Introduction to Internet of Things

Alexander Nelson

December 2, 2019

University of Arkansas - Department of Computer Science and Computer Engineering

Internet of Things

Internet of Things (IoT) – Network of devices, and connectivity to

interact & exchange data

What ramifications does IoT have for embedded systems?

1

History

Machine-to-Machine (M2M) Communication – Systems exchange

information w/ no user interaction

Caller ID (1968) – Phones needed to process analog waveform to

exchange identifier

Smart Meters & Load balancing (1977) → precursor to smart grid/ modern smart meters

Cellular M2M (1995) – GSM module “M1” - share data over

cellular network

Device-to-Device (D2D) – Direct M2M connection without

traversing WAN/core network

Either cellular or unlicensed spectrum (e.g. WiFi/Bluetooth)

2

History – Carnegie Mellon – Connected Coca-Cola machine1

In the mid-seventies expansion of the department caused people’s

offices to be located ever further away from the main terminal room

where the Coke machine stood. It got rather annoying to traipse down

to the third floor only to find the machine empty - or worse, to shell

out hard-earned cash to receive a recently loaded, still-warm Coke.

One day a couple of people got together to devise a solution.

They installed micro-switches in the Coke machine to sense how many

bottles were present in each of its six columns of bottles. The

switches were hooked up to CMUA, the PDP-10 that was then the main

departmental computer. A server program was written to keep tabs on

the Coke machine’s state, including how long each bottle had been in

the machine. When you ran the companion status inquiry program, you’d

get a display that might look like this:

EMPTY EMPTY 1h 3m

COLD COLD 1h 4m1https://www.cs.cmu.edu/~coke/history_long.txt 3

https://www.cs.cmu.edu/~coke/history_long.txt

History – Computer for the 21st Century (1991)

Precurser to PDAs / tablets / smart TVs

4

History

1999 – The term “Internet of Things” attributed to Kevin Ashton

(prefers Internet for Things)

2002 – Cooltown (HP Labs) – URLs with links to object

descriptors & actions

2008-2009 – Number of connected objects outnumbered connected

people

5

Forecast

Number of Connected Devices

6

How can 50B devices all be connected?

6

Wireless Networking Categories

• LPWAN – Low PowerWide Area Network

• WWAN - WirelessWide Area Network

• WPAN – WirelessPersonal Area

Network

• WLAN – WirelessLocal Area Network

7

WWANs

Wireless Networking Categories

2

2“Smart Cities Technologies” Ivan Nunes Da Silva and Rogerio Andrade –

ISBN 978-953-51-2808-3

8

WWAN – Wireless Wide Area Network

WWAN – Set of technologies that provide wireless access to

geographically distant sources

Includes:

• Cellular Technologies• 2G• 3G• LTE• LTE-M

• IEEE 802.16 – WiMAX• LPWAN Technologies

• LoRA• SigFox• Ingenu

• Mesh Networking?

9

Cellular Communications

Cellular Network – Communication network where last link is

wireless

Distributed over land areas – “cells”

3

3By Andrew pmk - SVG version of Frequency reuse.fig by Mozzerati, CC

BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=2155967 10

Cellular Communications

Advantages:

• More capacity than a single large transmitter, same frequencyused for multiple links in different cells

• Cell towers are closer – Mobile devices use less power thanwith single transmitter

• Larger coverage area than a single terrestrial transmitter –additional cell towers can be added indefinitely

11

Cellular Communications

Range is inversely proportional to frequency

CDMA2000 Network

12

WiMAX

WiMAX – Worldwide Interoperability for Microwave Access

Microwave meaning 300MHz-300GHz frequencies

Meant to provide “last-mile” broadband over wireless

Originally 30-40Mbps – Upgraded to 1Gbps in 2011

13

WiMAX

WiMAX – Worldwide Interoperability for Microwave Access

Microwave meaning 300MHz-300GHz frequencies

Meant to provide “last-mile” broadband over wireless

Originally 30-40Mbps – Upgraded to 1Gbps in 2011

Most WiMAX deployments are winding down

14

LPWAN Communications

LPWAN – Low Power Wide Area Network

Designed for long range communications at low bit rates

Data Rates – 0.3kbps-50kbps

15

LPWAN Communications

LPWAN – Low Power Wide Area Network

Designed for long range communications at low bit rates

Data Rates – 0.3kbps-50kbps

Intended for sensor-type deployments at long range

Power IoT/Smart-City type applications

16

LPWAN Communications

17

Mesh Networks

WANETs – Wireless Ad hoc Networks

MANETs – Mobile Ad hoc Networks

ad hoc – latin, literally “for this” – Does not rely on static

infrastructure

MANETs allow for nodes to move freely geographically

18

Mesh Networks

Mesh Networks as WWAN?

Communications technologies similar to cellular networks

Can provide WAN access to small devices through sink nodes

19

Wireless Network Challenges

Wireless Communication

Given a certain amount of RF frequency spectrum, how to

optimize communication?

Metrics:

• Throughput – Total network bits-per-second• Latency – Average time form packet creation to reception• Fairness – Do devices receive equal share of resource

(airtime)?

20

Multiple Access Techniques

If multiple wireless clients exist, how to divide resources?

Multiple Access Methods – Techniques for dividing resources

• CSMA – Carrier Sense Multiple Access• TDMA – Time Division Multiple Access• FDMA – Frequency Division Multiple Access• CDMA – Code Division Multiple Access• SDMA – Space Division Multiple Access

21

Carrier-Sense Multiple Access

CSMA – Carrier Sense Multiple Access

Nodes check to see if anyone is communicating

If channel is empty, they may start

22

Hidden Node Problem

Not detecting communication does not mean channel is clear

23

CSMA/CA

CSMA/CA – CSMA with Collision Avoidance

1. Carrier Sense – Listen for other transmission

2. Random Backoff – If channel is busy, backoff for random

amount of time

3. Request to Send/Clear to Send (RTS/CTS) – Access

Control Signals

4. Transmission – Send entire packet to Access Point (AP)

5. Acknowledgment – AP sends acknowledgment if packet is

received

6. Exponential Backoff – If no ACK, assume collision and

backoff

24

CSMA

Advantages

• Low latency if channel is not busy• No need for centralized control

Disadvantages

• Busy channel causes many collisions – low throughput & highenergy waste

25

TDMA

TDMA – Time Division Multiple Access

4

4By Mozzerati at English Wikipedia - 13:13, 2004 Sep 5 (UTC), CC BY-SA

3.0, https://commons.wikimedia.org/w/index.php?curid=32927708

26

TDMA

Advantages

• Nodes only need to listen during frame – save power• Guaranteed no collision

Disadvantages

• Lower Throughput – A node may not need to use their frame

27

FDMA

FDMA – Frequency Division Multiple Access

Divide available frequency into channels

Nodes communicate on their own channel

Wi-Fi FDMA – 5MHz channel width – 22MHz spectrum spread

28

CDMA

CDMA – Code Division Multiple Access

Use orthogonal psuedorandom codes to allow additive

communication on same spectrum

Four mutually orthogonal codes29

CDMA Example

30

CDMA

Advantages

• Multiple nodes may communicate at the same time• Flexible length of codes – dynamic allocation

Disadvantages

• Reduced throughput per device per frameThat is, takes n times as long to transmit a single bit, where n

is length of the code

• Subject to Near-Far problem

31

Near Far Problem

Problem with SNR for geographically disparate nodes

Near node Noise may be similar to magnitude of far node signal

32

Phase Shift Keying

Phase Shift Keying – PSK

Code division multiple access – Codes are multiplexed by phase

rather than time

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Protocols

OSI Model

The network technologies

under the four categories

implement the

Transport/Internet layers

of the TCP/IP Model

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Application Layer Protocols – HTTP

Hypertext Transfer Protocol (HTTP)

Hypertext Transfer

Protocol (HTTP)

Communication basis of

the World Wide Web

Implements a

Request–Response

protocol

35

HTTP Model

HTTP Model –

• Network of Nodes• Nodes contain some text• Nodes can be referenced by hyperlinks (links)• Hyperlinks are identified by Uniform Resource Locators

(URLs)

• URLs are Uniform Resource Identifiers (URIs) with specificschemes (HTTP/S)

• Clients request resources from servers based on URL

36

HTTP Requests

HTTP Requests–

• GET – Retrieve data and have no other effect• HEAD – Asks for response for a GET without the body• POST – Post a resource at a new URI• PUT – Store a resource under a specified URI• DELETE – Remove a resource at a URI• TRACE – Echo received requests to verify changes by

intermediates

• OPTIONS – What methods are available at the URL• CONNECT – Converts request connection to a TCP/IP

tunnel (for SSL)

• PATCH – Apply partial modifications to a resource

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How can HTTP be leveraged for Ubiquitous

Computing?

37

Web Services

What is a web service?

Set of functions that can be accessed over HTTP protocols

Provide response through a serialized data protocol (e.g. XML,

JSON)

Why use Web Services?

• Allow transmission of data from or to a remote server• Perform proprietary data transformations• Transmit data between programs

38

REST Webservices

REST – Representational State Transfer

Developed in tandem with HTTP 1.1 and formalized in 2000

Distill data transfer to a core set of principles

39

REST Architecture

Core Architectural Properties:

• Performance – Maximize network efficiency• Scalability – Support large number of components and

interactions

• Simplicity and Uniformity in interfaces• Visibility of communication between components• Portability of program code and data• Reliability of components to failures

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REST Architecture

Six guiding constraints:

• Client-Server Architecture/Model• Statelessness – No client context is stored on the server

between requests

• Cacheability – Clients can cache responses• Layered System – Client doesn’t know if it is connected

directly to the end server

• Code on demand – Temporarily extend functionality of clientby transferring executable code

• Uniform Interface

41

REST Methods

REST Web services use the available HTTP methods

Most often, REST services use four common methods:

• GET• PUT• POST• DELETE

Behavior depends on whether the URL specifies an element or a

collection

42

REST URLs

REST Services use URLs to specify data and method locations

Example:

http://example.com/api/path/?parameter=1&otherparameter=2

The URL will specify:

• HTTP (or HTTPS) as the transfer protocol• The server domain location• The path on the server to the particular function• Optional set of parameters following a ? and separated by &s

43

Collection vs. Element

Element (or Resource) – Object with a type

May have:

• Associated Data• Relationships to other resources• Set of methods that operate on it

Collection – Set of elements

44

GET Method

If the URL points to a single element

Example:

GET http://del.icio.us/api/ahnelson/bookmarks/a211528

Returns information about a specific bookmark

If the URL points to a collection:

Example:

GET http://del.icio.us/api/ahnelson/bookmarks

Returns information about all the bookmarks associated with the

user ahnelson

45

POST Method

POST – Creates a new object

URL specifies the collection to which the object should be added

Specify fields using optional parameters

Often returns the URL of the created object

46

PUT Method

PUT – Can be used to create or update existing record*(s)

URL specifies the resource to be modified

Can prevent creation using PUT by returning a 404 error if

resource doesn’t exist

Specify fields to modify using optional parameters

Typically returns the URL of the modified object

47

DELETE Method

DELETE – Remove record(s)

URL specifies the element or the collection to be deleted

Often returns an HTTP response of 204 (No Content) if successful

48

Responses

The Responses include an HTTP Response code and optional

information in serialized language

Response Codes:

• 200 – OK• 201 – Created• 202 – Accepted• 401 – Unauthorized• 403 – Forbidden• 404 – Not Found

And others

49

Example

Let’s look at an example using test data from the web:

https://jsonplaceholder.typicode.com/

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Application Layer Protocols –

MQTT

MQTT

MQTT – (Formerly MQ Telemetry Transport)

Developed in 1999 with goals of minimal battery draw and

bandwidth usage to connect oil pipelines over a satellite connection

Implements a publish–subscribe pattern

51

MQTT

MQTT Publish/Subscribe Pattern5

5https://www.hivemq.com/blog/mqtt-essentials-part2-publish-subscribe

52

Publish/Subscribe – Decoupling

Publish/Subscribe pattern decouples data by:

• Space Decoupling – Publisher/Subscriber do not need toknow each other (e.g. don’t need to know port or ip address)

• Time Decoupling – Publisher/Subscriber do not need to runat the same time

• Synchronization Decoupling – Operations on bothcomponents are not halted during publishing/receiving

53

Publish/Subscribe – Message Filtering

How does the broker (server) filter messages so that subscribers

only get correct messages?

• Subject-based Filtering – Filtering based on topic.Receiving client subscribes only to relevant topics. Topics are

slash-separated hierarchical URIs

• Content-based Filtering – When broker filters messagebased on specific content filter-language. Clients subscribe to

filter queries of messages they are interested in. (Message

may not be encrypted for this to work)

• Type-based Filtering – With Object Oriented Programming(OOP) languages, filtering based on type/class is common.

Subscriber could listen to all messages that are of the same

type.

54

MQTT – Client

MQTT Client – Any device connecting to an MQTT broker over

any network

e.g. Microcontroller over 6LoWPAN, Phone over Cellular, Server

over ethernet

Many client libraries are available for most languages

55

MQTT – Broker

MQTT Broker – Responsible for receiving, filtering, and sending

messages to clients

May be responsible for authentication and authorization

May be responsible for persisted clients and missed messages

Can handle thousands of concurrent clients

56

MQTT – Connection

MQTT Connection always from Client←→BrokerNever connecting directly with other clients

Once connection is established, it is kept open until client

disconnects

57

MQTT – Connect Message

Connect Message contains the following:

• clientId – identifer of each MQTT client (should be unique)• cleanSession (boolean) – if client wants persistent session• username* – authorization/authentication• password* – authorization/authentication• lastWillTopic* –• lastWillQos*• lastWillMessage*• lastWillRetain*• keepAlive – interval that client will sent “heartbeat” pings

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Will Message

“Last Will and Testament”

Will Message – Message sent in event of ungraceful disconnect

Message sent by broker on behalf of client

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MQTT – CONNACK Message

Connack message contains the following:

• sessionPresent (boolean) – Whether a persistent session existsfor the clientId

• returnCode (int)• 0 – Accepted• 1 – Refused – Unacceptable Protocol Version• 2 – Refused – Identifier Rejected• 3 – Refused – Server Unavailable• 4 – Refused – Bad Username/PW• 5 – Refused – Not Authorized

60

Publishing

After connection, clients may publish messages

Message Fields:

• packetId (int)• topicName (String)• QOS (int)• retainFlag (boolean)• payload (bytes)• dupFlag (boolean)

61

Publishing

Topic – Hierarchically structured string for message filtering

e.g. “UARK/CSCE5013/Sensor1/”

QoS – Quality of Service Level (0, 1, or 2)

Determines the guarantee of message reaching the other end

Retain-Flag – If message will be saved by broker as last known

good value

New subscribers will receive last retain-flag value

62

Publishing

Payload – Content of the message; data agnostic

Can be images, text, encrypted data, JSON, etc...

Packet Identifier – Unique identifier between client & broker

Identify message flow – only relevant for QOS >0

DUP flag – Indicates that message is a duplicate & resent because

of no ACK of original

Only relevant for QOS >0

63

Subscribing

Subscribe – Let broker know to forward messages based on topic

Subscribe message contains:

• packetId• Array of subscribing:

• Topics• QOS Levels

packetId – Verify that subscription happens exactly once

Confirmed by a SubACK from broker with return codes for each

subscription

64

Unsubscribe

Client can unsubscribe by posting an Unsubscribe message

Contains packetId, and topics to unsubscribe from

Confirmed by a unsubACK with a packetID

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Topics

Topics are UTF-8 (a string encoding) case sensitive strings used to

filter messages

Consists of one or more topic levels

uark/csce5013/sensor1/temperature

4-level topic

Topics must contain at least 1 character, and spaces are

acceptable (but discouraged!)

Forward slash at beginning is also acceptable, but discouraged

i.e. /this topic and this topic are different!

66

Topics – Wildcards

Wildcards can be used to subscribe to more than 1 topic at once

Wildcard Characters:

• “+” – Single Level Wildcard• “#” – Multi Level Wildcard

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Wildcard Examples

Example: Subscribing to uark/csce5013/+/temperature

• topic uark/csce5013/sensor1/temperature – Match• topic uark/csce5013/sensor2/humidity – No Match• topic /uark/csce5013/sensor1/temperature – No Match• topic uark/csce5013/sensor2/temperature – Match• topic uark/csce5013/Sensor1/Temperature – ?

Example: Subscribe to uark/csce5013/#

• uark/csce5013/sensor1/temparature – Match• uark/csce5013/sensor2/humidity – Match• uark/CSCE5013/ – No Match• uark/csce5013 – Match

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Topics – Best Practices

Best Practices for Topics:

• Do not use leading forward slash• Do not use spaces in topics• Keep topic short & concise• Use only ASCII characters• Embed a unique identifier or ClientId into the topic• Don’t subscribe to #• Plan for product/programming evolution• Use specific topics rather than general

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WWANsWireless Network ChallengesProtocolsApplication Layer Protocols – HTTPApplication Layer Protocols – MQTT