Unit -3
Topics to be covered
Design Principles for Web
Connectivity: Web Communication Protocols for connected devices, Message
Communication Protocols for connected devices, SOAP, REST, HTTP Restful and Web
Sockets. Internet Connectivity Principles: Internet Connectivity, Internet
based communication, IP addressing in IOT, Media Access control.
-------------------------------------------------------------------------------------------------------------------------------
Web Communication
Protocols for connected devices-The protocols are
used for communication between machines or between a machine and server. Due to
constraints in processing capabilities and the low power requirements of IoT
devices (which are generally meant to be deployed in environments with constant
battery power) with limited bandwidth capabilities, a need was felt for
dedicated standards and protocols especially designed for IoT. Since those who
manufacture IoT devices and those who create the IoT platforms are different,
this required industry standards and protocols that were not high on power
consumption, bandwidth usage, or processing power and could be adopted easily
by all IoT players— hardware manufacturers, software developers or cloud solutions/service
providers.
List of IoT communication protocols:
·
CoAP (Constrained Application Protocol)-Constrained
Application Protocol (CoAP) is an Internet
application protocol for constrained devices (defined in RFC 7228). It enables
constrained devices to communicate with the wider Internet using similar
protocols. CoAP is designed for use between devices
on the same constrained network, between devices and general nodes on the
Internet, and between devices on different constrained networks joined by the
Internet. It is an application layer protocol designed for network constrained
IoT devices like wireless sensor network nodes, and is often termed the
lightweight version of HTTP with support for REST APIs. It can run on most
devices that support UDP or a UDP analogue.
·
Bluetooth and
Bluetooth Low Energy-While MQTT and CoAP are
infrastructure-independent, which means that it doesn’t matter whether you’re
connected to a wired or a wireless network, Bluetooth provides only wireless communication
over radio frequency (2.4GHz spectrum in the ISM band) using an industry
standard that was initially used to share files between mobile phones and is
now powerful enough to play music (Advanced Audio Distribution Profile/A2DP),
stream data, or build your next IoT device.
Bluetooth, generally, is divided
into three categories.
o
Bluetooth
Classic: This is meant for high data rate applications like
streaming audio wirelessly.
o
Bluetooth
Smart or Low Energy/BLE: This is meant for low powered
battery-operated devices that stream low packets of data.
o
Bluetooth
SmartReady: These are
essentially the ‘hub’ devices such as computers, smartphones, etc. They support
both the ‘classic’ and ‘smart’ devices.
Bluetooth is a sophisticated ad
hoc networking protocol, and is now especially designed from the ground up
for IoT. It provides a stable connection and communication channel, which is
extremely low profile and low powered. An obvious example is fitness trackers,
which even though powered on throughout the day, can last for months on a
single charge or run on a coin cell battery, all thanks to BLE (Bluetooth Low
Energy). Bluetooth Classic has fixed profiles like UART over Bluetooth class
and A2DP class for audio streaming. On the other hand, Bluetooth Low Energy
provides GATT or Generic Attribute Profile, which allows users to define their
own
profile using
Bluetooth, like in the case of a heart rate monitor. BLE is extremely flexible
and useful in the IoT space..
Message Communication Protocols for connected
devices:
·
MQTT (Message
Queue Telemetry Transport)-It was created about 15 years back for monitoring
remote sensor nodes, and is designed to conserve both power and memory. It is
based on the ‘Publish Subscribe’ communication model, where a broker is
responsible for relaying messages to MQTT clients. This allows multiple clients
to post messages and receive updates on different topics from a central server
known as the MQTT broker. This is similar to subscribing to a YouTube channel,
where you get notified whenever a new video is posted. Using MQTT, a connected
device can subscribe to any number of topics
hosted by an MQTT broker.
SOAP-OAP (originally Simple Object Access Protocol) is a protocol
specification for exchanging structured information in the implementation of
web services in computer networks. Its purpose is to induce extensibility,
neutrality and independence. It uses XML Information Set for its message
format, and relies on application layer protocols, most often Hypertext
Transfer Protocol (HTTP) or Simple Mail Transfer Protocol (SMTP), for message
negotiation and transmission.
SOAP allows processes running on disparate operating systems (such
as Windows and Linux) to communicate using Extensible Markup Language (XML).
Since Web protocols like HTTP are installed and running on all operating
systems, SOAP allows clients to invoke web services and receive responses
independent of language and platforms. SOAP provides the Messaging Protocol
layer of a web services
protocol stack for web services. It is an XML-based protocol
consisting of three parts:
·
an envelope, which defines the message
·
·
structure and
how to process it
· a set of encoding
rules for expressing instances of application-defined datatypes
· a convention for
representing procedure calls and responses
SOAP
has three major characteristics:
·
extensibility (security and Web Services Addressing
are among the extensions under development)
·
neutrality (SOAP can operate over
any protocol such as HTTP, SMTP, TCP,
UDP,
or Java Message Service)
·
independence (SOAP allows for any programming model)
As an example of what SOAP procedures can do, an application can
send a SOAP request to a server that has web services enabled—such as a
real-estate price database—with the parameters for a search. The server then
returns a SOAP response (an XML-formatted document with the resulting data),
e.g., prices, location, features. Since the generated data comes in a
standardized machine-parsable format, the requesting
application can then integrate it directly.
The SOAP architecture
consists of several layers of specifications for:
·
Message format
·
Message Exchange Patterns (MEP)
·
Underlying transport protocol bindings
· Message
processing models
· Protocol extensibility
REST-REST (Representational State Transfer) is an architectural style for
developing web services. REST is popular due to its simplicity and the fact
that it builds upon existing systems and features of the internet's HTTP in
order to achieve its objectives, as opposed to creating new standards,
frameworks and technologies.
Advantages of REST-A primary benefit of using REST, both from a client and server's
perspective, is REST-based interactions happen using constructs that are
familiar to anyone who is accustomed to using the internet's Hypertext
Transfer Protocol (HTTP).
An example of this arrangement is REST-based interactions all
communicate their status using standard HTTP status codes. So, a 404 means a
requested resource wasn't found; a 401 code means the request wasn't
authorized, a 200 code means everything is OK; and a 500 means there was an
unrecoverable application error on the server. Similarly, details such as
encryption and data transport integrity are solved not by adding new frameworks
or technologies, but instead by relying on well-known Secure
Sockets Layer (SSL) encryption and Transport
Layer Security
(TLS).
Disadvantages of REST-The benefit of REST using HTTP constructs also creates restrictions,
however. Many of the limitations of HTTP likewise turn into shortcomings of the
REST architectural style. For example, HTTP does not store state-based
information between request-response cycles, which means REST-based
applications must be stateless and
any state management tasks must be performed by the client.
HTTP Restful-In REST architecture, a REST Server simply provides access to
resources and the REST client accesses and presents the resources. Here each
resource is identified by URIs/ Global IDs. REST uses various representations
to represent a resource like Text, JSON and XML. JSON is now the most popular
format being used in Web Services.
HTTP Methods
The following HTTP
methods are most commonly used in REST based architecture.
·
GET − Provides a read only access to a resource.
·
PUT − Used to create a new resource.
·
DELETE − Used to remove a resource.
· POST − Used
to update an existing resource or create a new
resource.
· OPTIONS −
Used to get the supported operations on a resource.
Restful Web Services-A web service is a collection of open protocols and standards used
for exchanging data between applications or systems. Software applications
written in various programming languages and running on various platforms can
use web services to exchange data over computer networks like the Internet in a
manner similar to inter-process communication on a single computer. This
interoperability (e.g., between Java and Python, or Windows and Linux
applications) is due to the use of open standards. Web services based on REST
Architecture are known as Restful Web Services.
Web Sockets-
WebSocket is a
computer communications protocol, providing full- duplex communication
channels over a single TCP connection.
The WebSocket protocol was
standardized by
the IETF as
RFC 6455
in 2011, and the WebSocket API in
Web IDL is being
standardized by the W3C.
WebSocket
is
a different TCP protocol from HTTP.
Both protocols are located at
layer 7 in the OSI model and, as such,
depend on TCP at layer
4. Although they
are different, RFC 6455 states
that WebSocket "is designed to work over HTTP ports 80 and 443 as well as
to support HTTP proxies and intermediaries" thus making it compatible with
the HTTP protocol. To achieve compatibility, the WebSocket handshake uses the HTTP Upgrade
header to change from the
HTTP protocol to the WebSocket protocol.
Internet
Connectivity-It defines various concepts mentioned below:
Internet
Service Providers (ISP)-Internet Service Provider (ISP) is a company
offering access to internet. They offer various services:
·
Internet Access
·
Domain name registration
·
Dial-up access
·
Leased line access
ISP
Types- ISPs can broadly be classified into six
categories as shown in the following diagram:
Fig 3.1 ISP Categories
Access Providers-They provide access to internet through telephone lines, cable Wi-Fi
or fiber optics.
Mailbox Provider-Such providers
offer mailbox hosting services.
Hosting ISPS-Hosting ISPs
offers e-mail, and other web hosting services such as virtual machines, clouds
etc.
Virtual ISPS-Such ISPs
offer internet access via other ISP services.
Free ISPS-Free ISPs do not
charge for internet services.
Connection Types-There
exists several ways to connect to the internet. Following are these connection
types available:
·
Dial-up Connection
·
ISDN
·
DSL
·
Cable TV Internet
connections
· Satellite
Internet connections
·
Wireless Internet
Connections
Dial-up Connection-Dial-up connection uses telephone line to connect PC to the
internet. It requires a modem to setup dial-up connection. This modem works as
an interface between PC and the telephone line. There is also a communication
program that instructs the modem to make a call to specific number provided by
an ISP.
Dial-up
connection uses either of the following protocols:
·
Serial Line Internet Protocol (SLIP)
· Point to Point
Protocol (PPP)
The following
diagram shows the accessing internet using modem:
Fig 3.2.1 Dial-up connections
ISDN-ISDN is acronym of
Integrated Services Digital Network. It establishes the connection using the
phone lines which carry digital signals instead of analog signals.
There
are two techniques to deliver ISDN services:
·
Basic Rate Interface (BRI)
· Primary Rate
Interface (PRI)
Key points:
·
The BRI ISDN consists of three distinct channels on
a single ISDN line: t1o 64kbps B (Bearer) channel and one 16kbps D (Delta or
Data) channels.
·
The PRI ISDN consists of 23 B
channels and one D channels with both have operating capacity of 64kbps
individually making a total transmission rate of 1.54Mbps.
The following diagram shows accessing internet using
ISDN connection:
Fig 3.2.2 ISDN Connections
DSL-DSL is acronym of
Digital Subscriber Line. It is a form of broadband connection as it provides
connection over ordinary telephone lines.
Following
are the several versions of DSL technique available today:
·
Asymmetric DSL (ADSL)
· Symmetric DSL (SDSL)
·
High bit-rate DSL
(HDSL)
·
Rate adaptive DSL
(RDSL)
· Very high
bit-rate DSL (VDSL)
·
ISDN DSL (IDSL)
All of the above
mentioned technologies differ in their upload and download speed, bit transfer
rate and level of service.
The following diagram shows that how we can connect to internet
using DSL technology:
Fig 3.2.3 DSL Connections
Cable TV Internet
Connection
Cable
TV Internet connection is provided through Cable TV lines. It
uses coaxial cable which is capable of transferring data at much higher speed
than common telephone line.
Key Points:
·
A cable modem is used to access this service, provided by the cable operator.
·
The Cable modem comprises of two connections: one
for internet service and other for Cable TV signals.
·
Since Cable TV internet connections
share a set amount of bandwidth with a group of customers, therefore, data
transfer rate also depends on number of customers using the internet at the
same time.
The following diagram shows that how internet is accessed using
Cable TV connection:
Fig 3.2.4 Cable TV Connections
Satellite Internet
Connection-Satellite Internet connection offers
high speed connection to the internet. There are two types of satellite
internet connection: one way connection or two way connection.
In one way connection, we can only download data but if we want to upload, we need a
dialup access through ISP over telephone line.
In two way connection, we can download and upload the data by the satellite. It does not
require any dialup connection.
The following diagram
shows how internet is accessed using satellite internet connection:
Fig 3.2.5
Satellite Connections
Wireless Internet
Connection-Wireless Internet Connection makes use
of radio frequency bands to connect to the internet and offers a very high
speed. The wireless internet connection can be obtained by either Wi-Fi or Bluetooth.
Key
Points:
· Wi-Fi wireless
technology is based on IEEE 802.11 standards which allow the electronic device
to connect to the internet.
·
Bluetooth wireless technology makes
use of short-wavelength radio waves and helps to
create personal area network (PAN).
Internet based
communication-In much of the world the Internet is
becoming the primary medium for communication in business. Internet
communication tools save money in a variety of ways. Email, instant messaging
and social networking are all free. There are many different kinds of Internet
communications tool, such as email, VoIP, forums, online chat and social
networking among others. Using the latest tools and methods of communicating
over the Internet is essential for bringing your business into the modern age
of communication and marketing.
VoIP and Internet
Telephony-It is common for voice communications to
be carried out over the Internet using voice over Internet protocol software.
VoIP allows you to call a telephone -- either a fixed or mobile phone -- over
the Internet. This is often considerably cheaper than calling from a telephone,
particularly with international calls. One of the most popular Internet
telephony tools is Skype. With Skype and similar Internet telephony tools, you
can conduct free voice conversations between two computers.
·
Email-The
original Internet communication tool, email is still an essential tool every
business should have. In spite of this, with the rise of messaging through
social networking sites and instant messages, email is not quite as important
as it used to be.
· Social Networking-Social networking is all
about forming groups, sharing online content and exchanging information. In
addition to being a major part of social life in the modern world, social
networking is an invaluable tool for Internet marketing since it provides a
user-friendly and highly accessible platform upon which to exchange information
on products and services. For example, if someone likes an article on your
business blog or website, he may decide to share it with his friends over
Facebook or Twitter.
· Forums-Forums, like email, have also been around
since the dawn of the Internet. Forums provide a place to exchange messages and
participate in conversations. The main differences from instant messaging are
that forums are generally public and the communications are not in real time.
Forums and their regular posters and readers form communities that can be
valuable to your business.
IP addressing in IOT- We can connect
Internet of Thing or device to the
Internet. How we connect depends ultimately on what we actually want to do with
the device. Shown below is a typical home network. This would normally consist
of a router / firewall that connect to your ISP (Internet Service Provider).
The connection to your ISP could by via ADSL or Ethernet using a fiber service
for example.
Fig 3.3 IP
addressing in Home Networks
When the home router connects to the ISP it will be assigned an IP address which is what is used to
communicate with servers or other service on the Internet. This is a public IP
address and is addressable by the internet. In the diagram above the public IP
address is 111.246.59.246.
This is your public IP address you used to connect to the cactus.io
server to view this page.182.73.155.114
(If there is more than one IP then you might be connecting using a
proxy server or VPN service), be aware that this IP address will change every
time that your home router is rebooted or reconnects to the ISP. Some ISP's
allow you to pay extra for a fixed IP address. However most will not for home
internet services.
Connect to a Web Server-When we enter a URL into our browser it will use a DNS server to
convert the name to an IP address. The DNS server would normally be provided by
your ISP. In the example above we are using cactus.io for the URL. The DNS
server would then return the IP address of 104.130.130.228. The browser will
then try to connect to the server via the router. The router will connect to
the remote server using the public IP address assigned to your router. The
server hosting cactus.io will then send data back to your router using your
public ip address (111.246.59.246). The router will
then transmit this data back to your PC using the private IP address of 192.168.1.10.
Connect to an Internal IoT
Device-We can connect to a web server running on
our IoT device by entering the IP address of http://192.168.1.45
into the browser URL. The connection will be made in this case via
the switch built into the home router. The switch knows what port the IoT
device is connected to and transmits and receives data via this port. The
router has no role in this network request as it's a private IP address and the
PC and IoT device are on the same network.
How to connect my device to the
Internet
This all depends on the
role of the device and we have the following options:
·
Option 1) We access this device only on the home /
business network
·
Option 2) The device only connects to a local /
remote server
·
Option 3) We access this device from the Internet
using a Static Public IP Address
· Option 4) We
access this device from the Internet using a Dynamic Public IP Address
Option 1) Access this device only on the home /
business network-In this scenario the IoT device is configuring as a
server. The easiest way is to assign a static IP address. This address is coded
into the sketch.
Fig 3.4 IP
addressing in Business Network
When a client connects to the IoT device it passes through the
switch and out to the device it is connected to. No routing is required here.
Option 2) Device connects
to a local / remote server-For this scenario the
IoT device initiates a connection to a local or remote server. This could be
using a http REST POST or configured as MQTT client. It could also be a custom
connection method as long as it initiates the connection to the remote service.
Because the device is creating the connection it allows us to use
DHCP and a dynamically assigned IP address.
Fig 3.5
Client-Server Communication
In the diagram above two of the devices send a HTTP REST Post to a
server in the cloud. If the remote server accepts the connection and data it
will generally respond with a 200 OK. The client will then close the connection
until the next post is sent.
Option 3) Access the Device from the Internet with Static
Public IP Address
The world is running out of IPV4 IP addresses. This means ISP's are
pretty strict on giving out static IP addresses. It's much easier for them to
use a dynamic pool of IP addresses to assign to their clients.
Generally home internet services are not available with a static IP
address. However you might be able to pay extra for this functionality. Some
business accounts are available with a static IP address. The most common
reason for wanting a static ip is for hosting a email server.
In this diagram above we could use http://1.127.48.156 or
http://1.127.48.156:49155 to connect to the IoT server. In the first URL we do
not specify a port number so the browser will use the default port of 80. In
the second URL we use the port 49155. By using a random private port number we
improve the security for our IoT server. If someone does a port scan they will
always check port 80 as it's a default. They might not bother scanning private
port numbers
If you have multiple IoT devices you can setup port forwarding on
the router to recognize different port numbers.
Option 4) Access the
Device from the Internet with Dynamic Public IP Address-One of the most common ways of dealing with a dynamic public (WAN)
IP addresses is to use a Dynamic DNS Service provider. Some of these services are free but most require a monthly
payment. Most routers these days support third party Dynamic DNS service
providers. You configure the router with the provider, username and password.
When the router detects a WAN interface IP address change it updates the DDNS
service provider with the new IP details.
Fig 3.7 Public IP Addressing
When you sign up with one of these providers you provide a domain
name you would like to use. In the example below the name we used is cactusio. This is a sub domain for dydns.com. When we enter
http://cactusio.dydns.com into the browser
it will do a dnslookup on cactusio.dydns.com. If it’s
a valid domain it will respond with the IP address which just happens to be the
public (WAN) IP address of the home / office
router.
The office router will detect the data packet matches a record in
the port forwarding table and pass the data onto the IoT device using the
static IP of 192.168.1.45. The IoT device will respond with the appropriate
html to view in the internet client browser.
Media Access control
In Layer 2 of a network, the Media Access Control (MAC) sub-layer
provides addressing and channel access control mechanisms that enable several
terminals or network nodes to communicate in a network.
The MAC sub-layer acts as an interface between the logical link
control (LLC) Ethernet sub-layer and Layer 1 (the physical layer). The MAC
sub-layer emulates a full-duplex logi
communication
channel in a multipoint network. This channel may provide unicast, multicast or
broadcast communication service. The MAC sub-layer uses MAC protocols to
prevent collisions. In Layer 2, multiple devices on the same physical link can
uniquely identify one another at the data link layer, by using the MAC
addresses that are assigned to all ports on a switch. A MAC algorithm accepts
as input a secret key and an arbitrary-length message to be authenticated, and
outputs a MAC address.
