CoAP (Constrained Application Protocol) is a RESTful protocol for low-powered devices that works like HTTP but over UDP. It uses a client-server model to send requests and responses asynchronously. The document provides an overview of CoAP, how it is implemented in Reactive Blocks using the Eclipse IoT Californium framework, and provides an example of using CoAP to control a Raspberry Pi car. Key points covered include installing Reactive Blocks, importing the CoAP libraries, and using the Set and Get Data via CoAP blocks to expose and access variables as a CoAP server or client.

1. CoAP
A summary of CoAP
and how to use it in Reactive Blocks
Request/Response via
in Reactive Blocks

2. CoAP: Overview
■ CoAP (constrained application protocl) is
a RESTful protocol for low powered
devices. It works like HTTP but over
UDP. It uses a client/server model.
■ CoAP emerged from the IETF standard
and is standardized on RFC 7252, see
https://tools.ietf.org/html/rfc7252
■ Alternatives to CoAP include HTTP,
MQTT, AMQP and CoAP
■ CoAP is typically used to send
commands or triggers to your nodes.
By default, CoAP uses port 5683 or port 5684
(secured). Make sure that traffic via these
ports is not blocked by your firewall.
Ports!
CoAP

3. CoAP
CoAP is like HTTP but made for M2M applications
■ Web protocol fulfilling M2M requirements in constrained environments
■ RESTful model with GET, POST, PUT, DELETE request methods
■ Message overhead is kept small, simple 4 byte header
■ Asynchronous message exchange
■ It runs over UDP with optional reliability and multicast support
■ URI support
■ DTLS based PSK, RPK and Certificate security
■ Simple proxy and caching capabilities
■ Built in discovery and multicast support
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4. Client/Server Pattern
CoAP uses a client server model but
unlike HTPP request/response are sent
asynchronously. In M2M interaction a
CoAP implementation can have both
client and server roles. A common use-
case is to have a CoAP node with
sensors and actuators act as a server. A
CoAP controller or monitoring device
then act as a client.
CoAP is a good choice if you want to be
able to send commands to your nodes or
trigger them.
serverclient
request
response
GET temperature
22.5 C
Example use case: A server has the
resource of interest, a temperature
sensor. The client monitors the
temperature by requesting readings of
the temperature value.
CoAP

5. A CoAP client sends a request to
monitor or modify variables of a
CoAp server
CoAP 5
CoAP Client CoAP Server
■ Code field is set to response code in the
CoAP message
■ It indicates the result of the attempt to
understand and satisfy the requests
■ The codes are fully defined in RFC7252
request
■ GET: Retrieve a representation for the
information that currently corresponds
to the resource identified by the request
■ POST: Requests that the representation
enclosed is processed
■ PUT: Request that the identified
resource is updated with the enclosed
representation
■ DELETE: Request that the identified
resource is deleted
Request method definition
response
The Server has the authority over
the current state of a resource/
variable.
Response code definition

6. March 2012 - Business Confidential - Bitreactive AS
How to get started
CoAP in Reactive Blocks

7. CoAP
Install Reactive Blocks
■ If you have Eclipse 4.4 or Eclipse 4.5, open the Marketplace
■ Search For Reactive Blocks
■ For detailed installation instructions, visit http://www.bitreactive.com/installation/
■ Reactive Blocks is free for open source projects
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8. CoAP
Reactive Blocks CoAP Implementation
■ The CoAP building blocks from the Reactive
Blocks libraries are based on the Eclipse IoT
Californium framework:
http://www.eclipse.org/californium/
■ The Californium framework is a Java
implementation of CoAP made for IoT cloud
services and JAVA SE embedded devices.
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9. CoAP
How to Get CoAP Libraries
■ After installing Reactive Blocks
■ In Eclipse, select File / Import / Reactive Blocks
/ Import Libraries, Projects and Building Blocks
■ Select the library Set and Get Data via CoAP
■ The CoAP library is automatically downloaded. It
includes blocks for the internal behaviour of the
Set and Get Data via CoAP library blocks
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10. CoAP
The Set and Get Data via CoAP library
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The Set and Get Data via CoAP library contains interfaces to expose or
access data. If you look inside these blocks you will find the CoAP
blocks covering the core of the CoAP functionalities
Interface to expose variables
Inside the block you will find the inner
core CoAP blocks

11. Integer Resource
Publish a named integer value on a CoAP server.
CoAP server: Blocks to expose variable of a CoAP server
String Resource
Publish a named string value on a CoAP server.
Boolean Resource
Publish a named boolean value on a CoAP server.
Advanced String Tree Resource
Publish String values on a CoAP server. With this block
you can initialize several parameters at once.
CoAP

12. Integer Get Request
Request a named integer value published on a CoAP server.
CoAP client: Blocks to read/monitor variables
String Get Request
Request a named string value published on a CoAP server.
Boolean Get Request
Request a named boolean value published on a CoAP server.
CoAP

13. Integer Set Request
Set a named integer value published on a CoAP server.
CoAP client: Blocks to change resource values
String Set Request
Set a named string value published on a CoAP server.
Boolean Set Request
Set a named boolean value published on a CoAP server.
CoAP

14. CoAP
Example: CoAP to control a Raspberry Pi Car
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Server Client
The variables controlling the
steering of the wheels are
published on the CoAP server
Here is a basic console implemented in
Java Swing running on a laptop. By
selecting the buttons you can set the
steering values left, right, stop, forward on
the CoAP server. You can also end the car
application by selecting kill app. The exit
button terminates the control panel

15. CoAP
CoAP interface of the server side
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The CoAP interface block includes several CoAP block to expose various
variables about the car. This includes the Advanced String Tree Resource
block that exposes the variables of the car steering direction

16. CoAP 16
CoAP interface of the client side
On the client side the String Set Request is used to control the car´s
movement. The Buffer block is used to buffer the incoming commands
since the String Set Request block can only handle one request at a time

17. CoAP
Read and learn more about CoAP in action
■ Do the CoAP tutorial from the Reactive Blocks IoT Tutorial Trail:
http://reference.bitreactive.com/tutorials/add-coap-to-your-application.html
■ Check out the Eclipse IoT Raspberry Pi Car blog posts:
http://www.bitreactive.com/remote-controlled-raspberry-pi-car-part-3-2/
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