| Internet-Draft | Dynamic Resource Linking for CoRE | February 2021 |
| Koster & Silverajan | Expires 26 August 2021 | [Page] |
This specification defines Link Bindings, which provide dynamic linking of state updates between resources, either on an endpoint or between endpoints, for systems using CoAP (RFC7252). This specification also defines Conditional Notification and Control Attributes that work with Link Bindings or with CoAP Observe (RFC7641).¶
The git repository for the draft is found at https://github.com/core-wg/dynlink¶
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 26 August 2021.¶
Copyright (c) 2021 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 (https://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.¶
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 Conditional Notification and Control Attributes for use with Link Bindings and with CoRE Observe [RFC7641].¶
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], [RFC6690] and [RFC7641]. This specification makes use of the following additional terminology:¶
A unidirectional logical link between a source resource and a destination resource, over which state information is synchronized.¶
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.¶
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.¶
This specification defines conditional attributes, which provide for fine-grained control of notification and state synchronization when using CoRE Observe [RFC7641] or Link Bindings (see Section 4). 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 marked as Observable in its link description SHOULD support these conditional attributes.¶
Note: In this draft, we assume that there are finite quantization effects in the internal or external updates to the value representing the state of a resource; specifically, that a resource state may be updated at any time with any valid value. We therefore avoid any continuous-time assumptions in the description of the conditional attributes and instead use the phrase "sampled value" to refer to a member of a sequence of values that may be internally observed from the resource state over time.¶
Conditional Notification Attributes define the conditions that trigger a notification. Conditional Notification Attributes SHOULD be evaluated on all potential notifications from a resource, whether resulting from an internal server-driven sampling process or from external update requests to the server.¶
The set of Conditional Notification Attributes defined here allow a client to control how often a client is interested in receiving notifications and how much a value should change for the new representation state to be interesting. One or more Conditional Notification Attributes MAY be included as query parameters in an Observe request.¶
Conditional Notification Attributes are defined below:¶
| Attribute | Parameter | Value |
|---|---|---|
| Greater Than | gt | xs:decimal |
| Less Than | lt | xs:decimal |
| Change Step | st | xs:decimal (>0) |
| Notification Band | band | xs:boolean |
| Edge | edge | xs:boolean |
When present, Greater Than indicates the upper limit value the sampled value SHOULD cross before triggering a notification. A notification is sent whenever the sampled value crosses the specified upper limit value, relative to the last reported value, and the time fpr pmin has elapsed since the last notification. The sampled value is sent in the notification. If the value continues to rise, no notifications are generated as a result of gt. If the value drops below the upper limit value then a notification is sent, subject again to the pmin time.¶
The Greater Than parameter can only be supported on resources with a scalar numeric value.¶
When present, Less Than indicates the lower limit value the resource value SHOULD cross before triggering a notification. A notification is sent when the samples value crosses the specified lower limit value, relative to the last reported value, and the time fpr pmin has elapsed since the last notification. The sampled value is sent in the notification. If the value continues to fall no notifications are generated as a result of lt. If the value rises above the lower limit value then a new notification is sent, subject to the pmin time.¶
The Less Than parameter can only be supported on resources with a scalar numeric value.¶
When present, the change step indicates how much the value representing a resource state SHOULD change before triggering a notification, compared to the old state. Upon reception of a query including the st attribute, the current resource state representing the most recently sampled value is reported, and then set as the last reported value (last_rep_v). When a subsequent sampled value or update of the resource state differs from the last reported state by an amount, positive or negative, greater than or equal to st, and the time for pmin has elapsed since the last notification, a notification is sent and the last reported value is updated to the new resource state sent in the notification. 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 resource states represented with a scalar numeric value.¶
Note: Due to sampling and other constraints, e.g. pmin, the change in resource states received in two sequential notifications may differ by more than st.¶
The notification band attribute allows a bounded or unbounded (based on a minimum or maximum) value range that may trigger multiple notifications. This enables use cases where different ranges results in differing behaviour. For example, in monitoring the temperature of machinery, whilst the temperature is in the normal operating range, only periodic updates are needed. However as the temperature moves to more abnormal ranges more frequent state updates may be sent to clients.¶
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). Notifications occur 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). Notifications occur 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, notification occurs when the resource value is greater than or equal to gt or when the resource value is less than or equal to lt.¶
If a band is specified in which the value of gt is less than that of lt, in-band notification occurs. That is, notification occurs whenever the resource value is between the gt and lt values, including equal to gt or lt.¶
If the band is specified in which the value of gt is greater than that of lt, out-of-band notification occurs. That is, notification occurs when the resource value not between the gt and lt values, excluding equal to gt and lt.¶
The Notification Band parameter can only be supported on resources with a scalar numeric value.¶
When present, the Edge attribute indicates interest for receiving notifications of either the falling edge or the rising edge transition of a boolean resource state. When the value of the Edge attribute is 0, the server notifies the client each time a resource state changes from True to False. When the value of the Edge attribute is 1, the server notifies the client each time a resource state changes from False to True.¶
The Edge attribute can only be supported on resources with a boolean value.¶
Conditional Control Attributes define the time intervals between consecutive notifications as well as the cadence of the measurement of the conditions that trigger a notification. Conditional Control Attributes can be used to configure the internal server-driven sampling process for performing measurements of the conditions of a resource. One or more Conditional Control Attributes MAY be included as query parameters in an Observe request.¶
Conditional Control Attributes are defined below:¶
| Attribute | Parameter | Value |
|---|---|---|
| Minimum Period (s) | pmin | xs:decimal (>0) |
| Maximum Period (s) | pmax | xs:decimal (>0) |
| Minimum Evaluation Period (s) | epmin | xs:decimal (>0) |
| Maximum Evaluation Period (s) | epmax | xs:decimal (>0) |
| Confirmable Notification | con | xs:boolean |
When present, the minimum period indicates the minimum time, in seconds, between two consecutive notifications (whether or not the resource state has changed). In the absence of this parameter, the minimum period is up to the server. The minimum period MUST be greater than zero otherwise the receiver MUST return a CoAP error code 4.00 "Bad Request" (or equivalent).¶
A server MAY update the resource state with the last sampled value that occured during the pmin interval, after the pmin interval expires.¶
Note: Due to finite quantization effects, the time between notifications may be greater than pmin even when the sampled value changes within the pmin interval. Pmin may or may not be used to drive the internal sampling process.¶
When present, the maximum period indicates the maximum time, in seconds, between two consecutive notifications (whether or not the resource state has changed). In the absence of this parameter, the maximum period is up to the server. The maximum period MUST be greater than zero and MUST be greater than, or equal to, the minimum period parameter (if present) otherwise the receiver MUST return a CoAP error code 4.00 "Bad Request" (or equivalent).¶
When present, the minimum evaluation period indicates the minimum time, in seconds, the client recommends to the server to wait between two consecutive measurements of the conditions of a resource since the client has no interest in the server doing more frequent measurements. When the minimum evaluation period expires after the previous measurement, the server MAY immediately perform a new measurement. In the absence of this parameter, the minimum evaluation period is not defined and thus not used by the server. The server MAY use pmin, if defined, as a guidance on the desired measurement cadence. The minimum evaluation period MUST be greater than zero otherwise the receiver MUST return a CoAP error code 4.00 "Bad Request" (or equivalent).¶
When present, the maximum evaluation period indicates the maximum time, in seconds, the server MAY wait between two consecutive measurements of the conditions of a resource. When the maximum evaluation period expires after the previous measurement, the server MUST immediately perform a new measurement. In the absence of this parameter, the maximum evaluation period is not defined and thus not used by the server. The maximum evaluation period MUST be greater than zero and MUST be greater than the minimum evaluation period parameter (if present) otherwise the receiver MUST return a CoAP error code 4.00 "Bad Request" (or equivalent).¶
When present with a value of 1 in a query, the con attribute indicates a notification MUST be confirmable, i.e., the server MUST send the notification in a confirmable CoAP message, to request an acknowledgement from the client. When present with a value of 0 in a query, the con attribute indicates a notification can be confirmable or non-confirmable, i.e., it can be sent in a confirmable or a non-confirmable CoAP message.¶
Conditional Notification Attributes and Conditional Control Attributes may be present in the same query. However, they are not defined at multiple prioritization levels. The server sends a notification whenever any of the parameter conditions are met, upon which it updates its last notification value and time to prepare for the next notification. Only one notification occurs when there are multiple conditions being met at the same time. The reference code below illustrates the logic to determine when a notification is to be sent.¶
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 )
);
}
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 content updates 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.¶
Conditional Notification Attributes defined in Section 3 can be used with Link Bindings in order to customize the notification behavior and timing.¶
A binding method defines the rules to generate the network-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.¶
This specification defines a new CoRE link attribute "bind". This is the identifier for a binding method which defines the rules to synchronize the destination resource. This attribute is mandatory.¶
| Attribute | Parameter | Value |
|---|---|---|
| Binding method | bind | xs:string |
The following table gives a summary of the binding methods defined in this specification.¶
| Name | Identifier | Location | Method |
|---|---|---|---|
| Polling | poll | Destination | GET |
| Observe | obs | Destination | GET + Observe |
| Push | push | Source | PUT |
| Execute | exec | Source | POST |
The description of a binding method defines the following aspects:¶
This is the value of the "bind" attribute used to identify the method.¶
This information indicates whether the binding entry is stored on the source or on the destination endpoint.¶
This is the REST method used in the Request/Response exchanges.¶
How Conditional Notification Attributes are used in the binding.¶
The binding methods are described in more detail below.¶
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).¶
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 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 parameters in the Observe request (see Section 3).¶
The Push method can be used to allow a source endpoint to replace an outdated resource state at the destination with a newer representation. When the Push method is assigned to a binding, the source endpoint sends PUT requests to the destination resource when the Conditional Notification Attributes are satisfied for the source resource. The source endpoint SHOULD only send a notification request if any included Conditional Notification Attributes are met. The binding entry for this method MUST be stored on the source endpoint.¶
An alternative means for a source endpoint to deliver change-of-state notifications to a destination resource is to use the Execute Method. While the Push method simply updates the state of the destination resource with the representation of the source resource, Execute can be used when the destination endpoint wishes to receive all state changes from a source. This allows, for example, the existence of a resource collection consisting of all the state changes at the destination endpoint. When the Execute method is assigned to a binding, the source endpoint sends POST requests to the destination resource when the Conditional Notification Attributes are satisfied for the source resource. The source endpoint SHOULD only send a notification request if any included Conditional Notification Attributes are met. The binding entry for this method MUST be stored on the source endpoint.¶
Note: Both the Push and the Execute methods are examples of Server Push mechanisms that are being researched in the Thing-to-Thing Research Group (T2TRG) [I-D.irtf-t2trg-rest-iot].¶
Since Binding involves the creation of a link between two resources, Web Linking and the CoRE Link-Format used to represent binding information. This involves the creation of a new relation type, "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.¶
The Binding Table is a special resource that describes the bindings on an endpoint. An endpoint offering a representation of the Binding Table resource SHOULD indicate its presence and enable its discovery by advertising a link at "/.well-known/core" [RFC6690]. If so, the Binding Table resource MUST be discoverable by using the Resource Type (rt) 'core.bnd'.¶
The Methods column defines the REST methods supported by the Binding Table, which are described in more detail below.¶
| Resource | rt= | Methods | Content-Format |
|---|---|---|---|
| Binding Table | core.bnd | GET, PUT | link-format |
The REST methods GET and PUT are used to manipulate a Binding Table. A GET request simply returns the current state of a Binding Table. A request with a PUT method and a content format of application/link-format is used to clear the bindings to the table or replaces its entire contents. All links in the payload of a PUT rquest MUST have a relation type "boundto".¶
The following example shows requests for discovering, retrieving and replacing bindings in a binding table.¶
Req: GET /.well-known/core?rt=core.bnd (application/link-format)
Res: 2.05 Content (application/link-format)
</bnd/>;rt=core.bnd;ct=40
Req: GET /bnd/
Res: 2.05 Content (application/link-format)
<coap://sensor.example.com/a/switch1/>;
rel=boundto;anchor=/a/fan,;bind="obs",
<coap://sensor.example.com/a/switch2/>;
rel=boundto;anchor=/a/light;bind="obs"
Req: PUT /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
Additional operations on the Binding Table can be specified in future documents. Such operations can include, for example, the usage of the iPATCH or PATCH methods [RFC8132] for fine-grained addition and removal of individual bindings or binding subsets.¶
When pmax and pmin are equal, the expected behaviour is that notifications will be sent every (pmin == pmax) seconds. However, these notifications can only be fulfilled by the server on a best effort basis. Because pmin and pmax are designed as acceptable tolerance bounds for sending state updates, a query from an interested client containing equal pmin and pmax values must not be seen as a hard real-time scheduling contract between the client and the server.¶
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 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 or the configuration of epmin and epmax values for 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 in addition to established Link Bindings.¶
When a server has multiple observations with different measurement cadences as defined by the epmin and epmax values, the server MAY evaluate all observations when performing the measurement of any one observation.¶
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.¶
This specification registers a new Resource Type Link Target Attribute 'core.bnd' in the Resource Type (rt=) registry established as per [RFC6690].¶
core.bnd¶
Description: See Section 5. This attribute value is used to discover the resource representing 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¶
This specification registers the new "boundto" link relation type as per [RFC8288].¶
boundto¶
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.¶
This specification. Note to RFC editor: please insert the RFC of this specification.¶
None¶
None¶
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. Hannes Tschofenig and Mert Ocak highlighted syntactical corrections in the usage of pmax and pmin in a query. Discussions with Ari Keraenen led to the addition of an extra binding method supporting POST operations. Alan Soloway contributed text leading to the inclusion of epmin and epmax. David Navarro proposed allowing for pmax to be equal to pmin.¶
Christian Groves Australia email: cngroves.std@gmail.com Zach Shelby ARM Vuokatti FINLAND phone: +358 40 7796297 email: zach.shelby@arm.com Matthieu Vial Schneider-Electric Grenoble France phone: +33 (0)47657 6522 eMail: matthieu.vial@schneider-electric.com Jintao Zhu Huawei Xi’an, Shaanxi Province China email: jintao.zhu@huawei.com¶
draft-ietf-core-dynlink-13¶
draft-ietf-core-dynlink-12¶
draft-ietf-core-dynlink-11¶
draft-ietf-core-dynlink-10¶
draft-ietf-core-dynlink-09¶
draft-ietf-core-dynlink-08¶
draft-ietf-core-dynlink-07¶
draft-ietf-core-dynlink-06¶
draft-ietf-core-dynlink-05¶
draft-ietf-core-dynlink-03¶
draft-ietf-core-dynlink-02¶
draft-ietf-core-dynlink-01¶
draft-ietf-core-dynlink Initial Version 00:¶
draft-groves-core-dynlink Draft Initial Version 00:¶
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.¶
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: pmin="10"
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 | | 23 Cel
16 | |
17 | |
18 | |
19 | | ____________
20 ____________ |<-----+ Header: 2.05
21 | 2.05 | 26 Cel Token: 0x4a
22 26 Cel | | Observe: 20
23 | | Payload: "26 Cel"
24 | |
25 | |
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"
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 | 23 Cel Token: 0x4a
18 23 Cel | | Observe: 16
19 | | Payload: "23 Cel"
20 | |
21 | |
22 | |
23 | |
24 | |
25 | |
26 | |
27 | |
28 | |
29 | |
30 | |
31 | |
32 | |
33 | |
34 | |
35 | |
36 | | ____________
37 ____________ |<-----+ Header: 2.05
38 | 2.05 | 23 Cel Token: 0x4a
39 23 Cel | | Observe: 37
40 | | Payload: "23 Cel"
41 | |
42 | |
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 | |
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 | |
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 | |