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Wednesday, 20 March 2019

Basic of IoT /networking - Part II

Functionality-based IoT Protocol Organization
  • Connectivity (6LowPAN, RPL)
  • Identification (EPC, uCode, IPv6, URIs)
  • Communication / Transport (WiFi, Bluetooth, LPWAN)
  • Discovery (Physical Web, mDNS, DNS-SD)
  • Data Protocols (MQTT, CoAP, AMQP, Websocket, Node)
  • Device Management (TR-069, OMA-DM)
  • Semantic (JSON-LD, Web Thing Model)
  • Multi-layer Frameworks (Alljoyn, IoTivity, Weave, Homekit)
MQTT
  •  Message Queue Telemetry Transport.
  • ISO standard (ISO/IEC PRF 20922).
  • It is a publish-subscribe-based lightweight messaging protocol for use in conjunction with the TCP/IP protocol.
  • MQTT was introduced by IBM in 1999 and standardized by OASIS in 2013
  • Designed to provide connectivity (mostly embedded) between applications and middle-wares on one side and networks communications on the other side.
  • A message broker controls the publish-subscribe messaging pattern.
  • A topic to which a client is subscribed is updated in the form of messages and distributed by the message broker.
  • Designed for :
               Remote connections
               Limited bandwidth
               Small-code footprint

MQTT Components


MQTT Methods




Communication

The protocol uses a publish/subscribe architecture (HTTP uses a request/response paradigm).

Publish/subscribe is event-driven and enables messages to be pushed to clients.

The central communication point is the MQTT broker, which is in rightful receivers.

Each client that publishes a message to the broker, includes a topic into the message. the topic is the routing information for the broker.

Each client that wants to receive messages subscribes to a certain and the broker delivers all messages with the matching topic to the client.

Therefor the clients don't have to know each other. They only communication over the topic.

This architecture enables highly scalable solutions without dependencies between the data producers and the data consumers.

MQTT Topics

A topic is a simple string that can have more hierarchy levels which are separated by a slash.

A sample topic for sending temperature data of the living room could be house/living-room/temperature.

On one hand the client (e.g. mobile device) can subscribe to the exact topic or on the other hand, it can use a wildcard.

The subscription to house/+/temperature would result in all messages sent to the previously mentioned topic house/living-room/temperature, as well as any topic with an arbitrary value in the place of living room, such as house/kitchen/temperature.

The plus of living sign is a signal level wild card and only allows arbitrary values for one hierarchy.

If more than one level needs to be subscribed, such as , the entire sub-tree, there is also a multilevel wildcard (#)

It allows to subscribe to all underlying hierarchy levels.

For examples house/# is subscribing to all topic beginning with house

Applications
  • Facebook Messenger uses MQTT for online chat.
  • Amazon Web Services use Amazon IoT with MQTT
  • Microsoft Azure IoT Hub uses MQTT as its main protocol for telemetry messages.
  • The EVERYTHING IoT platform uses MQTT as an M2M protocol for millions of connected products.
  • Adafruit launched a free MQTT cloud service for IoT experimenters called Adafruit IO.
SMQTT

Secure MQTT is an extension of MQTT which uses encryption based on lightweight attribute based encryption.

The main advantage of using encryption is the broadcast encryption feature, in which one message is encrypted and delivered to multiple other nodes, which is quite common in IoT applications.
In general, the algorithm consists of four main stages : setup, encryption, publish and decryption

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