| Internet Engineering Task Force | M. Veillette, Ed. |
| Internet-Draft | Trilliant Networks Inc. |
| Intended status: Informational | A. Pelov, Ed. |
| Expires: September 12, 2016 | Acklio |
| A. Somaraju | |
| Tridonic GmbH & Co KG | |
| R. Turner | |
| Landis+Gyr | |
| A. Minaburo | |
| Acklio | |
| March 11, 2016 |
Constrained Objects Language
draft-veillette-core-cool-01
This document describes a management function set adapted to constrained devices and constrained networks (e.g., low-power, lossy). CoOL objects (datastores, RPCs, actions and notifications) are defined using the YANG modelling language [I-D.ietf-netmod-rfc6020bis]. Interactions with these objects are performed using the CoAP web transfer protocol [RFC7252]. Payloads are encoded using the CBOR data format [RFC7049]. The mapping between YANG data models and the CBOR data format is defined in [I-D.veillette-core-yang-cbor-mapping].
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/.
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This Internet-Draft will expire on September 12, 2016.
Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.
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This document defines a CoAP function set for accessing YANG defined resources. YANG data models are encoded in CBOR based on the mapping rules defined in [I-D.veillette-core-yang-cbor-mapping]. YANG items are identified using a compact identifier called Structured Identifiers (SIDs) as defined in [I-D.somaraju-core-sid].
The resulting protocol based on CoAP, CBOR encoded data and structured identifiers (SID) has a low implementation footprint and low network bandwidth requirements and is suitable for both constrained devices and constrained networks as defined by [RFC7228]. This protocol is applicable to the different management topology options described by [I-D.ersue-constrained-mgmt]; centralized, distributed and hierarchical.
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].
The following terms are defined in [I-D.ietf-netmod-rfc6020bis]:
This specification also makes use of the following terminology:
The CoOL protocol is based on the client-server model. The CoOL server is the provider of the datastore resource(s) and the event stream resource(s). The CoOL client is the requester of these resources.
CoOL objects are defined using the YANG modeling language [RFC6020]. Interactions with these objects are performed using the Constrained Application Protocol (CoAP) [RFC7252]. Payloads are encoded using the Concise Binary Object Representation (CBOR) [RFC7049].
This specification is applicable to any transport and security protocols supported by CoAP. Implementers are free to select the most appropriate transport for the targeted applications.
+--------------+ +----------------------------------+ | CoOL client | | CoOL Server | | | | - Datastore resource(s) | | | | - Event stream resource(s) | +--------------+ +----------------------------------+ | CoAP client | <-------> | CoAP Server | +--------------+ +----------------------------------+ | | | | | Lower layers | | Lower layers | | | | | +--------------+ +----------------------------------+
This section lists the URIs recommended for the different CoOL resources. A CoOL server MAY implement a different set of URIs. See the Resource discovery section (Section 7.15) for more details on how a CoOL client can discover the list of URIs supported by a CoOL server using the “/.well-known/core” resource.
For example:
All these resources are optional at the exception of the default datastore resource. The CoAP response code 4.04 (Not Found) MUST be returned when a CoOL client tries to access a resource that is unavailable.
RPCs commit and cancel-commit defined in ietf-cool YANG module are available to perform the following operations on datastores:
This section defines the different interactions supported between a CoOL client and a CoOL server.
The GET method is used by CoOL clients to retrieve the entire contents of a datastore. Implementation of this function is optional and dependent of the capability of the CoOL server to transfer a relatively large response.
To retrieve all instantiated data nodes of a datastore resource, a CoOL client sends a CoAP GET request to the URI of the targeted datastore. If the request is accepted by the CoOL server, a 2.05 (Content) response code is returned. The payload of the GET response MUST carry a CBOR array containing the contents of the targeted datastore. The CBOR array MUST contain a list of pairs of delta and associated value. A delta represents the difference between the current SID and the SID of the previous pair within the CBOR array. Each value is encoded using the rules defined by [I-D.veillette-core-yang-cbor-mapping].
If the request is rejected by the CoOL server, a 5.01 Not implemented or 4.13 Request Entity Too Large response code is returned.
Example:
In this example, the CoOL server returns a datastore containing the following data nodes defined in the YANG module “ietf-system” [RFC7317] and YANG module “ietf-interfaces” [RFC7223]:
CoAP Request:
GET /c
CoAP response:
2.05 Content Content-Format(application/cool+cbor)
[
1529,
{
4 : "eth0", # name (SID 1533)
1 : "Ethernet adaptor", # description (SID 1530)
5 : 1179, # type (SID 1534), identity ethernetCsmacd
2 : true # enabled (SID 1531)
},
179, # clock (SID 1708)
{
1 : "2015-02-08T14:10:08Z09:00", # boot-datetime (SID 1709)
2 : "2015-04-04T09:32:51Z09:00" # current-datetime (SID 1710)
}
13, 60 # timezone-utc-offset (SID 1721)
]
The FETCH method is used by the CoOL client of retrieve a subset of the data nodes within a datastore.
To retrieve a list of data node instances, the CoOL client sends a CoAP FETCH request to the URI of the targeted datastore. The payload of the FETCH request contains the list of data node(s) instance to be retrieved. This list is encoded using a CBOR array, each entry containing an “instance-identifier” as defined by [I-D.veillette-core-yang-cbor-mapping]. Within each “instance-identifier”, data nodes are identified using SIDs as defined by [I-D.somaraju-core-sid].
SIDs within the list of “instance-identifier” are encoded using delta. A delta represents the different between the current SID and the SID of the previous entry within this list. The delta of the first entry within the list is set to the absolute SID value (current SID minus zero).
On successful processing of the CoAP request, the CoOL server MUST return a CoAP response with a response code 2.05 (Content).
When a single data node is requested, the payload of the GET response MUST carry the data node instance requested encoded using the rules defined in [I-D.veillette-core-yang-cbor-mapping].
When a multiple data nodes are requested, the payload of the GET response MUST carry a CBOR array containing the data node instance(s) requested. Each entry within this array MUST be encoding using the rules defined in [I-D.veillette-core-yang-cbor-mapping].
When a collection is returned (YANG container, YANG list or YANG list instance), delta(s) are computed using the requested SID as parent.
The CBOR value undefined (0xf7) must be returned for each data node requested but not currently available.
In this example, a CoOL client retrieves the leaf “/system-state/clock/current-datetime” (SID 1704) and the container “/system/clock” (SID 1719) containing the leaf “/system/clock/timezone/timezone-utc-offset/timezone-utc-offset” (SID 1721). These data nodes are defined in the YANG module “ietf-system” [RFC7317].
CoAP request:
FETCH /c Content-Format(application/cool+cbor) [1704, 15]
CoAP response:
2.05 Content Content-Format(application/cool+cbor)
[
"2015-10-08T14:10:08Z09:00", # current-datetime (SID 1704)
{ # clock (SID 1719)
2 : 540 # timezone-utc-offset (SID 1721)
}
]
CoAP requests and responses MUST be encoded in accordance with [RFC7252] or [I-D.ietf-core-coap-tcp-tls]. An encoding example is shown below:
CoAP request:
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver| T | TKL | Code (0x01) | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Token (0 to 8 bytes) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opt Delta (12)| Opt Length (1)| na | Opt Delta (3) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opt Length (2)| '/' | 'c' |1 1 1 1 1 1 1 1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x82 | 0x19 | 0x06 | 0xa8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x0f | +-+-+-+-+-+-+-+-+
CoAP response:
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Ver| T | TKL | Code (0x45) | Message ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Token (0 to 8 bytes) ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opt Delta (12)| Opt Length (1)| na |1 1 1 1 1 1 1 1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0xa2 | 0x78 | 0x19 | 0x32 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x30 | 0x31 | 0x35 | 0x2d | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x31 | 0x30 | 0x2d | 0x30 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x38 | 0x54 | 0x31 | 0x34 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x3a | 0x31 | 0x30 | 0x2d | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x30 | 0x38 | 0x5a | 0x30 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x39 | 0x3a | 0x30 | 0x30 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0xa1 | 0x02 | 0x19 | 0x02 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0x1c | +-+-+-+-+-+-+-+-+
The data type “instance-identifier” allows the selection of an instance of a specific data node within a list. In this example, a CoOL client retrieves the “/interfaces/interface/type” (SID 1529) leaf from the “/interfaces/interface” list. The “/interfaces/interface/name” associated to this interface is equal to “eth0”. This example is based on the YANG module “ietf-interfaces” [RFC7223].
CoAP request:
FETCH /c Content-Format(application/cool+cbor) [[1529, "eth0"]]
CoAP response:
2.05 Content Content-Format(application/cool+cbor) "Ethernet adaptor"
To retrieve all instances of a list, the CoOL client excludes from the “instance-identifier” the key(s) of the targeted list. The list returned is encoded using the rules defined in [I-D.veillette-core-yang-cbor-mapping] section 4.4.
In this example, a CoOL client retrieves the list “/interfaces/interface” (SID 1529). The response returns contain two instances, one for an Ethernet adaptor and one for a WIFI interface.
CoAP request:
FETCH /c Content-Format(application/cool+cbor) [1529]
CoAP response:
2.05 Content Content-Format(application/cool+cbor)
[
{
4 : "eth0", # name (SID 1533)
1 : "Ethernet adaptor", # description (SID 1530)
5 : 1179, # type (SID 1534), identity ethernetCsmacd
2 : true # enabled (SID 1531)
},
{
4 : "wlan0", # name (SID 1533)
1 : "WIFI ", # description (SID 1530)
5 : 1220, # type (SID 1534), identity ieee80211
2 : false # enabled (SID 1531)
}
]
To retrieve a list instance, the CoOL client MUST use an “instance-identifier” with a SID set to the targeted list and the key(s) set to the value(s) associated to the targeted instance.
In this example, the CoOL client requests the instance of the list “/interfaces/interface” (SID 1529) associated to the name “eth1”. The response returned by the CoOL server contains the targeted list instance formatted as YANG container.
CoAP request:
FETCH /c Content-Format(application/cool+cbor) [[1529, "eth1"]
CoAP response:
2.05 Content Content-Format(application/cool+cbor)
{
4 : "eth0" # name (SID 1533)
1 : "Ethernet adaptor" # description (SID 1530)
5 : 1179 # type (SID 1534), identity ethernetCsmacd
2 : true # enabled (SID 1531)
}
This “instance-identifier” extension allows the selection of a subset of data nodes within a list. This is accomplished by adding an extra element to the “instance-identifier”. This element contains the subset of data nodes to be returned encoded as CBOR array. Each entry within this CBOR array is set to the delta between the current SID and the SID of targeted container as specified in the first entry of the “instance-identifier”.
CoOL servers SHOULD implement this “instance-identifier” extension. When this extension is not supported, the CoOL server MUST ignore the third element of the “instance-identifier” and return the list instance as specified by the first two elements of the “instance-identifier”.
In this example, a CoOL client retrieves from within the “/interfaces/interface” list (SID 1528) the leafs “/interfaces/interface/type” (SID 1533) and “/interfaces/interface/enabled” (SID 1530). The CoOL client also includes in this request the selection of the leaf “/system/hostname” defined in “ietf-system” [RFC7317].
For example:
CoAP request:
FETCH /c Content-Format(application/cool+cbor) [ [1528, ["eth0"], [5, 2]], 211]
CoAP response:
2.05 Content Content-Format(application/cool+cbor)
[
{
5 : 1179, # type (SID 1533), identity ethernetCsmacd
2 : true # enabled (SID 1530)
},
"datatracker.ietf.org", # hostname (SID 1739)
]
This “instance-identifier” extension allows the efficient transfer of all instances of a data node within a YANG list. To retrieve all instances, the CoOL client excludes form the “instance-identifier” the key(s) of the list containing the targeted data node.
The response MUST be encoded as a CBOR ARRAY containing the available instances of the requested data node. This special encoding minimizes significantly this commonly used type of request.
In this example, a CoOL client retrieves all instances of data node “/interfaces-state/interface/name” (SID 1532).
Example:
CoAP request:
FETCH /c Content-Format(application/cool+cbor) [1532]
CoAP response:
2.05 Content Content-Format(application/cool+cbor) ["eth0", "eth1", "wlan0"]
The CoAP PUT method is used by CoOL clients to update the content of a datastore.
The URI of the PUT request MUST be set to the URI of the targeted datastore.
The payload of the PUT request MUST carry a CBOR array containing the new content of the datastore. The CBOR array MUST contain a list of pairs of delta and associated value. A delta represents the different between the current SID and the SID of the previous pair within the CBOR array. Each value is encoded using the rules defined by [I-D.veillette-core-yang-cbor-mapping].
On successful processing of the CoAP request, the CoOL server MUST return a CoAP response with a response code 2.04 (Changed).
A PUT request MUST be processed as an atomic transaction, if any of the data node transferred is rejected for any reason, the entire PUT request MUST be rejected and the CoOL server MUST return an appropriate error response as defined in section 6.
Example:
In this example, a CoOL client sets the default runtime datastore with these data nodes:
CoAP request:
PUT /c/r Content-Format(application/cool+cbor)
[
1727, 540, # timezone-utc-offset (SID 1721)
15, true, # enabled (SID 1742)
1, [ # server (SID 1743)
{
3 : "tic.nrc.ca", # name (SID 1746)
4 : true, # prefer (SID 1747)
5 : { # udp (SID 1748)
6 : "132.246.11.231", # address (SID 1749)
7 : 123 # port (SID 1750)
}
},
{
3 : "tac.nrc.ca", # name (SID 1746)
4 : false, # prefer (SID 1747)
5 : { # udp (SID 1748)
6 : "132.246.11.232" # address (SID 1749)
}
}
]
]
CoAP response:
2.04 Changed
The PATCH method is used by CoOL clients to modify a subset of a datastore.
To modify a datastore, the CoOL client sends a CoAP PATH request to the URI of the targeted datastore. The payload of the FETCH request contains the list of data node instance(s) to be updated, inserted or deleted. This list is encoded using a CBOR array and contains a sequence of pairs of “instance-identifier” and associated values.
Within each “instance-identifier”, data nodes are identified using SIDs as defined by [I-D.somaraju-core-sid]. SIDs within the list are encoded as delta.
On reception, the list is processed by the CoOL server as follows:
On successful processing of the CoAP request, the CoOL server MUST return a CoAP response with a response code 2.05 (Content).
A PATCH request MUST be processed as an atomic transaction, if any of the data nodes transferred is rejected for any reasons, the entire PATCH request MUST be rejected and the CoOL server MUST return an appropriate error response as defined in section 6.
Example:
In this example, a CoOL client performs the following operations:
CoAP request:
PATCH /c/r Content-Format(application/cool+cbor)
[
1742 , true, # enabled (1742)
[1, "tac.nrc.ca"], null, # server (SID 1743)
0, # server (SID 1743)
{
3 : "NTP Pool server 2", # name (SID 1746)
4 : true, # prefer (SID 1747)
5 : { # udp (SID 1748)
6 : "2620:10a:800f::11", # address (SID 1749)
}
}
[4, "tic.nrc.ca"], false # prefer (SID 1747)
]
CoAP response:
2.04 Changed
Protocol operations are defined using the YANG “rpc” or YANG “action” statements.
To execute a protocol operation, the CoOL client sents a CoAP POST request to the URI of the targeted datastore.
The payload of the POST request carries a CBOR array with up to two entries. The first entry carries the instance-identifier identifying the targeted protocol operation. The second entry carries the protocol operation input(s). Input(s) are present only if defined for the invoked protocol operation and used by the CoOL client. Input(s) are encoded using the rules defined for a YANG container, deltas are relative to the SID assigned to the protocol operation.
On successful completion on the protocol operation, the CoOL server returns a CoAP response with the response code set to 2.05 (Content). When output parameters are returned by the CoOL server, these parameter(s) are carried in the CoAP response payload. Output(s) are encoded using the rules defined for a YANG container, deltas are relative to the SID assigned to the protocol operation.
This example is based on the “activate-software-image” RPC defined in [I-D.ietf-netmod-rfc6020bis], assuming that this RPC is assigned to SID 1932, leaf image-name to SID 1933 and leaf status to SID 1934. These SIDs are defined strictly for the purpose of this example.
rpc activate-software-image { input { leaf image-name { type string; } } output { leaf status { type string; } } }
CoAP request:
POST /c Content-Format(application/cool+cbor)
[
1932,
{
1 : "acmefw-2.3" # image-name (SID 1933)
}
]
CoAP response:
2.05 Content
{
2 : "installed" # status (SID 1934)
}
This example is based on the “reset” action defined in [I-D.ietf-netmod-rfc6020bis] assuming that this action is assigned to SID 1902, leaf reset-at to SID 1903 and leaf reset-finished-at to SID 1904. These SIDs are defined strictly for the purpose of this example.
list server { key name; leaf name { type string; } action reset { input { leaf reset-at { type yang:date-and-time; mandatory true; } } output { leaf reset-finished-at { type yang:date-and-time; mandatory true; } } } }
CoAP request:
POST /c Content-Format(application/cool+cbor)
[
[1902, "myServer"],
{
1 : "2016-02-08T14:10:08Z09:00" # reset-at (SID 1903)
}
]
CoAP response:
2.05 Content
{
2 : "2016-08T14:10:08Z09:18" # reset-finished-at (SID 1904)
}
WARNING This section requires more work to address the following identified issues: * Retrieval of past events (e.g. start-time, stop-time) * Retrieval of specific events (e.g. filter) * Configuration persistence * Configuration of by a third entity (configuration tool) * Support of multicast * Event congestion-avoidance * Transfer reliability The current solution based on the observe CoAP option can be augmented or completely replaced by a future version of this draft.
Notifications are defined using the YANG “notification” statement. Subscriptions to an event stream and notification reporting are performed using an event stream resource. When multiple event stream resources are supported, the list of notifications associated with each stream is either pre-defined or configured in the CoOL server. CoOL clients MAY subscribe to one or more event stream resources.
To subscribe to an event stream resource, a CoOL client MUST send a CoAP GET with the Observe CoAP option set to 0. To unsubscribe, a CoOL client MAY send a CoAP reset or a CoAP GET with the Observe option set to 1. For more information on the observe mechanism, see [RFC7641].
Each notification transferred by a CoOL server to each of the registered CoOL clients is carried in a CoAP response with a response code set to 2.05 (Content). Each CoAP response MUST carry in its payload at least one notification but MAY carry multiple. Each notification is carried in a notification-payload defined in ietf-cool, see Appendix A. The notification-payload supports different meta-data associated to this notification, such as the notification identifier, event timestamp, sequence number, severity level and facility. All of these meta information are optional with the exception of the notification identifier.
The CoAP response payload is encoded using the rules defined for the PUT request. When multiple notifications are reported, the CoAP response payload carries a CBOR array, with each entry containing a notification.
This example is based on the “link-failure” and “interface-enabled” notifications defined in [I-D.ietf-netmod-rfc6020bis] assuming the following SID assignment:
These SIDs are defined strictly for the purpose of this example.
notification link-failure {
leaf if-name {
type leafref {
path "/interface/name";
}
}
leaf admin-status {
type leafref {
path "/interface[name = current()/../if-name]/admin-status";
}
}
}
container interfaces {
list interface {
key "name";
leaf name {
type string;
}
notification interface-enabled {
leaf by-user {
type string;
}
}
}
}
In this example, a CoOL client starts by registering to the default event stream resource “/c/e”.
CoAP request:
GET /c/e observe(0) Token(0x9372)
The CoOL server confirms this registration by returning a first CoAP response. The payload of this CoAP response may be empty or may carry the last notification reported by this server.
CoAP response:
2.05 Content Observe(52) Token(0xD937)
After detecting an event, the CoOL server sends its first notification to the registered CoOL client.
CoAP response:
2.05 Content Observe(53) Token(0xD937)
Content-Format(application/cool+cbor)
[
1010 , [1538, "eth0"], # _id (SID 1010)
1,{ # content (SID 1011)
1 : "bob" # by-user (SID 1539)
}
5 , "2016-03-08T14:10:08Z09:00", # timestamp (SID 1015)
]
To optimize communications or because of other constraints, the CoOL server might transfer multiple notifications in a single CoAP response.
CoAP response:
2.05 Content Observe(52) Token(0xD937)
Content-Format(application/cool+cbor)
[
[
1010 , [1538, "eth0"], # _id = interface-enabled (SID 1010)
1,{ # content (SID 1011)
1 : "jack" # by-user (SID 1539)
}
5 , "2016-03-12T15:49:51Z09:00", # timestamp (SID 1015)
],
[
1010 , 1942, # _id = link-failure (SID 1010)
1,{ # content (SID 1011)
1 : "eth0", # if-name (SID 1943)
1 : 1 # admin-status = up (SID 1944)
}
5 , "2016-03-12T15:50:06Z09:00", # timestamp (SID 1015)
]
]
Uri-Query is not currently used by this protocol. Uri-Host, Uri-Port and Uri-Path MUST be used as specified by [RFC6690] to target the CoOL resources as defined by section 3.
This version of CoOL doesn’t support the creation of resources (datastore or event stream). For this reason, the use of Location-Path and Location-Query is not required.
This option is not required since this protocol supports a single content format, “application/cool+cbor”.
This option MUST be supported as specified by [RFC6690].
This option MUST be supported as specified by [RFC6690].
This option MUST be supported as specified by [RFC6690]. Each ETag is associated to all schema nodes within a datastore.
When the UDP transport is used and a large payload need to be transferred, support of the CoAP block transfer as defined by [I-D.ietf-core-block] is recommended.
6.8. Working with Observe
A CoOL server MAY support state change notifications to some or all its leaf data nodes. When supported the CoOL server MUST implement the Server-Side requirements defined in [RFC7641] section 3 and the CoOL client MUST implement the Client-Side requirements defined in [RFC7641] section 4.
To start observing a leaf data node, a CoOL client MUST send a CoAP FETCH with the Observe CoAP option set to 0.
The payload of the FETCH request carries a CBOR array of instance-identifier. The first entry MUST be set to the “instance-identifier” of the data node instance observed. The following entries are optional and allow the selection of coincidental values, data nodes reported at the same time as the observed data node. Coincidental values are included in each notification reported, but changes to these extra data nodes MUST not trigger notification messages.
A subscription can be terminated by the CoOL client by returning a CoAP Reset message or by sending a GET request with an Observe CoAP option set to deregister (1). More details are available in [RFC7641].
Example:
In this example, a CoOL client subscribes to state changes of the data node “/system/ntp/enabled” (SID = 1742) and requests that data node “/system/hostname” (SID 1739) is reported as coincidental value.
A first response is immediately returned by the CoOL server to confirm the subscription and to report the current values of the requested data nodes.
Subsequent responses are returned by the CoOL server each time the state of data node “/system/ntp/enabled” changes.
CoAP request:
FETCH /c Content-Format(application/cool+cbor) Observe(0) [ [1742, "tic.nrc.ca"], -3 ]
CoAP response:
2.05 Content Content-Format(application/cool+cbor) Observe(2631) [ false, # enabled (SID 1742) "tic" # hostname (SID 1739) ]
CoAP response:
2.05 Content Content-Format(application/cool+cbor) Observe(2632) [ true, # enabled (SID 1742) "tic" # hostname (SID 1739) ]
The “/.well-known/core” resource is used by CoOL clients to discover resources implemented by CoOL servers. Each CoOL server MUST have an entry in the “/.well-known/core” resource for each datastore resource and event stream resource supported.
Resource discovery can be performed using a CoAP GET request. If successful, the CoAP response MUST have a response code set to 2.05 (Content), a Content-Format set to “application/link-format”, and a payload containing a list of web links.
To enable discovery of specific resource types, the CoAP server MUST support the query string “rt”.
Link format and the “/.well-known/core” resource are defined in [RFC6690].
Example:
CoAP request:
GET /.well-known/core
CoAP response:
2.05 Content Content-Format(application/link-format) </c>;rt="cool.datastore", </c/r>;rt="cool.datastore", </c/b>;rt="cool.datastore", </c/e>;rt="cool.event-stream",
In this example, a CoOL client retrieves the list of all resources available on a CoOL server.
Alternatively, the CoOL client may query for a specific resource type. In this example, the CoOL client queries for resource type (rt) “cool.datastore”.
CoAP request:
GET /.well-known/core?rt=cool.datastore
CoAP response:
2.05 Content Content-Format(application/link-format) </c>;rt="cool.datastore",
All CoAP response codes defined by [RFC7252] MUST be accepted and processed accordingly by CoOL clients. Optionally, client errors (CoAP response codes 4.xx) or server errors (CoAP response codes 5.xx) MAY have a payload providing further information about the cause of the error. This payload contains the “ error-payload” container (SID 1006) defined in the “ietf-cool” YANG module, see Appendix A.
Example:
CoAP response:
4.00 Bad Request (Content-Format: application/cool+cbor)
[
1006 , {
1 : 2, # error-code, SID 1007
2 : "Unknown data node 69687" # error-text, SID 1008
}
]
This application protocol relies on the lower layers to provide confidentiality, integrity, and availability. A typical approach to archive these requirements is to implement CoAP using the DTLS binding as defined in [RFC7252] section 9. Other approaches are possible to fulfill these requirements, such as the use of a network layer security mechanism as discussed in [I-D.bormann-core-ipsec-for-coap] or a link layer security mechanism for exchanges done within a single sub-network.
In some applications, different access rights to objects (data nodes, protocol operations and notifications) need to be granted to different CoOL clients. Different solutions are possible, such as the implementation of Access Control Lists (ACL) using YANG module(s) or the use of an authorization certificate as defined in [RFC5755]. These access control mechanisms need to be addressed in complementary specifications.
The Security Considerations section of CoAP [RFC7252] is especially relevant to this application protocol and should be reviewed carefully by implementers.
This draft makes use of the PATCH CoAP method as defined in [I-D.bormann-core-coap-fetch]. This method needs to be registered in the CoAP Method Codes sub-registry as defined in [RFC7252] section 12.1.1.
This draft makes use of the PATCH CoAP method as defined in [I-D.vanderstok-core-patch]. This method needs to be registered in the CoAP Method Codes sub-registry as defined in [RFC7252] section 12.1.1.
This document have been largely inspired by the extensive works done by Andy Bierman and Peter van der Stok on [I-D.vanderstok-core-comi]. [I-D.ietf-netconf-restconf] have also been a critical input to this work. The authors would like to thank the authors and contributors to these two drafts.
The authors would also like to thank Carsten Bormann for his help during the development of this document and his useful comments during the review process.
| [I-D.bormann-core-coap-fetch] | Bormann, C., "CoAP FETCH Method", Internet-Draft draft-bormann-core-coap-fetch-00, October 2015. |
| [I-D.ietf-core-block] | Bormann, C. and Z. Shelby, "Block-wise transfers in CoAP", Internet-Draft draft-ietf-core-block-18, September 2015. |
| [I-D.ietf-netmod-rfc6020bis] | Bjorklund, M., "The YANG 1.1 Data Modeling Language", Internet-Draft draft-ietf-netmod-rfc6020bis-11, February 2016. |
| [I-D.vanderstok-core-patch] | Stok, P. and A. Sehgal, "Patch Method for Constrained Application Protocol (CoAP)", Internet-Draft draft-vanderstok-core-patch-02, October 2015. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC6020] | Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010. |
| [RFC6690] | Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012. |
| [RFC7049] | Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013. |
| [RFC7252] | Shelby, Z., Hartke, K. and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014. |
| [RFC7317] | Bierman, A. and M. Bjorklund, "A YANG Data Model for System Management", RFC 7317, DOI 10.17487/RFC7317, August 2014. |
| [RFC7641] | Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015. |
| [I-D.bormann-core-ipsec-for-coap] | Bormann, C., "Using CoAP with IPsec", Internet-Draft draft-bormann-core-ipsec-for-coap-00, December 2012. |
| [I-D.ersue-constrained-mgmt] | Ersue, M., Romascanu, D. and J. Schoenwaelder, "Management of Networks with Constrained Devices: Problem Statement, Use Cases and Requirements", Internet-Draft draft-ersue-constrained-mgmt-03, February 2013. |
| [I-D.ietf-core-coap-tcp-tls] | Bormann, C., Lemay, S., Technologies, Z. and H. Tschofenig, "A TCP and TLS Transport for the Constrained Application Protocol (CoAP)", Internet-Draft draft-ietf-core-coap-tcp-tls-01, November 2015. |
| [I-D.ietf-netconf-restconf] | Bierman, A., Bjorklund, M. and K. Watsen, "RESTCONF Protocol", Internet-Draft draft-ietf-netconf-restconf-09, December 2015. |
| [I-D.vanderstok-core-comi] | Stok, P. and A. Bierman, "CoAP Management Interface", Internet-Draft draft-vanderstok-core-comi-09, March 2016. |
| [RFC5755] | Farrell, S., Housley, R. and S. Turner, "An Internet Attribute Certificate Profile for Authorization", RFC 5755, DOI 10.17487/RFC5755, January 2010. |
| [RFC7223] | Bjorklund, M., "A YANG Data Model for Interface Management", RFC 7223, DOI 10.17487/RFC7223, May 2014. |
| [RFC7228] | Bormann, C., Ersue, M. and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014. |
Module containing the different definitions required by the CoOL protocol.
module ietf-cool {
namespace "urn:ietf:ns:cool";
prefix cool;
organization
"IETF Core Working Group";
contact
"Ana Minaburo
<mailto:ana@ackl.io>
Abhinav Somaraju
<mailto:abhinav.somaraju@tridonic.com>
Alexander Pelov
<mailto:a@ackl.io>
Michel Veillette
<mailto:michel.veillette@trilliantinc.com>
Randy Turner
<mailto:Randy.Turner@landisgyr.com>";
description
"This module contains the different definitions required
by the CoOL protocol.";
revision 2016-01-01 {
description
"Initial revision.";
reference
"draft-veillette-core-cool";
}
// List of useful derived YANG data types for constrained devices
typedef sid {
type uint32;
description
"Structure Identifier value (SID).";
}
typedef utc-time {
type uint32;
description
"Unsigned 32-bit value representing the number of seconds
since 0 hours, 0 minutes, 0 seconds, on the 1st of January,
2000 UTC (Universal Coordinated Time).";
}
// Error payload
container error-payload {
description
"Optional payload of a client error (CoAP response 4.xx)
or server error (CoAP response 5.xx).";
leaf error-code {
mandatory true;
type enumeration {
enum ok {
value 0;
description
"The requested edit have been performed successfully.";
}
enum error {
value 1;
description "Unspecified error.";
}
enum malformed {
value 2;
description "Malformed CBOR payload.";
}
enum invalid {
value 3;
description "The value specified in the request can't be
apply to the target data node.";
}
enum doesNotExist {
value 4;
description "The target data node instance specified in
the request doesn't exist.";
}
enum alreadyExist {
value 5;
description "The target data node instance specified in
the request already exists.";
}
enum readOnly {
value 6;
description "Attempt to update a read-only data node.";
}
}
}
leaf error-text {
mandatory false;
type string;
description "Textual descriptions of the error.";
}
}
// Notification payload
identity facility-type {
description
"A facility code is used to specify the type of process that
is logging the message. Notifications from different facilities
may be handled differently. Other YANG module may add new
facility type as needed.";
}
identity os {
base facility-type;
}
identity protocol-stack {
base facility-type;
}
identity security {
base facility-type;
}
identity hardware-monitoring {
base facility-type;
}
identity application {
base facility-type;
}
container notification-payload {
leaf _id {
mandatory true;
type instance-identifier;
description
"Identifier associated to the notification reported.";
}
leaf timestamp {
mandatory false;
type utc-time;
description
"Event timestamp. Support of this field is optional
since its not expected that all implementations have
implement a real time clock and if so, this clock is
available at all time.";
}
leaf sequence-number {
mandatory false;
type uint32;
description
"Sequence number associated to each event created by CoOL
server within a specific event stream.";
}
leaf severity-level {
reference "RFC 5424";
mandatory false;
type enumeration {
enum emergency {
value 0;
description
"System is unusable.";
}
enum alert {
value 1;
description
"Should be corrected immediately.";
}
enum critical {
value 2;
description
"Critical conditions.";
}
enum error {
value 3;
description
"Error conditions.";
}
enum warning {
value 4;
description
"May indicate that an error will occur if action is
not taken.";
}
enum notice {
value 5;
description
"Events that are unusual, but not error conditions.";
}
enum informational {
value 6;
description
"Normal operational messages that require no action.";
}
enum debug {
value 7;
description
"Information useful to developers for debugging the
application.";
}
}
description
"Severity associated with this event.";
}
leaf facility {
mandatory false;
type identityref {
base facility-type;
}
description
"Type of process that is logging the message.";
reference "RFC 5424";
}
leaf content {
mandatory false;
type anydata;
description
"Notification container as defined by the notification YANG
statement.";
}
}
rpc commit {
description
"Used to commit the changes present in a candidate datastore on
the runtime datastore specify by the URI used to execute this
operation.";
input {
leaf datastore {
description
"Path of the datastore resource used as the source of the
commit operation. When not present, the default candidate
datastore resource is used.";
type string;
mandatory false;
}
leaf commit-date-time {
description
"When specified, the commit operation is postponed at the
specified date and time. When not present, the commit is
performed on reception of this RPC. Supports of this feature
is optional.";
type utc-time;
mandatory false;
}
leaf confirm-timeout {
description
"When present, a confirming commit MUST be received within
this period after the start of the commit process.
A confirming commit is a commit RPC without the
confirm-timeout field presents. Supports of this feature
is optional.";
type string;
mandatory false;
}
}
}
rpc cancel-commit {
description
"Cancels an ongoing scheduled or confirmed commit.";
}
}
Following is the “.sid” file generated for the “ietf-cool” YANG module. See [I-D.somaraju-core-sid] for more details on SID and “.sid” file.
{
"assignment-ranges": [
{
"entry-point": 1000,
"size": 100
}
],
"module-name": "ietf-cool",
"module-revision": "2016-01-01",
"items": [
{
"type": "identity",
"assigned": "2016-03-08T21:59:45Z",
"label": "ietf-cool:application",
"sid": 1000
},
{
"type": "identity",
"assigned": "2016-03-08T21:59:45Z",
"label": "ietf-cool:facility-type",
"sid": 1001
},
{
"type": "identity",
"assigned": "2016-03-08T21:59:45Z",
"label": "ietf-cool:hardware-monitoring",
"sid": 1002
},
{
"type": "identity",
"assigned": "2016-03-08T21:59:45Z",
"label": "ietf-cool:os",
"sid": 1003
},
{
"type": "identity",
"assigned": "2016-03-08T21:59:45Z",
"label": "ietf-cool:protocol-stack",
"sid": 1004
},
{
"type": "identity",
"assigned": "2016-03-08T21:59:45Z",
"label": "ietf-cool:security",
"sid": 1005
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/error-payload",
"sid": 1006
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/error-payload/error-code",
"sid": 1007
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/error-payload/error-text",
"sid": 1008
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/notification-payload",
"sid": 1009
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/notification-payload/_id",
"sid": 1010
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/notification-payload/content",
"sid": 1011
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/notification-payload/facility",
"sid": 1012
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/notification-payload/sequence-number",
"sid": 1013
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/notification-payload/severity-level",
"sid": 1014
},
{
"type": "node",
"assigned": "2016-03-08T21:59:45Z",
"label": "/notification-payload/timestamp",
"sid": 1015
},
{
"type": "rpc",
"assigned": "2016-03-08T21:59:45Z",
"label": "/cancel-commit",
"sid": 1016
},
{
"type": "rpc",
"assigned": "2016-03-08T21:59:45Z",
"label": "/commit",
"sid": 1017
},
{
"type": "rpc",
"assigned": "2016-03-08T21:59:45Z",
"label": "/commit/input/commit-date-time",
"sid": 1018
},
{
"type": "rpc",
"assigned": "2016-03-08T21:59:45Z",
"label": "/commit/input/confirm-timeout",
"sid": 1019
},
{
"type": "rpc",
"assigned": "2016-03-08T21:59:45Z",
"label": "/commit/input/datastore",
"sid": 1020
}
]
}