MQTT, Eclipse Paho and Java - Messaging for the Internet of Things

!

Andy Piper | @andypiper | @mqttorg
Eclipse Paho project co-lead, mqtt.org community lead

Eclipse Paho and MQTT Java Messaging in the
Internet of Things
Made available under the Eclipse Public License v1.0.

Developer Advocate @ Cloud Foundry
social web enthusiast
maker, educator, LEGO fan
OSS supporter / contributor
excited by “what’s next”, Internet of Things, etc.
member of #iotlondon and #m2miwg
@andypiper
apiper@gopivotal.com


Essential info!
!

@andypiper
@mqttorg
#paho #mqtt

!


The Plan:
!

1. What is Paho, M2M, MQTT?
2. What about Java?
!


pāho (verb) to broadcast,
make widely known, announce,
disseminate, transmit.
(via the Maori dictionary)

“...the Paho project has been created to
provide scalable open-source implementations
of open and standard messaging protocols
aimed at new, existing, and emerging
applications for Machine- to-Machine (M2M)
and Internet of Things (IoT)”
!


The Internet of Things / M2M
Key Trends 
1. New connected devices,
applications and services
 

Estimated Number of Active
Cellular M2M Connected
Devices 2010 to 2020

2. Lower system costs
3. Simplified development
4. Network operator focus and
investment

2010

2020
Source: Machina Research, July 2011


Just what is MQTT?

!


MQ Telemetry Transport
•Invented by IBM and Arcom in the late 1990s - initially used for e.g.
oil field and flood plain monitoring

•Contributed to the Eclipse Foundation under M2M announcements
at EclipseCon Europe 2011:

• The formation of a new M2M Industry Working Group at the Eclipse
Foundation, with Sierra Wireless, Eurotech and IBM as founding
members, to work on growing and scaling device connectivity
solutions with open source tools, frameworks and runtimes.

• The contribution of the IBM MQTT client code (C and Java) to a
new Eclipse project "Paho".

•Submitted to OASIS early 2013, specification under review


Design principles
Publish/subscribe messaging paradigm
as required by the majority of SCADA
and sensor applications.
Minimise the on-the-wire footprint.
Expect and cater for frequent network
disruption, cope with slow and poor
quality networks: built for low bandwidth,
high latency, unreliable, high cost
networks
Expect that client applications may have
very limited processing resources
available.
Provide traditional messaging qualities of
service where the environment allows

Design principles
Simple, minimal pub/sub messaging semantics
Asynchronous (“push”) delivery of messages to applications
Simple verbs / methods: connect, publish, (un)subscribe, disconnect

!
Minimised on-the-wire format:

•
•
•
•

Plain byte array message payload
No application message headers
Protocol compressed into bit-wise headers and variable length fields
Smallest possible packet size is 2 bytes 

In-built constructs to support loss of contact between client and server

•

“Last will and testament” to publish a message if the client goes
offline

•

Stateful “roll-forward” semantics and “durable” subscriptions


Concepts and topologies
!

(optional) bridge

broker

broker
topic/subtopic

publish

subscribe

!
topic/tree/of/items
topic/#
topic/+/other

keepalive
last will & testament
username/password

Qualities of Service
Three qualities of service for both publishing and subscribing:

QoS 0: At most once delivery (non-persistent)
– No retry semantics are defined in the protocol.
– The message arrives either once or not at all.

!

QoS 1: At least once delivery (persistent, dups possible)
– Client sends message with Message ID in the message
header
– Server acknowledges with a PUBACK control message
– Message resent with a DUP bit set If the PUBACK message is
not seen

!

QoS 2: Exactly once delivery (persistent)
– Uses additional flows to ensure that message is not duplicated
– Server acknowledges with a PUBREC control message
– Client releases message with a PUBREL control message
– Server acknowledges completion with a PUBCOMP control
message

Simple
Lightweight (CPU,Mem,**Net)
Data-centric
Distribution (pub/sub)
Range of QoS
=> developer/community interest!


What about HTTP?

!


Data-centricity
MQTT is agnostic of data content and
transfers simple byte arrays, making dripfeeds of updating information trivial.
!

HTTP is (basically) document-centric.


Simplicity
MQTT has few methods (publish/subscribe/
unsubscribe) and is quick to learn.
!

HTTP can be complex (although it is often
well-understood) - there are a multitude of
return codes and methods.
REST is a great principle but not always the
best for simple data applications (POST/PUT/
GET/DELETE? etc…)


Lightweight (network)
The smallest possible packet size for an MQTT
message is 2 bytes.
The protocol was optimised from the start for
unreliable, low-bandwidth, expensive, highlatency networks.
!

HTTP is relatively verbose - lots of "chatter" in
a POST


Easy distribution of data
MQTT distributes 1-to-none, 1-to-1 or 1-to-n
via the publish/subscribe mechanism  
→ very efficient
!

HTTP is point-to-point (can be mediated/
clustered but no distribution mechanism). To
distribute to multiple receivers a large
number of POSTs may be required.


Lightweight (memory/CPU)
MQTT has been trivially implemented on tiny
to larger platforms in very small libraries  
[IBM ref implementation = ~80Kb for full
broker]
!

HTTP (often with associated XML or JSON
libraries for SOAP and REST etc) can be
relatively large on top of OS network libraries
Plus... even if the client is small, consider
whether it is really necessary to run an HTTP
server on every device

Variable QoS
MQTT supports fire-and-forget or fire-andconfirm (aka QoS 0/1/2)
!

HTTP has no retry / confirmation / attempt at
once-only delivery. It is basically brittle, i.e.
retry needs to be written in at the
application level. Applications must also
handle timeouts.


Small and portable
- home hackers love it!


Brokers
http://mosquitto.org

!

C, small standalone binary, fast, standards-compliant/
complete, MQTT only

!

e.g. Ubuntu: sudo apt-get install mosquitto
e.g. OS X: brew install mosquitto

http://rabbitmq.com

!

Erlang, enterprise-quality, larger footprint, MQTT plugin to
AMQP (++) broker, not 100% complete (yet)

!

e.g. Ubuntu: sudo apt-get install rabbitmq
e.g. OS X: brew install rabbitmq


Basic demo (not using Java!)

!


The Java landscape

!


Clients
!
!

Eclipse Paho
http://eclipse.org/paho
!
!
!

Fusesource
http://mqtt-client.fusesource.org/
!
!
* both have Maven repos

Paho example (connect)

!
!

String tmpDir = System.getProperty("java.io.tmpdir");!
MqttDefaultFilePersistence dataStore = new MqttDefaultFilePersistence(tmpDir);!

!
!
!

try {!
!
!
!
!
!
!
!
!
!
!

// Construct the connection options object that contains connection parameters!
// such as cleanSession and LWT!
conOpt = new MqttConnectOptions();!
conOpt.setCleanSession(clean);!
if(password != null ) {!
conOpt.setPassword(this.password.toCharArray());!
}!
if(userName != null) {!
conOpt.setUserName(this.userName);!
}!

!

!
!

// Construct an MQTT blocking mode client!
client = new MqttClient(“tcp://m2m.eclipse.org:1883”,”javaClientDemo”, dataStore);!

!

// Set this wrapper as the callback handler!
client.setCallback(this);!

!

!
!
!
!
!
!
}

} catch (MqttException e) {!
!
e.printStackTrace();!
!
log("Unable to set up client: "+e.toString());!
!
System.exit(1);!
}!


Paho example (subscribe)
client.connect(conOpt);!
log("Connected to "+brokerUrl+" with client ID “+client.getClientId());!
// Subscribe to the requested topic!
log("Subscribing to topic ""+topicName+"" qos "+qos);!
client.subscribe(topicName, qos);!
// Continue waiting for messages until the Enter is pressed!
try {!
!
System.in.read();!
}!
// Disconnect the client from the server!
client.disconnect();!
log("Disconnected");!


Paho example (publish)
!
!
!
!
!

// Connect to the MQTT server!
client.connect(conOpt);!
!
String time = new Timestamp(System.currentTimeMillis()).toString();!
log("Publishing at: "+time+ " to topic ""+topicName+"" qos "+qos);!

!
!

// Create and configure a message!
MqttMessage message = new MqttMessage(payload);!
message.setQos(qos);!

!
!
!
!

// Send the message to the server, control is not returned until!
// it has been delivered to the server meeting the specified!
// quality of service.!
client.publish(topicName, message);!

!
!

// Disconnect the client!
client.disconnect();!

!


Where does Eclipse fit in?

!


Eclipse in the
M2M Universe


Open Ecosystem for M2M
Third Party Ecosystem
Open M2M
communication protocols

Intelligent
Gateways & Routers

Open M2M application 
framework and runtimes

Internet of 
Things

Open M2M 
development tools

M2M

Industry WorkGroup


Open M2M Communication Protocols
Third Party Ecosystem
Open M2M
communication protocols

Intelligent
Gateways & Routers

MQTT

OMA-DM

C Java Lua Javascript Python

M2M

Internet of 
Things

Industry WorkGroup


Projects:
" Paho
" Koneki
" Mihini 
!
" Ponte
" Kura
" Concierge
" SmartHome
" Mosquitto

Brokers
Eclipse M2M http://m2m.eclipse.org - Mosquitto!

!

moquette https://code.google.com/p/moquette-mqtt/
Uses netty; simple, may not be complete

!

ActiveMQ 5.9 http://activemq.apache.org/
Includes MQTT support; broader set of protocols

!

HiveMQ http://hivemq.com
Standalone Java MQTT broker; not open source


" plugins (security, logging, etc)
" lightweight and standalone
" WebSockets


Speaking of WebSockets…
MQTT and WebSockets are natural partners!
!

Eclipse Paho Javascript client supports MQTT
over WebSockets
!

IBM MQ, mosquitto, HiveMQ support this


Simple GUI Utility (Paho)


Eclipse tooling plugin (Paho)
Three basic controls
• Connect/Disconnect
• Publish
• Subscribe

!

Connection Parameters
• Username/password
• Keep alive
• Clean start
• LW&T


mqtt-shell
based on the Spring Shell technology
https://github.com/pidster-dot-org/mqtt-shell
$ mqtt-shell
mqtt> help
* connect - Connect to an MQTT Broker
* disconnect - Disconnect from an MQTT Broker
* exit - Exits the shell
* help - list all commands usage
* publish - Publish a message to an MQTT Broker
* subscribe - Subscribe to topics on an MQTT Broker
* subscriptions - List current subscriptions to topics on an MQTT Broker
* unsubscribe - Unsubscribe from topics on an MQTT Broker

!

mqtt> connect m2m.eclipse.org
Connected to m2m.eclipse.org
anonymous@m2m.eclipse.org> publish
You should specify option (--topic, --, --qos, --retained) for this command
anonymous@m2m.eclipse.org>


more more more!
Clojure support - MachineHead (based on Paho)
!
Android! Great for low-power apps.
e.g. mqttitude
!
Spring Integration support


Demos (with added JVM)

!


Getting involved
• Paho Bugzilla

→ bugs.eclipse.org

!

• much activity via mqtt.org community; interact more

via paho-dev mailing list (where relevant to Paho topics!)
!
• specification discussion via the MQTT Google Group
and mqtt.org wiki
!
• write-up use cases, build guides, share experiences etc
!
• hashtag Twitter discussions → #mqtt #paho (also follow
@mqttorg)

Thank you!
!
Please provide feedback to:
@andypiper
paho-dev mailing list
#mqtt #paho


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