CoRE Working Group M. Koster Internet-Draft Dogtiger Labs Intended status: Informational A. Soloway Expires: August 28, 2022 Qualcomm Technologies, Inc. B. Silverajan, Ed. Tampere University February 24, 2022 Conditional Attributes for Constrained RESTful Environments draft-ietf-core-conditional-attributes-02 Abstract This specification defines Conditional Notification and Control Attributes that work with CoAP Observe (RFC7641). Editor note The git repository for the draft is found at https://github.com/core- wg/conditional-attributes/ 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 August 28, 2022. Copyright Notice Copyright (c) 2022 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 Koster, et al. Expires August 28, 2022 [Page 1] Internet-Draft Conditional Attributes for CoRE February 2022 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Conditional Attributes . . . . . . . . . . . . . . . . . . . 3 3.1. Conditional Notification Attributes . . . . . . . . . . . 3 3.1.1. Greater Than (gt) . . . . . . . . . . . . . . . . . . 4 3.1.2. Less Than (lt) . . . . . . . . . . . . . . . . . . . 4 3.1.3. Change Step (st) . . . . . . . . . . . . . . . . . . 5 3.1.4. Notification Band (band) . . . . . . . . . . . . . . 5 3.1.5. Edge (edge) . . . . . . . . . . . . . . . . . . . . . 6 3.2. Conditional Control Attributes . . . . . . . . . . . . . 7 3.2.1. Minimum Period (pmin) . . . . . . . . . . . . . . . . 7 3.2.2. Maximum Period (pmax) . . . . . . . . . . . . . . . . 8 3.2.3. Minimum Evaluation Period (epmin) . . . . . . . . . . 8 3.2.4. Maximum Evaluation Period (epmax) . . . . . . . . . . 8 3.2.5. Confirmable Notification (con) . . . . . . . . . . . 8 3.3. Server processing of Conditional Attributes . . . . . . . 9 4. Implementation Considerations . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11 9. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 10.1. Normative References . . . . . . . . . . . . . . . . . . 13 10.2. Informative References . . . . . . . . . . . . . . . . . 13 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 13 A.1. Minimum Period (pmin) example . . . . . . . . . . . . . . 13 A.2. Maximum Period (pmax) example . . . . . . . . . . . . . . 14 A.3. Greater Than (gt) example . . . . . . . . . . . . . . . . 15 A.4. Greater Than (gt) and Period Max (pmax) example . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 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. Koster, et al. Expires August 28, 2022 [Page 2] Internet-Draft Conditional Attributes for CoRE February 2022 This specification defines Conditional Notification and Control Attributes for use with CoRE Observe [RFC7641]. 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 [RFC7641]. This specification makes use of the following additional terminology: Notification Band: A resource value range that may be bounded by a minimum and maximum value or may be unbounded having either a minimum or maximum value. 3. Conditional Attributes This specification defines conditional attributes, which provide for fine-grained control of notification and state synchronization when using CoRE Observe [RFC7641]. 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. 3.1. Conditional Notification Attributes 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. Koster, et al. Expires August 28, 2022 [Page 3] Internet-Draft Conditional Attributes for CoRE February 2022 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 | (none) | | | | | | Edge | edge | xs:boolean | +-------------------+-----------+-----------------+ Table 1: Conditional Notification Attributes 3.1.1. Greater Than (gt) 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 for 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. 3.1.2. Less Than (lt) 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 for pmin has elapsed since the last notification. The sampled value is sent in the notification. If the value continues to fall no notifications Koster, et al. Expires August 28, 2022 [Page 4] Internet-Draft Conditional Attributes for CoRE February 2022 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. 3.1.3. Change Step (st) 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. 3.1.4. Notification Band (band) 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. Its use is determined only by its presence, and not its value. Koster, et al. Expires August 28, 2022 [Page 5] Internet-Draft Conditional Attributes for CoRE February 2022 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. 3.1.5. Edge (edge) 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 (False), the server notifies the client each time a resource state changes from True to False. When the value of the Edge attribute is 1 (True), 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. Koster, et al. Expires August 28, 2022 [Page 6] Internet-Draft Conditional Attributes for CoRE February 2022 3.2. Conditional Control Attributes 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 | +-------------------------------+-----------+-----------------+ Table 2: Conditional Control Attributes 3.2.1. Minimum Period (pmin) 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. Koster, et al. Expires August 28, 2022 [Page 7] Internet-Draft Conditional Attributes for CoRE February 2022 3.2.2. Maximum Period (pmax) 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). 3.2.3. Minimum Evaluation Period (epmin) 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). 3.2.4. Maximum Evaluation Period (epmax) 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). 3.2.5. Confirmable Notification (con) When present with a value of 1 (True) 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 (False) 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. Koster, et al. Expires August 28, 2022 [Page 8] Internet-Draft Conditional Attributes for CoRE February 2022 3.3. Server processing of Conditional Attributes 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 ) ); } Figure 1: Code logic for conditional notification attribute interactions Koster, et al. Expires August 28, 2022 [Page 9] Internet-Draft Conditional Attributes for CoRE February 2022 4. Implementation Considerations 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. 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. 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. This specification defines conditional attributes that can be used with CoRE Observe relationships between CoAP clients and CoAP servers. However, it is recognised that the presence of 1 or more proxies between a client and a server can interfere with clients receiving resource updates, if a proxy does not supply resource representations when the value remains unchanged (eg if pmax is set, and the server sends multiple updates when the resource state contains the same value). A server SHOULD use the Max-Age option to mitigate this by setting Max-Age to be less than or equal to pmax. 5. Security Considerations The security considerations in Section 11 of [RFC7252] apply. Additionally, the security considerations in Section 7 of [RFC7641] also apply. 6. IANA Considerations This memo requests a new Conditional Attributes registry to ensure attributes map uniquely to parameter names. Koster, et al. Expires August 28, 2022 [Page 10] Internet-Draft Conditional Attributes for CoRE February 2022 +---------------------------+-----------+---------------+-----------+ | Attribute | Parameter | Value | Reference | +---------------------------+-----------+---------------+-----------+ | Minimum Period (s) | pmin | xs:decimal | This memo | | | | (>0) | | | | | | | | Maximum Period (s) | pmax | xs:decimal | This memo | | | | (>0) | | | | | | | | Minimum Evaluation Period | epmin | xs:decimal | This memo | | (s) | | (>0) | | | | | | | | Maximum Evaluation Period | epmax | xs:decimal | This memo | | (s) | | (>0) | | | | | | | | Confirmable Notification | con | xs:boolean | This memo | | | | | | | Greater Than | gt | xs:decimal | This memo | | | | | | | Less Than | lt | xs:decimal | This memo | | | | | | | Change Step | st | xs:decimal | This memo | | | | (>0) | | | | | | | | Notification Band | band | (none) | This memo | | | | | | | Edge | edge | xs:boolean | This memo | +---------------------------+-----------+---------------+-----------+ 7. Acknowledgements Hannes Tschofenig and Mert Ocak highlighted syntactical corrections in the usage of pmax and pmin in a query. David Navarro proposed allowing for pmax to be equal to pmin. 8. Contributors Koster, et al. Expires August 28, 2022 [Page 11] Internet-Draft Conditional Attributes for CoRE February 2022 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 9. Changelog draft-ietf-core-conditional-attributes-02 o Clarifications on usage and value of the band parameter o Implementation considerations for proxies added o Security considerations added o IANA considerations added draft-ietf-core-conditional-attributes-01 o Clarifications on True and False values for Edge and Con Attributes o Alan Soloway added as author draft-ietf-core-conditional-attributes-00 o Conditional Atttributes section from draft-ietf-core-dynlink-13 separated into own WG draft Koster, et al. Expires August 28, 2022 [Page 12] Internet-Draft Conditional Attributes for CoRE February 2022 10. References 10.1. 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 10.2. Informative References [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015, . 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. Minimum Period (pmin) example Koster, et al. Expires August 28, 2022 [Page 13] Internet-Draft Conditional Attributes for CoRE February 2022 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 | | Figure 2: Client registers and receives one notification of the current state and one of a new state state when pmin time expires. A.2. Maximum Period (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" 7 | | Observe: 0 (register) 8 | | 9 ____________ |<-----+ Header: 2.05 10 | 2.05 | Token: 0x4a 11 18.5 Cel | | Observe: 9 Koster, et al. Expires August 28, 2022 [Page 14] Internet-Draft Conditional Attributes for CoRE February 2022 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 | | Figure 3: Client registers and receives one notification of the current state, one of a new state and one of an unchanged state when pmax time expires. A.3. Greater Than (gt) example Koster, et al. Expires August 28, 2022 [Page 15] Internet-Draft Conditional Attributes for CoRE February 2022 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 4: Client registers and receives one notification of the current state and one of a new state when it passes through the greater than threshold of 25. A.4. 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 | | Koster, et al. Expires August 28, 2022 [Page 16] Internet-Draft Conditional Attributes for CoRE February 2022 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 5: 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 greater than threshold of 25. Authors' Addresses Michael Koster Dogtiger Labs 524 H Street Antioch, CA 94509 USA Email: michaeljohnkoster@gmail.com Koster, et al. Expires August 28, 2022 [Page 17] Internet-Draft Conditional Attributes for CoRE February 2022 Alan Soloway Qualcomm Technologies, Inc. 5775 Morehouse Drive San Diego 92121 USA Email: asoloway@qti.qualcomm.com Bilhanan Silverajan (editor) Tampere University Kalevantie 4 Tampere FI-33100 Finland Email: bilhanan.silverajan@tuni.fi Koster, et al. Expires August 28, 2022 [Page 18]