core P. van der Stok
Internet-Draft consultant
Intended status: Standards Track B. Greevenbosch
Expires: April 30, 2015 Huawei Technologies
A. Bierman
YumaWorks
J. Schoenwaelder
A. Sehgal
Jacobs University
October 27, 2014
CoAP Management Interface
draft-vanderstok-core-comi-05
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
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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 April 30, 2015.
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Copyright Notice
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document authors. All rights reserved.
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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
3. CoAP Interface . . . . . . . . . . . . . . . . . . . . . . . 11
4. MG Function Set . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Data Retrieval . . . . . . . . . . . . . . . . . . . . . 13
4.1.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1.2. Mapping of the 'select' Parameter . . . . . . . . . . 13
4.1.3. Retrieval Examples . . . . . . . . . . . . . . . . . 13
4.2. Data Editing . . . . . . . . . . . . . . . . . . . . . . 16
4.2.1. POST . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2.2. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2.3. DELETE . . . . . . . . . . . . . . . . . . . . . . . 17
4.3. Module Discovery . . . . . . . . . . . . . . . . . . . . 17
4.4. Error Return Codes . . . . . . . . . . . . . . . . . . . 18
5. Mapping YANG to CoMI payload . . . . . . . . . . . . . . . . 19
5.1. YANG Hash Generation . . . . . . . . . . . . . . . . . . 20
5.2. Re-Hash Procedure . . . . . . . . . . . . . . . . . . . . 20
5.3. ietf-yang-hash YANG Module . . . . . . . . . . . . . . . 21
5.3.1. YANG Re-Hash Example . . . . . . . . . . . . . . . . 23
5.4. The 'keys' Query Parameter . . . . . . . . . . . . . . . 24
6. Mapping YANG to CBOR . . . . . . . . . . . . . . . . . . . . 25
6.1. Conversion from YANG datatypes to CBOR datatypes . . . . 25
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8. Trap functions . . . . . . . . . . . . . . . . . . . . . . . 27
9. Object access management . . . . . . . . . . . . . . . . . . 27
9.1. Notify destinations . . . . . . . . . . . . . . . . . . . 27
10. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 27
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11. Security Considerations . . . . . . . . . . . . . . . . . . . 29
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
14. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 30
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
15.1. Normative References . . . . . . . . . . . . . . . . . . 31
15.2. Informative References . . . . . . . . . . . . . . . . . 32
Appendix A. Payload and Server sizes . . . . . . . . . . . . . . 35
Appendix B. Notational Convention for CBOR data . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
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] datastores. RESTCONF messages can be
encoded in XML [XML] or JSON. 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 exist 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
in line with the design objectives of 6lowpan [RFC4944] [RFC6775],
RPL [RFC6650], and CoAP [RFC7252].
RESTCONF uses the HTTP methods HEAD, OPTIONS, and PATCH, which are
not available in CoAP. The use of TCP is also a problem in HTTP.
The transport protocols available fo CoAP are much better suited to
constrained networks.
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CoMI is low resource oriented, uses CoAP, and only supports the
methods GET, PUT, POST and DELETE. CoMI uses CBOR as the data
format. To support small payloads, CoMI use an additional data
identifier string to number conversion to minimise CBOR payloads. 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. 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 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 payload of CoMI is encoded in CBOR [RFC7049] which is
automatically generated from JSON [JSON]. CBOR has a binary format
and hence has more coding efficiency than JSON.
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. 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.
CoMI uses a simple URI to access the management object resources.
Complexity introduced by module name, context specification, or row
selection, is expressed with uri-query attributes. The choice for
uri-query attributes makes the URI structure less context dependent.
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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
datastore
server
The following terms are defined in the YANG data modeling language
[RFC6020]:
container
data node
key
key leaf
leaf
leaf-list
list
The following terms are defined in RESTCONF protocol
[I-D.ietf-netconf-restconf]:
data resource
datastore resource
edit operation
query parameter
target resource
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unified datastore
The following terms are defined in this document:
YANG hash: CoMI object identifier, which is a 32-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.
The following list contains the abbreviations used in this document.
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.
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Client
+--------------------------------------------------------------+
| +--------------+ +--------------+ |
| | SMIv2 | > | YANG | > COAP |
| |description(2)| |description(1)| Request(3) |
| ---------------- +--------------+ [ * |
+-----------------------------*-----------[---------*----------+
* [ *
* [ +-----------+
mapping * security[ | Network |
* (8) [ | packet(4) |
* [ +-----------+
Server * [ *
+-----------------------------*-----------[---------*----------+
| * [ * |
| * Retrieval, |
| * Modification(5) |
| \*/ * |
| +-------------------------------------------------*--------+ |
| | +--------------+ +--------------+ +------------+ | |
| | | statistics | |configuration | |Operational | | |
| | | (6c) | | (6b) | | state(6a) | | |
| | +--------------+ +--------------+ +------------+ | |
| | variable store (6) * | |
| +-------------------------------------------------*--------+ |
| * |
| Variable |
| Instrumentation(7)|
+--------------------------------------------------------------+
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.
o The client receives the performance characteristics on a regular
basis or on request.
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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.
The components in Figure 1 have the following high-level
functionality.
o The instrumentation variables and parameters are described in the
YANG or SMIv2 language.
o Descriptions in the SMIv2 language are translated into the YANG
language.
o The YANG description serves as input to the writers of application
and instrumentation code and the humans analysing the returned
values (arrow from YANG description to Variable store). The
description is used to check the correctness of the CoAP request
and do the CBOR encoding.
o The CoAP request packs the request to read or set variables in the
packet payload, which is transmitted over the network using IP.
The CoAP request also receives values returned by the server in
the payload of a packet. On arrival of the packet in the server,
the payload is retrieved and decoded.
o Values are stored in the appropriate variables in the Variable
store, and or values are returned from the Variable store into the
payload of the packet. 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
Variable store.
o The network communication must be secured.
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.
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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 description: A description contains a set of named and
versioned modules. A module contains 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.
(2) SMIv2 description: A named module contains 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
looks like coap://entry.example.com/<path>?<query>. Fragments are
not supported. Allowed operations are PUT, 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/data/<identifier>.
(3.2) CoAP <query>: The query parameter is used to specify
additional (optional) aspects like the module name, the smi
context, 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 a
single JSON object. 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 entries in the
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Variable store. In addition, this component includes the code for
CoAP Observe and block options.
(6) Variable store: The store is composed of three parts:
Operational state, Configuration datastore, and Statistics (see
Section 2.1.
(7) Variable instrumentation: This code depends on implementation of
drivers and other node specific aspects.
(8) Security: The server MUST prevent unauthorized users from
reading or writing any data resources, however a standard access
control model for CoMI should be specified in a separate document.
DTLS is specified to secure CoAP communication.
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 datastore 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 datastore, to allow
stateless editing of any configuration variables.
The child schema nodes of the unified datastore 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
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can reference a data resource instance, or the datastore itself (to
retrieve the entire datastore or create a top-level data resource
instance). CoMI uses a 32-bit YANG hash value (based on the YANG
data node path identifier strings) to identify schema nodes in the
target resource URI.
Any message payload data is relative to the node specified in the
target resource URI in a request message. Each message is a well-
formed XML instance document or JSON object, corresponding to the
YANG schema definition specified by the target resource node. CoMI
uses the hash value for the data node identifier in the message
payloads, instead of the module-name prefixed identifier name like
RESTCONF. CoMI message payloads are based on the JSON encoding of a
RESTCONF message payload. The JSON identifier names are first
converted to their 32-bit YANG hash values and then the payload is
converted to CBOR.
3. CoAP Interface
In CoRE 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 mg resource has three sub-resources accessible with the paths:
/mg/data: YANG-based data with path "/mg/data" and using CBOR
content encoding format. This path represents a datastore
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.
/mg/moduri: URI indicating the location of the server module
information, with path "/mg/moduri" and CBOR content format. This
YANG data is encoded with plain identifier strings, not YANG hash
values.
/mg/yang-hash: URI indicating the location of the server YANG hash
information if any objects needed to be re-hashed by the server.
It has path "/mg/yang-hash" and is encoded in CBOR format. The
"ietf-yang-hash" module in 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.
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The "/mg/data" resource provides access to the YANG data resources as
described in Section 4. The "/mg/moduri" resource provides access to
a URI that can be used to retrieve an instance of the "ietf-yang-
library" module, defined in the RESTCONF draft. This module lists
the name, revision, and conformance information for each YANG module,
which a client needs to determine the YANG data model objects that
are supported by a server. This URI can be reference a local data
resource within the server, or reference a remote data resource, such
as a shared file server. The data resource identifiers are YANG hash
values, as described in Section 5.1.
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/data | core.mg.data | application/cbor |
| | | | |
| Module Set | /mg/moduri | core.mg.moduri | application/cbor |
| URI | | | |
| | | | |
| YANG Hash | /mg/yang-hash | core.mg.yang-hash | application/cbor |
| Info | | | |
+------------+---------------+-------------------+------------------+
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 datastore resource or a data resource |
| | |
| POST | Create a data resource |
| | |
| PUT | Create or replace a data resource |
| | |
| DELETE | Delete a data resource |
+-----------+-----------------------------------------------------+
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4.1. Data Retrieval
4.1.1. GET
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. 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.
There are optional query parameters for the GET method. A CoMI
server MAY implement these query parameters in order to allow common
data retrieval filtering functionality.
+----------------+--------------------------------------------------+
| Query | Description |
| Parameter | |
+----------------+--------------------------------------------------+
| content | Select config and/or non-config data resources |
| | |
| depth | Request limited sub-tree depth in the reply |
| | content |
| | |
| select | Request selected sub-trees from the target |
| | resource |
+----------------+--------------------------------------------------+
4.1.2. Mapping of the 'select' Parameter
TODO: discuss how only a limited subset of the select parameter is
used, and how the node names are changed to YANG hashes.
4.1.3. Retrieval Examples
The examples in this section use a JSON payload with one or more
entries describing the pair (objectID, value). CoMI transports the
CBOR format to transport the equivalent contents. The CBOR syntax of
the payloads is specified in Section 5.
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4.1.3.1. Single object values
A request to read the value 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/data.
A request to set the value 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.
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 (ObjectID,
value) pair.
In all examples: (1) the payload is expressed in JSON, although the
operational payload is specified to be in CBOR, and (2) the path is
expressed in readable names although the transported path is
expressed in numbers.
REQ: GET example.com/mg/data/system-state/clock/current-datetime
RES: 2.05 Content (Content-Format: application/cbor)
{
"current-datetime" : "2014-10-26T12:16:31Z"
}
TODO: convert the example above so it uses YANG hash values instead
of the string "current-datetime". Convert the target resource URI
string "system-state/clock/current-datetime" to a YANG hash value.
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:
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REQ: GET example.com/mg/data/system-state/clock
(Content-Format: application/cbor)
RES: 2.05 Content (Content-Format: application/cbor)
{
"clock" : {
"current-datetime" : "2014-10-26T12:16:51Z",
"boot-datetime" : "2014-10-21T03:00:00Z"
"timezone" : {
"timezone-location" : "Europe/Stockholm",
"timezone-utc-offset" : -60
}
}
}
TODO: convert the example above so it uses YANG hash values instead
of the strings "clock", "current-datetime", "boot-datetime",
"timezone", and "timezone-utc-offset". Convert the target resource
URI string "system-state/clock" to a YANG hash value.
The specified object can be a list. Accordingly, the returned
payload is composed of all the entries associated with the list.
Each entry is returned as a (entry name, value) pair. For example,
the GET of the ietf-ip/ipv6/neighbor list, sent by the client,
results in the following returned payload sent by the managed entity:
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REQ: GET example.com/mg/data/ietf-ip/ipv6/neighbor
(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"
}
]
}
TODO: convert the example above so it uses YANG hash values instead
of the strings "neighbor", "ip", and "link-layer-address". Convert
the target resource URI string "ietf-ip/ipv6/neighbor" to a YANG hash
value.
TODO: show examples using the "keys" parameter to select a specific
instance of a list entry.
4.2. Data Editing
CoMI allows datastore contents to be created, modified and deleted
using CoAP methods.
TODO: Should this be an optional feature? A server can choose to
only support YANG modules with read-only objects. MIN-ACCESS
conformance does not exist in YANG.
4.2.1. 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].
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There are no query parameters for the POST method.
TODO: how to support user-ordered lists in YANG? This is done with
the 'insert' and 'point' parameters in RESTCONF. In CoMI, a client
will have to replace the all list or leaf-list entries (e.g. PUT
parent container) to change the order or insert anywhere but last.
4.2.2. PUT
Data resource instances are created or replaced with the PUT method.
The PUT operation is supported in CoMI. 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.
TODO: how to support user-ordered lists in YANG? Same issue as for
POST.
4.2.3. 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.
4.3. Module Discovery
Management objects are discovered in a manner similar to the RESTCONF
protocol, not with the standard CoAP resource discovery. Only the
YANG module information needs to be retrieved by the client. The
YANG modules contain all the data resource schema and naming
information.
The "rt" attribute is used to filter resource queries as specified in
[RFC6690].
The resource "/mg/moduri" is used to retrieve the location of the
YANG module library information for the server. This data structure
is defined in the "ietf-yang-library" module in the RESTCONF draft.
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.
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TODO: Example:
Local:
REQ: GET example.com/mg/moduri
RES: 2.05 Content (Content-Format: application/cbor)
{
"moduri" : "example.com/mg/data/modules"
}
Remote:
REQ: GET example.com/mg/moduri
RES: 2.05 Content (Content-Format: application/cbor)
{
"moduri" : "example-remote-server.com/mg/data/group17/modules"
}
4.4. 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
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+-------------------------------+------------------+
| 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".
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5.1. YANG Hash Generation
The association between string value and string number is done
through a hash algorithm. The "murmur3" 32-bit hash algorithm is
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.
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 resulting 32-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 Procedure
A hash collision occurs if two different path identifier strings have
the same hash value. If the server has over 77,000 objects in its
YANG modules, then the probability of a collision is fairly high. 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.
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.
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Even though collisions are expected to happen rather rarely, they
needs 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 the altered identifier, 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 path? string
+--ro append? string
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>
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>
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Editor: Bert Greevenbosch
<mailto:andy@bert.greevenbosch@huawei.com>
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) 2014 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-05.txt
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
revision 2014-10-27 {
description
"Initial revision.";
reference
"RFC XXXX: CoMI Protocol.";
}
container yang-hash {
config false;
description
"Contains information on the YANG Hash values used by
the server.";
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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";
}
leaf path {
type string;
description
"The YANG identifier path expression that caused the
collision and is being remapped";
}
leaf append {
type string;
description
"The string that the server appended to the path
expression contained in the 'path' leaf to produce
a new path expression and therefore new hash value.
The YANG hash value for the new string (identified
by 'path' + 'append') is used to identify the
'path' object.";
}
}
}
}
5.3.1. YANG Re-Hash Example
In this example the server has an object that is already registered
when the "/foo:A/foo:B/foo:col1" object is processed. This object
path string hashes to value "a9abdcca". The server has appended the
string "_" to the path to produce a new hash ("ea7a2044") which does
not collide with any other objects.
The server would return the following information if the client
retrieved the "/mg/yang-hash" resource.
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REQ: GET example.com/mg/yang-hash
RES: 2.05 Content (Content-Format: application/cbor)
{
"ietf-yang-hash:yang-hash" : {
"rehash" : [
{
"hash" : 3933872196,
"path" :"/foo:A/foo:B/foo:col1",
"append" : "_"
}
]
}
}
5.4. 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 for the object are passed in order. The first
key leaf in the top-most list is the first key encoded in the 'keys'
parameter.
Example: 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:
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/foo:A/foo:B/foo:col1
The YANG has value for this identifier string "2846612682" (hex
"a9abdcca").
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/data/a9abdcca?keys=top,17,group1
6. Mapping YANG to CBOR
6.1. 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, | |
| | simple value 21) | |
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| | 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 ot 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 |
| | | descriptor. |
| | | |
| list | map (major type | Like the higher level map, the |
| | 5) | lower level map contains |
| | | descriptor number - value pairs |
| | | of the elements in the list. |
| | | |
| container | map (major type | The map contains descriptor |
| | 5) | number - 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. |
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+--------------+------------------+---------------------------------+
Table 1: Conversion of YANG datatypes to CBOR
7. Examples
TODO: add examples back with YANG hash values and a YANG module.
8. Trap functions
A trap can be set through the CoAP Observe [I-D.ietf-core-observe]
function. As regular with Observe, the client subscribes to the
variable by sending a GET request with an "Observe" option.
TODO: Observe example
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.
9. Object access management
Two topics are relevant: (1) the definition of the destination of
Notify messages, and (2) the creation and maintenance of "string to
number" tables.
9.1. Notify destinations
The destination of notifications need to be communicated to the
applications sending them. Draft [I-D.ietf-core-interfaces]
describes the binding of end-points to end-points on remote devices.
The object with type "binding table" contains a sequence of bindings.
The contents of bindings contains the methods, location, the interval
specifications, and the step value as suggested in
[I-D.ietf-core-interfaces]. The method "notify" has been added to
the binding methods "poll", "obs" and "push", to cater for the
binding of notification source to the receiver.
TODO: describe interface for NOTIFY destination definition.
10. 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
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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 |
+----------------+----------------+---------------------------------+
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].
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11. 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 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.
12. IANA Considerations
'rt="core.mg.data"' needs registration with IANA.
'rt="core.mg.moduri"' needs registration with IANA.
'rt="core.mg.yang-hash"' needs registration with IANA.
Content types to be registered:
o application/comi+cbor
13. Acknowledgements
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, Michael Verschoor, and Thomas Watteyne. The CBOR encoding
borrows extensively from Ladislav Lhotka's description on conversion
from YANG to JSON.
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14. Changelog
Changes from version 00 to version 01
o Focus on MIB only
o Introduced CBOR, JSON, removed BER
o defined mappings from SMI to xx
o Introduced the concept of addressable table rows
Changes from version 01 to version 02
o Focus on CBOR, used JSON for examples, removed XML and EXI
o added uri-query attributes mod and con to specify modules and
contexts
o Definition of CBOR string conversion tables for data reduction
o use of Block for multiple fragments
o Error returns generalized
o SMI - YANG - CBOR conversion
Changes from version 02 to version 03
o Added security considerations
Changes from version 03 to version 04
o Added design considerations section
o Extended comparison of management protocols in introduction
o Added automatic generation of CBOR tables
o Moved lowpan table to Appendix
Changes from version 04 to version 05
o Merged SNMP access with RESTCONF access to management objects in
small devices
o Added CoMI architecture section
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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.
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[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, "Blockwise transfers in CoAP",
draft-ietf-core-block-15 (work in progress), July 2014.
[I-D.ietf-core-observe]
Hartke, K., "Observing Resources in CoAP", draft-ietf-
core-observe-14 (work in progress), June 2014.
[I-D.ietf-json-rfc4627bis]
Bray, T., "The JSON Data Interchange Format", draft-ietf-
json-rfc4627bis-10 (work in progress), December 2013.
[I-D.ietf-netmod-yang-json]
Lhotka, L., "JSON Encoding of Data Modeled with YANG",
draft-ietf-netmod-yang-json-01 (work in progress), October
2014.
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[I-D.ietf-netconf-restconf]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", draft-ietf-netconf-restconf-02 (work in
progress), October 2014.
15.2. Informative References
[RFC1213] McCloghrie, K. and M. Rose, "Management Information Base
for Network Management of TCP/IP-based internets:MIB-II",
STD 17, RFC 1213, March 1991.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, June 2000.
[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.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[RFC4088] Black, D., McCloghrie, K., and J. Schoenwaelder, "Uniform
Resource Identifier (URI) Scheme for the Simple Network
Management Protocol (SNMP)", RFC 4088, June 2005.
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[RFC4113] Fenner, B. and J. Flick, "Management Information Base for
the User Datagram Protocol (UDP)", RFC 4113, June 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[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.
[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.
[RFC7317] Bierman, A. and M. Bjorklund, "A YANG Data Model for
System Management", RFC 7317, August 2014.
[I-D.ietf-core-groupcomm]
Rahman, A. and E. Dijk, "Group Communication for CoAP",
draft-ietf-core-groupcomm-25 (work in progress), September
2014.
[I-D.ietf-core-interfaces]
Shelby, Z. and M. Vial, "CoRE Interfaces", draft-ietf-
core-interfaces-01 (work in progress), December 2013.
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[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-6lo-lowpan-mib]
Schoenwaelder, J., Sehgal, A., Tsou, T., and C. Zhou,
"Definition of Managed Objects for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)", draft-ietf-
6lo-lowpan-mib-04 (work in progress), September 2014.
[I-D.ietf-lwig-coap]
Kovatsch, M., Bergmann, O., Dijk, E., He, X., and C.
Bormann, "CoAP Implementation Guidance", draft-ietf-lwig-
coap-01 (work in progress), July 2014.
[STD0001] "Official Internet Protocols Standard", Web
http://www.rfc-editor.org/rfcxx00.html, .
[XML] "Extensible Markup Language (XML)", Web
http://www.w3.org/xml, .
[JSON] "JavaScript Object Notation (JSON)", Web
http://www.json.org, .
[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, .
[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 , .
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[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.
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:
+---------------+------------+-------+-------+----------------------+
| 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.
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+-------------------------+-----------+------+------+----------+
| 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.
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The name of an optional field is preceded by a '?' character. This
means, that the field may be omitted if not required.
Authors' Addresses
Peter van der Stok
consultant
Phone: +31-492474673 (Netherlands), +33-966015248 (France)
Email: consultancy@vanderstok.org
URI: www.vanderstok.org
Bert Greevenbosch
Huawei Technologies Co., Ltd.
Huawei Industrial Base
Bantian, Longgang District
Shenzhen 518129
P.R. China
Email: bert.greevenbosch@huawei.com
Andy Bierman
YumaWorks
Email: andy@yumaworks.com
Juergen Schoenwaelder
Jacobs University
Campus Ring 1
Bremen 28759
Germany
Email: j.schoenwaelder@jacobs-university.de
Anuj Sehgal
Jacobs University
Campus Ring 1
Bremen 28759
Germany
Email: s.anuj@jacobs-university.de
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