   packets over the network to a managed constrained node.

   The different numbered components of Figure 1 are discussed according
   to component number.

   (1) YANG specification:  contains a set of named and versioned
      modules.

   (2) SMIv2 specification:  A named module specifies a set of variables
      and "conceptual tables".  There is an algorithm to translate SMIv2
      specifications to YANG specifications.

   (3) CoMI messages:  The CoMI client sends request messages to and
      receives response messages from the CoMI server.

   (4) Retrieval, generation:  The server and client parse the CoMI
      request/response and identify the corresponding instances in the
      datastore based on YANG specification.





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   (5) Datastore:  The store is composed of two parts: Operational state
      and Configuration datastore.  Datastore also supports RPCs and
      event streams.

   (6) Variable instrumentation:  This code depends on implementation of
      drivers and other node specific aspects.

   (7) Security:  The server MUST prevent unauthorized users from
      reading or writing any data resources.  CoMI relies on security
      protocols such as DTLS [RFC6347] to secure CoAP communication.

2.1.  Major differences between RESTCONF and CoMI

   CoMI uses CoAP/UDP as transport protocol and CBOR as payload format
   [I-D.ietf-core-yang-cbor].  RESTCONF uses HTTP/TCP as transport
   protocol and JSON [RFC7159] or XML [XML] as payload formats.  CoMI
   encodes YANG identifier strings as numbers, where RESTCONF does not.

   CoMI uses the methods FETCH and iPATCH, not used by RESTCONF.
   RESTCONF uses the HTTP methods HEAD, and OPTIONS, which are not used
   by CoMI.

   CoMI servers cannot change the order of user-ordered data.  CoMI does
   not support insert-mode (first, last, before, after) and insertion-
   point (before, after) which are supported by RESTCONF.  Many CoAP
   servers will not support date and time functions.  For that reason
   CoMI does not support the start, stop options for events.

   CoMI servers only implement the efficient "trim" mode for default
   values.

   The CoMI servers do not support the following RESTCONF functionality:

   o  The "fields" query parameter to query multiple instances.

   o  The 'filter' query that involves XML parsing, 'content', and
      'depth', query parameters.

2.2.  Compression of YANG identifiers

   In the YANG specification items are identified with a name string.
   In order to significantly reduce the size of identifiers used in
   CoMI, numeric object identifiers are used instead of these strings.
   The specific encoding of the object identifiers is not hard-wired in
   the protocol.

   Examples of object identifier encoding formats are described in
   [I-D.ietf-core-sid].



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3.  Example syntax

   This section presents the notation used for the examples.  The YANG
   specifications that are used throughout this document are shown in
   Appendix A.  The example specifications are taken over from existing
   modules and annotated with SIDs.  The values of the SIDs are taken
   over from [yang-cbor].

   CBOR is used to encode CoMI request- and response- payloads.  The
   CBOR syntax of the YANG payloads is specified in [RFC7049].  The
   payload examples are notated in Diagnostic notation (defined in
   section 6 of [RFC7049]) that can be automatically converted to CBOR.

   A YANG (item identifier, item value) pair is mapped to a CBOR (key,
   value) pair.  The YANG item value is encoded as specified in
   [I-D.ietf-core-yang-cbor].  The YANG item identifier can be a SID
   (single node identifier) or a CBOR array with the structure [SID,
   key1, key2] (list node identifier), where SID is a list identifier
   and the key values specify the list instance.  The YANG item value
   can be any CBOR major type.

   Delta encoding is used for the SIDs.  The notation +n is used when
   the SID has the value PREC+n where PREC is the SID of the parent
   container, or PREC is the SID of the preceding entity in a CBOR
   array.

   In all examples the resource path in the URI is expressed as a SID,
   represented as a base64 number.  SIDs in the payload are represented
   as decimal numbers.

4.  CoAP Interface

   In CoAP a group of links can constitute a Function Set.

   TODO: what will happen to term Function Set ?

   The format of the links is specified in [I-D.ietf-core-interfaces].
   This note specifies a Management Function Set. CoMI end-points that
   implement the CoMI management protocol support at least one
   discoverable management resource of resource type (rt): core.c, with
   path: /c, where c is short-hand for CoMI.  The path root /c is
   recommended but not compulsory (see Section 8).

   The path prefix /c has resources accessible with the following three
   paths:

   /c:  YANG-based data with path "/c" and using CBOR content encoding
      format.  This path represents a datastore resource which contains



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      YANG data resources as its descendant nodes.  The data nodes are
      identified with their SID with format /c/SID.

   /c/mod.uri:  URI identifying the location of the server module
      information, with path "/c/mod.uri" and CBOR content format.  This
      YANG data is encoded with plain identifier strings, not YANG
      encoded values.  An Entity Tag MUST be maintained for this
      resource by the server, which MUST be changed to a new value when
      the set of YANG modules in use by the server changes.

   /c/s:  String identifying the default stream resource to which YANG
      notification instances are appended.  Notification support is
      optional, so this resource will not exist if the server does not
      support any notifications.

   The mapping of YANG data node instances to CoMI resources is as
   follows: A YANG module describes a set of data trees composed of YANG
   data nodes.  Every data node of the YANG modules loaded in the CoMI
   server represents a resource of the datastore container (e.g.
   /c/<sid>

   When multiple instances of a list node exist, instance selection is
   possible as described in Section 5.2.4 and Section 5.2.3.1.

   TODO; reference to fetch and patch content formats.

   The profile of the management function set, with IF=core.c, is shown
   in the table below, following the guidelines of
   [I-D.ietf-core-interfaces]:

   +----------------+-------------+----------------+-------------------+
   | name           | path        | rt             | Data Type         |
   +----------------+-------------+----------------+-------------------+
   | Management     | /c          | core.c         | n/a               |
   |                |             |                |                   |
   | Data           | /c          | core.c.data    | application/cbor  |
   |                |             |                |                   |
   | Module Set URI | /c/mod.uri  | core.c.moduri  | application/cbor  |
   |                |             |                |                   |
   | Events         | /c/s        | core.c.stream  | application/cbor  |
   +----------------+-------------+----------------+-------------------+

5.  /c Function Set

   The /c Function Set provides a CoAP interface to manage YANG servers.

   The methods used by CoMI are:




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   +-----------+-------------------------------------------------------+
   | Operation | Description                                           |
   +-----------+-------------------------------------------------------+
   | GET       | Retrieve the datastore resource or a data resource    |
   |           |                                                       |
   | FETCH     | Retrieve (partial) data resource(s)                   |
   |           |                                                       |
   | POST      | Create a data resource, invoke RPC                    |
   |           |                                                       |
   | PUT       | Create or replace a data resource                     |
   |           |                                                       |
   | iPATCH    | Idem-potently create, replace, and delete data        |
   |           | resource(s) (partially)                               |
   |           |                                                       |
   | DELETE    | Delete a data resource                                |
   +-----------+-------------------------------------------------------+

   There is one query parameters for the GET, PUT, POST, and DELETE
   methods.

         +-----------------+------------------------------------+
         | Query Parameter | Description                        |
         +-----------------+------------------------------------+
         | k               | Select an instance of a list node  |
         +-----------------+------------------------------------+

   This parameter is not used for FETCH and iPATCH, because their
   request payloads support list instance selection.

5.1.  Using the 'k' query parameter

   The "k" (key) parameter specifies the instance of a list node.  The
   SID in the URI is followed by the (?k=key1, key2,..).  Where SID
   identifies a list node, and key1, key2 are the values of the key
   leaves that specify an instance of the list.

   Key values are encoded using the rules defined in the following
   table:













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   +-----------------------+------------------+------------------------+
   | YANG datatype         | Binary           | Text representation    |
   |                       | representation   |                        |
   +-----------------------+------------------+------------------------+
   | uint8,uint16,unit32,  | CBOR unsigned    | int_to_text(number)    |
   | uint64                | integer          |                        |
   |                       |                  |                        |
   | int8, int16,int32,    | CBOR negative    | base64 (CBOR           |
   | int64                 | integer          | representation)        |
   |                       |                  |                        |
   | decimal64             | CBOR decimal     | base64  (CBOR          |
   |                       | fractions        | representation         |
   |                       |                  |                        |
   | string                | CBOR text or     | text                   |
   |                       | string           |                        |
   |                       |                  |                        |
   | boolean               | CBOR false or    | "0" or "1"             |
   |                       | true             |                        |
   |                       |                  |                        |
   | enumeration           | CBOR unsigned    | int_to_text (number)   |
   |                       | integer          |                        |
   |                       |                  |                        |
   | bits                  | CBOR byte string | base64 (CBOR           |
   |                       |                  | representation)        |
   |                       |                  |                        |
   | binary                | CBOR byte string | base64 (binary value)  |
   |                       |                  |                        |
   | identityref           | CBOR unsigned    | int_to_text (number)   |
   |                       | integer          |                        |
   |                       |                  |                        |
   | union                 |                  | base64 (CBOR           |
   |                       |                  | representation)        |
   |                       |                  |                        |
   | List instance         | CBOR unsigned    | base64 (CBOR           |
   | identifier            | integer          | representation)        |
   |                       |                  |                        |
   | List instance         | CBOR array       | Base64 (CBOR           |
   | identifier            |                  | representation)        |
   +-----------------------+------------------+------------------------+

5.2.  Data Retrieval

   One or more data node instances can be retrieved by the client.  The
   operation is mapped to the GET method defined in section 5.8.1 of
   [RFC7252] and to the FETCH method defined in section 2 of
   [I-D.ietf-core-etch].





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   It is possible that the size of the payload is too large to fit in a
   single message.  In the case that management data is bigger than the
   maximum supported payload size, the Block mechanism from [RFC7959] is
   used, as explained in more detail in Section 7.

   CoMI uses the FETCH payload for retrieving a subset of the datastore.

   There are two additional query parameters for the GET and FETCH
   methods.

   +------------+------------------------------------------------------+
   | Query      | Description                                          |
   | Parameter  |                                                      |
   +------------+------------------------------------------------------+
   | c          | Control selection of configuration and non-          |
   |            | configuration data nodes (GET and FETCH)             |
   |            |                                                      |
   | d          | Control retrieval of default values.                 |
   +------------+------------------------------------------------------+

5.2.1.  Using the 'c' query parameter

   The 'c' (content) parameter controls how descendant nodes of the
   requested data nodes will be processed in the reply.

   The allowed values are:

     +-------+------------------------------------------------------+
     | Value | Description                                          |
     +-------+------------------------------------------------------+
     | c     | Return only configuration descendant data nodes      |
     |       |                                                      |
     | n     | Return only non-configuration descendant data nodes  |
     |       |                                                      |
     | a     | Return all descendant data nodes                     |
     +-------+------------------------------------------------------+

   This parameter is only allowed for GET and FETCH methods on datastore
   and data resources.  A 4.00 Bad Request error is returned if used for
   other methods or resource types.

   If this query parameter is not present, the default value is "a".

5.2.2.  Using the 'd' query parameter

   The "d" (with-defaults) parameter controls how the default values of
   the descendant nodes of the requested data nodes will be processed.




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   The allowed values are:

   +-------+-----------------------------------------------------------+
   | Value | Description                                               |
   +-------+-----------------------------------------------------------+
   | a     | All data nodes are reported| Defined as 'report-all' in   |
   |       | section 3.1 of [RFC6243].                                 |
   |       |                                                           |
   | t     | Data nodes set to the YANG default are not reported.      |
   |       | Defined as 'trim' in section 3.2 of [RFC6243].            |
   +-------+-----------------------------------------------------------+

   If the target of a GET or FETCH method is a data node that represents
   a leaf that has a default value, and the leaf has not been given a
   value yet, the server MUST return the leaf.

   If the target of a GET method is a data node that represents a
   container or list that has any child resources with default values,
   for the child resources that have not been given value yet, the
   server MUST not return the child resource if this query parameter is
   set to 't' and MUST return the child resource if this query parameter
   is set to 'a'.

   If this query parameter is not present, the default value is 't'.

5.2.3.  GET

   A request to read the values of a data node instance is sent with a
   confirmable CoAP GET message.  A single instance identifier is
   specified in the URI path prefixed with /c.

   FORMAT:
       GET /c/<instance identifier>

       2.05 Content (Content-Format: application/cbor)
       <data node value>

   The returned payload is composed of all the children associated with
   the specified data node instance.

   The instance identifier is a SID or a SID followed by the "k" query
   parameter.

5.2.3.1.  GET Examples

   Using for example the current-datetime leaf from Appendix A.1, a
   request is sent to retrieve the value of system-state/clock/current-
   datetime specified in container system-state.  The ID of system-



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   state/clock/current-datetime is 1719, encoded in base64 this yields
   a3.  The answer to the request returns a <value>, transported as a
   single CBOR string item.


   REQ: GET example.com/c/a3

   RES: 2.05 Content (Content-Format: application/cbor)
   "2014-10-26T12:16:31Z"

   For example, the GET of the clock node (ID = 1717; base64: a1), sent
   by the client, results in the following returned value sent by the
   server, transported as a CBOR map containing 2 pairs:


   REQ: GET example.com/c/a1

   RES: 2.05 Content (Content-Format: application/cbor)
   {
         +2 : "2014-10-26T12:16:51Z",   / ID 1719 /
         +1 : "2014-10-21T03:00:00Z"    / ID 1718 /
   }

   A "list" node can have multiple instances.  Accordingly, the returned
   payload of GET is composed of all the instances associated with the
   selected list node.

   For example, look at the example in Appendix A.3.  The GET of the
   /interfaces/interface/ (with identifier 1533, base64: X9) results in
   the following returned payload, transported as a CBOR array with 2
   elements.




















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   REQ: GET example.com/c/X9

   RES: 2.05 Content (Content-Format: application/cbor)
   [
    {+4 : "eth0",                / name  (ID 1537) /
     +1 : "Ethernet adaptor",    / description (ID 1534) /
     +5 : 1179,                  / type, (ID 1538) identity /
                                 / ethernetCsmacd (ID 1179) /
     +2 : true                   / enabled ( ID 1535) /
    },
    {+4 : "eth1",                / name (ID 1537) /
     +1 : "Ethernet adaptor",    / description (ID 1534) /
     +5 : 1179,                  / type, (ID 1538) identity /
                                 / ethernetCsmacd (ID 1179) /
     +2 : false                  / enabled /
     }
   ]

   It is equally possible to select a leaf of one instance of a list or
   a complete instance container with GET.  The instance identifier is
   the numeric identifier of the list followed by the specification of
   the values for the key leaves that uniquely identify the list
   instance.  The instance identifier looks like: SID?k=key-value.  The
   key of "interface" is the "name" leaf.  The example below requests
   the description leaf of the instance with name="eth0" (ID=1534,
   base64: X-).  The value of the description leaf is returned.


   REQ: GET example.com/c/X-?k="eth0"

   RES: 2.05 Content (Content-Format: application/cbor)
   "Ethernet adaptor"

5.2.4.  FETCH

   The FETCH is used to retrieve a list of data node values.  The FETCH
   Request payload contains a CBOR list of instance identifiers.

   FORMAT:
       FETCH /c/ Content-Format (application/YANG-fetch+cbor)
       <CBOR array of instance identifiers>

       2.05 Content (Content-Format: application/YANG-patch+cbor)
       <CBOR array of data node values>

   The instance identifier is a SID or a CBOR array containing the SID
   followed by key values that identify the list instance (sec 5.13.1 of
   [I-D.ietf-core-yang-cbor].  In the payload of the returned data node



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   values, delta encoding is used as described in
   [I-D.ietf-core-yang-cbor].

5.2.4.1.  FETCH examples

   The example uses the current-datetime leaf and the interface list
   from Appendix A.1.  In the following example the value of current-
   datetime (ID 1719)and the interface list (ID 1533) instance
   identified with name="eth0" are queried.


   REQ:  FETCH /c Content-Format (application/YANG-fetch+cbor)
         [ 1719,            / ID 1719 /
         [-186, "eth0"]   / ID 1533 with name = "eth0" /
         ]

   RES:  2.05 Content Content-Format (application/YANG-patch+cbor)
   [
     "2014-10-26T12:16:31Z",
    {
      +4 : "eth0",                / name (ID 1537) /
      +1 : "Ethernet adaptor",    / description (ID 1534) /
      +5 : 1179,                  / type (ID 1538), identity /
                                  / ethernetCsmacd (ID 1179) /
      +2 : true                   / enabled (ID 1535) /
     }
   ]

   TODO: align with future FETCH content format.

5.3.  Data Editing

   CoMI allows datastore contents to be created, modified and deleted
   using CoAP methods.

5.3.1.  Data Ordering

   A CoMI server SHOULD preserve the relative order of all user-ordered
   list and leaf-list entries that are received in a single edit
   request.  These YANG data node types are encoded as arrays so
   messages will preserve their order.

5.3.2.  POST

   Data resources are created with the POST method.  The CoAP POST
   operation is used in CoMI for creation of data resources and the
   invocation of "ACTION" and "RPC" resources.  Refer to Section 5.6 for
   details on "ACTION" and "RPC" resources.



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   A request to create the values of an instance of a container or leaf
   is sent with a confirmable CoAP POST message.  A single SID is
   specified in the URI path prefixed with /c.

   FORMAT:
       POST /c/<instance identifier> Content-Format(application/cbor)
       <data node value>

       2.01 Created (Content-Format: application/cbor)

   If the data resource already exists, then the POST request MUST fail
   and a "4.09 Conflict" status-line MUST be returned

   The instance identifier is a SID or a SID followed by the "k" query
   parameter.

5.3.2.1.  Post example

   The example uses the interface list from Appendix A.1.  Example is
   creating a new version of the container interface (ID = 1533):

   REQ: POST /c/X9 Content-Format(application/cbor)
         {
           +4 : "eth0",             / name (ID 1537) /
           +1 : "Ethernet adaptor", / description (ID 1534) /
           +5 : 1179,               / type (ID 1538), identity /
                                    / ethernetCsmacd (ID 1179) /
           +2 : true                / enabled (ID 1535) /
         }

   RES: 2.01 Created (Content-Format: application/cbor)

5.3.3.  PUT

   Data resource instances are created or replaced with the PUT method.
   The PUT operation is supported in CoMI.  A request to set the value
   of a data node instance is sent with a confirmable CoAP PUT message.

   FORMAT:
       PUT /c/<instance identifier> Content-Format(application/cbor)
       <data node value>

       2.01 Created

   The instance identifier is a SID or a SID followed by the "k" query
   parameter.





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5.3.3.1.  PUT example

   The example uses the interface list from Appendix A.1.  Example is
   renewing an instance of the list interface (ID = 1533) with key
   name="eth0":


   REQ:  PUT /c/X9?k="eth0" Content-Format(application/cbor)
         {
           +4 : "eth0",             / name (ID 1537) /
           +1 : "Ethernet adaptor", / description (ID 1534) /
           +5 : 1179,               / type (ID 1538), identity /
                                    / ethernetCsmacd ( ID 1179) /
           +2 : true                / enabled (ID 1535) /
         }
   RES:  2.04 Changed

5.3.4.  iPATCH

   One or multiple data resource instances are replaced with the idem-
   potent iPATCH method [I-D.ietf-core-etch].  A request is sent with a
   confirmable CoAP iPATCH message.

   There are no query parameters for the iPATCH method.

   The processing of the iPATCH command is specified by the CBOR
   payload.  The CBOR patch payload describes the changes to be made to
   target YANG data nodes [I-D.bormann-appsawg-cbor-merge-patch].  If
   the CBOR patch payload contains data node instances that are not
   present in the target, these instances are added or silently ignored
   dependent of the payload information.  If the target contains the
   specified instance, the contents of the instances are replaced with
   the values of the payload.  Null values indicate the removal of
   existing values.

   FORMAT:
       iPATCH /c Content-Format(application/YANG-patch+cbor)
       <set of data node instances>

       2.04 Changed

5.3.4.1.  iPATCH example

   The example uses the interface list from Appendix A.3, and the
   timezone-utc-offset leaf from Appendix A.1.  In the example one leaf
   (timezone-utc-offset ) and one container (interface) instance are
   changed.




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   REQ: iPATCH /c Content-Format(application/YANG-patch+cbor)
   [
     [1533, "eth0"] ,                / interface (ID = 1533) /
       {
         +4 : "eth0",                / name (ID 1537) /
         +1 : "Ethernet adaptor",    / description (ID 1534) /
         +5 : 1179,                  / type (ID 1538), identity /
                                     / ethernetCsmacd (ID 1179) /
         +2 : true                   / enabled (ID 1535) /
       },
     +203 , 60          / timezone-utc-offset (delta = 1736-1533) /
   ]

   RES: 2.04 Changed

   TODO: Align with future cbor-merge-patch content format.

5.3.5.  DELETE

   Data resource instances are deleted with the DELETE method.  The
   RESTCONF DELETE operation is supported in CoMI.

   FORMAT:
       Delete /c/<instance identifier>

       2.02 Deleted

   The instance identifier is a SID or a SID followed by the "k" query
   parameter.

5.3.5.1.  DELETE example

   The example uses the interface list from Appendix A.3.  Example is
   deleting an instance of the container interface (ID = 1533):

   REQ:   DELETE /c/X9?k="eth0"

   RES:   2.02 Deleted

5.4.  Full Data Store access

   The methods GET, PUT, POST, and DELETE can be used to return,
   replace, create, and delete the whole data store respectively.








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   FORMAT:
       GET /c
       2.05 Content (Content-Format: application/cbor)
       <array of data node instances>

      PUT /c
      (Content-Format: application/cbor)
       <array of data node instances>
      2.04 Changed

      POST /c
      (Content-Format: application/cbor)
       <array of data node instances>
      2.01 Created

      DELETE /c
      2.02 Deleted


   The array of data node instances represents an array of all root
   nodes in the data store after the PUT, POST and GET method
   invocations.

5.4.1.  Full Data Store examples

   The example uses the interface list and the clock container from
   Appendix A.3.  Assume that the data store contains two root objects:
   the list interface (ID 1533) with one instance and the container
   Clock (ID 1717).  After invocation of GET an array with these two
   objects is returned:





















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   RQ:  GET /c
   RES: 2.05 Content Content-Format (application/YANG-patch+cbor)
   [
     {1717:
        { +2: "2016-10-26T12:16:31Z", / current-datetime (ID 1719) /
          +1: "2014-10-05T09:00:00Z"  / boot-datetime (ID 1718) /
        },
     -186:                            / clock (ID 1533) /
        {
          +4 : "eth0",                / name (ID 1537) /
          +1 : "Ethernet adaptor",    / description (ID 1534) /
          +5 : 1179,                  / type (ID 1538), identity: /
                                      / ethernetCsmacd (ID 1179) /
          +2 : true                   / enabled (ID 1535) /
         }
       }
   ]

5.5.  Notify functions

   Notification by the server to a selection of clients when an event
   occurs in the server is an essential function for the management of
   servers.  CoMI allows events specified in YANG [RFC5277] to be
   notified to a selection of requesting clients.  The server appends
   newly generated events to a stream.  There is one, so-called
   "default", stream in a CoMI server.  The /c/s resource identifies the
   default stream.  The server MAY create additional stream resources.
   When a CoMI server generates an internal event, it is appended to the
   chosen stream, and the content of a notification instance is ready to
   be sent to all CoMI clients which observe the chosen stream resource.

   Reception of generated notification instances is enabled with the
   CoAP Observe [RFC7641] function.  The client subscribes to the
   notifications by sending a GET request with an "Observe" option,
   specifying the /c/s resource when the default stream is selected.

   Every time an event is generated, the chosen stream is cleared, and
   the generated notification instance is appended to the chosen
   stream(s).  After appending the instance, the contents of the
   instance is sent to all clients observing the modified stream.

   FORMAT:
     Get /<stream-resource>
         Content-Format(application/YANG-patch+cbor) Observe(0)

   2.05 Content Content-Format(application/YANG-patch+cbor)
   <set of data node instances>




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5.5.1.  Notify Examples

   Suppose the server generates the event specified in Appendix A.4.  By
   executing a GET on the /c/s resource the client receives the
   following response:


   REQ:  GET /c/s Observe(0) Token(0x93)

   RES:  2.05 Content Content-Format(application/YANG-patch+cbor)
                           Observe(12) Token(0x93)
   {
      60010 :                  / example-port-fault (ID 60010) /
       {
         +1 : "0/4/21",       / port-name (ID 60011) /
         +2 : "Open pin 2"    / port-fault (ID 60012) /
       },
      60010 :                  / example-port-fault (ID 60010) /
       {
         +1 : "1/4/21",       / port-name (ID 60011) /
         +2 : "Open pin 5"    / port-fault (ID 60012) /
       }
   }


   In the example, the request returns a success response with the
   contents of the last two generated events.  Consecutively the server
   will regularly notify the client when a new event is generated.

   To check that the client is still alive, the server MUST send
   confirmable notifications once in a while.  When the client does not
   confirm the notification from the server, the server will remove the
   client from the list of observers [RFC7641].

5.6.  RPC statements

   The YANG "action" and "RPC" statements specify the execution of a
   Remote procedure Call (RPC) in the server.  It is invoked using a
   POST method to an "Action" or "RPC" resource instance.  The Request
   payload contains the values assigned to the input container when
   specified with the action station.  The Response payload contains the
   values of the output container when specified.

   The returned success response code is 2.05 Content.







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   FORMAT:
    POST /c/<instance identifier>
              Content-Format(application/YANG-patch+cbor)
   <input node value>

   2.05 Content Content-Format (application/YANG-patch+cbor)
   <output node value>


   There "k" query parameter is allowed for the POST method when used
   for an action invocation.

5.6.1.  RPC Example

   The example is based on the YANG action specification of
   Appendix A.2.  A server list is specified and the action "reset" (ID
   60002, base64: Opq), that is part of a "server instance" with key
   value "myserver", is invoked.

   REQ:  POST /c/Opq?k="myserver"
                 Content-Format(application/YANG-patch+cbor)
   {
     +1 : "2016-02-08T14:10:08Z09:00" / reset-at (ID 60003) /
   }

   RES:  2.05 Content Content-Format(application/YANG-patch+cbor)
   {
     +2 : "2016-02-08T14:10:08Z09:18" / reset-finished-at (ID 60004)/
   }

6.  Access to MIB Data

   Appendix A.5 shows a YANG module mapped from the SMI specification
   "IP-MIB" [RFC4293].  The following example shows the
   "ipNetToPhysicalEntry" list with 2 instances, using diagnostic
   notation without delta encoding.















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  {
     60021 :                     / list ipNetToPhysicalEntry /
     [
       {
         60022 : 1,              / ipNetToPhysicalIfIndex /
         60023 : 1,              / ipNetToPhysicalNetAddressType: ipv4 /
         60024 : h'0A000033',    / ipNetToPhysicalNetAddress /
         60025 : h'00000A01172D',/ ipNetToPhysicalPhysAddress /
         60026 : 2333943,        / ipNetToPhysicalLastUpdated /
         60027 : 4,              / ipNetToPhysicalType: static /
         60028 : 1,              / ipNetToPhysicalState: reachable /
         60029 : 1               / ipNetToPhysicalRowStatus: active /
       },
       {
         60022 : 1,              / ipNetToPhysicalIfIndex /
         60023 : 1,              / ipNetToPhysicalNetAddressType: ipv4 /
         60024 : h'09020304',    / ipNetToPhysicalNetAddress  /
         60025 : h'00000A36200A',/ ipNetToPhysicalPhysAddress /
         60026 : 2329836,        / ipNetToPhysicalLastUpdated /
         60027 : 3,              / ipNetToPhysicalType: dynamic /
         60028 : 6,              / ipNetToPhysicalState: unknown /
         60029 : 1               / ipNetToPhysicalRowStatus: active /
       }
     ]
  }

   The IPv4 addresses A.0.0.33 and 9.2.3.4 are encoded in CBOR as
   h'0A000033' and h'09020304' respectively.  In the following example
   exactly one instance is requested from the ipNetToPhysicalEntry (ID
   60021, base64: Oz1).  The h'09020304' value is encoded in base64 as
   AJAgME.

   In this example one instance of /ip/ipNetToPhysicalEntry that matches
   the keys ipNetToPhysicalIfIndex = 1, ipNetToPhysicalNetAddressType =
   ipv4 and ipNetToPhysicalNetAddress = 9.2.3.4 (h'09020304', base64:
   AJAgME).















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   REQ: GET example.com/c/Oz1?k="1,1,AJAgME"

   RES: 2.05 Content (Content-Format: application/YANG-patch+cbor)
   {
      +1 : 1,                  / ( SID 60022 ) /
      +2 : 1,                  / ( SID 60023 ) /
      +3 : h'09020304',        / ( SID 60024 ) /
      +4 : h'00000A36200A',    / ( SID 60025 ) /
      +5 : 2329836,            / ( SID 60026 ) /
      +6 : 3,                  / ( SID 60027 ) /
      +7 : 6,                  / ( SID 60028 ) /
      +8 : 1                   / ( SID 60029 ) /
   }

7.  Use of Block

   The CoAP protocol provides reliability by acknowledging the UDP
   datagrams.  However, when large pieces of text need to be transported
   the datagrams get fragmented, thus creating constraints on the
   resources in the client, server and intermediate routers.  The block
   option [RFC7959] allows the transport of the total payload in
   individual blocks of which the size can be adapted to the underlying
   transport sizes such as: (UDP datagram size ~64KiB, IPv6 MTU of 1280,
   IEEE 802.15.4 payload of 60-80 bytes).  Each block is individually
   acknowledged to guarantee reliability.

   Notice that the Block mechanism splits the data at fixed positions,
   such that individual data fields may become fragmented.  Therefore,
   assembly of multiple blocks may be required to process the complete
   data field.

   Beware of race conditions.  Blocks are filled one at a time and care
   should be taken that the whole data representation is sent in
   multiple blocks sequentially without interruption.  In the server,
   values are changed, lists are re-ordered, extended or reduced.  When
   these actions happen during the serialization of the contents of the
   variables, the transported results do not correspond with a state
   having occurred in the server; or worse the returned values are
   inconsistent.  For example: array length does not correspond with
   actual number of items.  It may be advisable to use CBOR maps or CBOR
   arrays of undefined length which are foreseen for data streaming
   purposes.

8.  Resource Discovery

   The presence and location of (path to) the management data are
   discovered by sending a GET request to "/.well-known/core" including
   a resource type (RT) parameter with the value "core.c" [RFC6690].



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   Upon success, the return payload will contain the root resource of
   the management data.  It is up to the implementation to choose its
   root resource, but it is recommended that the value "/c" is used,
   where possible.  The example below shows the discovery of the
   presence and location of management data.


     REQ: GET /.well-known/core?rt=core.c

     RES: 2.05 Content </c>; rt="core.c"


   Management objects MAY be discovered with the standard CoAP resource
   discovery.  The implementation can add the encoded values of the
   object identifiers to /.well-known/core with rt="core.c.data".  The
   available objects identified by the encoded values can be discovered
   by sending a GET request to "/.well-known/core" including a resource
   type (RT) parameter with the value "core.c.data".  Upon success, the
   return payload will contain the registered encoded values and their
   location.  The example below shows the discovery of the presence and
   location of management data.


     REQ: GET /.well-known/core?rt=core.c.data

     RES: 2.05 Content </c/BaAiN>; rt="core.c.data",
     </c/CF_fA>; rt="core.c.data"


   Lists of encoded values may become prohibitively long.  It is
   discouraged to provide long lists of objects on discovery.
   Therefore, it is recommended that details about management objects
   are discovered by reading the YANG module information stored in for
   example the "ietf-comi-yang-library" module
   [I-D.veillette-core-cool-library].  The resource "/c/mod.uri" is used
   to retrieve the location of the YANG module library.

   The module list can be stored locally on each server, or remotely on
   a different server.  The latter is advised when the deployment of
   many servers are identical.











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     Local in example.com server:

     REQ: GET example.com/c/mod.uri

     RES: 2.05 Content (Content-Format: application/cbor)
     {
       "mod.uri" : "example.com/c/modules"
     }


     Remote in example-remote-server:

     REQ: GET example.com/c/mod.uri

     RES: 2.05 Content (Content-Format: application/cbor)
     {
       "moduri" : "example-remote-server.com/c/group17/modules"
     }


   Within the YANG module library all information about the module is
   stored such as: module identifier, identifier hierarchy, grouping,
   features and revision numbers.

9.  Error Handling

   In case a request is received which cannot be processed properly, the
   CoMI server MUST return an error message.  This error message MUST
   contain a CoAP 4.xx or 5.xx response code, and SHOULD include
   additional information in the payload.

   Such an error message payload is a text string, using the following
   structure:


   CoMI error: xxxx "error text"


   The characters xxxx represent one of the values from the table below,
   and the OPTIONAL "error text" field contains a human readable
   explanation of the error.










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   +----------------+----------------+---------------------------------+
   | CoMI Error     | CoAP Error     | Description                     |
   | Code           | Code           |                                 |
   +----------------+----------------+---------------------------------+
   | 0              | 4.xx           | General error                   |
   |                |                |                                 |
   | 1              | 4.13           | Request too big                 |
   |                |                |                                 |
   | 2              | 4.00           | Response too big                |
   |                |                |                                 |
   | 3              | 4.00           | Unknown identifier              |
   |                |                |                                 |
   | 4              | 4.00           | Invalid value                   |
   |                |                |                                 |
   | 5              | 4.05           | Attempt to write read-only      |
   |                |                | variable                        |
   |                |                |                                 |
   | 6              | 5.01           | No access                       |
   |                |                |                                 |
   | 7              | 4.00           | Wrong type                      |
   |                |                |                                 |
   | 8              | 4.15           | Unknown encoding                |
   |                |                |                                 |
   | 9              | 4.0            | Wrong value                     |
   |                |                |                                 |
   | 10             | 4.0            | Not created                     |
   |                |                |                                 |
   | 11             | 4.04           | Resource unavailable            |
   |                |                |                                 |
   | 12             | 4.01           | Authorization error             |
   |                |                |                                 |
   | 13             | 4.0            | Bad attribute                   |
   |                |                |                                 |
   | 14             | 4.0            | Unknown attribute               |
   |                |                |                                 |
   | 15             | 4.0            | Missing attribute               |
   +----------------+----------------+---------------------------------+

   The CoMI error codes are motivated by the error-status values defined
   in [RFC3416], and the error tags defined in
   [I-D.ietf-netconf-restconf].

10.  Security Considerations

   For secure network management, it is important to restrict access to
   configuration variables only to authorized parties.  This requires
   integrity protection of both requests and responses, and depending on
   the application encryption.



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   CoMI re-uses the security mechanisms already available to CoAP as
   much as possible.  This includes DTLS [RFC6347] for protected access
   to resources, as well suitable authentication and authorization
   mechanisms.

   Among the security decisions that need to be made are selecting
   security modes and encryption mechanisms (see [RFC7252]).  This
   requires a trade-off, as the NoKey mode gives no protection at all,
   but is easy to implement, whereas the X.509 mode is quite secure, but
   may be too complex for constrained devices.

   In addition, mechanisms for authentication and authorization may need
   to be selected.

   CoMI avoids defining new security mechanisms as much as possible.
   However some adaptations may still be required, to cater for CoMI's
   specific requirements.

11.  IANA Considerations

   'rt="core.c"' needs registration with IANA.

   'rt="core.c.data"' needs registration with IANA.

   'rt="core.c.moduri"' needs registration with IANA.

   'rt="core.c.stream"' needs registration with IANA.

   Content types to be registered:

   o  application/YANG-patch+cbor

   o  application/YANG-fetch+cbor

12.  Acknowledgements

   We are very grateful to Bert Greevenbosch who was one of the original
   authors of the CoMI specification and specified CBOR encoding and use
   of hashes.

   Mehmet Ersue and Bert Wijnen explained the encoding aspects of PDUs
   transported under SNMP.  Carsten Bormann has given feedback on the
   use of CBOR.

   Timothy Carey has provided the text for Appendix B.

   The draft has benefited from comments (alphabetical order) by Rodney
   Cummings, Dee Denteneer, Esko Dijk, Michael van Hartskamp, Juergen



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   Schoenwaelder, Anuj Sehgal, Zach Shelby, Hannes Tschofenig, Michael
   Verschoor, and Thomas Watteyne.

13.  Changelog

   Changes from version 00 to version 01

   o  Focus on MIB only

   o  Introduced CBOR, JSON, removed BER

   o  defined mappings from SMI to xx

   o  Introduced the concept of addressable table rows

   Changes from version 01 to version 02

   o  Focus on CBOR, used JSON for examples, removed XML and EXI

   o  added uri-query attributes mod and con to specify modules and
      contexts

   o  Definition of CBOR string conversion tables for data reduction

   o  use of Block for multiple fragments

   o  Error returns generalized

   o  SMI - YANG - CBOR conversion

   Changes from version 02 to version 03

   o  Added security considerations

   Changes from version 03 to version 04

   o  Added design considerations section

   o  Extended comparison of management protocols in introduction

   o  Added automatic generation of CBOR tables

   o  Moved lowpan table to Appendix

   Changes from version 04 to version 05

   o  Merged SNMP access with RESTCONF access to management objects in
      small devices



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   o  Added CoMI architecture section

   o  Added RESTCONf NETMOD description

   o  Rewrote section 5 with YANG examples

   o  Added server and payload size appendix

   o  Removed Appendix C for now.  It will be replaced with a YANG
      example.

   Changes from version 04 to version 05

   o  Extended examples with hash representation

   o  Added keys query parameter text

   o  Added select query parameter text

   o  Better separation between specification and instance

   o  Section on discovery updated

   o  Text on rehashing introduced

   o  Elaborated SMI MIB example

   o  YANG library use described

   o  use of BigEndian/LittleEndian in Hash generation specified

   Changes from version 05 to version 06

   o  Hash values in payload as hexadecimal and in URL in base64 numbers

   o  Streamlined CoMI architecture text

   o  Added select query parameter text

   o  Data editing optional

   o  Text on Notify added

   o  Text on rehashing improved with example

   Changes from version 06 to version 07

   o  reduced payload size by removing JSON hierarchy



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   o  changed rehash handling to support small clients

   o  added LWM2M comparison

   o  Notification handling as specified in YANG

   o  Added Patch function

   o  Rehashing completely reviewed

   o  Discover type of YANG name encoding

   o  Added new resource types

   o  Read-only servers introduced

   o  Multiple updates explained

   Changes from version 07 to version 08

   o  Changed YANG Hash algorithm to use module name instead of prefix

   o  Added rehash bit to allow return values to identify rehashed nodes
      in the response

   o  Removed /c/mod.set resource since this is not needed

   o  Clarified that YANG Hash is done even for unimplemented objects

   o  YANG lists transported as CBOR maps of maps

   o  Adapted examples with more CBOR explanation

   o  Added CBOR code examples in new appendix

   o  Possibility to use other than default stream

   o  Added text and examples for Patch payload

   o  Repaired some examples

   o  Added appendices on hash clash probability and hash clash storage
      overhead

   Changes from version 08 to version 09

   o  Removed hash and YANG to CBOR sections




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   o  removed hashes from examples.

   o  Added RPC

   o  Added content query parameter.

   o  Added default handling.

   o  Listed differences with RESTCONF

   Changes from version 09 to version 10.  This is the merge of cool-01
   with comi-09.

   o  Merged with CoOL SIDs

   o  Introduced iPATCH, PATCH and FETCH

   o  Update of LWM2M comparison

   o  Added appendix with module examples

   o  Removed introductory text

   o  Removed references

   Changes from version 10 to version 11

   o  Introduction streamlined

   o  Error codes streamlined

   o  Examples updated to latest SID values

   o  Update of the YANG specifications in the appendix

14.  References

14.1.  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>.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
              <http://www.rfc-editor.org/info/rfc5277>.




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   [RFC6243]  Bierman, A. and B. Lengyel, "With-defaults Capability for
              NETCONF", RFC 6243, DOI 10.17487/RFC6243, June 2011,
              <http://www.rfc-editor.org/info/rfc6243>.

   [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>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <http://www.rfc-editor.org/info/rfc7252>.

   [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>.

   [RFC7959]  Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
              the Constrained Application Protocol (CoAP)", RFC 7959,
              DOI 10.17487/RFC7959, August 2016,
              <http://www.rfc-editor.org/info/rfc7959>.

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)", RFC 7641,
              DOI 10.17487/RFC7641, September 2015,
              <http://www.rfc-editor.org/info/rfc7641>.

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-18 (work in
              progress), October 2016.

   [I-D.ietf-core-etch]
              Stok, P., Bormann, C., and A. Sehgal, "Patch and Fetch
              Methods for Constrained Application Protocol (CoAP)",
              draft-ietf-core-etch-04 (work in progress), November 2016.

   [I-D.bormann-appsawg-cbor-merge-patch]
              Bormann, C. and P. Stok, "CBOR Merge Patch", draft-
              bormann-appsawg-cbor-merge-patch-00 (work in progress),
              March 2016.

   [I-D.ietf-core-yang-cbor]
              Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A.
              Minaburo, "CBOR Encoding of Data Modeled with YANG",
              draft-ietf-core-yang-cbor-03 (work in progress), October
              2016.




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14.2.  Informative References

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578,
              DOI 10.17487/RFC2578, April 1999,
              <http://www.rfc-editor.org/info/rfc2578>.

   [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410,
              DOI 10.17487/RFC3410, December 2002,
              <http://www.rfc-editor.org/info/rfc3410>.

   [RFC3416]  Presuhn, R., Ed., "Version 2 of the Protocol Operations
              for the Simple Network Management Protocol (SNMP)",
              STD 62, RFC 3416, DOI 10.17487/RFC3416, December 2002,
              <http://www.rfc-editor.org/info/rfc3416>.

   [RFC4293]  Routhier, S., Ed., "Management Information Base for the
              Internet Protocol (IP)", RFC 4293, DOI 10.17487/RFC4293,
              April 2006, <http://www.rfc-editor.org/info/rfc4293>.

   [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>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <http://www.rfc-editor.org/info/rfc6347>.

   [RFC6643]  Schoenwaelder, J., "Translation of Structure of Management
              Information Version 2 (SMIv2) MIB Modules to YANG
              Modules", RFC 6643, DOI 10.17487/RFC6643, July 2012,
              <http://www.rfc-editor.org/info/rfc6643>.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
              <http://www.rfc-editor.org/info/rfc6690>.

   [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>.



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   [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>.

   [I-D.ietf-core-interfaces]
              Shelby, Z., Vial, M., Koster, M., and C. Groves, "Reusable
              Interface Definitions for Constrained RESTful
              Environments", draft-ietf-core-interfaces-07 (work in
              progress), December 2016.

   [I-D.ietf-core-sid]
              Somaraju, A., Veillette, M., Pelov, A., Turner, R., and A.
              Minaburo, "YANG Schema Item iDentifier (SID)", draft-ietf-
              core-sid-00 (work in progress), October 2016.

   [I-D.veillette-core-cool]
              Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A.
              Minaburo, "Constrained Objects Language", draft-veillette-
              core-cool-02 (work in progress), July 2016.

   [I-D.veillette-core-cool-library]
              Veillette, M., "Constrained YANG Module Library", draft-
              veillette-core-cool-library-00 (work in progress), August
              2016.

   [XML]      "Extensible Markup Language (XML)",
              Web http://www.w3.org/xml.

   [OMA]      "OMA-TS-LightweightM2M-V1_0-20131210-C", Web
              http://technical.openmobilealliance.org/Technical/
              current_releases.aspx.

   [OMNA]     "Open Mobile Naming Authority (OMNA)", Web
              http://http://technical.openmobilealliance.org/Technical/
              technical-information/omna.

   [netconfcentral]
              "NETCONF Central: library of YANG modules",
              Web http://www.netconfcentral.org/modulelist.

   [mibreg]   "Structure of Management Information (SMI) Numbers (MIB
              Module Registrations)", Web
              http://www.iana.org/assignments/smi-numbers/
              smi-numbers.xhtml/.

   [yang-cbor]
              "yang-cbor Registry", Web https://github.com/core-wg/yang-
              cbor/tree/master/registry/.



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Appendix A.  YANG example specifications

   This appendix shows 5 YANG example specifications taken over from as
   many existing YANG modules.  The YANG modules are available from
   [netconfcentral].  Each YANG item identifier is accompanied by its
   SID shown after the "//" comment sign, taken from [yang-cbor].

A.1.  ietf-system

   Excerpt of the YANG module ietf-system [RFC7317].

   module ietf-system {
     container system {                   // SID 1715
       container clock {                  // SID 1734
         choice timezone {
           case timezone-name {
             leaf timezone-name {         // SID 1735
               type timezone-name;
             }
           }
           case timezone-utc-offset {
             leaf timezone-utc-offset {   // SID 1736
               type int16 {
               }
             }
           }
         }
       }
       container ntp {                    // SID 1750
         leaf enabled {                   // SID 1751
           type boolean;
           default true;
         }
         list server {                    // SID 1752
           key name;
           leaf name {                    // SID 1755
             type string;
           }
           choice transport {
             case udp {
               container udp {            // SID 1757
                 leaf address {           // SID 1758
                   type inet:host;
                 }
                 leaf port {              // SID 1759
                   type inet:port-number;
                 }
               }



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             }
           }
           leaf association-type {        // SID 1753
             type enumeration {
               enum server {
               }
               enum peer {
               }
               enum pool {
               }
             }
           }
           leaf iburst {                  // SID 1754
             type boolean;
           }
           leaf prefer {                  // SID 1756
             type boolean;
             default false;
           }
         }
       }
     container system-state {             // SID 1716
       container clock {                  // SID 1717
         leaf current-datetime {          // SID 1719
           type yang:date-and-time;
         }
         leaf boot-datetime {             // SID 1718
           type yang:date-and-time;
         }
       }
     }
   }


A.2.  server list

   Taken over from [RFC7950] section 7.15.3.














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   module example-server-farm {
     yang-version 1.1;
     namespace "urn:example:server-farm";
     prefix "sfarm";

     import ietf-yang-types {
       prefix "yang";
     }

     list server {                        // SID 60000
       key name;
       leaf name {                        // SID 60001
         type string;
       }
       action reset {                     // SID 60002
         input {
           leaf reset-at {                // SID 60003
             type yang:date-and-time;
             mandatory true;
            }
          }
          output {
            leaf reset-finished-at {      // SID 60004
              type yang:date-and-time;
              mandatory true;
            }
          }
        }
      }
   }


A.3.  interfaces

   Excerpt of the YANG module ietf-interfaces [RFC7223].
















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   module ietf-interfaces {
     container interfaces {               // SID 1505
       list interface {                   // SID 1533
         key "name";
         leaf name {                      // SID 1537
           type string;
         }
         leaf description {               // SID 1534
           type string;
         }
         leaf type {                      // SID 1538
           type identityref {
             base interface-type;
           }
           mandatory true;
         }

         leaf enabled {                   // SID 1535
           type boolean;
           default "true";
         }

         leaf link-up-down-trap-enable {  // SID 1536
           if-feature if-mib;
           type enumeration {
             enum enabled {
               value 1;
             }
             enum disabled {
               value 2;
             }
           }
         }
       }
     }
   }


A.4.  Example-port

   Notification example defined within this document.










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   module example-port {
           ...
           notification example-port-fault {   // SID 60010
             description
               "Event generated if a hardware fault on a
                line card port is detected";
             leaf port-name {                  // SID 60011
               type string;
               description "Port name";
             }
             leaf port-fault {                 // SID 60012
               type string;
               description "Error condition detected";
             }
           }
         }

A.5.  IP-MIB

   The YANG translation of the SMI specifying the IP-MIB [RFC4293],
   extended with example SID numbers, yields:


module IP-MIB {
  import IF-MIB {
    prefix if-mib;
  }
  import INET-ADDRESS-MIB {
    prefix inet-address;
  }
  import SNMPv2-TC {
    prefix smiv2;
  }
  import ietf-inet-types {
    prefix inet;
  }
  import yang-smi {
    prefix smi;
  }
  import ietf-yang-types {
    prefix yang;
  }

  container ip {                            // SID 60020
    list ipNetToPhysicalEntry {             // SID 60021
      key "ipNetToPhysicalIfIndex ipNetToPhysicalNetAddressType ipNetToPhysicalNetAddress";
      leaf ipNetToPhysicalIfIndex {         // SID 60022
        type if-mib:InterfaceIndex;



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      }
      leaf ipNetToPhysicalNetAddressType {  // SID 60023
        type inet-address:InetAddressType;
      }
      leaf ipNetToPhysicalNetAddress {      // SID 60024
        type inet-address:InetAddress;
      }
      leaf ipNetToPhysicalPhysAddress {     // SID 60025
        type yang:phys-address {
          length "0..65535";
        }
      }
      leaf ipNetToPhysicalLastUpdated {     // SID 60026
        type yang:timestamp;
      }
      leaf ipNetToPhysicalType {            // SID 60027
        type enumeration {
          enum "other" {
            value 1;
          }
          enum "invalid" {
            value 2;
          }
          enum "dynamic" {
            value 3;
          }
          enum "static" {
            value 4;
          }
          enum "local" {
            value 5;
          }
        }
      }
      leaf ipNetToPhysicalState {           // SID 60028
        type enumeration {
          enum "reachable" {
            value 1;
          }
          enum "stale" {
            value 2;
          }
          enum "delay" {
            value 3;
          }
          enum "probe" {
            value 4;
          }



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          enum "invalid" {
            value 5;
          }
          enum "unknown" {
            value 6;
          }
          enum "incomplete" {
            value 7;
          }
        }
      }
      leaf ipNetToPhysicalRowStatus {       // SID 60029
        type smiv2:RowStatus;
    }  // list ipNetToPhysicalEntry
  }  // container ip
}  // module IP-MIB


Appendix B.  Comparison with LWM2M

B.1.  Introduction

   CoMI and LWM2M [OMA], both, provide RESTful device management
   services over CoAP.  Differences between the designs are highlighted
   in this section.

   The intent of the LWM2M protocol is to provide a single protocol to
   control and manage IoT devices.  This means the IoT device implements
   and uses the same LWM2M agent function for the actuation and sensing
   features of the IoT device as well as for the management of the IoT
   device.  The intent of CoMI Interface as described in the Abstract
   section of this document is to provide management of constrained
   devices and devices in constrained networks using RESTCONF and YANG.
   This implies that the device, although reusing the CoAP protocol,
   would need a separate CoAP based agent in the future to control the
   actuation and sensing features of the device and another CoMI agent
   that performs the management functions.

   It should be noted that the mapping of a LWM2M server to YANG is
   specified in [YANGlwm2m].  The converted server can be invoked with
   CoMI as specified in this document.

   For the purposes of managing IoT devices the following points related
   to the protocols compare how management resources are defined,
   identified, encoded and updated.






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B.2.  Defining Management Resources

   Management resources in LWM2M (LWM2M objects) are defined using a
   standardized number.  When a new management resource is defined,
   either by a standards organization or a private enterprise, the
   management resource is registered with the Open Mobile Naming
   Authority [OMNA] in order to ensure different resource definitions do
   not use the same identifier.  CoMI, by virtue of using YANG as its
   data modeling language, allows enterprises and standards
   organizations to define new management resources (YANG nodes) within
   YANG modules without having to register each individual management
   resource.  Instead YANG modules are scoped within a registered name
   space.  As such, the CoMI approach provides additional flexibility in
   defining management resources.  Likewise, since CoMI utilizes YANG,
   existing YANG modules can be reused.  The flexibility and reuse
   capabilities afforded to CoMI can be useful in management of devices
   like routers and switches in constrained networks.  However for
   management of IoT devices, the usefulness of this flexibility and
   applicability of reuse of existing YANG modules may not be warranted.
   The reason is that IoT devices typically do not require complex sets
   of configuration or monitoring operations required by devices like a
   router or a switch.  To date, OMA has defined approximately 15
   management resources for constrained and non-constrained mobile or
   fixed IoT devices while other 3rd Party SDOs have defined another 10
   management resources for their use in non-constrained IoT devices.
   Likewise, the Constrained Object Language [I-D.veillette-core-cool]
   which is used by CoMI when managing constrained IoT devices uses YANG
   schema item identifiers, which are registered with IANA, in order to
   define management resources that are encoded using CBOR when
   targeting constrained IoT Devices.

B.3.  Identifying Management Resources

   As LWM2M and CoMI can similarly be used to manage IoT devices,
   comparison of the CoAP URIs used to identify resources is relevant as
   the size of the resource URI becomes applicable for IoT devices in
   constrained networks.  LWM2M uses a flat identifier structure to
   identify management resources and are identified using the LWM2M
   object's identifier, instance identifier and optionally resource
   identifier (for access to and object's attributes).  For example,
   identifier of a device object (object id = 3) would be "/3/0" and
   identification of the device object's manufacturer attribute would be
   "/3/0/0".  Effectively LWM2M identifiers for management resources are
   between 4 and 10 bytes in length.

   CoMI is expected to be used to manage constrained IoT devices.  CoMI
   utilizes the YANG schema item identifier[SID] that identify the
   resources.  CoMI recommends that IoT device expose resources to



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   identify the data stores and event streams of the CoMI agent.
   Individual resources (e.g., device object) are not directly
   identified but are encoded within the payload.  As such the
   identifier of the CoMI resource is smaller (4 to 7 bytes) but the
   overall payload size isn't smaller as resource identifiers are
   encoded on the payload.

B.4.  Encoding of Management Resources

   LWM2M provides a separation of the definition of the management
   resources from how the payloads are encoded.  As of the writing of
   this document LWM2M encodes LWM2M encodes payload data in Type-
   length-value (TLV), JSON or plain text formats.  JSON encoding is the
   most common encoding scheme with TLV encoding used on the simplest
   IoT devices.  CoMI's use of CBOR provides a more efficient transfer
   mechanism [RFC7049] than the current LWM2M encoding formats.

   In situations where resources need to be modified, CoMI uses the CoAP
   PATCH operation resources only require a partial update.  LWM2M does
   not currently use the CoAP PATCH operation but instead uses the CoAP
   PUT and POST operations which are less efficient.

Authors' Addresses

   Peter van der Stok
   consultant

   Phone: +31-492474673 (Netherlands), +33-966015248 (France)
   Email: consultancy@vanderstok.org
   URI:   www.vanderstok.org


   Andy Bierman
   YumaWorks
   685 Cochran St.
   Suite #160
   Simi Valley, CA  93065
   USA

   Email: andy@yumaworks.com











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Internet-Draft                    CoMI                      January 2017


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

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


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

   Email: a@ackl.io


































van der Stok, et al.      Expires July 22, 2017                [Page 46]


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