MQTTA nice way to connect 'things' in IoT

Henri Cavalcante

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Message Queue Telemetry Transport is a publish-subscribe lightweight protocol who runs over TCP protocol, it's very fast and simple and runs pretty well over high latencies and unreliable networks.

What is it?

NodeJS Installation

$ curl -sL https://deb.nodesource.com/setup_5.x | sudo -E bash -$ sudo apt-get install -y nodejs

$ brew install node

$ curl --silent --location https://rpm.nodesource.com/setup_5.x | bash -$ yum -y install nodejs

Debian / Ubuntu

Red Hat / CentOS / Fedora

OSX

Windows

https://nodejs.org/en/download/

MQTT Installation

$ sudo npm install --global mqtt

ClientServer (Mosca.JS)

$ sudo npm install --global mosca bunyan

$ mosca -v +++.+++: ,+++ +++; '+++ +++. ++.+++.++ ++.++ ++,'+ `+',++ ++,++ +` +, +: .+ .+ +; +; '+ '+ +` +` +` +. +: ,+ `+ ++ +; '+ ;+ + +. +` +. +: ,+ `+ +' '+ + +. +` +. +: ,+ `+ :+. '+ +++++. +` +. +: ,+ `+ ++ '+ +++++. +` +. +: ,+ `+ ++ '+ + +. +` +. +: ,+ `+ +: +: '+ ;+ + +. +` +. +: .+ .+ +; +; '+ '+ + +. +` +. +: ++;++ ++'++ ++'+' + +. +` +. +: +++ +++. ,++' + +.

$ mqtt sub -h localhost -t hello -v

$ mqtt pub -h localhost -t hello -m GDGNatal

Standard for IoT

OASIS is pleased to announce that MQTT Version 3.1.1 from the OASIS Message Queuing Telemetry Transport (MQTT) TC has been approved by the membership as an OASIS Standard.

Subscr

ibe

Publish-subscribe

Client 3BrokerTopic

Client 1

Client 2

Publish

SubscribeDeliver

Delive

r

bit 7 6 5 4 3 2 1 0

Byte 1 Message Type DUP flag QoS level RETAIN

Byte 2 Remaining Length

Lightweight

MQTT Header

$ echo "GET / HTTP/1.1" | wc -c15 Bytes$ curl "http://localhost:1880/teste/" -v 2>&1 | grep '>' | cut -c 3- | wc -c84 Bytes

HTTP Header

Message TypeMnemonic Enum Description

Reserved 0 Reserved

CONNECT 1 Client request to connect to Server

CONNACK 2 Connect Acknowledgment

PUBLISH 3 Publish message

PUBACK 4 Publish Acknowledgment

PUBREC 5 Publish Received (assured delivery part 1)

PUBREL 6 Publish Release (assured delivery part 2)

PUBCOMP 7 Publish Complete (assured delivery part 3)

SUBSCRIBE 8 Client Subscribe request

SUBACK 9 Subscribe Acknowledgment

UNSUBSCRIBE 10 Client Unsubscribe request

UNSUBACK 11 Unsubscribe Acknowledgment

PINGREQ 12 PING Request

PINGRESP 13 PING Response

DISCONNECT 14 Client is Disconnecting

Reserved 15 Reserved

Position: byte 1, bits 7-4.Represented as a 4-bit unsigned value. The enumerations for this version of the protocol are shown in the table below.

Flags

Name Bit position Description

DUP 3 Duplicate delivery

QoS 2-1 Quality of Service

RETAIN 0 RETAIN flag

DUP Flag

This flag is set when the client or server attempts to re-deliver a PUBLISH, PUBREL, SUBSCRIBE or UNSUBSCRIBE message. This applies to messages where the value of QoS is greater than zero (0), and an acknowledgment is required. When the DUP bit is set, the variable header includes a Message ID.The recipient should treat this flag as a hint as to whether the message may have been previously received. It should not be relied on to detect duplicates.

Name Bit position Description

DUP 3 Duplicate delivery

QoS 2-1 Quality of Service

RETAIN 0 RETAIN flag

Quality of Service Level

QOS Level Description

0 (00) At most once

1 (01) At least once

2 (10) Exactly once

Name Bit position Description

DUP 3 Duplicate delivery

QoS 2-1 Quality of Service

RETAIN 0 RETAIN flag

Quality of Service Level 0 (At most once)

BrokerTopic

Client 1PUBLISH

(3)

● You have a complete or almost stable connection between sender and receiver. A classic use case is when connecting a test client or a front end application to a MQTT broker over a wired connection.

● You don’t care if one or more messages are lost once a while. That is sometimes the case if the data is not that important or will be send at short intervals, where it is okay that messages might get lost.

● You don’t need any message queuing. Messages are only queued for disconnected clients if they have QoS 1 or 2 and a persistent session.

Quality of Service Level 1 (At least once)

BrokerTopic

PUBLISH (3)

PUBACK (4)Client 1

● You need to get every message and your use case can handle duplicates. The most often used QoS is level 1, because it guarantees the message arrives at least once. Of course your application must be tolerating duplicates and process them accordingly.

● You can’t bear the overhead of QoS 2. Of course QoS 1 is a lot fast in delivering messages without the guarantee of level 2.

Quality of Service Level 2 (Exactly once)

BrokerTopic

PUBLISH (3)

PUBREC (5)Client 1 PUBREL (6)

PUBCOMP (7)

● It is critical to your application to receive all messages exactly once. This is often the case if a duplicate delivery would do harm to application users or subscribing clients. You should be aware of the overhead and that it takes a bit longer to complete the QoS 2 flow.

Retain bit

Name Bit position Description

DUP 3 Duplicate delivery

QoS 2-1 Quality of Service

RETAIN 0 RETAIN flag

This flag is only used on PUBLISH messages. When a client sends a PUBLISH to a server, if the Retain flag is set (1), the server should hold on to the message after it has been delivered to the current subscribers.When a new subscription is established on a topic, the last retained message on that topic should be sent to the subscriber with the Retain flag set. If there is no retained message, nothing is sent

Authorization and Authentication

const mosca = require('mosca');const server = new mosca.Server({});const authenticate = (client, username, password, callback) => { const authorized = (username === 'gdg' && password.toString() === '123'); if (authorized) client.user = username; callback(null, authorized);}const authorizePublish = (client, topic, payload, callback) => { callback(null, true);}const authorizeSubscribe = (client, topic, callback) => { callback(null, true);}server.on('ready', () => { server.authenticate = authenticate; server.authorizePublish = authorizePublish; server.authorizeSubscribe = authorizeSubscribe;});

Any question?

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