[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 draft-ietf-core-comi

core                                                     P. van der Stok
Internet-Draft                                                consultant
Intended status: Standards Track                              A. Bierman
Expires: January 6, 2016                                       YumaWorks
                                                        J. Schoenwaelder
                                                       Jacobs University
                                                               A. Sehgal
                                                              consultant
                                                            July 5, 2015


                       CoAP Management Interface
                     draft-vanderstok-core-comi-07

Abstract

   This document describes a network management interface for
   constrained devices, called CoMI.  CoMI is an adaptation of the
   RESTCONF protocol for use in constrained devices and networks.  It is
   designed to reduce the message sizes, server code size, and
   application development complexity.  The Constrained Application
   Protocol (CoAP) is used to access management data resources specified
   in YANG, or SMIv2 converted to YANG.  The payload of the CoMI message
   is encoded in Concise Binary Object Representation (CBOR).

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 January 6, 2016.





van der Stok, et al.     Expires January 6, 2016                [Page 1]


Internet-Draft                    CoMI                         July 2015


Copyright Notice

   Copyright (c) 2015 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.  Design considerations . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
       1.2.1.  Tree Diagrams . . . . . . . . . . . . . . . . . . . .   6
   2.  CoMI Architecture . . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  RESTCONF/YANG Architecture  . . . . . . . . . . . . . . .  10
     2.2.  Compression of data-node instance identifier  . . . . . .  10
   3.  CoAP Interface  . . . . . . . . . . . . . . . . . . . . . . .  11
   4.  MG Function Set . . . . . . . . . . . . . . . . . . . . . . .  13
     4.1.  Data Retrieval  . . . . . . . . . . . . . . . . . . . . .  14
       4.1.1.  GET . . . . . . . . . . . . . . . . . . . . . . . . .  14
       4.1.2.  Mapping of the 'select' Parameter . . . . . . . . . .  14
       4.1.3.  Retrieval Examples  . . . . . . . . . . . . . . . . .  15
     4.2.  Data Editing  . . . . . . . . . . . . . . . . . . . . . .  26
       4.2.1.  Data Ordering . . . . . . . . . . . . . . . . . . . .  27
       4.2.2.  POST  . . . . . . . . . . . . . . . . . . . . . . . .  27
       4.2.3.  PUT . . . . . . . . . . . . . . . . . . . . . . . . .  27
       4.2.4.  PATCH . . . . . . . . . . . . . . . . . . . . . . . .  27
       4.2.5.  DELETE  . . . . . . . . . . . . . . . . . . . . . . .  28
       4.2.6.  Editing Multiple Resources  . . . . . . . . . . . . .  28
     4.3.  Notify functions  . . . . . . . . . . . . . . . . . . . .  29
     4.4.  Use of Block  . . . . . . . . . . . . . . . . . . . . . .  31
     4.5.  Resource Discovery  . . . . . . . . . . . . . . . . . . .  32
     4.6.  Error Return Codes  . . . . . . . . . . . . . . . . . . .  34
   5.  Mapping YANG to CoMI payload  . . . . . . . . . . . . . . . .  35
     5.1.  YANG Hash Generation  . . . . . . . . . . . . . . . . . .  36
     5.2.  Re-Hash Error Procedure . . . . . . . . . . . . . . . . .  36
     5.3.  ietf-yang-hash YANG Module  . . . . . . . . . . . . . . .  37
     5.4.  YANG Re-Hash Examples . . . . . . . . . . . . . . . . . .  40
       5.4.1.  Multiple Modules  . . . . . . . . . . . . . . . . . .  42
       5.4.2.  Same Module . . . . . . . . . . . . . . . . . . . . .  43



van der Stok, et al.     Expires January 6, 2016                [Page 2]


Internet-Draft                    CoMI                         July 2015


       5.4.3.  Same Module and Same Path Length  . . . . . . . . . .  44
     5.5.  YANG Hash in URL  . . . . . . . . . . . . . . . . . . . .  45
   6.  Mapping YANG to CBOR  . . . . . . . . . . . . . . . . . . . .  46
     6.1.  High level encoding . . . . . . . . . . . . . . . . . . .  46
     6.2.  Conversion from YANG datatypes to CBOR datatypes  . . . .  46
   7.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .  48
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  49
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  49
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  50
   11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .  50
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  52
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  52
     12.2.  Informative References . . . . . . . . . . . . . . . . .  54
   Appendix A.  Payload and Server sizes . . . . . . . . . . . . . .  56
   Appendix B.  Notational Convention for CBOR data  . . . . . . . .  58
   Appendix C.  comparison with LWM2M  . . . . . . . . . . . . . . .  59
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  59

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.

   The draft [I-D.ietf-netconf-restconf] describes a REST-like interface
   called RESTCONF, which uses HTTP methods to access structured data
   defined in YANG [RFC6020].  RESTCONF allows access to data resources
   contained in NETCONF [RFC6241] data-stores.  RESTCONF messages can be
   encoded in XML [XML] or JSON [RFC7159].  The GET method is used to
   retrieve data resources and the POST, PUT, PATCH, and DELETE methods
   are used to create, replace, merge, and delete data resources.

   A large amount of Management Information Base (MIB) [RFC3418]
   specifications already exists for monitoring purposes.  This data can
   be accessed in RESTCONF if the server converts the SMIv2 modules to
   YANG, using the mapping rules defined in [RFC6643].

   The CoRE Management Interface (CoMI) is intended to work on
   standardized data-sets in a stateless client-server fashion.  The
   RESTCONF protocol is adapted and optimized for use in constrained
   environments, using CoAP instead of HTTP.  Standardized data sets
   promote interoperability between small devices and applications from
   different manufacturers.  Stateless communication is encouraged to
   keep communications simple and the amount of state information small



van der Stok, et al.     Expires January 6, 2016                [Page 3]


Internet-Draft                    CoMI                         July 2015


   in line with the design objectives of 6lowpan [RFC4944] [RFC6775],
   RPL [RFC6650], and CoAP [RFC7252].

   RESTCONF uses the HTTP methods HEAD, and OPTIONS, which are not
   available in CoAP.  HTTP uses TCP which is not recommended for CoAP.
   The transport protocols available to CoAP are much better suited for
   constrained networks.

   CoMI is low resource oriented, uses CoAP, and only supports the
   methods GET, PUT, PATCH, POST and DELETE.  The payload of CoMI is
   encoded in CBOR [RFC7049] which is automatically generated from JSON
   [RFC7159].  CBOR has a binary format and hence has more coding
   efficiency than JSON.  To promote small packets, CoMI uses an
   additional "data-identifier string-to-number conversion" to minimise
   CBOR payloads and URI length.  It is assumed that the managed device
   is the most constrained entity.  The client might be more capable,
   however this is not necessarily the case.

   Currently, small managed devices need to support at least two
   protocols: CoAP and SNMP [RFC3411].  When the MIB can be accessed
   with the CoAP protocol, the SNMP protocol can be replaced with the
   CoAP protocol.  Although the SNMP server size is not huge (see
   Appendix A), the code for the security aspects of SMIv3 [RFC3414] is
   not negligible.  Using CoAP to access secured management objects
   reduces the code complexity of the stack in the constrained device,
   and harmonizes applications development.

   The objective of CoMI is to provide a CoAP based Function Set that
   reads and sets values of managed objects in devices to (1) initialize
   parameter values at start-up, (2) acquire statistics during
   operation, and (3) maintain nodes by adjusting parameter values
   during operation.

   The end goal of CoMI is to provide information exchange over the CoAP
   transport protocol in a uniform manner as a first step to the full
   management functionality as specified in
   [I-D.ersue-constrained-mgmt].

1.1.  Design considerations

   CoMI supports discovery of resources, accompanied by reading, writing
   and notification of resource values.  As such it is close to the
   device management of the Open Mobile Alliance described in [OMA].  A
   comparison between CoMI and LWM2M management can be found in
   Appendix C.  CoMI supports MIB modules which have been translated
   from SMIv2 to YANG, using [RFC6643].  This mapping is read-only so
   writable SMIv2 objects need to be converted to YANG using an
   implementation-specific mapping.



van der Stok, et al.     Expires January 6, 2016                [Page 4]


Internet-Draft                    CoMI                         July 2015


   CoMI uses a simple URI to access the management object resources.
   Complexity introduced by instance selection, or multiple object
   specification is expressed with uri-query attributes.  The choice for
   uri-query attributes makes the URI structure less context dependent.

   The YANG data model contains a lot of information that can be
   exploited by automation tools and need not be transported in the
   request messages, ultimately leading to reduced message sizes.

1.2.  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, data-store, and server.

   The following terms are defined in the YANG data modelling language
   [RFC6020]: 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, data-store resource, edit
   operation, query parameter, target resource, and unified data-store.

   The following terms are defined in this document:

   YANG hash:  CoMI object identifier, which is a 30-bit numeric hash of
      the YANG object identifier string for the object.  When a YANG
      hash value is printed in a request target URI, error-path or other
      string, then the lowercase hexadecimal representation is used.
      Leading zeros are used so the value uses 8 hex characters.

   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-node 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 the default stream.

   The following list contains the abbreviations used in this document.




van der Stok, et al.     Expires January 6, 2016                [Page 5]


Internet-Draft                    CoMI                         July 2015


   XXXX:  TODO, and others to follow.

1.2.1.  Tree Diagrams

   A simplified graphical representation of the data model is used in
   this document.  The meaning of the symbols in these diagrams is as
   follows:

      Brackets "[" and "]" enclose list keys.

      Abbreviations before data node names: "rw" means configuration
      data (read-write) and "ro" state data (read-only).

      Symbols after data node names: "?" means an optional node, "!"
      means a presence container, and "*" denotes a list and leaf-list.

      Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

      Ellipsis ("...") stands for contents of subtrees that are not
      shown.

2.  CoMI Architecture

   This section describes the CoMI architecture to use CoAP for the
   reading and modifying of instrumentation variables used for the
   management of the instrumented node.
























van der Stok, et al.     Expires January 6, 2016                [Page 6]


Internet-Draft                    CoMI                         July 2015


   Client
   +--------------------------------------------------------------+
   | +----------------+    +----------------+                     |
   | |    SMIv2       | >  |      YANG      |    >     COAP       |
   | |specification(2)|    |specification(1)|       Request(3)    |
   | +----------------+    +----------------+[         *          |
   +-----------------------------*-----------[---------*----------+
                                 *           [         *
                                 *           [    +-----------+
                         mapping *   security[    |  Network  |
                                 *      (8)  [    | packet(4) |
                                 *           [    +-----------+
   Server                        *           [         *
   +-----------------------------*-----------[---------*----------+
   |                             *           [         *          |
   |                             *                 Retrieval,     |
   |                             *               Modification(5)  |
   |                            \*/                    *          |
   | +-------------------------------------------------*--------+ |
   | |                    +--------------+       +------------+ | |
   | |                    |configuration |       |Operational | | |
   | |                    |     (6b)     |       |  state(6a) | | |
   | |                    +--------------+       +------------+ | |
   | |                    variable store (6)           *        | |
   | +-------------------------------------------------*--------+ |
   |                                                   *          |
   |                                                Variable      |
   |                                            Instrumentation(7)|
   +--------------------------------------------------------------+


                   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.

   Objectives are:

   o  Equip a constrained node with a management server that provides
      information about the operational characteristics of the code
      running in the constrained node.

   o  The server provides this information in a variable store that
      contains values describing the performance characteristics and the
      code parameter values.





van der Stok, et al.     Expires January 6, 2016                [Page 7]


Internet-Draft                    CoMI                         July 2015


   o  The client receives the performance characteristics on a regular
      basis or on request.

   o  The client sets the parameter values in the server at bootstrap
      and intermittently when operational conditions change.

   o  The constrained network requires the payload to be as small as
      possible, and the constrained server memory requirements should be
      as small as possible.

   For interoperability it is required that in addition to using the
   Internet Protocol for data transport:

   o  The names, type, and semantics of the instrumentation variables
      are standardized.

   o  The instrumentation variables are described in a standard
      language.

   o  The signature of the CoAP request in the server is standardized.

   o  The format of the packet payload is standardized.

   o  The notification from server to client is standardized.

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

   (1) YANG specification:  contains a set of named and versioned
      modules.  A module specifies a hierarchy of named and typed
      resources.  A resource is uniquely identified by a sequence of its
      name and the names of the enveloping resources following the
      hierarchy order.  The YANG specification serves as input to the
      writers of application and instrumentation code and the humans
      analysing the returned values (arrow from YANG specification to
      Variable store).  The specification can be used to check the
      correctness of the CoAP request and do the CBOR encoding.

   (2) SMIv2 specification:  A named module specifies a set of variables
      and "conceptual tables".  Named variables have simple types.
      Conceptual tables are composed of typed named columns.  The
      variable name and module name identify the variable uniquely.
      There is an algorithm to translate SMIv2 specifications to YANG
      specifications.

   (3) CoAP request:  The CoAP request needs a Universal Resource
      Identifier (URI) and the payload of the packet to send a request.
      The URI is composed of the schema, server, path and query and



van der Stok, et al.     Expires January 6, 2016                [Page 8]


Internet-Draft                    CoMI                         July 2015


      looks like coap://entry.example.com/<path>?<query>.  Fragments are
      not supported.  Allowed operations are PUT, PATCH, GET, DELETE,
      and POST.  New variables can be created with POST when they exist
      in the YANG specification.  The Observe option can be used to
      return variable values regularly or on event occurrence
      (notification).

   (3.1) CoAP <path>:  The path identifies the variable in the form
      "/mg/<hash-value>".

   (3.2) CoAP <query>:  The query parameter is used to specify
      additional (optional) aspects like the module name, list instance,
      and others.  The idea is to keep the path simple and put
      variations on variable specification in the query.

   (3.3) CoAP discovery:  Discovery of the variables is done with
      standard CoAP resource discovery using /.well-known/core with
      ?rt=/core.mg.

   (4) Network packet:  The payload contains the CBOR encoding of JSON
      objects.  This object corresponds to the converted RESTCONF
      message payload.

   (5) Retrieval, modification:  The server needs to parse the CBOR
      encoded message and identify the corresponding instances in the
      Variable store.  In addition, this component includes the code for
      CoAP Observe and block options.

   (6) Variable store:  The store is composed of two parts: Operational
      state and Configuration data-store (see Section 2.1).  CoMI does
      not differentiate between variable store types.  The Variable
      store contains data-node instances.  Values are stored in the
      appropriate instances, and or values are returned from the
      instances into the payload of the packet.

   (7) Variable instrumentation:  This code depends on implementation of
      drivers and other node specific aspects.  The Variable
      instrumentation code stores the values of the parameters into the
      appropriate places in the operational code.  The variable
      instrumentation code reads current execution values from the
      operational code and stores them in the appropriate instances.

   (8) Security:  The server MUST prevent unauthorized users from
      reading or writing any data resources.  CoMI relies on DTLS
      [RFC6347] which is specified to secure CoAP communication.






van der Stok, et al.     Expires January 6, 2016                [Page 9]


Internet-Draft                    CoMI                         July 2015


2.1.  RESTCONF/YANG Architecture

   CoMI adapts the RESTCONF architecture so data exchange and
   implementation requirements are optimized for constrained devices.

   The RESTCONF protocol uses a unified data-store to edit conceptual
   data structures supported by the server.  The details of transaction
   preparation and non-volatile storage of the data are hidden from the
   RESTCONF client.  CoMI also uses a unified data-store, to allow
   stateless editing of configuration variables and the notification of
   operational variables.

   The child schema nodes of the unified data-store include all the top-
   level YANG data nodes in all the YANG modules supported by the
   server.  The YANG data structures represent a hierarchy of data
   resources.  The client discovers the list of YANG modules, and
   important conformance information such as the module revision dates,
   YANG features supported, and YANG deviations required.  The
   individual data nodes are discovered indirectly by parsing the YANG
   modules supported by the server.

   The YANG data definition statements contain a lot of information that
   can help automation tools, developers, and operators use the data
   model correctly and efficiently.  The YANG definitions and server
   YANG module capability advertisements provide an "API contract" that
   allow a client to determine the detailed server management
   capabilities very quickly.  CoMI allows access to the same data
   resources as a RESTCONF server, except the messages are optimized to
   reduce identifier and payload size.

   RESTCONF uses a simple algorithmic mapping from YANG to URI syntax to
   identify the target resource of a retrieval or edit operation.  A
   client can construct operations or scripts using a predictable
   syntax, based on the YANG data definitions.  The target resource URI
   can reference a data resource instance, or the data-store itself (to
   retrieve the entire data-store or create a top-level data resource
   instance).  CoMI uses a compression algorithm to reduce the size of
   the data-node instance identifier (see Section 2.2.

2.2.  Compression of data-node instance identifier

   The RESTCONF protocol uses the full path of the desired data resource
   in the target resource URI.  The JSON encoding will include the
   module name string to specify the YANG module.  If a representation
   of the target resource is included in the request or response message
   in RESTCONF messages, then the data definition name string is used to
   identify each node in the message.  The module namespace (or name)
   may also be present in these identifiers.



van der Stok, et al.     Expires January 6, 2016               [Page 10]


Internet-Draft                    CoMI                         July 2015


   In order to greatly 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.

   YANG Hash is the default encoding for object identifiers.  This
   encoding in considered to be "unstructured" since the particular
   values for each object are determined by a hash algorithm.  It is
   possible for 2 different objects to generate the same hash value.  If
   this occurs, then the client and server will both need to rehash the
   colliding object identifiers to new unused hash values.

   In order to eliminate the need for rehashing, CoMI allows for
   alternate "structured" object identifier encoding formats.
   Structured object identifier MUST be managed such that no object ID
   collisions are possible, and therefore no rehash procedures are
   needed.  Structured object identifiers can also be selected to
   minimize the size of a subset of the object identifiers (e.g., the
   most requested objects).

   In Section 4.5 the discovery of the object ID compression scheme is
   described.

3.  CoAP Interface

   In CoAP a group of links can constitute a 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.mg, with path: /mg,
   where mg is short-hand for management.  The name /mg is recommended
   but not compulsory (see Section 4.5).

   The path prefix /mg has resources accessible with the following five
   paths:

   /mg:  YANG-based data with path "/mg" and using CBOR content encoding
      format.  This path represents a data-store resource which contains
      YANG data resources as its descendant nodes.  All identifiers
      referring to YANG data nodes within this path are encoded as YANG
      hash values (see Section 5.5).

   /mg/mod.uri:  URI identifying the location of the server module
      information, with path "/mg/mod.uri" and CBOR content format.
      This YANG data is encoded with plain identifier strings, not YANG
      hash values.





van der Stok, et al.     Expires January 6, 2016               [Page 11]


Internet-Draft                    CoMI                         July 2015


   /mg/mod.set:  String identifying the module set ID in use by the
      server, which is defined as the 'module-set-id' leaf in the ietf-
      yang-library module.  This resource MUST change to a new value
      when the set of YANG modules in use by the server changes.

   /mg/num.typ:  String identifying the object ID numbering scheme used
      by the CoMI server.  The only value defined in this document is
      'yanghash' to indicate that the YANG Hash numbering scheme defined
      in this document is used.  It is possible for other object
      numbering schemes to be defined outside the scope of this
      document.

   /mg/srv.typ:  String identifying the CoMI server type.  The value
      'ro' indicates that the server is a read-only server and no
      editing operations are supported.  A read-only server is not
      required to provide YANG deviation statements for any writable
      YANG data nodes.  The value 'rw' indicates that the server is a
      read-write server and editing operations are supported.  A read-
      write server is required to provide YANG deviation statements for
      any writable YANG data nodes that are not fully implemented.

   /mg/yh.uri:  URI indicating the location of the server YANG hash
      information if any objects needed to be re-hashed by the server.
      It has the path "/mg/yh.uri" and is encoded in CBOR format.  The
      "ietf-yang-hash" module of Section 5.3 is used to define the
      syntax and semantics of this data structure.  This YANG data is
      encoded with plain identifier strings, not YANG hash values.  The
      server will only have this resource if there are any objects that
      needed to be re-hashed due to a hash collision.

   /mg/stream:  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 root of a data tree in a YANG module loaded in the
   CoMI server represents a resource of the server.  All data root
   descendants represent sub-resources.

   The resource identifiers of the instances of the YANG specifications
   are YANG hash values, as described in Section 5.1.  When multiple
   instances of a list node exist, the instance selection is described
   in Section 4.1.3.4






van der Stok, et al.     Expires January 6, 2016               [Page 12]


Internet-Draft                    CoMI                         July 2015


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

   +--------------+-------------+-------------------+------------------+
   | name         | path        | rt                | Data Type        |
   +--------------+-------------+-------------------+------------------+
   | Management   | /mg         | core.mg           | n/a              |
   |              |             |                   |                  |
   | Data         | /mg         | core.mg.data      | application/cbor |
   |              |             |                   |                  |
   | Module Set   | /mg/mod.uri | core.mg.moduri    | application/cbor |
   | URI          |             |                   |                  |
   |              |             |                   |                  |
   | Module Set   | /mg/mod.set | core.mg.modset    | application/cbor |
   | ID           |             |                   |                  |
   |              |             |                   |                  |
   | Numbering    | /mg/num.typ | core.mg.num-type  | application/cbor |
   | Type         |             |                   |                  |
   |              |             |                   |                  |
   | Server Type  | /mg/srv.typ | core.mg.srv-type  | application/cbor |
   |              |             |                   |                  |
   | YANG Hash    | /mg/yh.uri  | core.mg.yang-hash | application/cbor |
   | Info         |             |                   |                  |
   |              |             |                   |                  |
   | Events       | /mg/stream  | core.mg.stream    | application/cbor |
   +--------------+-------------+-------------------+------------------+

4.  MG Function Set

   The MG Function Set provides a CoAP interface to perform a subset of
   the functions provided by RESTCONF.

   A subset of the operations defined in RESTCONF are used in CoMI:

   +-----------+------------------------------------------------------+
   | Operation | Description                                          |
   +-----------+------------------------------------------------------+
   | GET       | Retrieve the data-store resource or a data resource  |
   |           |                                                      |
   | POST      | Create a data resource                               |
   |           |                                                      |
   | PUT       | Create or replace a data resource                    |
   |           |                                                      |
   | PATCH     | Replace a data resource partially                    |
   |           |                                                      |
   | DELETE    | Delete a data resource                               |
   +-----------+------------------------------------------------------+



van der Stok, et al.     Expires January 6, 2016               [Page 13]


Internet-Draft                    CoMI                         July 2015


4.1.  Data Retrieval

4.1.1.  GET

   One or more instances of data resources are retrieved by the client
   with the GET method.  The RESTCONF GET operation is supported in
   CoMI.  The same constraints apply as defined in section 3.3 of
   [I-D.ietf-netconf-restconf].  The operation is mapped to the GET
   method defined in section 5.8.1 of [RFC7252].

   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
   [I-D.ietf-core-block] is used, as explained in more detail in
   Section 4.4.

   There are two query parameters for the GET method.  A CoMI server
   MUST implement the keys parameter and MAY implement the select
   parameter to allow common data retrieval filtering functionality.

   +----------------+--------------------------------------------------+
   | Query          | Description                                      |
   | Parameter      |                                                  |
   +----------------+--------------------------------------------------+
   | keys           | Request to select instances of a YANG definition |
   |                |                                                  |
   | select         | Request selected sub-trees from the target       |
   |                | resource                                         |
   +----------------+--------------------------------------------------+

   The "keys" parameter is used to specify a specific instance of the
   resource.  When keys is not specified, all instances are returned.
   When no or one instance of the resource exists, the keys parameter is
   not needed.

4.1.2.  Mapping of the 'select' Parameter

   RESTCONF uses the 'select' parameter to specify an expression which
   can represent a subset of all data nodes within the target resource
   [I-D.ietf-netconf-restconf].  This parameter is useful for filtering
   sub-trees and retrieving only a subset that a managing application is
   interested in.

   However, filtering is a resource intensive task and not all
   constrained devices can be expected to have enough computing
   resources such that they will be able to successfully filter and
   return a subset of a sub-tree.  This is especially likely to be true
   with Class 0 devices that have significantly lesser RAM than 10 KiB



van der Stok, et al.     Expires January 6, 2016               [Page 14]


Internet-Draft                    CoMI                         July 2015


   [RFC7228].  Since CoMI is targeted at constrained devices and
   networks, only a limited subset of the 'select' parameter is used
   here.

   Unlike the RESTCONF 'select' parameter, CoMI does not use object
   names in "XPath" or "path-expr" format to identify the subset that
   needs to be filtered.  Parsing XML is resource intensive for
   constrained devices [management] and using object names can lead to
   large message sizes.  Instead, CoMI utilizes the YANG hashes
   described in Section 5 to identify the sub-trees that should be
   filtered from a target resource.  Using these hashes ensures that a
   constrained node can identify the target sub-tree without expending
   many resources and that the messages generated are also efficiently
   encoded.

   The implementation of the 'select' parameter is already optional for
   constrained devices, however, even when implemented it is expected to
   be a best effort feature, rather than a service that nodes must
   provide.  This implies that if a node receives the 'select' parameter
   specifying a set of sub-trees that should be returned, it will only
   return those that it is able to.

4.1.3.  Retrieval Examples

   In all examples the path is expressed in readable names and as a hash
   value of the name (where the hash value in the payload is expressed
   as a hexadecimal number, and the hash value in the URL as a base64
   number).  The examples in this section use a JSON payload with one or
   more entries describing the pair (identifier, value).  CoMI
   transports the CBOR format to transport the equivalent contents.  The
   CBOR syntax of the payloads is specified in Section 5.

4.1.3.1.  Single instance retrieval

   A request to read the values of instances of a management object or
   the leaf of an object is sent with a confirmable CoAP GET message.  A
   single object is specified in the URI path prefixed with /mg.

   Using for example the clock container from [RFC7317], a request is
   sent to retrieve the value of clock/current-datetime specified in
   module system-state.  The answer to the request returns a
   (identifier, value) pair.









van der Stok, et al.     Expires January 6, 2016               [Page 15]


Internet-Draft                    CoMI                         July 2015


   REQ: GET example.com/mg/system-state/clock/current-datetime

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

   The YANG hash value for 'current-datetime' is calculated by
   constructing the schema node identifier for the object:

   /sys:system-state/sys:clock/sys:current-datetime

   The 30 bit murmur3 hash value is calculated on this string
   (0x15370408 and VNwQI).  The request using this hash value is shown
   below:


   REQ: GET example.com/mg/VNwQI

   RES: 2.05 Content (Content-Format: application/cbor)
   {
       0x15370408 : "2014-10-26T12:16:31Z"
   }

   The specified object can be an entire object.  Accordingly, the
   returned payload is composed of all the leaves associated with the
   object.  Each leaf is returned as a (YANG hash, value) pair.  For
   example, the GET of the clock object, sent by the client, results in
   the following returned payload sent by the managed entity:


   REQ: GET example.com/mg/system-state/clock
      (Content-Format: application/cbor)

   RES: 2.05 Content (Content-Format: application/cbor)
   {
         "clock/current-datetime" : "2014-10-26T12:16:51Z",
         "clock/boot-datetime" : "2014-10-21T03:00:00Z"
   }

   The YANG hash values for 'clock', 'current-datetime', and 'boot-
   datetime' are calculated by constructing the schema node identifier
   for the objects, and then calculating the 30 bit murmur3 hash values
   (shown in parenthesis):

   /sys:system-state/sys:clock (0x2eb2fa3b and usvo7)
   /sys:system-state/sys:clock/sys:current-datetime (0x15370408)
   /sys:system-state/sys:clock/sys:boot-datetime (0x1fa25361)



van der Stok, et al.     Expires January 6, 2016               [Page 16]


Internet-Draft                    CoMI                         July 2015


   The request using the hash values is shown below:


   REQ: GET example.com/mg/usvo7
      (Content-Format: application/cbor)

   RES: 2.05 Content (Content-Format: application/cbor)
   {
         0x15370408 : "2014-10-26T12:16:51Z",
         0x1fa25361 : "2014-10-21T03:00:00Z"
   }

4.1.3.2.  Multiple instance retrieval

   A "list" node can have multiple instances.  Accordingly, the returned
   payload is composed of all the instances associated with the list
   node.  Each instance is returned as a (identifier, value) pair.  The
   "keys" query parameter is used to identify a specific list instance
   by specifying a given index value (see Section 4.1.3.4).

   For example, the GET of the /interfaces/interface/ipv6/neighbor
   instance identified with interface index "eth0" [RFC7223], sent by
   the client, results in the following returned payload sent by the
   managed entity:


   REQ: GET example.com/mg/interfaces/interface/ipv6/neighbor?keys=eth0
      (Content-Format: application/cbor)

   RES: 2.05 Content (Content-Format: application/cbor)
   {
      "neighbor":[
        {
           "ip" : "fe80::200:f8ff:fe21:67cf",
           "link-layer-address" : "00:00::10:01:23:45"
        },
        {
           "ip" : "fe80::200:f8ff:fe21:6708",
           "link-layer-address" : "00:00::10:54:32:10"
        },
        {
           "ip" : "fe80::200:f8ff:fe21:88ee",
           "link-layer-address" : "00:00::10:98:76:54"
        }
      ]
   }





van der Stok, et al.     Expires January 6, 2016               [Page 17]


Internet-Draft                    CoMI                         July 2015


   The YANG hash values for 'neighbor', 'ip', and 'link-layer-address'
   are calculated by constructing the schema node identifier for the
   objects, and then calculating the 30 bit murmur3 hash values (shown
   in parenthesis):

  /if:interfaces/if:interface/ip:ipv6/ip:neighbor (0x2354bc49 and jVLxJ)
  /if:interfaces/if:interface/ip:ipv6/ip:neighbor/ip:ip
      (0x20b8907e and guJB_)
  /if:interfaces/if:interface/ip:ipv6/ip:neighbor/ip:link-layer-address
     (0x16f47fd8)

   The request using the hash values is shown below:


   REQ: GET example.com/mg/jVLxJ?keys=eth0
      (Content-Format: application/cbor)

   RES: 2.05 Content (Content-Format: application/cbor)
   {
      0x2354bc49 : [
        {
           0x20b8907e : "fe80::200:f8ff:fe21:67cf",
           0x16f47fd8 : "00:00::10:01:23:45"
        },
        {
           0x20b8907e : "fe80::200:f8ff:fe21:6708",
           0x16f47fd8 : "00:00::10:54:32:10"
        },
        {
           0x20b8907e : "fe80::200:f8ff:fe21:88ee",
           0x16f47fd8 : "00:00::10:98:76:54"
        }
      ]
   }

4.1.3.3.  Access to MIB Data

   The YANG translation of the SMI specifying the
   ipNetToMediaTable [RFC4293] yields:












van der Stok, et al.     Expires January 6, 2016               [Page 18]


Internet-Draft                    CoMI                         July 2015


   container IP-MIB {
     container ipNetToPhysicalTable {
       list ipNetToPhysicalEntry {
          key "ipNetToPhysicalIfIndex
               ipNetToPhysicalNetAddressType
               ipNetToPhysicalNetAddress";
          leaf ipNetToMediaIfIndex {
             type: int32;
          }
          leaf ipNetToPhysicalIfIndex {
            type if-mib:InterfaceIndex;
          }
          leaf ipNetToPhysicalNetAddressType {
            type inet-address:InetAddressType;
          }
          leaf ipNetToPhysicalNetAddress {
            type inet-address:InetAddress;
          }
          leaf ipNetToPhysicalPhysAddress {
            type yang:phys-address {
               length "0..65535";
            }
          }
          leaf ipNetToPhysicalLastUpdated {
            type yang:timestamp;
          }
          leaf ipNetToPhysicalType {
            type enumeration { ... }
          }
          leaf ipNetToPhysicalState {
            type enumeration { ... }
          }
          leaf ipNetToPhysicalRowStatus {
            type snmpv2-tc:RowStatus;
          }
       }
    }

   The following example shows an "ipNetToPhysicalTable" with 2
   instances, using JSON encoding:











van der Stok, et al.     Expires January 6, 2016               [Page 19]


Internet-Draft                    CoMI                         July 2015


   {
     "IP-MIB/ipNetToPhysicalTable/ipNetToPhysicalEntry" : [
           {
             "ipNetToPhysicalIfIndex" : 1,
             "ipNetToPhysicalNetAddressType" : "ipv4",
             "ipNetToPhysicalNetAddress" : "10.0.0.51",
             "ipNetToPhysicalPhysAddress" : "00:00:10:01:23:45",
             "ipNetToPhysicalLastUpdated" : "2333943",
             "ipNetToPhysicalType" : "static",
             "ipNetToPhysicalState" : "reachable",
             "ipNetToPhysicalRowStatus" : "active"
           },
           {
             "ipNetToPhysicalIfIndex" : 1,
             "ipNetToPhysicalNetAddressType" : "ipv4",
             "ipNetToPhysicalNetAddress" : "9.2.3.4",
             "ipNetToPhysicalPhysAddress" : "00:00:10:54:32:10",
             "ipNetToPhysicalLastUpdated" : "2329836",
             "ipNetToPhysicalType" : "dynamic",
             "ipNetToPhysicalState" : "unknown",
             "ipNetToPhysicalRowStatus" : "active"
           }
         ]
       }
     }
   }

   The YANG hash values for 'ipNetToPhysicalEntry' and its child nodes
   are calculated by constructing the schema node identifier for the
   objects, and then calculating the 30 bit murmur3 hash values (shown
   in parenthesis):




















van der Stok, et al.     Expires January 6, 2016               [Page 20]


Internet-Draft                    CoMI                         July 2015


 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable (0x30b7bc3f and wt7w_)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry
    (0x1067f289 and QZ_KJ)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry/
    ip-mib:ipNetToPhysicalIfIndex (0x00d38564)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry/
    ip-mib:ipNetToPhysicalNetAddressType (0x2745e222)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry/
    ip-mib:ipNetToPhysicalNetAddress (0x387804eb)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry/
    ip-mib:ipNetToPhysicalPhysAddress (0x1a51514a)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry/
    ip-mib:ipNetToPhysicalLastUpdated (0x03f95578)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry/
    ip-mib:ipNetToPhysicalType (0x24ade115)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry/
    ip-mib:ipNetToPhysicalState (0x09e640ef)
 /ip-mib:IP-MIB/ip-mib:ipNetToPhysicalTable/ip-mib:ipNetToPhysicalEntry/
    ip-mib:ipNetToPhysicalRowStatus (0x3b5c1ab6)

   The following example shows a request for the entire
   ipNetToPhysicalTable.  Since all the instances are requested, no
   "keys" query parameter is needed.




























van der Stok, et al.     Expires January 6, 2016               [Page 21]


Internet-Draft                    CoMI                         July 2015


   REQ: GET example.com/mg/wt7w_

   RES: 2.05 Content (Content-Format: application/cbor)
   {
         0x1067f289 : [
           {
             0x00d38564 : 1,
             0x2745e222 : "ipv4",
             0x387804eb : "10.0.0.51",
             0x1a51514a : "00:00:10:01:23:45",
             0x03f95578 : "2333943",
             0x24ade115 : "static",
             0x09e640ef : "reachable",
             0x3b5c1ab6 : "active"
           },
           {
             0x00d38564 : 1,
             0x2745e222 : "ipv4",
             0x387804eb : "9.2.3.4",
             0x1a51514a : "00:00:10:54:32:10",
             0x03f95578 : "2329836",
             0x24ade115 : "dynamic",
             0x09e640ef : "unknown",
             0x3b5c1ab6 : "active"
           }
         ]
   }

4.1.3.4.  The 'keys' Query Parameter

   There is a mandatory query parameter that MUST be supported by
   servers called "keys".  This parameter is used to specify the key
   values for an instance of an object identified by a YANG hash value.
   Any key leaf values of the instance are passed in order.  The first
   key leaf in the top-most list is the first key encoded in the 'keys'
   parameter.

   The key leafs from top to bottom and left to right are encoded as a
   comma-delimited list.  If a key leaf value is missing then all values
   for that key leaf are returned.

   Example: In this example exactly 1 instance is requested from the
   ipNetToPhysicalEntry (from a previous example).








van der Stok, et al.     Expires January 6, 2016               [Page 22]


Internet-Draft                    CoMI                         July 2015


   REQ: GET example.com/mg/QZ_KJ?keys=1,ipv4,10.0.0.51

   RES: 2.05 Content (Content-Format: application/cbor)
   {
      0x1067f289 : [
         {
           0x00d38564 : 1,
           0x2745e222 : "ipv4",
           0x387804eb : "10.0.0.51",
           0x1a51514a : "00:00:10:01:23:45",
           0x03f95578 : "2333943",
           0x24ade115 : "static",
           0x09e640ef : "reachable",
           0x3b5c1ab6 : "active"
         }
      ]
   }

   An example illustrates the syntax of keys query parameter.  In this
   example the following YANG module is used:


     module foo-mod {
       namespace foo-mod-ns;
       prefix foo;

       list A {
         key "key1 key2";
         leaf key1 { type string; }
         leaf key2 { type int32; }
         list B {
           key "key3";
           leaf key3 { type string; }
           leaf col1 { type uint32; }
         }
       }
     }


   The path identifier for the leaf "col1" is the following string:


      /foo:A/foo:B/foo:col1


   The YANG hash for this identifier string has values: 0xa9abdcca and
   pq9zK).




van der Stok, et al.     Expires January 6, 2016               [Page 23]


Internet-Draft                    CoMI                         July 2015


   The following string represents the RESTCONF target resource URI
   expression for the "col1" leaf for the key values "top", 17, and
   "group1":


      /restconf/data/foo-mod:A="top",17/B="group1"/col1


   The following string represents the CoMI target resource identifier
   for the same instance of the "col1" leaf:


      /mg/pq9zK?keys="top",17,"group1"


4.1.3.5.  The 'select' Query Parameter

   The select parameter is used along with the GET method to provide a
   sub-tree filter mechanism.  A list of YANG hashes that should be
   filtered is provided along with a list of keys identifying the
   instances that should be returned.  When the keys parameter is used
   together with the select, the key values are added in brackets
   without using the "keys=" text.

   The following example shows an "ipNetToPhysicalTable" (from a
   previous example) with 4 instances, using JSON encoding:

























van der Stok, et al.     Expires January 6, 2016               [Page 24]


Internet-Draft                    CoMI                         July 2015


   {
     "IP-MIB/ipNetToPhysicalTable/ipNetToPhysicalEntry" : [
           {
             "ipNetToPhysicalIfIndex" : 1,
             "ipNetToPhysicalNetAddressType" : "ipv4",
             "ipNetToPhysicalNetAddress" : "10.0.0.51",
             "ipNetToPhysicalPhysAddress" : "00:00:10:01:23:45",
             "ipNetToPhysicalLastUpdated" : "2333943",
             "ipNetToPhysicalType" : "static",
             "ipNetToPhysicalState" : "reachable",
             "ipNetToPhysicalRowStatus" : "active"
           },
           {
             "ipNetToPhysicalIfIndex" : 1,
             "ipNetToPhysicalNetAddressType" : "ipv4",
             "ipNetToPhysicalNetAddress" : "9.2.3.4",
             "ipNetToPhysicalPhysAddress" : "00:00:10:54:32:10",
             "ipNetToPhysicalLastUpdated" : "2329836",
             "ipNetToPhysicalType" : "dynamic",
             "ipNetToPhysicalState" : "unknown",
             "ipNetToPhysicalRowStatus" : "active"
           },
           {
             "ipNetToPhysicalIfIndex" : 2,
             "ipNetToPhysicalNetAddressType" : "ipv4",
             "ipNetToPhysicalNetAddress" : "10.24.2.53",
             "ipNetToPhysicalPhysAddress" : "00:00:10:28:19:CA",
             "ipNetToPhysicalLastUpdated" : "2124368",
             "ipNetToPhysicalType" : "static",
             "ipNetToPhysicalState" : "unknown",
             "ipNetToPhysicalRowStatus" : "active"
           },
           {
             "ipNetToPhysicalIfIndex" : 3,
             "ipNetToPhysicalNetAddressType" : "ipv4",
             "ipNetToPhysicalNetAddress" : "192.168.2.12",
             "ipNetToPhysicalPhysAddress" : "00:00:10:29:11:32",
             "ipNetToPhysicalLastUpdated" : "1925384",
             "ipNetToPhysicalType" : "dynamic",
             "ipNetToPhysicalState" : "reachable",
             "ipNetToPhysicalRowStatus" : "active"
           }
         ]
       }
     }
   }





van der Stok, et al.     Expires January 6, 2016               [Page 25]


Internet-Draft                    CoMI                         July 2015


   Data may be retrieved using the select query parameter in the
   following way:

   REQ: GET example.com/mg/?select=wt7w_(ipv4,reachable)

   RES: 2.05 Content (Content-Format: application/cbor)
   {
      0x1067f289 : [
         {
           0x00d38564 : 1,
           0x2745e222 : "ipv4",
           0x387804eb : "10.0.0.51",
           0x1a51514a : "00:00:10:01:23:45",
           0x03f95578 : "2333943",
           0x24ade115 : "static",
           0x09e640ef : "reachable",
           0x3b5c1ab6 : "active"
           },
           {
             0x00d38564 : 3,
             0x2745e222 : "ipv4",
             0x387804eb : "192.168.2.12",
             0x1a51514a : "00:00:10:29:11:32",
             0x03f95578 : "1925384",
             0x24ade115 : "dynamic",
             0x09e640ef : "reachable",
             0x3b5c1ab6 : "active"
           }
      ]
   }

   In this example exactly 2 instances are returned as response from the
   ipNetToPhysicalTable because both those instances match the provided
   keys.

   Supposing there were multiple YANG hashes with their own sets of keys
   that were to be filtered, the select query parameter can be used to
   retrieve results from these in one go as well.  The following string
   represents the CoMI target resource identifier when multiple YANG
   hashes, with their own sets of keys are queried:

       /mg/?select=hash1(hash1-key1,hash1-key2,...),hash2(hash2-key1)...

4.2.  Data Editing

   CoMI allows data-store contents to be created, modified and deleted
   using CoAP methods.




van der Stok, et al.     Expires January 6, 2016               [Page 26]


Internet-Draft                    CoMI                         July 2015


   Data-editing is an optional feature.  The server will indicate its
   editing capability with the "/core.rg.srv-type resource type.  If the
   value is 'rw' then the server supports editing operations.  If the
   value is 'ro' then the server does not support editing operations.

4.2.1.  Data Ordering

   A CoMI server is not required to support entry insertion of lists and
   leaf-lists that are ordered by the user (i.e., YANG statement
   "ordered-by user").  The 'insert' and 'point' query parameters from
   RESTCONF are not used in CoMI.

   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.

4.2.2.  POST

   Data resource instances are created with the POST method.  The
   RESTCONF POST operation is supported in CoMI, however it is only
   allowed for creation of data resources.  The same constraints apply
   as defined in section 3.4.1 of [I-D.ietf-netconf-restconf].  The
   operation is mapped to the POST method defined in section 5.8.2 of
   [RFC7252].

   There are no query parameters for the POST method.

4.2.3.  PUT

   Data resource instances are created or replaced with the PUT method.
   The PUT operation is supported in CoMI.  A request to set the values
   of instances of an object/leaf is sent with a confirmable CoAP PUT
   message.  The Response is piggybacked to the CoAP ACK message
   corresponding with the Request.  The same constraints apply as
   defined in section 3.5 of [I-D.ietf-netconf-restconf].  The operation
   is mapped to the PUT method defined in section 5.8.3 of [RFC7252].

   There are no query parameters for the PUT method.

4.2.4.  PATCH

   Data resource instances are partially replaced with the PATCH method
   [I-D.vanderstok-core-patch].  The PATCH operation is supported in
   CoMI.  A request to set the values of instances of a subset of the
   values of the resource is sent with a confirmable CoAP PATCH message.
   The Response is piggybacked to the CoAP ACK message corresponding
   with the Request.  The same constraints apply as defined in section



van der Stok, et al.     Expires January 6, 2016               [Page 27]


Internet-Draft                    CoMI                         July 2015


   3.5 of [I-D.ietf-netconf-restconf].  The operation is mapped to the
   PATCH method defined in [I-D.vanderstok-core-patch].

   There are no query parameters for the PATCH method.

4.2.5.  DELETE

   Data resource instances are deleted with the DELETE method.  The
   RESTCONF DELETE operation is supported in CoMI.  The same constraints
   apply as defined in section 3.7 of [I-D.ietf-netconf-restconf].  The
   operation is mapped to the DELETE method defined in section 5.8.4 of
   [RFC7252].

   There are no optional query parameters for the PUT method.

4.2.6.  Editing Multiple Resources

   Editing multiple data resources at once can allow a client to use
   fewer messages to make a configuration change.  It also allows
   multiple edits to all be applied or none applied, which is not
   possible if the data resources are edited one at a time.

   It is easy to add multiple entries at once.  The "PATCH" method can
   be used to simply patch the parent node(s) of the data resources to
   be added.  If multiple top-level data resources need to be added,
   then the data-store itself ('/mg') can be patched.

   If other operations need to be performed, or multiple operations need
   to be performed at once, then the YANG Patch
   [I-D.ietf-netconf-yang-patch] media type can be used with the PATCH
   method.  A YANG patch is an ordered list of edits on the target
   resource, which can be a specific data node instance, or the data-
   store itself.  The resource type used by YANG Patch is 'application/
   yang.patch'.  A status message is returned in the response, using
   resource type 'application/yang.patch.status'.

   The following YANG tree diagram describes the YANG Patch structure,
   Each 'edit' list entry has its own operation, sub-resource target,
   and new value (if needed).












van der Stok, et al.     Expires January 6, 2016               [Page 28]


Internet-Draft                    CoMI                         July 2015


     +--rw yang-patch
         +--rw patch-id?   string
         +--rw comment?    string
         +--rw edit* [edit-id]
            +--rw edit-id      string
            +--rw operation    enumeration
            +--rw target       target-resource-offset
            +--rw point?       target-resource-offset
            +--rw where?       enumeration
            +--rw value


   The YANG Hash values for the YANG Patch request objects are
   calculated as follows:


   0b346308: /ypatch:yang-patch
   29988080: /ypatch:yang-patch/ypatch:patch-id
   0c258737: /ypatch:yang-patch/ypatch:comment
   316beed6: /ypatch:yang-patch/ypatch:edit
   2f51f9f7: /ypatch:yang-patch/ypatch:edit/ypatch:edit-id
   28f4669e: /ypatch:yang-patch/ypatch:edit/ypatch:operation
   2cb909c9: /ypatch:yang-patch/ypatch:edit/ypatch:target
   387d0cd8: /ypatch:yang-patch/ypatch:edit/ypatch:point
   21899571: /ypatch:yang-patch/ypatch:edit/ypatch:where
   1d86d302: /ypatch:yang-patch/ypatch:edit/ypatch:value


   Refer to [I-D.ietf-netconf-yang-patch] for more details on the YANG
   Patch request and response contents.

4.3.  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.  There is one, so-
   called "default", stream in a CoMI server.  The /mg/stream resource
   identifies the default stream.  When a CoMI server generates an
   internal event, it is appended to the default stream, and the
   contents of a notification instance is ready to be sent to all CoMI
   clients which observe the default stream resource.

   Reception of generated notification instances is enabled with the
   CoAP Observe [I-D.ietf-core-observe] function.  The client subscribes
   to the notifications by sending a GET request with an "Observe"
   option, specifying the /mg/stream resource.




van der Stok, et al.     Expires January 6, 2016               [Page 29]


Internet-Draft                    CoMI                         July 2015


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

   Suppose the server generates the event specified with:


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

   }

   The YANG Hash values for this notification are assigned as follows:


   1eed4674: /ep:example-port-fault
   0cec9c71: /ep:example-port-fault/ep:port-name
   228d3fa1: /ep:example-port-fault/ep:fault

   }

   By executing a GET on the /mg/stream resource the client receives the
   following response:











van der Stok, et al.     Expires January 6, 2016               [Page 30]


Internet-Draft                    CoMI                         July 2015


   REQ: GET example.com/mg/stream
       (observe option register)

   RES: 2.05 Content (Content-Format: application/cbor)
   {
      "example-port-fault" : {
         "port-name" : "0/4/21",
         "port-fault" : "Open pin 2"
      }
   }

   TODO: fix YANG Hash/CBOR encoding example

   RES: 2.05 Content (Content-Format: application/cbor)
   {
      1eed4674 : {
         cec9c71 : "0/4/21",
         228d3fa1 : "Open pin 2"
      }
   }




   In the example, the request returns a success response with the
   contents of the last generated event.  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 [I-D.ietf-core-observe].

   In the registration request, the client MAY include a "Response-To-
   Uri-Host" and optionally "Response-To-Uri-Port" option as defined in
   [I-D.becker-core-coap-sms-gprs].  In this case, the observations
   SHOULD be sent to the address and port indicated in these options.
   This can be useful when the client wants the managed device to send
   the trap information to a multicast address.

4.4.  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 [I-D.ietf-core-block] allows the transport of the total
   payload in individual blocks of which the size can be adapted to the



van der Stok, et al.     Expires January 6, 2016               [Page 31]


Internet-Draft                    CoMI                         July 2015


   underlying fragment 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.

   The block size is specified as exponents of the power 2.  The SZX
   exponent value can have 7 values ranging from 0 to 6 with associated
   block sizes given by 2**(SZX+4); for example SZX=0 specifies block
   size 16, and SZX=3 specifies block size 128.

   The block number of the block to transmit can be specified.  There
   are two block options: Block1 option for the request payload
   transported with PUT, POST or PATCH, and the block2 option for the
   response payload with GET.  Block1 and block2 can be combined.
   Examples showing the use of block option in conjunction with observer
   options are provided in [I-D.ietf-core-block].

   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.

4.5.  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.mg" [RFC6690].
   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 "/mg" 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.mg

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


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




van der Stok, et al.     Expires January 6, 2016               [Page 32]


Internet-Draft                    CoMI                         July 2015


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

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


   Lists of hash 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 following the RESTCONF protocol.  The YANG module
   information is stored in the "ietf-yang-library" module
   [I-D.ietf-netconf-restconf].  The resource "/mg/mod.uri" is used to
   retrieve the location of the YANG module library.

   Since many constrained servers within a deployment are likely to be
   similar, the module list can be stored locally on each server, or
   remotely on a different server.


     Local in example.com server:

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

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


     Remote in example-remote-server:

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

     RES: 2.05 Content (Content-Format: application/cbor)
     {
       "moduri" : "example-remote-server.com/mg/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.

   The hash identifier is obtained as specified in Section 5.1.  When a
   collision occurred in the name space of the target server, a rehash
   is executed as explained in Section 5.2.





van der Stok, et al.     Expires January 6, 2016               [Page 33]


Internet-Draft                    CoMI                         July 2015


4.6.  Error Return Codes

   The RESTCONF return status codes defined in section 6 of the RESTCONF
   draft are used in CoMI error responses, except they are converted to
   CoAP error codes.

   TODO: complete RESTCONF to CoAP error code mappings

   TODO: assign an error cpde for a rehash-error.










































van der Stok, et al.     Expires January 6, 2016               [Page 34]


Internet-Draft                    CoMI                         July 2015


           +-------------------------------+------------------+
           | RESTCONF Status Line          | CoAP Status Code |
           +-------------------------------+------------------+
           | 100 Continue                  | none?            |
           |                               |                  |
           | 200 OK                        | 2.05             |
           |                               |                  |
           | 201 Created                   | 2.01             |
           |                               |                  |
           | 202 Accepted                  | none?            |
           |                               |                  |
           | 204 No Content                | ?                |
           |                               |                  |
           | 304 Not Modified              | 2.03             |
           |                               |                  |
           | 400 Bad Request               | 4.00             |
           |                               |                  |
           | 403 Forbidden                 | 4.03             |
           |                               |                  |
           | 404 Not Found                 | 4.04             |
           |                               |                  |
           | 405 Method Not Allowed        | 4.05             |
           |                               |                  |
           | 409 Conflict                  | none?            |
           |                               |                  |
           | 412 Precondition Failed       | 4.12             |
           |                               |                  |
           | 413 Request Entity Too Large  | 4.13             |
           |                               |                  |
           | 414 Request-URI Too Large     | 4.00             |
           |                               |                  |
           | 415 Unsupported Media Type    | 4.15             |
           |                               |                  |
           | 500 Internal Server Error     | 5.00             |
           |                               |                  |
           | 501 Not Implemented           | 5.01             |
           |                               |                  |
           | 503 Service Unavailable       | 5.03             |
           +-------------------------------+------------------+

5.  Mapping YANG to CoMI payload

   A mapping for the encoding of YANG data in CBOR is necessary for the
   efficient transport of management data in the CoAP payload.  Since
   object names may be rather long and may occur repeatedly, CoMI allows
   for association of a given object path identifier string value with
   an integer, called a "YANG hash".




van der Stok, et al.     Expires January 6, 2016               [Page 35]


Internet-Draft                    CoMI                         July 2015


5.1.  YANG Hash Generation

   The association between string value and string number is done
   through a hash algorithm.  The 30 least significant bits of the
   "murmur3" 32-bit hash algorithm are used.  This hash algorithm is
   described online at http://en.wikipedia.org/wiki/MurmurHash.
   Implementation are available online, including at
   https://code.google.com/p/smhasher/wiki/MurmurHash.  When converting
   4 input bytes to a 32-bit integer in the hash algorithm, the Little-
   Endian convention MUST be used.

   The hash is generated for the string representing the object path
   identifier.  A canonical representation of the path identifier is
   used.

      Prefix values are used on every node.

      The prefix values defined in the YANG module containing the data
      object are used for the path expression.  For external modules,
      this is the value of the 'prefix' sub-statement in the 'import'
      statement for each external module.

      Path expressions for objects which augment data nodes in external
      modules are calculated in the augmenting module, using the prefix
      values in the augmenting module.

      Choice and case node names are not included in the path
      expression.  Only 'container', 'list', 'leaf', 'leaf-list', and
      'anyxml' nodes are listed in the path expression.

   The "murmur3_32" hash function is executed for the entire path
   string.  The value '42' is used as the seed for the hash function.
   The YANG hash is subsequently calculated by taking the 30 least
   significant bits.

   The resulting 30-bit number is used by the server, unless the value
   is already being used for a different object by the server.  In this
   case, the re-hash procedure in the following section is executed.

5.2.  Re-Hash Error Procedure

   A hash collision occurs if two different path identifier strings have
   the same hash value.  If the server has over 30,000 objects in its
   YANG modules, then the probability of a collision is 10% or higher.
   If a hash collision occurs on the server, then the object that is
   causing the conflict has to be altered, such that the new hash value
   does not conflict with any value already in use by the server.




van der Stok, et al.     Expires January 6, 2016               [Page 36]


Internet-Draft                    CoMI                         July 2015


   In most cases, the hash function is expected to produce unique values
   for all the objects supported by a constrained device.  Given a known
   set of YANG modules, both server and client can calculate the YANG
   hashes independently, and offline.

   Even though collisions are expected to happen rather rarely, they
   need to be considered.  Collisions can be detected before deployment,
   if the vendor knows which modules are supported by the server, and
   hence all YANG hashes can be calculated.  Collisions are only an
   issue when they occur at the same server.  The client needs to
   discover any re-hash mappings on a per server basis.

   If the server needs to re-hash any object identifiers, then it MUST
   create a "rehash-map" entry for all its rehashed objects, as
   described in the following YANG module.

5.3.  ietf-yang-hash YANG Module

   The "ietf-yang-hash" YANG module is used by the server to report any
   objects that have been mapped to produce a new hash value that does
   not conflict with any other YANG hash values used by the server.

   YANG tree diagram for "ietf-yang-hash" module:


     +--ro yang-hash
         +--ro rehash* [hash]
            +--ro hash      uint32
            +--ro object*
               +--ro module     string
               +--ro newhash    uint32
               +--ro pathlen?   uint32
               +--ro path?      string



   <CODE BEGINS> file "ietf-yang-hash@2015-06-06.yang"

   module ietf-yang-hash {
     namespace "urn:ietf:params:xml:ns:yang:ietf-yang-hash";
     prefix "yh";

     organization
       "IETF CORE (Constrained RESTful Environments) Working Group";

     contact
       "WG Web:   <http://tools.ietf.org/wg/core/>
        WG List:  <mailto:core@ietf.org>



van der Stok, et al.     Expires January 6, 2016               [Page 37]


Internet-Draft                    CoMI                         July 2015


        WG Chair: Carsten Bormann
                  <mailto:cabo@tzi.org>

        WG Chair: Andrew McGregor
                  <mailto:andrewmcgr@google.com>

        Editor:   Peter van der Stok
                  <mailto:consultancy@vanderstok.org>

        Editor:   Andy Bierman
                  <mailto:andy@yumaworks.com>

        Editor:   Juergen Schoenwaelder
                  <mailto:j.schoenwaelder@jacobs-university.de>

        Editor:   Anuj Sehgal
                  <mailto:s.anuj@jacobs-university.de>";

     description
       "This module contains re-hash information for the CoMI protocol.

        Copyright (c) 2015 IETF Trust and the persons identified as
        authors of the code.  All rights reserved.

        Redistribution and use in source and binary forms, with or
        without modification, is permitted pursuant to, and subject
        to the license terms contained in, the Simplified BSD License
        set forth in Section 4.c of the IETF Trust's Legal Provisions
        Relating to IETF Documents
        (http://trustee.ietf.org/license-info).

        This version of this YANG module is part of RFC XXXX; see
        the RFC itself for full legal notices.";

     // RFC Ed.: replace XXXX with actual RFC number and remove this
     // note.

     // RFC Ed.: remove this note
     // Note: extracted from draft-vanderstok-core-comi-07.txt

     // RFC Ed.: update the date below with the date of RFC publication
     // and remove this note.
     revision 2015-06-06 {
       description
         "Initial revision.";
       reference
         "RFC XXXX: CoMI Protocol.";
     }



van der Stok, et al.     Expires January 6, 2016               [Page 38]


Internet-Draft                    CoMI                         July 2015


     container yang-hash {
       config false;
       description
         "Contains information on the YANG Hash values used by
          the server.";

       list rehash {
         key hash;
         description
           "Each entry describes an re-hash mapping in use by
            the server.";

         leaf hash {
           type uint32;
           description
             "The hash value that has a collision.  This hash value
              cannot be used on the server.  The rehashed
              value for each affected object must be used instead.";
         }

         list object {
           min-elements 2;

           description
             "Each entry identifies one of the objects involved in the
              hash collision and contains the rehash information for
              that object.";

           leaf module {
             type string;
             mandatory true;
             description
               "The module name for this object.";
           }

           leaf newhash {
             type uint32;
             mandatory true;
             description
               "The new hash value for this object.";
           }

           leaf pathlen {
             type uint32;
             description
               "The length of the path expression of the object with
                this hash value.  This object MUST be included
                for any objects in the rehash entry with the



van der Stok, et al.     Expires January 6, 2016               [Page 39]


Internet-Draft                    CoMI                         July 2015


                same 'module' value.";
           }

           leaf path {
             type string;
             description
               "The path expression of the object with
                this hash value. This object MUST be included
                for any objects in the rehash entry with the
                same 'module' and 'pathlen' values.";
           }

         }
       }
     }
   }

   <CODE ENDS>


5.4.  YANG Re-Hash Examples

   In this example there are three YANG modules, "foo", "bar", and
   "bar1".



























van der Stok, et al.     Expires January 6, 2016               [Page 40]


Internet-Draft                    CoMI                         July 2015


   module foo {
     namespace "http://example.com/ns/foo";
     prefix "f";
     revision 2015-06-07;

     container A {
       list B {
         key name;
         leaf name { type string; }
         leaf col1 { type int32; }
         leaf counter1 { type uint32; }
       }
     }
   }

   module bar {
     namespace "http://example.com/ns/bar";
     prefix "b";
     revision 2015-06-07;

     leaf bar { type string; }
   }

   module bar1 {
     namespace "http://example.com/ns/bar1";
     prefix "b1";
     import foo { prefix f; }
     revision 2015-06-07;

     augment /f:A/f:B {
       leaf bar1 { type string; }
     }
   }


   This set of 3 YANG modules containing a total of 7 objects produces
   the following object list.  Note that actual hash values are not
   shown, since these modules do not actually cause the YANG Hash
   clashes described in the examples.












van der Stok, et al.     Expires January 6, 2016               [Page 41]


Internet-Draft                    CoMI                         July 2015


      Object    Path               Hash

   foo:

      container /f:A                h1
      list      /f:A/f:B            h2
      leaf      /f:A/f:B/f:name     h3
      leaf      /f:A/f:B/f:col1     h4
      leaf      /f:A/f:B/f:counter1 h5

   bar:

      leaf      /b:bar              h6

   bar1:

     leaf      /f:A/f:B/b1:bar1     h7


5.4.1.  Multiple Modules

   In this example, assume that the following 3 objects produce the same
   hash value, so 'h3', 'h6', and 'h7' have the same value (e.g.
   '1234'):

   The client might retrieve the container "/f:A" which could cause its
   sub-nodes to be returned.  Instead, the server will return a message
   with the resource type "core.mg.", representing the "yang-hash" data
   structure.






















van der Stok, et al.     Expires January 6, 2016               [Page 42]


Internet-Draft                    CoMI                         July 2015


   REQ: GET example.com/mg/h1

   RES: 4.00 "Bad Request" (Content-Format: application/cbor)
   {
      "ietf-yang-hash:yang-hash" : {
        "rehash" : [
           {
             "hash" : 1234,
              "object" : [
                {
                  "module" : "foo",
                  "newhash" : 5678
                },
                {
                  "module" : "bar",
                  "newhash" : 3579
                },
                {
                  "module" : "bar1",
                  "newhash" : 8182
                }
              ]
           }
        ]
     }
   }


5.4.2.  Same Module

   In this example, assume that the following 4 objects produce the same
   hash value, so 'h3', 'h5', 'h6', and 'h7' all have the same value
   (e.g. '1234'):

   The client might retrieve the list "/f:A/f:B" which would cause its
   sub-nodes to be returned.  Instead, the server will return a message
   with the resource type "core.mg.yanh-hash", representing the "yang-
   hash" data structure.  Note that the "pathlen" field is not needed
   for the 'h6' and 'h7' objects.












van der Stok, et al.     Expires January 6, 2016               [Page 43]


Internet-Draft                    CoMI                         July 2015


   REQ: GET example.com/mg/h2?keys="entry1"

   RES: 4.00 "Bad Request" (Content-Format: application/cbor)
   {
      "ietf-yang-hash:yang-hash" : {
        "rehash" : [
           {
             "hash" : 1234,
              "object" : [
                {
                  "module" : "foo",
                  "newhash" : 5678,
                  "pathlen" : 15
                },
                {
                  "module" : "foo",
                  "newhash" : 7863,
                  "pathlen" : 19
                },
                {
                  "module" : "bar",
                  "newhash" : 3579
                },
                {
                  "module" : "bar1",
                  "newhash" : 8182
                }
              ]
           }
        ]
     }
   }


5.4.3.  Same Module and Same Path Length

   In this example, assume that the following 5 objects produce the same
   hash value, so 'h3', 'h4', 'h5', 'h6', and 'h7' all have the same
   value (e.g. '1234'):

   The client might retrieve the list "/f:A/f:B" which would cause its
   sub-nodes to be returned.  Instead, the server will return a message
   with the resource type "core.mg.yang-hash", representing the "yang-
   hash" data structure.  The "path" leaf is included 2 entries because
   the "module" and "pathlen" values are the same for the objects.






van der Stok, et al.     Expires January 6, 2016               [Page 44]


Internet-Draft                    CoMI                         July 2015


   REQ: GET example.com/mg/h2?keys="entry2"

   RES: 4.00 "Bad Request" (Content-Format: application/cbor)
   {
      "ietf-yang-hash:yang-hash" : {
        "rehash" : [
           {
             "hash" : 1234,
              "object" : [
                {
                  "module" : "foo",
                  "newhash" : 5678,
                  "pathlen" : 15,
                  "path" : "/f:A/f:B/f:name"
                },
                {
                  "module" : "foo",
                  "newhash" : 7863,
                  "pathlen" : 15,
                  "path" : "/f:A/f:B/f:col1"
                },
                {
                  "module" : "foo",
                  "newhash" : 9172,
                  "pathlen" : 19
                },
                {
                  "module" : "bar",
                  "newhash" : 3579
                },
                {
                  "module" : "bar1",
                  "newhash" : 8182
                }
              ]
           }
        ]
     }
   }


5.5.  YANG Hash in URL

   When a URL contains a YANG hash, it is encoded using base64url "URL
   and Filename safe" encoding as specified in [RFC4648].

   The hash H is represented as a 30-bit integer, divided into five
   6-bit integers as follows:



van der Stok, et al.     Expires January 6, 2016               [Page 45]


Internet-Draft                    CoMI                         July 2015


   B1 = (H & 0x3f000000) >> 24
   B2 = (H & 0xfc0000) >> 18
   B3 = (H & 0x03f000) >> 12
   B4 = (H & 0x000fc0) >> 6
   B5 =  H & 0x00003f

   Subsequently, each 6-bit integer Bx is translated into a character Cx
   using Table 2 from [RFC4648], and a string is formed by concatenating
   the characters in the order C1, C2, C3, C4, C5.

   For example, the YANG hash 0x29abdcca is encoded as "pq9zK".

6.  Mapping YANG to CBOR

6.1.  High level encoding

   When encoding YANG variables in CBOR, the CBOR encodings entry is a
   map.  The key is the YANG hash of entry variable, whereas the value
   contains its value.

   For encoding of the variable values, a CBOR datatype is used.
   Section 6.2 provides the mapping between YANG datatypes and CBOR
   datatypes.

6.2.  Conversion from YANG datatypes to CBOR datatypes

   Table 1 defines the mapping between YANG datatypes and CBOR
   datatypes.

   Elements of types not in this table, and of which the type cannot be
   inferred from a type in this table, are ignored in the CBOR encoding
   by default.  Examples include the "description" and "key" elements.
   However, conversion rules for some elements to CBOR MAY be defined
   elsewhere.

   +--------------+------------------+---------------------------------+
   | YANG type    | CBOR type        | Specification                   |
   +--------------+------------------+---------------------------------+
   | int8, int16, | unsigned int     | The CBOR integer type depends   |
   | int32,       | (major type 0)   | on the sign of the actual       |
   | int64,       | or negative int  | value.                          |
   | uint16,      | (mayor type 1)   |                                 |
   | uint32,      |                  |                                 |
   | uint64,      |                  |                                 |
   | decimal64    |                  |                                 |
   |              |                  |                                 |
   | boolean      | either "true"    |                                 |
   |              | (major type 7,   |                                 |



van der Stok, et al.     Expires January 6, 2016               [Page 46]


Internet-Draft                    CoMI                         July 2015


   |              | simple value 21) |                                 |
   |              | or "false"       |                                 |
   |              | (major type 7,   |                                 |
   |              | simple value 20) |                                 |
   |              |                  |                                 |
   | string       | text string      |                                 |
   |              | (major type 3)   |                                 |
   |              |                  |                                 |
   | enumeration  | unsigned int     |                                 |
   |              | (major type 0)   |                                 |
   |              |                  |                                 |
   | bits         | array of text    | Each text string contains the   |
   |              | strings          | name of a bit value that is     |
   |              |                  | set.                            |
   |              |                  |                                 |
   | binary       | byte string      |                                 |
   |              | (major type 2)   |                                 |
   |              |                  |                                 |
   | empty        | null (major type | TBD: This MAY not be applicable |
   |              | 7, simple value  | to true MIBs, as SNMP may not   |
   |              | 22)              | support empty variables...      |
   |              |                  |                                 |
   | union        |                  | Similar to the JSON             |
   |              |                  | transcription from              |
   |              |                  | [I-D.ietf-netmod-yang-json],    |
   |              |                  | the elements in a union MUST be |
   |              |                  | determined using the procedure  |
   |              |                  | specified in section 9.12 of    |
   |              |                  | [RFC6020].                      |
   |              |                  |                                 |
   | leaf-list    | array (major     | The array is encapsulated in    |
   |              | type 4)          | the map associated with the     |
   |              |                  | YANG variable.                  |
   |              |                  |                                 |
   | list         | array (major     | Each array element contains a   |
   |              | type 4) of maps  | map of associated YANG hash -   |
   |              | (major type 5)   | value pairs.                    |
   |              |                  |                                 |
   | container    | map (major type  | The map contains YANG hash -    |
   |              | 5)               | value pairs corresponding to    |
   |              |                  | the elements in the container.  |
   |              |                  |                                 |
   | smiv2:oid    | array of         | Each integer contains an        |
   |              | integers         | element of the OID, the first   |
   |              |                  | integer in the array            |
   |              |                  | corresponds to the most left    |
   |              |                  | element in the OID.             |
   +--------------+------------------+---------------------------------+



van der Stok, et al.     Expires January 6, 2016               [Page 47]


Internet-Draft                    CoMI                         July 2015


               Table 1: Conversion of YANG datatypes to CBOR

7.  Error Handling

   In case a request is received which cannot be processed properly, the
   managed entity 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 encoded in CBOR, using the following
   structure:

   TODO: Adapt RESTCONF <errors> data structure for use in CoMI.  Need
   to select the most important fields like <error-path>.


   errorMsg     : ErrorMsg;

   *ErrorMsg {
     errorCode  : uint;
     ?errorText : tstr;
   }

   The variable "errorCode" has one of the values from the table below,
   and the OPTIONAL "errorText" field contains a human readable
   explanation of the error.

   +----------------+----------------+---------------------------------+
   | CoMI Error     | CoAP Error     | Description                     |
   | Code           | Code           |                                 |
   +----------------+----------------+---------------------------------+
   | 0              | 4.00           | General error                   |
   |                |                |                                 |
   | 1              | 4.00           | Malformed CBOR data             |
   |                |                |                                 |
   | 2              | 4.00           | Incorrect CBOR datatype         |
   |                |                |                                 |
   | 3              | 4.00           | Unknown MIB variable            |
   |                |                |                                 |
   | 4              | 4.00           | Unknown conversion table        |
   |                |                |                                 |
   | 5              | 4.05           | Attempt to write read-only      |
   |                |                | variable                        |
   |                |                |                                 |
   | 0..2           | 5.01           | Access exceptions               |
   |                |                |                                 |
   | 0..18          | 5.00           | SMI error status                |
   +----------------+----------------+---------------------------------+



van der Stok, et al.     Expires January 6, 2016               [Page 48]


Internet-Draft                    CoMI                         July 2015


   The CoAP error code 5.01 is associated with the exceptions defined in
   [RFC3416] and CoAP error code 5.00 is associated with the error-
   status defined in [RFC3416].

8.  Security Considerations

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

   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 authorisation
   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 authorisation 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.

9.  IANA Considerations

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

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

   'rt="core.mg.modset"' needs registration with IANA.

   'rt="core.mg.yang-hash"' needs registration with IANA.

   'rt="core.mg.yang-stream"' needs registration with IANA.

   Content types to be registered:

   o  application/comi+cbor







van der Stok, et al.     Expires January 6, 2016               [Page 49]


Internet-Draft                    CoMI                         July 2015


10.  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.  The draft has benefited from comments
   (alphabetical order) by Dee Denteneer, Esko Dijk, Michael van
   Hartskamp, Zach Shelby, Michel Veillette, Michael Verschoor, and
   Thomas Watteyne.  The CBOR encoding borrows extensively from Ladislav
   Lhotka's description on conversion from YANG to JSON.

   This material is based upon work supported by Philips Research,
   Huawei, and The Space & Terrestrial Communications Directorate
   (S&TCD); the latter under Contract No.  W15P7T-13-C-A616.  Any
   opinions, findings and conclusions or recommendations expressed in
   this material are those of the author(s) and do not necessarily
   reflect the views of Philips Research, Huawei, or The Space &
   Terrestrial Communications Directorate (S&TCD).

   Juergen Schoenwaelder and Anuj Sehgal were partly funded by Flamingo,
   a Network of Excellence project (ICT-318488) supported by the
   European Commission under its Seventh Framework Programme.

11.  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



van der Stok, et al.     Expires January 6, 2016               [Page 50]


Internet-Draft                    CoMI                         July 2015


   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

   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




van der Stok, et al.     Expires January 6, 2016               [Page 51]


Internet-Draft                    CoMI                         July 2015


   o  Yang libary 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 hierachy

   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

12.  References

12.1.  Normative References

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





van der Stok, et al.     Expires January 6, 2016               [Page 52]


Internet-Draft                    CoMI                         July 2015


   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, July 2008.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC7049]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", RFC 7049, October 2013.

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252, June 2014.

   [I-D.becker-core-coap-sms-gprs]
              Becker, M., Li, K., Kuladinithi, K., and T. Poetsch,
              "Transport of CoAP over SMS", draft-becker-core-coap-sms-
              gprs-05 (work in progress), August 2014.

   [I-D.ietf-core-block]
              Bormann, C. and Z. Shelby, "Block-wise transfers in CoAP",
              draft-ietf-core-block-17 (work in progress), March 2015.

   [I-D.ietf-core-observe]
              Hartke, K., "Observing Resources in CoAP", draft-ietf-
              core-observe-16 (work in progress), December 2014.

   [I-D.ietf-netmod-yang-json]
              Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              draft-ietf-netmod-yang-json-04 (work in progress), June
              2015.

   [I-D.ietf-netconf-restconf]
              Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", draft-ietf-netconf-restconf-06 (work in
              progress), June 2015.

   [I-D.vanderstok-core-patch]
              Stok, P. and A. Sehgal, "Patch Method for Constrained
              Application Protocol (CoAP)", draft-vanderstok-core-
              patch-00 (work in progress), March 2015.





van der Stok, et al.     Expires January 6, 2016               [Page 53]


Internet-Draft                    CoMI                         July 2015


12.2.  Informative References

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

   [RFC3410]  Case, J., Mundy, R., Partain, D., and B. Stewart,
              "Introduction and Applicability Statements for Internet-
              Standard Management Framework", RFC 3410, December 2002.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              December 2002.

   [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
              (USM) for version 3 of the Simple Network Management
              Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.

   [RFC3416]  Presuhn, R., "Version 2 of the Protocol Operations for the
              Simple Network Management Protocol (SNMP)", STD 62, RFC
              3416, December 2002.

   [RFC3418]  Presuhn, R., "Management Information Base (MIB) for the
              Simple Network Management Protocol (SNMP)", STD 62, RFC
              3418, December 2002.

   [RFC4293]  Routhier, S., "Management Information Base for the
              Internet Protocol (IP)", RFC 4293, April 2006.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, September 2007.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)", RFC
              6241, June 2011.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC6643]  Schoenwaelder, J., "Translation of Structure of Management
              Information Version 2 (SMIv2) MIB Modules to YANG
              Modules", RFC 6643, July 2012.

   [RFC6650]  Falk, J. and M. Kucherawy, "Creation and Use of Email
              Feedback Reports: An Applicability Statement for the Abuse
              Reporting Format (ARF)", RFC 6650, June 2012.



van der Stok, et al.     Expires January 6, 2016               [Page 54]


Internet-Draft                    CoMI                         July 2015


   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, August 2012.

   [RFC6775]  Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
              "Neighbor Discovery Optimization for IPv6 over Low-Power
              Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
              November 2012.

   [RFC7223]  Bjorklund, M., "A YANG Data Model for Interface
              Management", RFC 7223, May 2014.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228, May 2014.

   [RFC7317]  Bierman, A. and M. Bjorklund, "A YANG Data Model for
              System Management", RFC 7317, August 2014.

   [I-D.ietf-core-interfaces]
              Shelby, Z. and M. Vial, "CoRE Interfaces", draft-ietf-
              core-interfaces-02 (work in progress), November 2014.

   [I-D.ersue-constrained-mgmt]
              Ersue, M., Romascanu, D., and J. Schoenwaelder,
              "Management of Networks with Constrained Devices: Problem
              Statement, Use Cases and Requirements", draft-ersue-
              constrained-mgmt-03 (work in progress), February 2013.

   [I-D.ietf-lwig-coap]
              Kovatsch, M., Bergmann, O., and C. Bormann, "CoAP
              Implementation Guidance", draft-ietf-lwig-coap-02 (work in
              progress), June 2015.

   [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.

   [DTLS-size]
              Hummen, R., Shafagh, H., Raza, S., Voigt, T., and K.
              Wehrle, "Delegation-based Authentication and Authorization
              for the IP-based Internet of Things", Web
              http://www.vs.inf.ethz.ch/publ/papers/
              mshafagh_secon14.pdf.






van der Stok, et al.     Expires January 6, 2016               [Page 55]


Internet-Draft                    CoMI                         July 2015


   [dcaf]     Bormann, C., Bergmann, O., and S. Gerdes, "Delegated
              Authenticated Authorization for Constrained Environments",
              Private Information .

   [openwsn]  Watteijne, T., "Coap size in Openwsn", Web
              http://builder.openwsn.org/.

   [Erbium]   Kovatsch, M., "Erbium Memory footprint for coap-18",
              Private Communication .

   [management]
              Schoenwalder, J. and A. Sehgal, "Management of the
              Internet of Things", Web http://cnds.eecs.jacobs-
              university.de/slides/2013-im-iot-management.pdf, 2013.

   [I-D.ietf-netconf-yang-patch]
              Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
              Media Type", draft-ietf-netconf-yang-patch-04 (work in
              progress), June 2015.

Appendix A.  Payload and Server sizes

   This section provides information on code sizes and payload sizes for
   a set of management servers.  Approximate code sizes are:



























van der Stok, et al.     Expires January 6, 2016               [Page 56]


Internet-Draft                    CoMI                         July 2015


   +---------------+------------+-------+-------+----------------------+
   | Code          | processor  | Text  | Data  | reference            |
   +---------------+------------+-------+-------+----------------------+
   | Observe agent | erbium     | 800   | n/a   | [Erbium]             |
   |               |            |       |       |                      |
   | CoAP server   | MSP430     | 1K    | 6     | [openwsn]            |
   |               |            |       |       |                      |
   | SNMP server   | ATmega128  | 9K    | 700   | [management]         |
   |               |            |       |       |                      |
   | Secure SNMP   | ATmega128  | 30K   | 1.5K  | [management]         |
   |               |            |       |       |                      |
   | DTLS server   | ATmega128  | 37K   | 2K    | [management]         |
   |               |            |       |       |                      |
   | NETCONF       | ATmega128  | 23K   | 627   | [management]         |
   |               |            |       |       |                      |
   | JSON parser   | CC2538     | 4.6K  | 8     | [dcaf]               |
   |               |            |       |       |                      |
   | CBOR parser   | CC2538     | 1.5K  | 2.6K  | [dcaf]               |
   |               |            |       |       |                      |
   | DTLS server   | ARM7       | 15K   | 4     | [I-D.ietf-lwig-coap] |
   |               |            |       |       |                      |
   | DTLS server   | MSP430     | 15K   | 4     | [DTLS-size]          |
   |               |            |       |       |                      |
   | Certificate   | MSP430     | 23K   |       | [DTLS-size]          |
   |               |            |       |       |                      |
   | Crypto        | MSP430     | 2-8K  |       | [DTLS-size]          |
   +---------------+------------+-------+-------+----------------------+

   Thomas says that the size of the CoAP server is rather arbitrary, as
   its size depends mostly on the implementation of the underlying
   library modules and interfaces.

   Payload sizes are compared for the following request payloads, where
   each attribute value is null (N.B. these sizes are educated guesses,
   will be replaced with generated data).  The identifier are assumed to
   be a string representation of the OID.  Sizes for SysUpTime differ
   due to preambles of payload.  "CBOR opt" stands for CBOR payload
   where the strings are replaced by table numbers.













van der Stok, et al.     Expires January 6, 2016               [Page 57]


Internet-Draft                    CoMI                         July 2015


     +-------------------------+-----------+------+------+----------+
     | Request                 | BERR SNMP | JSON | CBOR | CBOR opt |
     +-------------------------+-----------+------+------+----------+
     | IPnetTOMediaTable       | 205       | 327  | ~327 | ~51      |
     |                         |           |      |      |          |
     | lowpanIfStatsTable      |           | 710  | 614  | 121      |
     |                         |           |      |      |          |
     | sysUpTime               | 29        | 13   | ~13  | 20       |
     |                         |           |      |      |          |
     | RESTCONF example        |           |      |      |          |
     +-------------------------+-----------+------+------+----------+

Appendix B.  Notational Convention for CBOR data

   To express CBOR structures [RFC7049], this document uses the
   following conventions:

   A declaration of a CBOR variable has the form:

      name : datatype;

   where "name" is the name of the variable, and "datatype" its CBOR
   datatype.

   The name of the variable has no encoding in the CBOR data.

   "datatype" can be a CBOR primitive such as:

   tstr:  A text string (major type 3)

   uint:  An unsigned integer (major type 0)

   map(x,y):  A map (major type 5), where each first element of a pair
      is of datatype x, and each second element of datatype y.  A '.'
      character for either x or y means that all datatypes for that
      element are valid.

   A datatype can also be a CBOR structure, in which case the variable's
   "datatype" field contains the name of the CBOR structure.  Such CBOR
   structure is defined by a character sequence consisting of first its
   name, then a '{' character, then its subfields and finally a '}'
   character.

   A CBOR structure can be encapsulated in an array, in which case its
   name in its definition is preceded by a '*' character.  Otherwise the
   structure is just a grouping of fields, but without actual encoding
   of such grouping.




van der Stok, et al.     Expires January 6, 2016               [Page 58]


Internet-Draft                    CoMI                         July 2015


   The name of an optional field is preceded by a '?' character.  This
   means, that the field may be omitted if not required.

Appendix C.  comparison with LWM2M

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

   Unlike CoMI, which enables the use of SMIv2 and YANG data models for
   device management, LWM2M defines a new object resource model.  This
   means that data models need to be redefined in order to use LWM2M.
   In contrast, CoMI provides access to a large variety of SMIv2 and
   YANG data modules that can be used immediately.

   Objects and resources within CoMI are identified with a YANG hash
   value, however, each object is described as a link in the CoRE Link
   Format by LWM2M.  This approach by LWM2M can lead to larger complex
   URIs and more importantly payloads can grow large in size.  Using a
   hash value to represent the objects and resources allows URIs and
   payloads to be smaller in size, which is important for constrained
   devices that may not have enough resources to process large messages.

   LWM2M encodes payload data in Type-length-value (TLV), JSON or plain
   text formats.  While the TLV encoding is binary and can result in
   reduced message sizes, JSON and plain text are likely to result in
   large message sizes when lots of resources are being monitored or
   configured.  Furthermore, CoMI's use of CBOR gives it an advantage
   over the LWM2M's TLV encoding as well since this too is more
   efficient [citation needed].

   CoMI is aligned with RESTCONF for constrained devices and uses YANG
   data models that have objects containing resources organized in a
   tree-like structure.  On the other hand, LWM2M uses a very flat data
   model that follows the "object/instance/resouce" format, with no
   possibility to have subresouces.  Complex data models are, as such,
   harder to model with LWM2M.

   In situations where resources need to be modified, CoMI uses the CoAP
   PATCH operation when resources are modified partially.  However,
   LWM2M uses the CoAP PUT and POST operations, even when a subset of
   the resource needs modifications.

Authors' Addresses







van der Stok, et al.     Expires January 6, 2016               [Page 59]


Internet-Draft                    CoMI                         July 2015


   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


   Juergen Schoenwaelder
   Jacobs University
   Campus Ring 1
   Bremen  28759
   Germany

   Email: j.schoenwaelder@jacobs-university.de


   Anuj Sehgal
   consultant
   Campus Ring 1
   Bremen  28759
   Germany

   Email: anuj@iurs.org

















van der Stok, et al.     Expires January 6, 2016               [Page 60]


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/