CoRE Working Group Z. Shelby
Internet-Draft ARM
Intended status: Informational M. Koster
Expires: April 25, 2019 SmartThings
C. Groves
J. Zhu
Huawei
B. Silverajan, Ed.
Tampere University of Technology
October 22, 2018
Dynamic Resource Linking for Constrained RESTful Environments
draft-ietf-core-dynlink-07
Abstract
For CoAP (RFC7252), Dynamic linking of state updates between
resources, either on an endpoint or between endpoints, is defined
with the concept of Link Bindings. This specification defines
conditional observation attributes that work with Link Bindings or
with CoAP Observe (RFC7641).
Editor note
The git repository for the draft is found at https://github.com/core-
wg/dynlink
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 https://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 25, 2019.
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Copyright Notice
Copyright (c) 2018 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Link Bindings . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. The "bind" attribute and Binding Methods . . . . . . . . 4
3.1.1. Polling . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Observe . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.3. Push . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Link Relation . . . . . . . . . . . . . . . . . . . . . . 6
4. Binding and Resource Observation Attributes . . . . . . . . . 6
4.1. Minimum Period (pmin) . . . . . . . . . . . . . . . . . . 7
4.2. Maximum Period (pmax) . . . . . . . . . . . . . . . . . . 7
4.3. Change Step (st) . . . . . . . . . . . . . . . . . . . . 7
4.4. Greater Than (gt) . . . . . . . . . . . . . . . . . . . . 8
4.5. Less Than (lt) . . . . . . . . . . . . . . . . . . . . . 8
4.6. Notification Band (band) . . . . . . . . . . . . . . . . 8
4.7. Attribute Interactions . . . . . . . . . . . . . . . . . 9
5. Binding Table . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Implementation Considerations . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. Interface Description . . . . . . . . . . . . . . . . . . 12
8.2. Link Relation Type . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 13
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
12.1. Normative References . . . . . . . . . . . . . . . . . . 15
12.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 16
A.1. Greater Than (gt) example . . . . . . . . . . . . . . . . 16
A.2. Greater Than (gt) and Period Max (pmax) example . . . . . 17
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
IETF Standards for machine to machine communication in constrained
environments describe a REST protocol [RFC7252] and a set of related
information standards that may be used to represent machine data and
machine metadata in REST interfaces. CoRE Link-format [RFC6690] is a
standard for doing Web Linking [RFC8288] in constrained environments.
This specification introduces the concept of a Link Binding, which
defines a new link relation type to create a dynamic link between
resources over which state updates are conveyed. Specifically, a
Link Binding is a unidirectional link for binding the states of
source and destination resources together such that updates to one
are sent over the link to the other. CoRE Link Format
representations are used to configure, inspect, and maintain Link
Bindings. This specification additionally defines a set of
conditional Observe Attributes for use with Link Bindings and with
the standalone CoRE Observe [RFC7641] method.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This specification requires readers to be familiar with all the terms
and concepts that are discussed in [RFC8288] and [RFC6690]. This
specification makes use of the following additional terminology:
Link Binding: A unidirectional logical link between a source
resource and a destination resource, over which state information
is synchronized.
State Synchronization: Depending on the binding method (Polling,
Observe, Push) different REST methods may be used to synchronize
the resource values between a source and a destination. The
process of using a REST method to achieve this is defined as
"State Synchronization". The endpoint triggering the state
synchronization is the synchronization initiator.
Notification Band: A resource value range that results in state
sychronization. The value range may be bounded by a minimum and
maximum value or may be unbounded having either a minimum or
maximum value.
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3. Link Bindings
In a M2M RESTful environment, endpoints may directly exchange the
content of their resources to operate the distributed system. For
example, a light switch may supply on-off control information that
may be sent directly to a light resource for on-off control.
Beforehand, a configuration phase is necessary to determine how the
resources of the different endpoints are related to each other. This
can be done either automatically using discovery mechanisms or by
means of human intervention and a so-called commissioning tool. In
this specification such an abstract relationship between two
resources is defined, called a link Binding. The configuration phase
necessitates the exchange of binding information so a format
recognized by all CoRE endpoints is essential. This specification
defines a format based on the CoRE Link-Format to represent binding
information along with the rules to define a binding method which is
a specialized relationship between two resources. The purpose of
such a binding is to synchronize the content between a source
resource and a destination resource. The destination resource MAY be
a group resource if the authority component of the destination URI
contains a group address (either a multicast address or a name that
resolves to a multicast address). Since a binding is unidirectional,
the binding entry defining a relationship is present only on one
endpoint. The binding entry may be located either on the source or
the destination endpoint depending on the binding method.
3.1. The "bind" attribute and Binding Methods
A binding method defines the rules to generate the web-transfer
exchanges that synchronize state between source and destination
resources. By using REST methods content is sent from the source
resource to the destination resource.
In order to use binding methods, this specification defines a special
CoRE link attribute "bind". This is the identifier of a binding
method which defines the rules to synchronize the destination
resource. This attribute is mandatory.
+----------------+-----------+------------+
| Attribute | Parameter | Value |
+----------------+-----------+------------+
| Binding method | bind | xsd:string |
+----------------+-----------+------------+
Table 1: The bind attribute
The following table gives a summary of the binding methods defined in
this specification.
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+---------+------------+-------------+---------------+
| Name | Identifier | Location | Method |
+---------+------------+-------------+---------------+
| Polling | poll | Destination | GET |
| | | | |
| Observe | obs | Destination | GET + Observe |
| | | | |
| Push | push | Source | PUT |
+---------+------------+-------------+---------------+
Table 2: Binding Method Summary
The description of a binding method must define the following
aspects:
Identifier: This is the value of the "bind" attribute used to
identify the method.
Location: This information indicates whether the binding entry is
stored on the source or on the destination endpoint.
REST Method: This is the REST method used in the Request/Response
exchanges.
Conditions: A binding method definition must state how the condition
attributes of the abstract binding definition are actually used in
this specialized binding.
The binding methods are described in more detail below.
3.1.1. Polling
The Polling method consists of sending periodic GET requests from the
destination endpoint to the source resource and copying the content
to the destination resource. The binding entry for this method MUST
be stored on the destination endpoint. The destination endpoint MUST
ensure that the polling frequency does not exceed the limits defined
by the pmin and pmax attributes of the binding entry. The copying
process MAY filter out content from the GET requests using value-
based conditions (e.g based on the Change Step, Less Than, Greater
Than attributes).
3.1.2. Observe
The Observe method creates an observation relationship between the
destination endpoint and the source resource. On each notification
the content from the source resource is copied to the destination
resource. The creation of the observation relationship requires the
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CoAP Observation mechanism [RFC7641] hence this method is only
permitted when the resources are made available over CoAP. The
binding entry for this method MUST be stored on the destination
endpoint. The binding conditions are mapped as query string
parameters (see Section 4).
3.1.3. Push
When the Push method is assigned to a binding, the source endpoint
sends PUT requests to the destination resource when the binding
condition attributes are satisfied for the source resource. The
source endpoint MUST only send a notification request if the binding
conditions are met. The binding entry for this method MUST be stored
on the source endpoint.
3.2. Link Relation
Since Binding involves the creation of a link between two resources,
Web Linking and the CoRE Link-Format are a natural way to represent
binding information. This involves the creation of a new relation
type, named "boundto". In a Web link with this relation type, the
target URI contains the location of the source resource and the
context URI points to the destination resource.
4. Binding and Resource Observation Attributes
In addition to "bind", this specification further defines Web link
attributes allowing a fine-grained control of the type of state
synchronization along with the conditions that trigger an update.
When resource interfaces following this specification are made
available over CoAP, the CoAP Observation mechanism [RFC7641] MAY
also be used to observe any changes in a resource, and receive
asynchronous notifications as a result. A resource using an
interface description defined in this specification and marked as
Observable in its link description SHOULD support these observation
parameters.
In addition, the set of parameters are defined here allow a client to
control how often a client is interested in receiving notifications
and how much a resource value should change for the new
representation to be interesting, as query parameters.
These query parameters MUST be treated as resources that are read
using GET and updated using PUT, and MUST NOT be included in the
Observe request. Multiple parameters MAY be updated at the same time
by including the values in the query string of a PUT. Before being
updated, these parameters have no default value.
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These attributes are defined below:
+--------------------+-----------+------------------+
| Attribute | Parameter | Value |
+--------------------+-----------+------------------+
| Minimum Period (s) | pmin | xsd:integer (>0) |
| | | |
| Maximum Period (s) | pmax | xsd:integer (>0) |
| | | |
| Change Step | st | xsd:decimal (>0) |
| | | |
| Greater Than | gt | xsd:decimal |
| | | |
| Less Than | lt | xsd:decimal |
| | | |
| Notification Band | band | xsd:boolean |
+--------------------+-----------+------------------+
Table 3: Binding Attributes Summary
4.1. Minimum Period (pmin)
When present, the minimum period indicates the minimum time to wait
(in seconds) before triggering a new state synchronization (even if
it has changed). In the absence of this parameter, the minimum
period is up to the synchronization initiator. The minimum period
MUST be greater than zero otherwise the receiver MUST return a CoAP
error code 4.00 "Bad Request" (or equivalent).
4.2. Maximum Period (pmax)
When present, the maximum period indicates the maximum time in
seconds between two consecutive state synchronizations (regardless if
it has changed). In the absence of this parameter, the maximum
period is up to the synchronization initiator. The maximum period
MUST be greater than zero and MUST be greater than the minimum period
parameter (if present) otherwise the receiver MUST return a CoAP
error code 4.00 "Bad Request" (or equivalent).
4.3. Change Step (st)
When present, the change step indicates how much the value of a
resource SHOULD change before triggering a new state synchronization
(compared to the value of the previous synchronization). Upon
reception of a query including the st attribute the current value
(CurrVal) of the resource is set as the initial value (STinit). Once
the resource value differs from the STinit value (i.e. CurrVal >=
STinit + ST or CurrVal <= STint - ST) then a new state
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synchronization occurs. STinit is then set to the state
synchronization value and new state synchronizations are based on a
change step against this value. The change step MUST be greater than
zero otherwise the receiver MUST return a CoAP error code 4.00 "Bad
Request" (or equivalent).
The Change Step parameter can only be supported on resources with an
atomic numeric value.
Note: Due to the state synchronization based update of STint it may
result in that resource value received in two sequential state
synchronizations differs by more than st.
4.4. Greater Than (gt)
When present, Greater Than indicates the upper limit value the
resource value SHOULD cross before triggering a new state
synchronization. State synchronization only occurs when the resource
value exceeds the specified upper limit value. The actual resource
value is used for the synchronization rather than the gt value. If
the value continues to rise, no new state synchronizations are
generated as a result of gt. If the value drops below the upper
limit value and then exceeds the upper limit then a new state
synchronization is generated.
4.5. Less Than (lt)
When present, Less Than indicates the lower limit value the resource
value SHOULD cross before triggering a new state synchronization.
State synchronization only occurs when the resource value is less
than the specified lower limit value. The actual resource value is
used for the synchronization rather than the lt value. If the value
continues to fall no new state synchronizations are generated as a
result of lt. If the value rises above the lower limit value and
then drops below the lower limit then a new state synchronization is
generated.
4.6. Notification Band (band)
The notification band attribute allows a bounded or unbounded (based
on a minimum or maximum) value range that may trigger multiple state
synchronizations. This enables use cases where different ranges
results in differing behaviour. For example: monitoring the
temperature of machinery. Whilst the temperature is in the normal
operating range only periodic observations are needed. However as
the temperature moves to more abnormal ranges more frequent
synchronization/reporting may be needed.
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Without a notification band, a transition across a less than (lt), or
greater than (gt) limit only generates one notification. This means
that it is not possible to describe a case where multiple
notifications are sent so long as the limit is exceeded.
The band attribute works as a modifier to the behaviour of gt and lt.
Therefore, if band is present in a query, gt, lt or both, MUST be
included.
When band is present with the lt attribute, it defines the lower
bound for the notification band (notification band minimum). State
synchronization occurs when the resource value is equal to or above
the notification band minimum. If lt is not present there is no
minimum value for the band.
When band is present with the gt attribute, it defines the upper
bound for the notification band (notification band maximum). State
synchronization occurs when the resource value is equal to or below
the notification band maximum. If gt is not present there is no
maximum value for the band.
If band is present with both the gt and lt attributes, two kinds of
signaling bands are specified.
If a band is specified in which the value of gt is less than that of
lt, in-band signaling occurs. State synchronization occurs whenever
the resource value is between the notification band minimum and
maximum or is equal to the notification band minimum or maximum.
On the other hand if the band is specified in which the value of gt
is greater than that of lt, out-of-band signaling occurs. State
synchronization occurs whenever the resource value is outside the
notification band minimum and maximum or is equal to the notification
band minimum or maximum.
4.7. Attribute Interactions
Pmin, pmax, st, gt and lt may be present in the same query.
Parameters are not defined at multiple prioritization levels.
Instead, the server state machine generates a notification whenever
any of the parameter conditions are met, after which it performs a
reset on all the requested conditions. State synchronization also
occurs only once even if there are multiple conditions being met at
the same time. The reference code below illustrates how
notifications are generated.
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bool notifiable( Resource * r ) {
#define BAND r->band
#define SCALAR_TYPE ( num_type == r->type )
#define STRING_TYPE ( str_type == r->type )
#define BOOLEAN_TYPE ( bool_type == r->type )
#define PMIN_EX ( r->last_sample_time - r->last_rep_time >= r->pmin )
#define PMAX_EX ( r->last_sample_time - r->last_rep_time > r->pmax )
#define LT_EX ( r->v < r->lt ^ r->last_rep_v < r->lt )
#define GT_EX ( r->v > r->gt ^ r->last_rep_v > r->gt )
#define ST_EX ( abs( r->v - r->last_rep_v ) >= r->st )
#define IN_BAND ( ( r->gt <= r->v && r->v <= r->lt ) || ( r->lt <= r->gt && r->gt <= r->v ) || ( r->v <= r->lt && r->lt <= r->gt ) )
#define VB_CHANGE ( r->vb != r->last_rep_vb )
#define VS_CHANGE ( r->vs != r->last_rep_vs )
return (
PMIN_EX &&
( SCALAR_TYPE ?
( ( !BAND && ( GT_EX || LT_EX || ST_EX || PMAX_EX ) ) ||
( BAND && IN_BAND && ( ST_EX || PMAX_EX) ) )
: STRING_TYPE ?
( VS_CHANGE || PMAX_EX )
: BOOLEAN_TYPE ?
( VB_CHANGE || PMAX_EX )
: false )
);
}
Figure 1: Code logic for attribute interactions for observe
notification
5. Binding Table
The Binding table is a special resource that gives access to the
bindings on a endpoint. This section defines a REST interface for
Binding table resources. The Binding table resource MUST support the
Binding interface defined below. The interface supports the link-
format type.
The if= column defines the Interface Description (if=) attribute
value to be used in the CoRE Link Format for a resource conforming to
that interface. When this value appears in the if= attribute of a
link, the resource MUST support the corresponding REST interface
described in this section. The resource MAY support additional
functionality, which is out of scope for this specification.
Although this interface description is intended to be used with the
CoRE Link Format, it is applicable for use in any REST interface
definition.
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The Methods column defines the REST methods supported by the
interface, which are described in more detail below.
+-----------+----------+-------------------+-----------------+
| Interface | if= | Methods | Content-Formats |
+-----------+----------+-------------------+-----------------+
| Binding | core.bnd | GET, POST, DELETE | link-format |
+-----------+----------+-------------------+-----------------+
Table 4: Binding Interface Description
The Binding interface is used to manipulate a binding table. A
request with a POST method and a content format of application/link-
format simply appends new bindings to the table. All links in the
payload MUST have a relation type "boundto". A GET request simply
returns the current state of a binding table whereas a DELETE request
empties the table. Individual entries may be deleted from the table
by specifying the resource path in a DELETE request.
The following example shows requests for adding, retrieving and
deleting bindings in a binding table.
Req: POST /bnd/ (Content-Format: application/link-format)
<coap://sensor.example.com/s/light>;
rel="boundto";anchor="/a/light";bind="obs";pmin="10";pmax="60"
Res: 2.04 Changed
Req: GET /bnd/
Res: 2.05 Content (application/link-format)
<coap://sensor.example.com/s/light>;
rel="boundto";anchor="/a/light";bind="obs";pmin="10";pmax="60"
Req: DELETE /bnd/a/light
Res: 2.04 Changed
Req: DELETE /bnd/
Res: 2.04 Changed
Figure 2: Binding Interface Example
6. Implementation Considerations
When using multiple resource bindings (e.g. multiple Observations of
resource) with different bands, consideration should be given to the
resolution of the resource value when setting sequential bands. For
example: Given BandA (Abmn=10, Bbmx=20) and BandB (Bbmn=21, Bbmx=30).
If the resource value returns an integer then notifications for
values between and inclusive of 10 and 30 will be triggered. Whereas
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if the resolution is to one decimal point (0.1) then notifications
for values 20.1 to 20.9 will not be triggered.
The use of the notification band minimum and maximum allow for a
synchronization whenever a change in the resource value occurs.
Theoretically this could occur in-line with the server internal
sample period for the determining the resource value. Implementors
SHOULD consider the resolution needed before updating the resource,
e.g. updating the resource when a temperature sensor value changes by
0.001 degree versus 1 degree.
The initiation of a link binding can be delegated from a client to a
link state machine implementation, which can be an embedded client or
a configuration tool. Implementation considerations have to be given
to how to monitor transactions made by the configuration tool with
regards to link bindings, as well as any errors that may arise with
establishing link bindings as well as with established link bindings.
7. Security Considerations
Consideration has to be given to what kinds of security credentials
the state machine of a configuration tool or an embedded client needs
to be configured with, and what kinds of access control lists client
implementations should possess, so that transactions on creating link
bindings and handling error conditions can be processed by the state
machine.
8. IANA Considerations
8.1. Interface Description
The specification registers the "binding" CoRE interface description
link target attribute value as per [RFC6690].
Attribute Value: core.bnd
Description: The binding interface is used to manipulate a binding
table which describes the link bindings between source and
destination resources for the purposes of synchronizing their
content.
Reference: This specification. Note to RFC editor: please insert the
RFC of this specification.
Notes: None
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8.2. Link Relation Type
This specification registers the new "boundto" link relation type as
per [RFC8288].
Relation Name: boundto
Description: The purpose of a boundto relation type is to indicate
that there is a binding between a source resource and a
destination resource for the purposes of synchronizing their
content.
Reference: This specification. Note to RFC editor: please insert
the RFC of this specification.
Notes: None
Application Data: None
9. Acknowledgements
Acknowledgement is given to colleagues from the SENSEI project who
were critical in the initial development of the well-known REST
interface concept, to members of the IPSO Alliance where further
requirements for interface types have been discussed, and to Szymon
Sasin, Cedric Chauvenet, Daniel Gavelle and Carsten Bormann who have
provided useful discussion and input to the concepts in this
specification. Christian Amsuss supplied a comprehensive review of
draft -06.
10. Contributors
Matthieu Vial
Schneider-Electric
Grenoble
France
Phone: +33 (0)47657 6522
EMail: matthieu.vial@schneider-electric.com
11. Changelog
draft-ietf-core-dynlink-07
o Added reference code to illustrate attribute interactions for
observations
draft-ietf-core-dynlink-06
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o Document restructure and refactoring into three main sections
o Clarifications on band usage
o Implementation considerations introduced
o Additional text on security considerations
draft-ietf-core-dynlink-05
o Addition of a band modifier for gt and lt, adapted from draft-
groves-core-obsattr
o Removed statement prescribing gt MUST be greater than lt
draft-ietf-core-dynlink-03
o General: Reverted to using "gt" and "lt" from "gth" and "lth" for
this draft owing to concerns raised that the attributes are
already used in LwM2M with the original names "gt" and "lt".
o New author and editor added.
draft-ietf-core-dynlink-02
o General: Changed the name of the greater than attribute "gt" to
"gth" and the name of the less than attribute "lt" to "lth" due to
conlict with the core resource directory draft lifetime "lt"
attribute.
o Clause 6.1: Addressed the editor's note by changing the link
target attribute to "core.binding".
o Added Appendix A for examples.
draft-ietf-core-dynlink-01
o General: The term state synchronization has been introduced to
describe the process of synchronization between destination and
source resources.
o General: The document has been restructured the make the
information flow better.
o Clause 3.1: The descriptions of the binding attributes have been
updated to clarify their usage.
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o Clause 3.1: A new clause has been added to discuss the
interactions between the resources.
o Clause 3.4: Has been simplified to refer to the descriptions in
3.1. As the text was largely duplicated.
o Clause 4.1: Added a clarification that individual resources may be
removed from the binding table.
o Clause 6: Formailised the IANA considerations.
draft-ietf-core-dynlink Initial Version 00:
o This is a copy of draft-groves-core-dynlink-00
draft-groves-core-dynlink Draft Initial Version 00:
o This initial version is based on the text regarding the dynamic
linking functionality in I.D.ietf-core-interfaces-05.
o The WADL description has been dropped in favour of a thorough
textual description of the REST API.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
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12.2. Informative References
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
Appendix A. Examples
This appendix provides some examples of the use of binding attribute
/ observe attributes.
Note: For brevity the only the method or response code is shown in
the header field.
A.1. Greater Than (gt) example
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Observed CLIENT SERVER Actual
t State | | State
____________ | | ____________
1 | |
2 unknown | | 18.5 Cel
3 +----->| Header: GET
4 | GET | Token: 0x4a
5 | | Uri-Path: temperature
6 | | Uri-Query: gt="25"
7 | | Observe: 0 (register)
8 | |
9 ____________ |<-----+ Header: 2.05
10 | 2.05 | Token: 0x4a
11 18.5 Cel | | Observe: 9
12 | | Payload: "18.5 Cel"
13 | |
14 | |
15 | | ____________
16 ____________ |<-----+ Header: 2.05
17 | 2.05 | 26 Cel Token: 0x4a
18 26 Cel | | Observe: 16
29 | | Payload: "26 Cel"
20 | |
21 | |
Figure 3: Client Registers and Receives one Notification of the
Current State and One of a New State when it passes through the
greather than threshold of 25.
A.2. Greater Than (gt) and Period Max (pmax) example
Observed CLIENT SERVER Actual
t State | | State
____________ | | ____________
1 | |
2 unknown | | 18.5 Cel
3 +----->| Header: GET
4 | GET | Token: 0x4a
5 | | Uri-Path: temperature
6 | | Uri-Query: pmax="20";gt="25"
7 | | Observe: 0 (register)
8 | |
9 ____________ |<-----+ Header: 2.05
10 | 2.05 | Token: 0x4a
11 18.5 Cel | | Observe: 9
12 | | Payload: "18.5 Cel"
13 | |
14 | |
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15 | |
16 | |
17 | |
18 | |
19 | |
20 | |
21 | |
22 | |
23 | |
24 | |
25 | |
26 | |
27 | |
28 | |
29 | | ____________
30 ____________ |<-----+ Header: 2.05
31 | 2.05 | 23 Cel Token: 0x4a
32 23 Cel | | Observe: 30
33 | | Payload: "23 Cel"
34 | |
35 | |
36 | | ____________
37 ____________ |<-----+ Header: 2.05
38 | 2.05 | 26 Cel Token: 0x4a
39 26 Cel | | Observe: 37
40 | | Payload: "26 Cel"
41 | |
42 | |
Figure 4: Client Registers and Receives one Notification of the
Current State, one when pmax time expires and one of a new State when
it passes through the greather than threshold of 25.
Authors' Addresses
Zach Shelby
ARM
Kidekuja 2
Vuokatti 88600
FINLAND
Phone: +358407796297
Email: zach.shelby@arm.com
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Michael Koster
SmartThings
665 Clyde Avenue
Mountain View 94043
USA
Email: michael.koster@smartthings.com
Christian Groves
Australia
Email: cngroves.std@gmail.com
Jintao Zhu
Huawei
No.127 Jinye Road, Huawei Base, High-Tech Development District
Xi'an, Shaanxi Province
China
Email: jintao.zhu@huawei.com
Bilhanan Silverajan (editor)
Tampere University of Technology
Korkeakoulunkatu 10
Tampere FI-33720
Finland
Email: bilhanan.silverajan@tut.fi
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