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CoAP vs MQTT: IoT Protocols Guide

This document provides information about CoAP and MQTT, two protocols commonly used in IoT. CoAP is designed for constrained devices and networks, uses UDP, and has features like resource discovery and asynchronous subscription. MQTT is built on TCP/IP, uses a publish/subscribe messaging pattern with message brokers, and supports quality of service and retain flags. The document includes links to further resources about both protocols.

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abirami
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53 views42 pages

CoAP vs MQTT: IoT Protocols Guide

This document provides information about CoAP and MQTT, two protocols commonly used in IoT. CoAP is designed for constrained devices and networks, uses UDP, and has features like resource discovery and asynchronous subscription. MQTT is built on TCP/IP, uses a publish/subscribe messaging pattern with message brokers, and supports quality of service and retain flags. The document includes links to further resources about both protocols.

Uploaded by

abirami
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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CoAP and

MQTT

Antonio Liñán Colina,


Zolertia
http://electronicdesign.com/iot/mqtt-and-coap-underlying-protocols-iot
03-coap
• UDP-reliable (confirmable), SMS supported
• CoRE Link-format (GET /.well known/core)
• Client/Server
• IANA Registered (error codes, content format)
• Resource Discovery and asynchronous subscription
• Four-bytes compact header
• Multicast and one-to-one supported
• HTTP verbs GET, PUT, POST, DELETE
• HTTP-like header (Options)
• URI (Uniform Resource Identifier)

http://coap.technology/
https://tools.ietf.org/html/rfc7252
http://www.slideshare.net/zdshelby/coap-tutorial
CoAP URI
coap://[aaaa::c30c:0:0:1234]:5683/actuators/leds?color=b
Host Port Path Query
http://www.slideshare.net/paolopat/mqtt-iot-protocols-comparison
apps/er-coap
apps/rest-engine
apps/er-coap
apps/rest-engine
apps/er-coap
apps/rest-engine
Resource declaration

URI Query

Function to invoke whenever


Resource implementation
there’s a GET request

The CoAP Accept option can be


used to indicate which Content-
Format is acceptable to the client.

examples/zolertia/tutorial/03-coap/resources/res-adxl345.c
Importing the Resource

Resource activation

examples/zolertia/tutorial/03-coap/resources/er-example-server.c
Search resources to include
in the “resources” directory

REST engine and CoAP libraries

examples/zolertia/tutorial/03-coap/resources/Makefile
https://addons.mozilla.org/en-US/firefox/addon/copper-270430/
http://people.inf.ethz.ch/mkovatsc/copper.php
Border Router
IPv6/6LoWPAN

er-example-server
CoAP server in Contiki OS

Copper CoAP user-agent


On Firefox browse the CoAP Server,
discover and learn its resources

examples/zolertia/tutorial/02-ipv6/03-client-and-server
TIP: enable the DEBUG to 1 to print more information about the processes
taking place inside the CoAP and REST libraries (all .c files inside!)

apps/er-coap
apps/rest-engine
Pong! – check the CoAP server is online

examples/zolertia/tutorial/03-coap/resources/er-example-server.c
Discover – learn the Resources the CoAP server has

examples/zolertia/tutorial/03-coap/resources/er-example-server.c
Hover over the resources to learn its attributes

examples/zolertia/tutorial/03-coap/resources/er-example-server.c
POST/PUT – change the LEDs state (on or off)

examples/zolertia/tutorial/03-coap/resources/er-example-server.c
GET – read the ADXL345 with JSON format (application/json)

examples/zolertia/tutorial/03-coap/resources/er-example-server.c
OBSERVE – get notifications about an event (press the user button)

examples/zolertia/tutorial/03-coap/resources/er-example-server.c
04-mqtt
• On top of TCP/IP
• Publish/Subscribe messaging pattern
• Message Broker distributes topics to clients
• Topics are UTF-8 string-based with hierarchical structure
• No direct connection between clients
• Quality of Service
• Retain-Flag: new subscribed clients will received last value
• Last Will: notify other clients when disconnected ungracefully
• KeepAlive: ping request messages to the bróker
• Clients have to know beforehand the structure of the data published to a
topic
• MQTT is data-agnostic

http://mqtt.org
CONNECT
Waits for a connection to be established with the server

DISCONNECT
Waits for the MQTT client to finish any pending task and closes the TCP session

SUBSCRIBE
Request the server to subscribe the client to one or more topics

UNSUBSCRIBE
Request the server to subscribe the client to one or more topics

PUBLISH
Updates a topic with data
http://www.hivemq.com/blog/how-to-get-started-with-mqtt
http://www.slideshare.net/paolopat/mqtt-iot-protocols-comparison
Topics starting with $ are special
These are reserved for the broker
statistics

http://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices
Required to be included in the process using MQTT

apps/mqtt
To start the MQTT client this function should be called first
The max_segment_size is the TCP chunk of data to be sent (default is 32 bytes)
The client_id is a string identifying the client

apps/mqtt
The keep_alive value is used by a timer waiting a PINGRES from the broken,
if expired and no response is obtained, it triggers a disconnection
apps/mqtt
Message ID (mid) is zero for QoS=0
apps/mqtt
apps/mqtt
apps/mqtt
Border Router
IPv6/6LoWPAN

mqtt-demo
The MQTT client publishing to the MQTT bróker
topic “zolertia/evt/status” and test.mosquitto.org
subscribed to “zolertia/cmd/leds”

mqtt_client.py
Paho MQTT client
Subscribed to the “zolertia/evt/status”
topic, used to check the example

examples/zolertia/tutorial/04-mqtt
examples/zolertia/tutorial/04-mqtt
static void
mqtt_event(struct mqtt_connection *m, mqtt_event_t event, void *data)
{
switch(event) {
case MQTT_EVENT_CONNECTED: {
printf("APP - Application has a MQTT connection\n");
state = STATE_CONNECTED;
break;
}
case MQTT_EVENT_DISCONNECTED: {
printf("APP - MQTT Disconnect. Reason %u\n", *((mqtt_event_t *)data));
state = STATE_DISCONNECTED;
process_poll(&mqtt_demo_process);case MQTT_EVENT_SUBACK: {
break; printf("APP - Application is subscribed to topic successfully\n");
} break;
case MQTT_EVENT_PUBLISH: { }
case MQTT_EVENT_UNSUBACK:
pub_handler(msg_ptr->topic, strlen(msg_ptr->topic), {
msg_ptr->payload_chunk,
msg_ptr->payload_length); printf("APP - Application is unsubscribed to topic successfully\n");
break; break;
} }
case MQTT_EVENT_PUBACK: {
printf("APP - Publishing complete.\n");
break;
}
}
examples/zolertia/tutorial/04-mqtt
DISCONNECTED: mqtt_disconnect(…)
STATE_INIT: mqtt_register(…)

STATE_REGISTERED: mqtt_connect(…)

STATE_CONNECTING: ctimer checking(…)

STATE_CONNECTED: mqtt_subscribe(…)

STATE_PUBLISHING: etimer_set(publish interval)

examples/zolertia/tutorial/04-mqtt
Set default configuration values

Create topic/subscription/id strings (STATE_INIT)

Polls the state machine as described before

examples/zolertia/tutorial/04-mqtt
TIP: enable the DEBUG to 1 to print more information about the processes
taking place inside the MQTT library

apps/mqtt/mqtt.c
MQTT demo client running on the Z1 mote

Paho MQTT client in Python subscribed

Mosquitto publishing to turn a LED on

examples/zolertia/tutorial/04-mqtt
Antonio Liñán Colina
alinan@zolertia.com
antonio.lignan@gmail.com

Twitter: @4Li6NaN
LinkedIn: Antonio Liñan Colina
github.com/alignan
hackster.io/alinan

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