Internet DRAFT - draft-jimenez-t2trg-coap-functionality-lwm2m
draft-jimenez-t2trg-coap-functionality-lwm2m
Network Working Group J. Jimenez
Internet-Draft Ericsson
Intended status: Informational October 31, 2016
Expires: May 4, 2017
CoAP functionality expected in a LWM2M system
draft-jimenez-t2trg-coap-functionality-lwm2m-00
Abstract
This document provides a strawman summary of information that should
be used for the LWM2M specification [LWM2M]. LWM2M is based on CoAP,
on top of which it describes certain management interfaces and data
models that go beyond the CoAP specifications itself. However LWM2M
does not describe all behavior that should be expected from
implementations of the CoAP specifications. This document attempts
to clarify what should be present in a LWM2M system beyond what is
specified in the LWM2M documents. Additionally, this document also
adds information about IPSO Objects [IPSO] and their usage with LWM2M
as application protocol.
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 May 4, 2017.
Copyright Notice
Copyright (c) 2016 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
Jimenez Expires May 4, 2017 [Page 1]
Internet-Draftdraft-jimenez-t2trg-coap-functionality-lwm2m October 2016
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Interaction Model . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Device and Manager configuration. . . . . . . . . . . . . 3
3.2. Device to Device configuration. . . . . . . . . . . . . . 4
3.3. Device to Application configuration. . . . . . . . . . . 4
4. Data Model . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Web Linking . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Collaboration . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Informative References . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The current LWM2M protocol is probably the main Device Management
protocol based on CoAP today. It defines the application layer
communication protocol between a LWM2M Server and a LWM2M Client,
which is located in a LWM2M Device.
2. Terminology
The LWM2M Specification tends to use its own terminology for client,
server, etc. In this document, we use the existing terminology from
[RFC7252].
For example the use of LWM2M "Client" and "Server" and the roles they
play has confused developers that are initiating on the protocol,
mainly because a CoAP server runs on the device, just like a LWM2M
client does. Moreover, most LWM2M devices will often work both as
client and server depending on the interfaces used, it would be good
to explore the use of terms like "servients" for devices that
regularly support both.
Similarly, the reference to existing drafts of RFCs often can mislead
the reader to believe that the full RFC has been implemented. It
would be better to state the support to an IETF CoRE WG document when
applicable.
For example, the Registration interface in LWM2M is based on the CoAP
Resource Directory. However, it is not sufficient to implement just
Jimenez Expires May 4, 2017 [Page 2]
Internet-Draftdraft-jimenez-t2trg-coap-functionality-lwm2m October 2016
the interface described to obtain the benefits provided by the CoAP
Resource Directory.
3. Interaction Model
LWM2M has been created with a strong focus on centralizing control
and management. Devices set associations with their manager and all
traffic is directed to the cloud. All this is fine but in the
process some functionalities that could be used locally device to
device and device to application have not been explicitly described.
Below we have common configurations that make use of LWM2M.
o (1) Device and Manager configuration.
o (2) Device to Device configuration.
o (3) Device to Application configuration.
Device +
+--------+--------+ | (1) +----------+--------------+
| | | | LWM2M | | LWM2M Server |
| LWM2M | IPSO | | <-------------> | Manager +--------------+
+--------+--------+ | | | BS Server |
| | | +----------+--------------+
| CoAP | | (2)
+--------+--------+ | CoAP+IPSO +----------+
| | | | <-------------> | Device |
| UDP | TCP | | +----------+
+-----------------+ | (3)
| IPv6 | | CoAP+IPSO +-------------------------+
| | | <-------------> | User / Application |
+-----------------+ | +-------------------------+
+
3.1. Device and Manager configuration.
This is covered by common LWM2M compliant implementations we have
today. However there are upcoming RFCs and drafts that greatly
enhance LWM2M with more CoAP features.
For example TCP support is soon going to be added to CoAP. The draft
[I-D.ietf-core-coap-tcp-tls] outlines the changes required to use
CoAP over TCP, TLS, and WebSockets transports.
Support for features like PATCH/FETCH [I-D.ietf-core-etch] could be
greatly beneficial for things like firmware upgrade or observing
relatively large sets of resources.
Jimenez Expires May 4, 2017 [Page 3]
Internet-Draftdraft-jimenez-t2trg-coap-functionality-lwm2m October 2016
For systems in which endpoints work behind a gateway or use LWM2M for
managing the gateways, it might be good to implement other types of
cryptographic protection than DTLS. For example some of the setups
using OSCoAP [I-D.ietf-core-object-security] allow for "smarter"
gateways.
3.2. Device to Device configuration.
Beyond what is described in the LWM2M documentation, devices will
often talk to each other. Specially in cases when all devices are
under the same subnet, this could be pretty common. For example
devices could be more resilient if they did not have to contact their
manager constantly; in case of lack of internet connectivity the
local IoT network would still function. Managers could just set
policies on the devices and they would operate more autonomously.
For this setup to take place, LWM2M would use more of the device-to-
device functionality of CoAP. A more complete Resource Directory
implementation [I-D.ietf-core-resource-directory] would be needed,
either on the LWM2M server in addition to the registration interface
or standalone. Devices should be able to perform lookup on that RD
and get the series of links to resources elsewhere. They should be
able to find new functionality through /.well-known/core. If not,
they should be able to use IP multicast as expressed on [RFC7390].
Needless to say, it is assumed that devices would be running a CoAP
Server on them and would support CoAP Observe [RFC7641], so that
devices can subscribe to updates from one another, thus becoming more
autonomous.
There are also updates on ACE security framework, that allow for
securing the communication between two devices via an Authorization
Server [I-D.ietf-ace-oauth-authz].
The current LWM2M Data Model needs more expressiveness when it comes
to data types; More on that in Section 4. Also Web Linking will be
dealt at Section 5.
3.3. Device to Application configuration.
In some other cases applications would be running on the phone
connecting locally to sensors and/or control actuators. A smartphone
can access directly a CoAP home sensor using a mutually authenticated
'https' request, provided its home router runs a HTTP to CoAP (HC)
proxy and is configured with the appropriate certificate. For this
scenario to happen, the GW should implement a HC proxy. It is highly
recommended then that they make use of [I-D.ietf-core-http-mapping]
to properly do the URI mapping and specific ABNF queries.
Jimenez Expires May 4, 2017 [Page 4]
Internet-Draftdraft-jimenez-t2trg-coap-functionality-lwm2m October 2016
Just like other devices, smartphone applications should be able to
discover devices using standard methods, thus they would need access
to the RD as well.
4. Data Model
The LWM2M Object Model is specified in [LWM2M]. Other models that
build on it like IPSOs or OneM2M have spawned out of it. They
normally introduce incremental features. They usually allow for
performing any set of operations on a device through a CoAP
interface. Resources are exposed as Objects using the same data
model used for management.
For example, in the case of a temperature sensor we can access and
subscribe to the readings of the device (using [IPSO]).
Req: GET /3303/0/5700 Observe_Option=1
Res: 2.05 Content (25 C)
Res (Notify): 2.05 Content (26 C)
There has also been much work on different serialization and
compression mechanisms that LWM2M could consider adopting. A
serialized JSON file like the one below could be greatly compressed
(about 46% max, depending on the case) using CBOR representation
format [RFC7049] instead.
{ "e": [{
"bn": "/3303/0",
"e": [{
"n": "5700",
"v": 20.0 }, {
"n": "5701",
"v": "c" }, {
"n": "5603",
"v": 10 }, {
"n": "5604",
"v": 40
}], }, {
"bn": "/3302/0",
"e": [{
"n": "5500",
"v": true }, {
"n": "5501",
"v": 23
} ]}]}
LWM2M ResourceIDs at the moment have no specific semantic meaning
like ObjectIDs do. Adding a similar registry for ResourceIDs could
Jimenez Expires May 4, 2017 [Page 5]
Internet-Draftdraft-jimenez-t2trg-coap-functionality-lwm2m October 2016
be useful. Specially to those using LWM2M for their applications.
For example IPSO uses such ResourceIDs to register resources
univocally, so that the string _5701_ consistently represents units.
5. Web Linking
One thing that that could be very useful in the future is some form
of Web Link resource type. ObjectLinks are not sufficient to
represent links between devices or applications. There has been much
work on web linking on [RFC6690] that could be used in the LWM2M
spec. For example a new Data Type named "Web Link" could be a
simple, yet useful addition. Instead of the current
_ObjectID:InstanceID_ expressed now, a full WebLink would be used.
That would take advantage of other features like
[I-D.ietf-core-links-json] or even newer Object Models.
Other use cases contemplate some form of Object Redirection to help
decouple management and applications. LWM2M expects that the
management servers will observe resources and collect telemetry on
the management server itself. If LWM2M is to be used as application
protocol as well as management, it should provide a way for
applications or CoAP Clients to observe resources on the devices,
together with their required credentials. Such credentials should be
stored on the device in some way, maybe a new Object.
6. Collaboration
To further develop the relationship between the LWM2M specification
and other specifications based on CoAP, it would also be advisable to
foster collaboration between organizations developing CoAP-based
standard implementations. At the moment there is no forum for inter
group communication nor discussion. That should change.
The IETF CoRE WG has quite some people also interested in device
management. Communication would be mutually beneficial. Example of
that work is on COMI [I-D.ietf-core-yang-cbor] or data model
translation.
OMA LWM2M already has benefited from workshops that gather most of
the industry, such as [IOTSI] and [IOTSU]. Similarly, specifications
can be developed in the IETF with a view to be directly usable in
LWM2M.
7. Informative References
Jimenez Expires May 4, 2017 [Page 6]
Internet-Draftdraft-jimenez-t2trg-coap-functionality-lwm2m October 2016
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE)", draft-ietf-ace-oauth-
authz-04 (work in progress), October 2016.
[I-D.ietf-core-coap-tcp-tls]
Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets",
draft-ietf-core-coap-tcp-tls-05 (work in progress),
October 2016.
[I-D.ietf-core-etch]
Stok, P., Bormann, C., and A. Sehgal, "Patch and Fetch
Methods for Constrained Application Protocol (CoAP)",
draft-ietf-core-etch-03 (work in progress), October 2016.
[I-D.ietf-core-http-mapping]
Castellani, A., Loreto, S., Rahman, A., Fossati, T., and
E. Dijk, "Guidelines for HTTP-to-CoAP Mapping
Implementations", draft-ietf-core-http-mapping-16 (work in
progress), October 2016.
[I-D.ietf-core-links-json]
Li, K., Rahman, A., and C. Bormann, "Representing CoRE
Formats in JSON and CBOR", draft-ietf-core-links-json-06
(work in progress), July 2016.
[I-D.ietf-core-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security of CoAP (OSCOAP)", draft-ietf-core-
object-security-00 (work in progress), October 2016.
[I-D.ietf-core-resource-directory]
Shelby, Z., Koster, M., Bormann, C., and P. Stok, "CoRE
Resource Directory", draft-ietf-core-resource-directory-08
(work in progress), July 2016.
[I-D.ietf-core-yang-cbor]
Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A.
Minaburo, "CBOR Encoding of Data Modeled with YANG",
draft-ietf-core-yang-cbor-02 (work in progress), July
2016.
[IOTSI] IAB, "IoT Workshop for Semantic Interoperability (IOTSI)",
2016, <https://www.iab.org/activities/workshops/iotsi/>.
Jimenez Expires May 4, 2017 [Page 7]
Internet-Draftdraft-jimenez-t2trg-coap-functionality-lwm2m October 2016
[IOTSU] IAB, "Internet of Things Software Update Workshop
(IoTSU)", 2016, <https://www.iab.org/activities/workshops/
iotsu/>.
[IPSO] IPSO, "IPSO Object Model", n.d.,
<http://ipso-alliance.github.io/pub/>.
[LWM2M] OMA, "LWM2M specification", n.d.,
<http://technical.openmobilealliance.org/Technical/
technical-information/release-program/current-releases/
oma-lightweightm2m-v1-0>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<http://www.rfc-editor.org/info/rfc6690>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <http://www.rfc-editor.org/info/rfc7049>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, DOI 10.17487/
RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for
the Constrained Application Protocol (CoAP)", RFC 7390,
DOI 10.17487/RFC7390, October 2014,
<http://www.rfc-editor.org/info/rfc7390>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641, DOI 10.17487/
RFC7641, September 2015,
<http://www.rfc-editor.org/info/rfc7641>.
Author's Address
Jaime Jimenez
Ericsson
Phone: +358-442-992-827
Email: jaime.jimenez@ericsson.com
Jimenez Expires May 4, 2017 [Page 8]
