Network Working Group C. Jennings Internet-Draft Cisco Intended status: Standards Track Z. Shelby Expires: January 4, 2018 ARM J. Arkko A. Keranen Ericsson C. Bormann Universitaet Bremen TZI July 3, 2017 Media Types for Sensor Measurement Lists (SenML) draft-ietf-core-senml-10 Abstract This specification defines media types for representing simple sensor measurements and device parameters in the Sensor Measurement Lists (SenML). Representations are defined in JavaScript Object Notation (JSON), Concise Binary Object Representation (CBOR), eXtensible Markup Language (XML), and Efficient XML Interchange (EXI), which share the common SenML data model. A simple sensor, such as a temperature sensor, could use this media type in protocols such as HTTP or CoAP to transport the measurements of the sensor or to be configured. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 4, 2018. Jennings, et al. Expires January 4, 2018 [Page 1] Internet-Draft SenML July 2017 Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements and Design Goals . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. SenML Structure and Semantics . . . . . . . . . . . . . . . . 6 4.1. Base Fields . . . . . . . . . . . . . . . . . . . . . . . 6 4.2. Regular Fields . . . . . . . . . . . . . . . . . . . . . 6 4.3. Considerations . . . . . . . . . . . . . . . . . . . . . 7 4.4. Resolved Records . . . . . . . . . . . . . . . . . . . . 8 4.5. Associating Meta-data . . . . . . . . . . . . . . . . . . 9 4.6. Configuration and Actuation usage . . . . . . . . . . . . 9 5. JSON Representation (application/senml+json) . . . . . . . . 9 5.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10 5.1.1. Single Datapoint . . . . . . . . . . . . . . . . . . 11 5.1.2. Multiple Datapoints . . . . . . . . . . . . . . . . . 11 5.1.3. Multiple Measurements . . . . . . . . . . . . . . . . 12 5.1.4. Resolved Data . . . . . . . . . . . . . . . . . . . . 13 5.1.5. Multiple Data Types . . . . . . . . . . . . . . . . . 14 5.1.6. Collection of Resources . . . . . . . . . . . . . . . 14 5.1.7. Setting an Actuator . . . . . . . . . . . . . . . . . 14 6. CBOR Representation (application/senml+cbor) . . . . . . . . 15 7. XML Representation (application/senml+xml) . . . . . . . . . 17 8. EXI Representation (application/senml+exi) . . . . . . . . . 19 9. Fragment Identification Methods . . . . . . . . . . . . . . . 22 9.1. Fragment Identification Examples . . . . . . . . . . . . 22 10. Usage Considerations . . . . . . . . . . . . . . . . . . . . 23 11. CDDL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 12.1. Units Registry . . . . . . . . . . . . . . . . . . . . . 25 12.2. SenML Label Registry . . . . . . . . . . . . . . . . . . 28 12.3. Media Type Registration . . . . . . . . . . . . . . . . 30 12.3.1. senml+json Media Type Registration . . . . . . . . . 30 Jennings, et al. Expires January 4, 2018 [Page 2] Internet-Draft SenML July 2017 12.3.2. sensml+json Media Type Registration . . . . . . . . 32 12.3.3. senml+cbor Media Type Registration . . . . . . . . . 33 12.3.4. sensml+cbor Media Type Registration . . . . . . . . 34 12.3.5. senml+xml Media Type Registration . . . . . . . . . 35 12.3.6. sensml+xml Media Type Registration . . . . . . . . . 37 12.3.7. senml+exi Media Type Registration . . . . . . . . . 38 12.3.8. sensml+exi Media Type Registration . . . . . . . . . 39 12.4. XML Namespace Registration . . . . . . . . . . . . . . . 41 12.5. CoAP Content-Format Registration . . . . . . . . . . . . 41 13. Security Considerations . . . . . . . . . . . . . . . . . . . 41 14. Privacy Considerations . . . . . . . . . . . . . . . . . . . 41 15. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 42 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 42 16.1. Normative References . . . . . . . . . . . . . . . . . . 42 16.2. Informative References . . . . . . . . . . . . . . . . . 43 Appendix A. Links Extension . . . . . . . . . . . . . . . . . . 45 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45 1. Overview Connecting sensors to the Internet is not new, and there have been many protocols designed to facilitate it. This specification defines new media types for carrying simple sensor information in a protocol such as HTTP or CoAP. This format was designed so that processors with very limited capabilities could easily encode a sensor measurement into the media type, while at the same time a server parsing the data could relatively efficiently collect a large number of sensor measurements. SenML can be used for a variety of data flow models, most notably data feeds pushed from a sensor to a collector, and the web resource model where the sensor is requested as a resource representation (e.g., "GET /sensor/temperature"). There are many types of more complex measurements and measurements that this media type would not be suitable for. SenML strikes a balance between having some information about the sensor carried with the sensor data so that the data is self describing but it also tries to make that a fairly minimal set of auxiliary information for efficiency reason. Other information about the sensor can be discovered by other methods such as using the CoRE Link Format [RFC6690]. SenML is defined by a data model for measurements and simple meta- data about measurements and devices. The data is structured as a single array that contains a series of SenML Records which can each contain fields such as an unique identifier for the sensor, the time the measurement was made, the unit the measurement is in, and the current value of the sensor. Serializations for this data model are Jennings, et al. Expires January 4, 2018 [Page 3] Internet-Draft SenML July 2017 defined for JSON [RFC7159], CBOR [RFC7049], XML, and Efficient XML Interchange (EXI) [W3C.REC-exi-20140211]. For example, the following shows a measurement from a temperature gauge encoded in the JSON syntax. [ {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1} ] In the example above, the array has a single SenML Record with a measurement for a sensor named "urn:dev:ow:10e2073a01080063" with a current value of 23.1 degrees Celsius. 2. Requirements and Design Goals The design goal is to be able to send simple sensor measurements in small packets on mesh networks from large numbers of constrained devices. Keeping the total size of payload under 80 bytes makes this easy to use on a wireless mesh network. It is always difficult to define what small code is, but there is a desire to be able to implement this in roughly 1 KB of flash on a 8 bit microprocessor. Experience with power meters and other large scale deployments has indicated that the solution needs to support allowing multiple measurements to be batched into a single HTTP or CoAP request. This "batch" upload capability allows the server side to efficiently support a large number of devices. It also conveniently supports batch transfers from proxies and storage devices, even in situations where the sensor itself sends just a single data item at a time. The multiple measurements could be from multiple related sensors or from the same sensor but at different times. The basic design is an array with a series of measurements. The following example shows two measurements made at different times. The value of a measurement is given by the "v" field, the time of a measurement is in the "t" field, the "n" field has a unique sensor name, and the unit of the measurement is carried in the "u" field. [ {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09, "v":23.5}, {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020091e+09, "v":23.6} ] To keep the messages small, it does not make sense to repeat the "n" field in each SenML Record so there is a concept of a Base Name which is simply a string that is prepended to the Name field of all Jennings, et al. Expires January 4, 2018 [Page 4] Internet-Draft SenML July 2017 elements in that record and any records that follow it. So a more compact form of the example above is the following. [ {"bn":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09, "v":23.5}, {"u":"Cel","t":1.276020091e+09, "v":23.6} ] In the above example the Base Name is in the "bn" field and the "n" fields in each Record are the empty string so they are omitted. Some devices have accurate time while others do not so SenML supports absolute and relative times. Time is represented in floating point as seconds and values greater than zero represent an absolute time relative to the Unix epoch while values of 0 or less represent a relative time in the past from the current time. A simple sensor with no absolute wall clock time might take a measurement every second, batch up 60 of them, and then send the batch to a server. It would include the relative time each measurement was made compared to the time the batch was sent in each SenML Record. The server might have accurate NTP time and use the time it received the data, and the relative offset, to replace the times in the SenML with absolute times before saving the SenML Pack in a document database. 3. 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 [RFC2119]. This document also uses the following terms: SenML Record: One measurement or configuration instance in time presented using the SenML data model. SenML Pack: One or more SenML Records in an array structure. SenML Label: A short name used in SenML Records to denote different SenML fields (e.g., "v" for "value"). SenML Field: A component of a record that associates a value to a SenML Label for this record. This document uses the terms "attribute" and "tag" where they occur with the underlying technologies (XML, CBOR [RFC7049], and Link Jennings, et al. Expires January 4, 2018 [Page 5] Internet-Draft SenML July 2017 Format [RFC6690]), not for SenML concepts per se. Note that "attribute" has been widely used previously as a synonym for SenML "field", though. 4. SenML Structure and Semantics Each SenML Pack carries a single array that represents a set of measurements and/or parameters. This array contains a series of SenML Records with several fields described below. There are two kinds of fields: base and regular. The base fields can be included in any SenML Record and they apply to the entries in the Record. Each base field also applies to all Records after it up to, but not including, the next Record that has that same base field. All base fields are optional. Regular fields can be included in any SenML Record and apply only to that Record. 4.1. Base Fields Base Name: This is a string that is prepended to the names found in the entries. Base Time: A base time that is added to the time found in an entry. Base Unit: A base unit that is assumed for all entries, unless otherwise indicated. If a record does not contain a Unit value, then the Base Unit is used. Otherwise the value found in the Unit (if any) is used. Base Value: A base value is added to the value found in an entry, similar to Base Time. Base Sum: A base sum is added to the sum found in an entry, similar to Base Time. Version: Version number of media type format. This field is an optional positive integer and defaults to 5 if not present. [RFC Editor: change the default value to 10 when this specification is published as an RFC and remove this note] 4.2. Regular Fields Name: Name of the sensor or parameter. When appended to the Base Name field, this must result in a globally unique identifier for the resource. The name is optional, if the Base Name is present. If the name is missing, Base Name must uniquely identify the resource. This can be used to represent a large array of measurements from the same sensor without having to repeat its identifier on every measurement. Jennings, et al. Expires January 4, 2018 [Page 6] Internet-Draft SenML July 2017 Unit: Units for a measurement value. Optional. Value: Value of the entry. Optional if a Sum value is present, otherwise required. Values are represented using basic data types. This specification defines floating point numbers ("v" field for "Value"), booleans ("vb" for "Boolean Value"), strings ("vs" for "String Value") and binary data ("vd" for "Data Value"). Exactly one value field MUST appear unless there is Sum field in which case it is allowed to have no Value field. Sum: Integrated sum of the values over time. Optional. This field is in the units specified in the Unit value multiplied by seconds. Time: Time when value was recorded. Optional. Update Time: An optional time in seconds that represents the maximum time before this sensor will provide an updated reading for a measurement. This can be used to detect the failure of sensors or communications path from the sensor. 4.3. Considerations The SenML format can be extended with further custom fields. Both new base and regular fields are allowed. See Section 12.2 for details. Implementations MUST ignore fields they don't recognize unless that field has a label name that ends with the '_' character in which case an error MUST be generated. All SenML Records in a Pack MUST have the same version number. This is typically done by adding a Base Version field to only the first Record in the Pack. Systems reading one of the objects MUST check for the Version field. If this value is a version number larger than the version which the system understands, the system SHOULD NOT use this object. This allows the version number to indicate that the object contains mandatory to understand fields. New version numbers can only be defined in an RFC that updates this specification or it successors. The Name value is concatenated to the Base Name value to get the name of the sensor. The resulting name needs to uniquely identify and differentiate the sensor from all others. It is RECOMMENDED that the full names are represented as URIs [RFC3986] or URNs [RFC2141]. One way to create a unique name is to include some bit string that has guaranteed uniqueness (such as a 1-wire address) that is assigned to the device. Some of the examples in this draft use the device URN type as specified in [I-D.arkko-core-dev-urn]. UUIDs [RFC4122] are another way to generate a unique name. Note that long-term stable Jennings, et al. Expires January 4, 2018 [Page 7] Internet-Draft SenML July 2017 unique identifiers are problematic for privacy reasons and should be used with care or avoided as described in [RFC7721]. The resulting concatenated name MUST consist only of characters out of the set "A" to "Z", "a" to "z", "0" to "9", "-", ":", ".", "/", or "_" and it MUST start with a character out of the set "A" to "Z", "a" to "z", or "0" to "9". This restricted character set was chosen so that these names can be directly used as in other types of URI including segments of an HTTP path with no special encoding and can be directly used in many databases and analytic systems. [RFC5952] contains advice on encoding an IPv6 address in a name. If the Record has no Unit, the Base Unit is used as the Unit. Having no Unit and no Base Unit is allowed. If either the Base Time or Time value is missing, the missing field is considered to have a value of zero. The Base Time and Time values are added together to get the time of measurement. A time of zero indicates that the sensor does not know the absolute time and the measurement was made roughly "now". A negative value is used to indicate seconds in the past from roughly "now". A positive value is used to indicate the number of seconds, excluding leap seconds, since the start of the year 1970 in UTC. If only one of the Base Sum or Sum value is present, the missing field is considered to have a value of zero. The Base Sum and Sum values are added together to get the sum of measurement. If neither the Base Sum or Sum are present, then the measurement does not have a sum value. If the Base Value or Value is not present, the missing field(s) are considered to have a value of zero. The Base Value and Value are added together to get the value of the measurement. Representing the statistical characteristics of measurements, such as accuracy, can be very complex. Future specification may add new fields to provide better information about the statistical properties of the measurement. 4.4. Resolved Records Sometimes it is useful to be able to refer to a defined normalized format for SenML records. This normalized format tends to get used for big data applications and intermediate forms when converting to other formats. A SenML Record is referred to as "resolved" if it does not contain any base values and has no relative times, but the base values of the Jennings, et al. Expires January 4, 2018 [Page 8] Internet-Draft SenML July 2017 SenML Pack (if any) are applied to the Record. That is, name and base name are concatenated, base time is added to the time of the Record, if the Record did not contain Unit the Base Unit is applied to the record, etc. In addition the records need to be in chronological order. An example of this is show in Section 5.1.4. Future specification that defines new base fields need to specify how the field is resolved. 4.5. Associating Meta-data SenML is designed to carry the minimum dynamic information about measurements, and for efficiency reasons does not carry significant static meta-data about the device, object or sensors. Instead, it is assumed that this meta-data is carried out of band. For web resources using SenML Packs, this meta-data can be made available using the CoRE Link Format [RFC6690]. The most obvious use of this link format is to describe that a resource is available in a SenML format in the first place. The relevant media type indicator is included in the Content-Type (ct=) link attribute (which is defined for the Link Format in Section 7.2.1 of [RFC7252]). 4.6. Configuration and Actuation usage SenML can also be used for configuring parameters and controlling actuators. When a SenML Pack is sent (e.g., using a HTTP/CoAP POST or PUT method) and the semantics of the target are such that SenML is interpreted as configuration/actuation, SenML Records are interpreted as a request to change the values of given (sub)resources (given as names) to given values at the given time(s). 5. JSON Representation (application/senml+json) For the SenML fields shown in Table 1, the SenML labels are used as the JSON object member names within JSON objects representing the JSON SenML Records. Jennings, et al. Expires January 4, 2018 [Page 9] Internet-Draft SenML July 2017 +---------------+-------+---------+ | Name | label | Type | +---------------+-------+---------+ | Base Name | bn | String | | Base Time | bt | Number | | Base Unit | bu | String | | Base Value | bv | Number | | Base Sum | bs | Number | | Version | bver | Number | | Name | n | String | | Unit | u | String | | Value | v | Number | | String Value | vs | String | | Boolean Value | vb | Boolean | | Data Value | vd | String | | Value Sum | s | Number | | Time | t | Number | | Update Time | ut | Number | | Link | l | String | +---------------+-------+---------+ Table 1: JSON SenML Labels The root JSON value consists of an array with one JSON object for each SenML Record. All the fields in the above table MAY occur in the records with member values of the type specified in the table. Only the UTF-8 form of JSON is allowed. Characters in the String Value are encoded using the escape sequences defined in [RFC7159]. Octets in the Data Value are base64 encoded with URL safe alphabet as defined in Section 5 of [RFC4648], with padding omitted. Systems receiving measurements MUST be able to process the range of floating point numbers that are representable as an IEEE double precision floating point numbers [IEEE.754.1985]. The number of significant digits in any measurement is not relevant, so a reading of 1.1 has exactly the same semantic meaning as 1.10. If the value has an exponent, the "e" MUST be in lower case. The mantissa SHOULD be less than 19 characters long and the exponent SHOULD be less than 5 characters long. This allows time values to have better than micro second precision over the next 100 years. 5.1. Examples Jennings, et al. Expires January 4, 2018 [Page 10] Internet-Draft SenML July 2017 5.1.1. Single Datapoint The following shows a temperature reading taken approximately "now" by a 1-wire sensor device that was assigned the unique 1-wire address of 10e2073a01080063: [ {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1} ] 5.1.2. Multiple Datapoints The following example shows voltage and current now, i.e., at an unspecified time. [ {"bn":"urn:dev:ow:10e2073a01080063:","n":"voltage","u":"V","v":120.1}, {"n":"current","u":"A","v":1.2} ] The next example is similar to the above one, but shows current at Tue Jun 8 18:01:16.001 UTC 2010 and at each second for the previous 5 seconds. [ {"bn":"urn:dev:ow:10e2073a0108006:","bt":1.276020076001e+09, "bu":"A","bver":5, "n":"voltage","u":"V","v":120.1}, {"n":"current","t":-5,"v":1.2}, {"n":"current","t":-4,"v":1.3}, {"n":"current","t":-3,"v":1.4}, {"n":"current","t":-2,"v":1.5}, {"n":"current","t":-1,"v":1.6}, {"n":"current","v":1.7} ] Note that in some usage scenarios of SenML the implementations MAY store or transmit SenML in a stream-like fashion, where data is collected over time and continuously added to the object. This mode of operation is optional, but systems or protocols using SenML in this fashion MUST specify that they are doing this. SenML defines a separate media type to indicate Sensor Streaming Measurement Lists (SensML) for this usage (see Section 12.3.1). In this situation the SensML stream can be sent and received in a partial fashion, i.e., a measurement entry can be read as soon as the SenML Record is received and not have to wait for the full SensML Stream to be complete. Jennings, et al. Expires January 4, 2018 [Page 11] Internet-Draft SenML July 2017 For instance, the following stream of measurements may be sent via a long lived HTTP POST from the producer of a SensML to the consumer of that, and each measurement object may be reported at the time it was measured: [ {"bn":"urn:dev:ow:10e2073a01080063","bt":1.320067464e+09, "bu":"%RH","v":21.2}, {"t":10,"v":21.3}, {"t":20,"v":21.4}, {"t":30,"v":21.4}, {"t":40,"v":21.5}, {"t":50,"v":21.5}, {"t":60,"v":21.5}, {"t":70,"v":21.6}, {"t":80,"v":21.7}, ... 5.1.3. Multiple Measurements The following example shows humidity measurements from a mobile device with a 1-wire address 10e2073a01080063, starting at Mon Oct 31 13:24:24 UTC 2011. The device also provides position data, which is provided in the same measurement or parameter array as separate entries. Note time is used to for correlating data that belongs together, e.g., a measurement and a parameter associated with it. Finally, the device also reports extra data about its battery status at a separate time. [ {"bn":"urn:dev:ow:10e2073a01080063","bt":1.320067464e+09, "bu":"%RH","v":20}, {"u":"lon","v":24.30621}, {"u":"lat","v":60.07965}, {"t":60,"v":20.3}, {"u":"lon","t":60,"v":24.30622}, {"u":"lat","t":60,"v":60.07965}, {"t":120,"v":20.7}, {"u":"lon","t":120,"v":24.30623}, {"u":"lat","t":120,"v":60.07966}, {"u":"%EL","t":150,"v":98}, {"t":180,"v":21.2}, {"u":"lon","t":180,"v":24.30628}, {"u":"lat","t":180,"v":60.07967} ] The size of this example represented in various forms, as well as that form compressed with gzip is given in the following table. Jennings, et al. Expires January 4, 2018 [Page 12] Internet-Draft SenML July 2017 +----------+------+-----------------+ | Encoding | Size | Compressed Size | +----------+------+-----------------+ | JSON | 573 | 206 | | XML | 649 | 235 | | CBOR | 254 | 196 | | EXI | 162 | 185 | +----------+------+-----------------+ Table 2: Size Comparisons 5.1.4. Resolved Data The following shows the example from the previous section show in resolved format. [ {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067464e+09, "v":20}, {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067464e+09, "v":24.30621}, {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067464e+09, "v":60.07965}, {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067524e+09, "v":20.3}, {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067524e+09, "v":24.30622}, {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067524e+09, "v":60.07965}, {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067584e+09, "v":20.7}, {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067584e+09, "v":24.30623}, {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067584e+09, "v":60.07966}, {"n":"urn:dev:ow:10e2073a01080063","u":"%EL","t":1.320067614e+09, "v":98}, {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067644e+09, "v":21.2}, {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067644e+09, "v":24.30628}, {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067644e+09, "v":60.07967} ] Jennings, et al. Expires January 4, 2018 [Page 13] Internet-Draft SenML July 2017 5.1.5. Multiple Data Types The following example shows a sensor that returns different data types. [ {"bn":"urn:dev:ow:10e2073a01080063:","n":"temp","u":"Cel","v":23.1}, {"n":"label","vs":"Machine Room"}, {"n":"open","vb":false}, {"n":"nfv-reader","vd":"aGkgCg"} ] 5.1.6. Collection of Resources The following example shows the results from a query to one device that aggregates multiple measurements from another devices. The example assumes that a client has fetched information from a device at 2001:db8::2 by performing a GET operation on http://[2001:db8::2] at Mon Oct 31 16:27:09 UTC 2011, and has gotten two separate values as a result, a temperature and humidity measurement as well as the results from another device at http://[2001:db8::1] that also had a temperature and humidity. Note that the last record would use the Base Name from the 3rd record but the Base Time from the first record. [ {"bn":"2001:db8::2/","bt":1.320078429e+09, "n":"temperature","u":"Cel","v":25.2}, {"n":"humidity","u":"%RH","v":30}, {"bn":"2001:db8::1/","n":"temperature","u":"Cel","v":12.3}, {"n":"humidity","u":"%RH","v":67} ] 5.1.7. Setting an Actuator The following example show the SenML that could be used to set the current set point of a typical residential thermostat which has a temperature set point, a switch to turn on and off the heat, and a switch to turn on the fan override. [ {"bn":"urn:dev:ow:10e2073a01080063:"}, {"n":"temp","u":"Cel","v":23.1}, {"n":"heat","u":"/","v":1}, {"n":"fan","u":"/","v":0} ] Jennings, et al. Expires January 4, 2018 [Page 14] Internet-Draft SenML July 2017 In the following example two different lights are turned on. It is assumed that the lights are on a network that can guarantee delivery of the messages to the two lights within 15 ms (e.g. a network using 802.1BA [IEEE802.1ba-2011] and 802.1AS [IEEE802.1as-2011] for time synchronization). The controller has set the time of the lights coming on to 20 ms in the future from the current time. This allows both lights to receive the message, wait till that time, then apply the switch command so that both lights come on at the same time. [ {"bt":1.320078429e+09,"bu":"/","n":"2001:db8::3","v":1}, {"n":"2001:db8::4","v":1} ] The following shows two lights being turned off using a non deterministic network that has a high odds of delivering a message in less than 100 ms and uses NTP for time synchronization. The current time is 1320078429. The user has just turned off a light switch which is turning off two lights. Both lights are dimmed to 50% brightness immediately to give the user instant feedback that something is changing. However given the network, the lights will probably dim at somewhat different times. Then 100 ms in the future, both lights will go off at the same time. The instant but not synchronized dimming gives the user the sensation of quick responses and the timed off 100 ms in the future gives the perception of both lights going off at the same time. [ {"bt":1.320078429e+09,"bu":"/","n":"2001:db8::3","v":0.5}, {"n":"2001:db8::4","v":0.5}, {"n":"2001:db8::3","t":0.1,"v":0}, {"n":"2001:db8::4","t":0.1,"v":0} ] 6. CBOR Representation (application/senml+cbor) The CBOR [RFC7049] representation is equivalent to the JSON representation, with the following changes: o For JSON Numbers, the CBOR representation can use integers, floating point numbers, or decimal fractions (CBOR Tag 4); however a representation SHOULD be chosen such that when the CBOR value is converted back to an IEEE double precision floating point value, it has exactly the same value as the original Number. For the version number, only an unsigned integer is allowed. Jennings, et al. Expires January 4, 2018 [Page 15] Internet-Draft SenML July 2017 o Characters in the String Value are encoded using a definite length text string (type 3). Octets in the Data Value are encoded using a definite length byte string (type 2). o For compactness, the CBOR representation uses integers for the labels, as defined in Table 3. This table is conclusive, i.e., there is no intention to define any additional integer map keys; any extensions will use string map keys. This allows translators converting between CBOR and JSON representations to convert also all future labels without needing to update implementations. +---------------+-------+------------+ | Name | Label | CBOR Label | +---------------+-------+------------+ | Version | bver | -1 | | Base Name | bn | -2 | | Base Time | bt | -3 | | Base Units | bu | -4 | | Base Value | bv | -5 | | Base Sum | bs | -6 | | Name | n | 0 | | Units | u | 1 | | Value | v | 2 | | String Value | vs | 3 | | Boolean Value | vb | 4 | | Value Sum | s | 5 | | Time | t | 6 | | Update Time | ut | 7 | | Data Value | vd | 8 | | Link | l | 9 | +---------------+-------+------------+ Table 3: CBOR representation: integers for map keys o For streaming SensML in CBOR representation, the array containing the records SHOULD be a CBOR indefinite length array while for non-streaming SenML, a definite length array MUST be used. The following example shows a dump of the CBOR example for the same sensor measurement as in Section 5.1.2. Jennings, et al. Expires January 4, 2018 [Page 16] Internet-Draft SenML July 2017 0000 87 a7 21 78 1b 75 72 6e 3a 64 65 76 3a 6f 77 3a |..!x.urn:dev:ow:| 0010 31 30 65 32 30 37 33 61 30 31 30 38 30 30 36 3a |10e2073a0108006:| 0020 22 fb 41 d3 03 a1 5b 00 10 62 23 61 41 20 05 00 |".A...[..b#aA ..| 0030 67 76 6f 6c 74 61 67 65 01 61 56 02 fb 40 5e 06 |gvoltage.aV..@^.| 0040 66 66 66 66 66 a3 00 67 63 75 72 72 65 6e 74 06 |fffff..gcurrent.| 0050 24 02 fb 3f f3 33 33 33 33 33 33 a3 00 67 63 75 |$..?.333333..gcu| 0060 72 72 65 6e 74 06 23 02 fb 3f f4 cc cc cc cc cc |rrent.#..?......| 0070 cd a3 00 67 63 75 72 72 65 6e 74 06 22 02 fb 3f |...gcurrent."..?| 0080 f6 66 66 66 66 66 66 a3 00 67 63 75 72 72 65 6e |.ffffff..gcurren| 0090 74 06 21 02 f9 3e 00 a3 00 67 63 75 72 72 65 6e |t.!..>...gcurren| 00a0 74 06 20 02 fb 3f f9 99 99 99 99 99 9a a3 00 67 |t. ..?.........g| 00b0 63 75 72 72 65 6e 74 06 00 02 fb 3f fb 33 33 33 |current....?.333| 00c0 33 33 33 |333| 00c3 7. XML Representation (application/senml+xml) A SenML Pack or Stream can also be represented in XML format as defined in this section. Only the UTF-8 form of XML is allowed. Characters in the String Value are encoded using the escape sequences defined in [RFC7159]. Octets in the Data Value are base64 encoded with URL safe alphabet as defined in Section 5 of [RFC4648]. The following example shows an XML example for the same sensor measurement as in Section 5.1.2. The SenML Stream is represented as a sensml element that contains a series of senml elements for each SenML Record. The SenML fields are represented as XML attributes. For each field defined in this document, the following table shows the SenML labels, which are used for the XML attribute name, as well as the according restrictions on the XML attribute values ("type") as used in the XML senml elements. Jennings, et al. Expires January 4, 2018 [Page 17] Internet-Draft SenML July 2017 +---------------+-------+---------+ | Name | Label | Type | +---------------+-------+---------+ | Base Name | bn | string | | Base Time | bt | double | | Base Unit | bu | string | | Base Value | bv | double | | Base Sum | bs | double | | Base Version | bver | int | | Name | n | string | | Unit | u | string | | Value | v | double | | String Value | vs | string | | Data Value | vd | string | | Boolean Value | vb | boolean | | Value Sum | s | double | | Time | t | double | | Update Time | ut | double | | Link | l | string | +---------------+-------+---------+ Table 4: XML SenML Labels The RelaxNG schema for the XML is: Jennings, et al. Expires January 4, 2018 [Page 18] Internet-Draft SenML July 2017 default namespace = "urn:ietf:params:xml:ns:senml" namespace rng = "http://relaxng.org/ns/structure/1.0" senml = element senml { attribute bn { xsd:string }?, attribute bt { xsd:double }?, attribute bv { xsd:double }?, attribute bs { xsd:double }?, attribute bu { xsd:string }?, attribute bver { xsd:int }?, attribute l { xsd:string }?, attribute n { xsd:string }?, attribute s { xsd:double }?, attribute t { xsd:double }?, attribute u { xsd:string }?, attribute ut { xsd:double }?, attribute v { xsd:double }?, attribute vb { xsd:boolean }?, attribute vs { xsd:string }?, attribute vd { xsd:string }? } sensml = element sensml { senml+ } start = sensml 8. EXI Representation (application/senml+exi) For efficient transmission of SenML over e.g. a constrained network, Efficient XML Interchange (EXI) can be used. This encodes the XML Schema structure of SenML into binary tags and values rather than ASCII text. An EXI representation of SenML SHOULD be made using the strict schema-mode of EXI. This mode however does not allow tag extensions to the schema, and therefore any extensions will be lost in the encoding. For uses where extensions need to be preserved in EXI, the non-strict schema mode of EXI MAY be used. The EXI header MUST include an "EXI Options", as defined in [W3C.REC-exi-20140211], with an schemaId set to the value of "a" indicating the schema provided in this specification. Future revisions to the schema can change the value of the schemaId to allow for backwards compatibility. When the data will be transported over Jennings, et al. Expires January 4, 2018 [Page 19] Internet-Draft SenML July 2017 CoAP or HTTP, an EXI Cookie SHOULD NOT be used as it simply makes things larger and is redundant to information provided in the Content-Type header. The following is the XSD Schema to be used for strict schema guided EXI processing. It is generated from the RelaxNG. The following shows a hexdump of the EXI produced from encoding the following XML example. Note this example is the same information as the first example in Section 5.1.2 in JSON format. Jennings, et al. Expires January 4, 2018 [Page 20] Internet-Draft SenML July 2017 Which compresses with EXI to the following displayed in hexdump: 0000 a0 30 0d 84 80 79 d5 c9 b8 e9 91 95 d8 e9 bd dc |.0...y..........| 0010 e8 c4 c1 94 c8 c0 dc cd 84 c0 c4 c0 e0 c0 c0 d8 |................| 0020 cc e9 82 5d 9b db 1d 18 59 d9 48 0d 58 ac 42 60 |...]....Y.H.X.B`| 0030 18 e1 2c 6e ae 4e 4c ad ce 84 06 82 41 90 0e |..,n.NL.....A..| 003f The above example used the bit packed form of EXI but it is also possible to use a byte packed form of EXI which can makes it easier for a simple sensor to produce valid EXI without really implementing EXI. Consider the example of a temperature sensor that produces a value in tenths of degrees Celsius over a range of 0.0 to 55.0. It would produce an XML SenML file such as: The compressed form, using the byte alignment option of EXI, for the above XML is the following: 0000 a0 00 48 80 6c 20 01 07 1d 75 72 6e 3a 64 65 76 |..H.l ...urn:dev| 0010 3a 6f 77 3a 31 30 65 32 30 37 33 61 30 31 30 38 |:ow:10e2073a0108| 0020 30 30 36 33 02 05 43 65 6c 01 00 e7 01 01 00 03 |0063..Cel.......| 0030 01 |.| 0031 A small temperature sensor device that only generates this one EXI file does not really need an full EXI implementation. It can simply hard code the output replacing the 1-wire device ID starting at byte 0x20 and going to byte 0x2F with it's device ID, and replacing the value "0xe7 0x01" at location 0x37 and 0x38 with the current temperature. The EXI Specification [W3C.REC-exi-20140211] contains the full information on how floating point numbers are represented, but for the purpose of this sensor, the temperature can be converted to an integer in tenths of degrees (231 in this example). EXI stores 7 bits of the integer in each byte with the top bit set to one if there are further bytes. So the first bytes at is set to low 7 bits of the integer temperature in tenths of degrees plus 0x80. In this example 231 & 0x7F + 0x80 = 0xE7. The second byte is set to the Jennings, et al. Expires January 4, 2018 [Page 21] Internet-Draft SenML July 2017 integer temperature in tenths of degrees right shifted 7 bits. In this example 231 >> 7 = 0x01. 9. Fragment Identification Methods A SenML Pack typically consists of multiple SenML Records and for some applications it may be useful to be able to refer with a Fragment Identifier to a single record, or a set of records, in a Pack. The fragment identifier is only interpreted by a client and does not impact retrieval of a representation. The SenML Fragment Identification is modeled after CSV Fragment Identifiers [RFC7111]. To select a single SenML Record, the "rec" scheme followed by a single number is used. For the purpose of numbering records, the first record is at position 1. A range of records can be selected by giving the first and the last record number separated by a '-' character. Instead of the second number, the '*' character can be used to indicate the last SenML Record in the Pack. A set of records can also be selected using a comma separated list of record positions or ranges. (We use the term "selecting a record" for identifying it as part of the fragment, not in the sense of isolating it from the Pack -- the record still needs to be interpreted as part of the Pack, e.g., using the base values defined in earlier records) 9.1. Fragment Identification Examples The 3rd SenML Record from "coap://example.com/temp" resource can be selected with: coap://example.com/temp#rec=3 Records from 3rd to 6th can be selected with: coap://example.com/temp#rec=3-6 Records from 19th to the last can be selected with: coap://example.com/temp#rec=19-* The 3rd and 5th record can be selected with: coap://example.com/temp#rec=3,5 To select the Records from third to fifth, the 10th record, and all from 19th to the last: Jennings, et al. Expires January 4, 2018 [Page 22] Internet-Draft SenML July 2017 coap://example.com/temp#rec=3-5,10,19-* 10. Usage Considerations The measurements support sending both the current value of a sensor as well as the an integrated sum. For many types of measurements, the sum is more useful than the current value. For example, an electrical meter that measures the energy a given computer uses will typically want to measure the cumulative amount of energy used. This is less prone to error than reporting the power each second and trying to have something on the server side sum together all the power measurements. If the network between the sensor and the meter goes down over some period of time, when it comes back up, the cumulative sum helps reflect what happened while the network was down. A meter like this would typically report a measurement with the units set to watts, but it would put the sum of energy used in the "s" field of the measurement. It might optionally include the current power in the "v" field. While the benefit of using the integrated sum is fairly clear for measurements like power and energy, it is less obvious for something like temperature. Reporting the sum of the temperature makes it easy to compute averages even when the individual temperature values are not reported frequently enough to compute accurate averages. Implementors are encouraged to report the cumulative sum as well as the raw value of a given sensor. Applications that use the cumulative sum values need to understand they are very loosely defined by this specification, and depending on the particular sensor implementation may behave in unexpected ways. Applications should be able to deal with the following issues: 1. Many sensors will allow the cumulative sums to "wrap" back to zero after the value gets sufficiently large. 2. Some sensors will reset the cumulative sum back to zero when the device is reset, loses power, or is replaced with a different sensor. 3. Applications cannot make assumptions about when the device started accumulating values into the sum. Typically applications can make some assumptions about specific sensors that will allow them to deal with these problems. A common assumption is that for sensors whose measurement values are always positive, the sum should never get smaller; so if the sum does get smaller, the application will know that one of the situations listed above has happened. Jennings, et al. Expires January 4, 2018 [Page 23] Internet-Draft SenML July 2017 11. CDDL For reference, the JSON and CBOR representations can be described with the common CDDL [I-D.greevenbosch-appsawg-cbor-cddl] specification in Figure 1. SenML-Pack = [1* record] record = { ? bn => tstr, ; Base Name ? bt => numeric, ; Base Time ? bu => tstr, ; Base Units ? bv => numeric, ; Base Value ? bs => numeric, ; Base Sum ? bver => uint, ; Base Version ? n => tstr, ; Name ? u => tstr, ; Units ? s => numeric, ; Value Sum ? t => numeric, ; Time ? ut => numeric, ; Update Time ? l => tstr, ; Link ? ( v => numeric // ; Numeric Value vs => tstr // ; String Value vb => bool // ; Boolean Value vd => binary-value ) ; Data Value * key-value-pair } ; now define the generic versions key-value-pair = ( label => value ) label = non-b-label / b-label non-b-label = tstr .regexp "[A-Zac-z0-9][-_:.A-Za-z0-9]*" / uint b-label = tstr .regexp "b[-_:.A-Za-z0-9]+" / nint value = tstr / binary-value / numeric / bool numeric = number / decfrac Figure 1: Common CDDL specification for CBOR and JSON SenML For JSON, we use text labels and base64url-encoded binary data (Figure 2). Jennings, et al. Expires January 4, 2018 [Page 24] Internet-Draft SenML July 2017 bver = "bver" n = "n" s = "s" bn = "bn" u = "u" t = "t" bt = "bt" v = "v" ut = "ut" bu = "bu" vs = "vs" vd = "vd" bv = "bv" vb = "vb" l = "l" bs = "bs" binary-value = tstr ; base64url encoded Figure 2: JSON-specific CDDL specification for SenML For CBOR, we use integer labels and native binary data (Figure 3). bver = -1 n = 0 s = 5 bn = -2 u = 1 t = 6 bt = -3 v = 2 ut = 7 bu = -4 vs = 3 vd = 8 bv = -5 vb = 4 l = 9 bs = -6 binary-value = bstr Figure 3: CBOR-specific CDDL specification for SenML 12. IANA Considerations Note to RFC Editor: Please replace all occurrences of "RFC-AAAA" with the RFC number of this specification. 12.1. Units Registry IANA will create a registry of SenML unit symbols. The primary purpose of this registry is to make sure that symbols uniquely map to give type of measurement. Definitions for many of these units can be found in location such as [NIST811] and [BIPM]. Units marked with an asterisk are NOT RECOMMENDED to be produced by new implementations, but are in active use and SHOULD be implemented by consumers that can use the related base units. +----------+------------------------------------+-------+-----------+ | Symbol | Description | Type | Reference | +----------+------------------------------------+-------+-----------+ | m | meter | float | RFC-AAAA | | kg | kilogram | float | RFC-AAAA | | g | gram* | float | RFC-AAAA | | s | second | float | RFC-AAAA | | A | ampere | float | RFC-AAAA | | K | kelvin | float | RFC-AAAA | Jennings, et al. Expires January 4, 2018 [Page 25] Internet-Draft SenML July 2017 | cd | candela | float | RFC-AAAA | | mol | mole | float | RFC-AAAA | | Hz | hertz | float | RFC-AAAA | | rad | radian | float | RFC-AAAA | | sr | steradian | float | RFC-AAAA | | N | newton | float | RFC-AAAA | | Pa | pascal | float | RFC-AAAA | | J | joule | float | RFC-AAAA | | W | watt | float | RFC-AAAA | | C | coulomb | float | RFC-AAAA | | V | volt | float | RFC-AAAA | | F | farad | float | RFC-AAAA | | Ohm | ohm | float | RFC-AAAA | | S | siemens | float | RFC-AAAA | | Wb | weber | float | RFC-AAAA | | T | tesla | float | RFC-AAAA | | H | henry | float | RFC-AAAA | | Cel | degrees Celsius | float | RFC-AAAA | | lm | lumen | float | RFC-AAAA | | lx | lux | float | RFC-AAAA | | Bq | becquerel | float | RFC-AAAA | | Gy | gray | float | RFC-AAAA | | Sv | sievert | float | RFC-AAAA | | kat | katal | float | RFC-AAAA | | m2 | square meter (area) | float | RFC-AAAA | | m3 | cubic meter (volume) | float | RFC-AAAA | | l | liter (volume)* | float | RFC-AAAA | | m/s | meter per second (velocity) | float | RFC-AAAA | | m/s2 | meter per square second | float | RFC-AAAA | | | (acceleration) | | | | m3/s | cubic meter per second (flow rate) | float | RFC-AAAA | | l/s | liter per second (flow rate)* | float | RFC-AAAA | | W/m2 | watt per square meter (irradiance) | float | RFC-AAAA | | cd/m2 | candela per square meter | float | RFC-AAAA | | | (luminance) | | | | bit | bit (information content) | float | RFC-AAAA | | bit/s | bit per second (data rate) | float | RFC-AAAA | | lat | degrees latitude (note 2) | float | RFC-AAAA | | lon | degrees longitude (note 2) | float | RFC-AAAA | | pH | pH value (acidity; logarithmic | float | RFC-AAAA | | | quantity) | | | | dB | decibel (logarithmic quantity) | float | RFC-AAAA | | dBW | decibel relative to 1 W (power | float | RFC-AAAA | | | level) | | | | Bspl | bel (sound pressure level; | float | RFC-AAAA | | | logarithmic quantity)* | | | | count | 1 (counter value) | float | RFC-AAAA | | / | 1 (Ratio e.g., value of a switch, | float | RFC-AAAA | Jennings, et al. Expires January 4, 2018 [Page 26] Internet-Draft SenML July 2017 | | note 1) | | | | % | 1 (Ratio e.g., value of a switch, | float | RFC-AAAA | | | note 1)* | | | | %RH | Percentage (Relative Humidity) | float | RFC-AAAA | | %EL | Percentage (remaining battery | float | RFC-AAAA | | | energy level) | | | | EL | seconds (remaining battery energy | float | RFC-AAAA | | | level) | | | | 1/s | 1 per second (event rate) | float | RFC-AAAA | | 1/min | 1 per minute (event rate, "rpm")* | float | RFC-AAAA | | beat/min | 1 per minute (Heart rate in beats | float | RFC-AAAA | | | per minute)* | | | | beats | 1 (Cumulative number of heart | float | RFC-AAAA | | | beats)* | | | | S/m | Siemens per meter (conductivity) | float | RFC-AAAA | +----------+------------------------------------+-------+-----------+ Table 5 o Note 1: A value of 0.0 indicates the switch is off while 1.0 indicates on and 0.5 would be half on. The preferred name of this unit is "/". For historical reasons, the name "%" is also provided for the same unit - but note that while that name strongly suggests a percentage (0..100) -- it is however NOT a percentage, but the absolute ratio! o Note 2: Assumed to be in WGS84 unless another reference frame is known for the sensor. New entries can be added to the registration by either Expert Review or IESG Approval as defined in [RFC5226]. Experts should exercise their own good judgment but need to consider the following guidelines: 1. There needs to be a real and compelling use for any new unit to be added. 2. Units should define the semantic information and be chosen carefully. Implementors need to remember that the same word may be used in different real-life contexts. For example, degrees when measuring latitude have no semantic relation to degrees when measuring temperature; thus two different units are needed. 3. These measurements are produced by computers for consumption by computers. The principle is that conversion has to be easily be done when both reading and writing the media type. The value of a single canonical representation outweighs the convenience of easy human representations or loss of precision in a conversion. Jennings, et al. Expires January 4, 2018 [Page 27] Internet-Draft SenML July 2017 4. Use of SI prefixes such as "k" before the unit is not recommended. Instead one can represent the value using scientific notation such a 1.2e3. The "kg" unit is exception to this rule since it is an SI base unit; the "g" unit is provided for legacy compatibility. 5. For a given type of measurement, there will only be one unit type defined. So for length, meters are defined and other lengths such as mile, foot, light year are not allowed. For most cases, the SI unit is preferred. 6. Symbol names that could be easily confused with existing common units or units combined with prefixes should be avoided. For example, selecting a unit name of "mph" to indicate something that had nothing to do with velocity would be a bad choice, as "mph" is commonly used to mean miles per hour. 7. The following should not be used because the are common SI prefixes: Y, Z, E, P, T, G, M, k, h, da, d, c, n, u, p, f, a, z, y, Ki, Mi, Gi, Ti, Pi, Ei, Zi, Yi. 8. The following units should not be used as they are commonly used to represent other measurements Ky, Gal, dyn, etg, P, St, Mx, G, Oe, Gb, sb, Lmb, mph, Ci, R, RAD, REM, gal, bbl, qt, degF, Cal, BTU, HP, pH, B/s, psi, Torr, atm, at, bar, kWh. 9. The unit names are case sensitive and the correct case needs to be used, but symbols that differ only in case should not be allocated. 10. A number after a unit typically indicates the previous unit raised to that power, and the / indicates that the units that follow are the reciprocal. A unit should have only one / in the name. 11. A good list of common units can be found in the Unified Code for Units of Measure [UCUM]. 12.2. SenML Label Registry IANA will create a new registry for SenML labels. The initial content of the registry is: Jennings, et al. Expires January 4, 2018 [Page 28] Internet-Draft SenML July 2017 +---------------+-------+------+----------+----+---------+ | Name | Label | CBOR | XML Type | ID | Note | +---------------+-------+------+----------+----+---------+ | Base Name | bn | -2 | string | a | RFCXXXX | | Base Sum | bs | -6 | double | a | RFCXXXX | | Base Time | bt | -3 | double | a | RFCXXXX | | Base Unit | bu | -4 | string | a | RFCXXXX | | Base Value | bv | -5 | double | a | RFCXXXX | | Base Version | bver | -1 | int | a | RFCXXXX | | Boolean Value | vb | 4 | boolean | a | RFCXXXX | | Data Value | vd | 8 | string | a | RFCXXXX | | Name | n | 0 | string | a | RFCXXXX | | String Value | vs | 3 | string | a | RFCXXXX | | Time | t | 6 | double | a | RFCXXXX | | Unit | u | 1 | string | a | RFCXXXX | | Update Time | ut | 7 | double | a | RFCXXXX | | Value | v | 2 | double | a | RFCXXXX | | Value Sum | s | 5 | double | a | RFCXXXX | | Link | l | 9 | string | a | RFCXXXX | +---------------+-------+------+----------+----+---------+ Table 6: SenML Labels Note to RFC Editor. Please replace RFCXXXX with the number for this RFC. All new entries must define the Label Name, Label, and XML Type but the CBOR labels SHOULD be left empty as CBOR will use the string encoding for any new labels. The ID fields contains the EXI schemaId value of the first Schema which includes this label or is empty if this label was not intended for use with EXI. The Note field SHOULD contain information about where to find out more information about this label. The JSON, CBOR, and EXI types are derived from the XML type. All XML numeric types such as double, float, integer and int become a JSON Number. XML boolean and string become a JSON Boolean and String respectively. CBOR represents numeric values with a CBOR type that does not loose any information from the JSON value. EXI uses the XML types. New entries can be added to the registration by either Expert Review or IESG Approval as defined in [RFC5226]. Experts should exercise their own good judgment but need to consider that shorter labels should have more strict review. Jennings, et al. Expires January 4, 2018 [Page 29] Internet-Draft SenML July 2017 All new SenML labels that have "base" semantics (see Section 4.1) MUST start with character 'b'. Regular labels MUST NOT start with that character. Extensions that add a label that is intended for use with XML need to create a new RelaxNG scheme that includes all the labels in the IANA registry. Extensions that add a label that is intended for use with EXI need to create a new XSD Schema that includes all the labels in the IANA registry and then allocate a new EXI schemaId value. Moving to the next letter in the alphabet is the suggested way to create the new value for the EXI schemaId. Any labels with previously blank ID values SHOULD be updated in the IANA table to have their ID set to this new schemaId value. Extensions that are mandatory to understand to correctly process the Pack MUST have a label name that ends with the '_' character. 12.3. Media Type Registration The following registrations are done following the procedure specified in [RFC6838] and [RFC7303]. Clipboard formats are defined for the JSON and XML form of lists but do not make sense for streams or other formats. Note to RFC Editor - please remove this paragraph. Note that a request for media type review for senml+json was sent to the media- types@iana.org on Sept 21, 2010. A second request for all the types was sent on October 31, 2016. 12.3.1. senml+json Media Type Registration Type name: application Subtype name: senml+json Required parameters: none Optional parameters: none Encoding considerations: Must be encoded as using a subset of the encoding allowed in [RFC7159]. See RFC-AAAA for details. This simplifies implementation of very simple system and does not impose any significant limitations as all this data is meant for machine to machine communications and is not meant to be human readable. Jennings, et al. Expires January 4, 2018 [Page 30] Internet-Draft SenML July 2017 Security considerations: Sensor data can contain a wide range of information ranging from information that is very public, such the outside temperature in a given city, to very private information that requires integrity and confidentiality protection, such as patient health information. This format does not provide any security and instead relies on the transport protocol that carries it to provide security. Given applications need to look at the overall context of how this media type will be used to decide if the security is adequate. Interoperability considerations: Applications should ignore any JSON key value pairs that they do not understand. This allows backwards compatibility extensions to this specification. The "bver" field can be used to ensure the receiver supports a minimal level of functionality needed by the creator of the JSON object. Published specification: RFC-AAAA Applications that use this media type: The type is used by systems that report e.g., electrical power usage and environmental information such as temperature and humidity. It can be used for a wide range of sensor reporting systems. Fragment identifier considerations: Fragment identification for application/senml+json is supported by using fragment identifiers as specified by RFC-AAAA. Additional information: Magic number(s): none File extension(s): senml Windows Clipboard Name: "JSON Sensor Measurement List" Macintosh file type code(s): none Macintosh Universal Type Identifier code: org.ietf.senml-json conforms to public.text Person & email address to contact for further information: Cullen Jennings Intended usage: COMMON Restrictions on usage: None Author: Cullen Jennings Jennings, et al. Expires January 4, 2018 [Page 31] Internet-Draft SenML July 2017 Change controller: IESG 12.3.2. sensml+json Media Type Registration Type name: application Subtype name: sensml+json Required parameters: none Optional parameters: none Encoding considerations: Must be encoded as using a subset of the encoding allowed in [RFC7159]. See RFC-AAAA for details. This simplifies implementation of very simple system and does not impose any significant limitations as all this data is meant for machine to machine communications and is not meant to be human readable. Security considerations: Sensor data can contain a wide range of information ranging from information that is very public, such the outside temperature in a given city, to very private information that requires integrity and confidentiality protection, such as patient health information. This format does not provide any security and instead relies on the transport protocol that carries it to provide security. Given applications need to look at the overall context of how this media type will be used to decide if the security is adequate. Interoperability considerations: Applications should ignore any JSON key value pairs that they do not understand. This allows backwards compatibility extensions to this specification. The "bver" field can be used to ensure the receiver supports a minimal level of functionality needed by the creator of the JSON object. Published specification: RFC-AAAA Applications that use this media type: The type is used by systems that report e.g., electrical power usage and environmental information such as temperature and humidity. It can be used for a wide range of sensor reporting systems. Fragment identifier considerations: Fragment identification for application/senml+json is supported by using fragment identifiers as specified by RFC-AAAA. Additional information: Magic number(s): none Jennings, et al. Expires January 4, 2018 [Page 32] Internet-Draft SenML July 2017 File extension(s): sensml Macintosh file type code(s): none Person & email address to contact for further information: Cullen Jennings Intended usage: COMMON Restrictions on usage: None Author: Cullen Jennings Change controller: IESG 12.3.3. senml+cbor Media Type Registration Type name: application Subtype name: senml+cbor Required parameters: none Optional parameters: none Encoding considerations: Must be encoded as using [RFC7049]. See RFC-AAAA for details. Security considerations: Sensor data can contain a wide range of information ranging from information that is very public, such the outside temperature in a given city, to very private information that requires integrity and confidentiality protection, such as patient health information. This format does not provide any security and instead relies on the transport protocol that carries it to provide security. Given applications need to look at the overall context of how this media type will be used to decide if the security is adequate. Interoperability considerations: Applications should ignore any key value pairs that they do not understand. This allows backwards compatibility extensions to this specification. The "bver" field can be used to ensure the receiver supports a minimal level of functionality needed by the creator of the CBOR object. Published specification: RFC-AAAA Applications that use this media type: The type is used by systems that report e.g., electrical power usage and environmental Jennings, et al. Expires January 4, 2018 [Page 33] Internet-Draft SenML July 2017 information such as temperature and humidity. It can be used for a wide range of sensor reporting systems. Fragment identifier considerations: Fragment identification for application/senml+cbor is supported by using fragment identifiers as specified by RFC-AAAA. Additional information: Magic number(s): none File extension(s): senmlc Macintosh file type code(s): none Macintosh Universal Type Identifier code: org.ietf.senml-cbor conforms to public.data Person & email address to contact for further information: Cullen Jennings Intended usage: COMMON Restrictions on usage: None Author: Cullen Jennings Change controller: IESG 12.3.4. sensml+cbor Media Type Registration Type name: application Subtype name: sensml+cbor Required parameters: none Optional parameters: none Encoding considerations: Must be encoded as using [RFC7049]. See RFC-AAAA for details. Security considerations: Sensor data can contain a wide range of information ranging from information that is very public, such the outside temperature in a given city, to very private information that requires integrity and confidentiality protection, such as patient health information. This format does not provide any security and instead relies on the transport protocol that carries it to provide Jennings, et al. Expires January 4, 2018 [Page 34] Internet-Draft SenML July 2017 security. Given applications need to look at the overall context of how this media type will be used to decide if the security is adequate. Interoperability considerations: Applications should ignore any key value pairs that they do not understand. This allows backwards compatibility extensions to this specification. The "bver" field can be used to ensure the receiver supports a minimal level of functionality needed by the creator of the CBOR object. Published specification: RFC-AAAA Applications that use this media type: The type is used by systems that report e.g., electrical power usage and environmental information such as temperature and humidity. It can be used for a wide range of sensor reporting systems. Fragment identifier considerations: Fragment identification for application/senml+cbor is supported by using fragment identifiers as specified by RFC-AAAA. Additional information: Magic number(s): none File extension(s): sensmlc Macintosh file type code(s): none Person & email address to contact for further information: Cullen Jennings Intended usage: COMMON Restrictions on usage: None Author: Cullen Jennings Change controller: IESG 12.3.5. senml+xml Media Type Registration Type name: application Subtype name: senml+xml Required parameters: none Jennings, et al. Expires January 4, 2018 [Page 35] Internet-Draft SenML July 2017 Optional parameters: none Encoding considerations: Must be encoded as using [W3C.REC-xml-20081126]. See RFC-AAAA for details. Security considerations: Sensor data can contain a wide range of information ranging from information that is very public, such the outside temperature in a given city, to very private information that requires integrity and confidentiality protection, such as patient health information. This format does not provide any security and instead relies on the transport protocol that carries it to provide security. Given applications need to look at the overall context of how this media type will be used to decide if the security is adequate. Interoperability considerations: Applications should ignore any XML tags or attributes that they do not understand. This allows backwards compatibility extensions to this specification. The "bver" attribute in the senml XML tag can be used to ensure the receiver supports a minimal level of functionality needed by the creator of the XML. Published specification: RFC-AAAA Applications that use this media type: The type is used by systems that report e.g., electrical power usage and environmental information such as temperature and humidity. It can be used for a wide range of sensor reporting systems. Fragment identifier considerations: Fragment identification for application/senml+xml is supported by using fragment identifiers as specified by RFC-AAAA. Additional information: Magic number(s): none File extension(s): senmlx Windows Clipboard Name: "XML Sensor Measurement List" Macintosh file type code(s): none Macintosh Universal Type Identifier code: org.ietf.senml-xml conforms to public.xml Person & email address to contact for further information: Cullen Jennings Jennings, et al. Expires January 4, 2018 [Page 36] Internet-Draft SenML July 2017 Intended usage: COMMON Restrictions on usage: None Author: Cullen Jennings Change controller: IESG 12.3.6. sensml+xml Media Type Registration Type name: application Subtype name: sensml+xml Required parameters: none Optional parameters: none Encoding considerations: Must be encoded as using [W3C.REC-xml-20081126]. See RFC-AAAA for details. Security considerations: Sensor data can contain a wide range of information ranging from information that is very public, such the outside temperature in a given city, to very private information that requires integrity and confidentiality protection, such as patient health information. This format does not provide any security and instead relies on the transport protocol that carries it to provide security. Given applications need to look at the overall context of how this media type will be used to decide if the security is adequate. Interoperability considerations: Applications should ignore any XML tags or attributes that they do not understand. This allows backwards compatibility extensions to this specification. The "bver" attribute in the senml XML tag can be used to ensure the receiver supports a minimal level of functionality needed by the creator of the XML. Published specification: RFC-AAAA Applications that use this media type: The type is used by systems that report e.g., electrical power usage and environmental information such as temperature and humidity. It can be used for a wide range of sensor reporting systems. Fragment identifier considerations: Fragment identification for application/senml+xml is supported by using fragment identifiers as specified by RFC-AAAA. Jennings, et al. Expires January 4, 2018 [Page 37] Internet-Draft SenML July 2017 Additional information: Magic number(s): none File extension(s): sensmlx Macintosh file type code(s): none Person & email address to contact for further information: Cullen Jennings Intended usage: COMMON Restrictions on usage: None Author: Cullen Jennings Change controller: IESG 12.3.7. senml+exi Media Type Registration Type name: application Subtype name: senml+exi Required parameters: none Optional parameters: none Encoding considerations: Must be encoded as using [W3C.REC-exi-20140211]. See RFC-AAAA for details. Security considerations: Sensor data can contain a wide range of information ranging from information that is very public, such the outside temperature in a given city, to very private information that requires integrity and confidentiality protection, such as patient health information. This format does not provide any security and instead relies on the transport protocol that carries it to provide security. Given applications need to look at the overall context of how this media type will be used to decide if the security is adequate. Interoperability considerations: Applications should ignore any XML tags or attributes that they do not understand. This allows backwards compatibility extensions to this specification. The "bver" attribute in the senml XML tag can be used to ensure the receiver supports a minimal level of functionality needed by the creator of Jennings, et al. Expires January 4, 2018 [Page 38] Internet-Draft SenML July 2017 the XML. Further information on using schemas to guide the EXI can be found in RFC-AAAA. Published specification: RFC-AAAA Applications that use this media type: The type is used by systems that report e.g., electrical power usage and environmental information such as temperature and humidity. It can be used for a wide range of sensor reporting systems. Fragment identifier considerations: Fragment identification for application/senml+exi is supported by using fragment identifiers as specified by RFC-AAAA. Additional information: Magic number(s): none File extension(s): senmle Macintosh file type code(s): none Macintosh Universal Type Identifier code: org.ietf.senml-exi conforms to public.data Person & email address to contact for further information: Cullen Jennings Intended usage: COMMON Restrictions on usage: None Author: Cullen Jennings Change controller: IESG 12.3.8. sensml+exi Media Type Registration Type name: application Subtype name: sensml+exi Required parameters: none Optional parameters: none Encoding considerations: Must be encoded as using [W3C.REC-exi-20140211]. See RFC-AAAA for details. Jennings, et al. Expires January 4, 2018 [Page 39] Internet-Draft SenML July 2017 Security considerations: Sensor data can contain a wide range of information ranging from information that is very public, such the outside temperature in a given city, to very private information that requires integrity and confidentiality protection, such as patient health information. This format does not provide any security and instead relies on the transport protocol that carries it to provide security. Given applications need to look at the overall context of how this media type will be used to decide if the security is adequate. Interoperability considerations: Applications should ignore any XML tags or attributes that they do not understand. This allows backwards compatibility extensions to this specification. The "bver" attribute in the senml XML tag can be used to ensure the receiver supports a minimal level of functionality needed by the creator of the XML. Further information on using schemas to guide the EXI can be found in RFC-AAAA. Published specification: RFC-AAAA Applications that use this media type: The type is used by systems that report e.g., electrical power usage and environmental information such as temperature and humidity. It can be used for a wide range of sensor reporting systems. Fragment identifier considerations: Fragment identification for application/senml+exi is supported by using fragment identifiers as specified by RFC-AAAA. Additional information: Magic number(s): none File extension(s): sensmle Macintosh file type code(s): none Person & email address to contact for further information: Cullen Jennings Intended usage: COMMON Restrictions on usage: None Author: Cullen Jennings Change controller: IESG Jennings, et al. Expires January 4, 2018 [Page 40] Internet-Draft SenML July 2017 12.4. XML Namespace Registration This document registers the following XML namespaces in the IETF XML registry defined in [RFC3688]. URI: urn:ietf:params:xml:ns:senml Registrant Contact: The IESG. XML: N/A, the requested URIs are XML namespaces 12.5. CoAP Content-Format Registration IANA is requested to assign CoAP Content-Format IDs for the SenML media types in the "CoAP Content-Formats" sub-registry, within the "CoRE Parameters" registry [RFC7252]. All IDs are assigned from the "Expert Review" (0-255) range. The assigned IDs are show in Table 7. +-------------------------+-----+ | Media type | ID | +-------------------------+-----+ | application/senml+json | TBD | | application/sensml+json | TBD | | application/senml+cbor | TBD | | application/sensml+cbor | TBD | | application/senml+xml | TBD | | application/sensml+xml | TBD | | application/senml+exi | TBD | | application/sensml+exi | TBD | +-------------------------+-----+ Table 7: CoAP Content-Format IDs 13. Security Considerations See Section 14. Further discussion of security properties can be found in Section 12.3. 14. Privacy Considerations Sensor data can range from information with almost no security considerations, such as the current temperature in a given city, to highly sensitive medical or location data. This specification provides no security protection for the data but is meant to be used inside another container or transport protocol such as S/MIME or HTTP with TLS that can provide integrity, confidentiality, and authentication information about the source of the data. Jennings, et al. Expires January 4, 2018 [Page 41] Internet-Draft SenML July 2017 15. Acknowledgement We would like to thank Alexander Pelov, Andrew McClure, Andrew Mcgregor, Bjoern Hoehrmann, Christian Amsuess, Christian Groves, Daniel Peintner, Jan-Piet Mens, Joe Hildebrand, John Klensin, Karl Palsson, Lennart Duhrsen, Lisa Dusseault, Lyndsay Campbell, Martin Thomson, Michael Koster, and Stephen Farrell, for their review comments. 16. References 16.1. Normative References [BIPM] Bureau International des Poids et Mesures, "The International System of Units (SI)", 8th edition, 2006. [IEEE.754.1985] Institute of Electrical and Electronics Engineers, "Standard for Binary Floating-Point Arithmetic", IEEE Standard 754, August 1985. [NIST811] Thompson, A. and B. Taylor, "Guide for the Use of the International System of Units (SI)", NIST Special Publication 811, 2008. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, . [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008, . [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, . Jennings, et al. Expires January 4, 2018 [Page 42] Internet-Draft SenML July 2017 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013, . [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303, DOI 10.17487/RFC7303, July 2014, . [W3C.REC-exi-20140211] Schneider, J., Kamiya, T., Peintner, D., and R. Kyusakov, "Efficient XML Interchange (EXI) Format 1.0 (Second Edition)", World Wide Web Consortium Recommendation REC- exi-20140211, February 2014, . [W3C.REC-xml-20081126] Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC- xml-20081126, November 2008, . 16.2. Informative References [I-D.arkko-core-dev-urn] Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource Names for Device Identifiers", draft-arkko-core-dev-urn-03 (work in progress), July 2012. [I-D.greevenbosch-appsawg-cbor-cddl] Birkholz, H., Vigano, C., and C. Bormann, "CBOR data definition language (CDDL): a notational convention to express CBOR data structures", draft-greevenbosch-appsawg- cbor-cddl-10 (work in progress), March 2017. Jennings, et al. Expires January 4, 2018 [Page 43] Internet-Draft SenML July 2017 [I-D.ietf-core-links-json] Li, K., Rahman, A., and C. Bormann, "Representing Constrained RESTful Environments (CoRE) Link Format in JSON and CBOR", draft-ietf-core-links-json-08 (work in progress), April 2017. [IEEE802.1as-2011] IEEE, "IEEE Standard for Local and Metropolitan Area Networks - Timing and Synchronization for Time-Sensitive Applications in Bridged Local Area Networks", 2011. [IEEE802.1ba-2011] IEEE, "IEEE Standard for Local and metropolitan area networks--Audio Video Bridging (AVB) Systems", 2011. [RFC2141] Moats, R., "URN Syntax", RFC 2141, DOI 10.17487/RFC2141, May 1997, . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, DOI 10.17487/RFC4122, July 2005, . [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, DOI 10.17487/RFC5952, August 2010, . [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, . [RFC7111] Hausenblas, M., Wilde, E., and J. Tennison, "URI Fragment Identifiers for the text/csv Media Type", RFC 7111, DOI 10.17487/RFC7111, January 2014, . [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy Considerations for IPv6 Address Generation Mechanisms", RFC 7721, DOI 10.17487/RFC7721, March 2016, . Jennings, et al. Expires January 4, 2018 [Page 44] Internet-Draft SenML July 2017 [UCUM] Schadow, G. and C. McDonald, "The Unified Code for Units of Measure (UCUM)", Regenstrief Institute and Indiana University School of Informatics, 2013, . Appendix A. Links Extension A field to support a link extension for SenML is defined as a string field by this specification. The link extension can be used for additional information about a SenML Record. The definition and usage of the contents of this value are specified in [I-D.ietf-core-links-json]. For JSON and XML the field has a label of "l" and a value that is a string. The following shows an example of the links extension. [ {"bn":"urn:dev:ow:10e2073a01080063:","bt":1.320078429e+09, "l":"[{\"href\":\"humidity\",\"foo\":\"bar\"}]", "n":"temperature","u":"Cel","v":27.2}, {"n":"humidity","u":"%RH","v":80} ] Authors' Addresses Cullen Jennings Cisco 400 3rd Avenue SW Calgary, AB T2P 4H2 Canada Email: fluffy@iii.ca Zach Shelby ARM 150 Rose Orchard San Jose 95134 USA Phone: +1-408-203-9434 Email: zach.shelby@arm.com Jennings, et al. Expires January 4, 2018 [Page 45] Internet-Draft SenML July 2017 Jari Arkko Ericsson Jorvas 02420 Finland Email: jari.arkko@piuha.net Ari Keranen Ericsson Jorvas 02420 Finland Email: ari.keranen@ericsson.com Carsten Bormann Universitaet Bremen TZI Postfach 330440 Bremen D-28359 Germany Phone: +49-421-218-63921 Email: cabo@tzi.org Jennings, et al. Expires January 4, 2018 [Page 46]