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Computer Network
Welcome to the course of computer network. In this course we are going to learn about very basic concepts of computer network. We start with the introduction and internet application in which we will discuss about networking models , data communication - Modulation, Multiplexing techniques, Packet switching , Network technology like LAN , WAN, IEEE MAC, ethernet ,IP, various Protocol and network management - VoIP, network security and SNMP IOT

Introduction to
Computer Network

Computer Network

What is Computer Network?
Uses of Computer Network
Evolution of computer network

Computer Network:
Computer network is a digital telecommunication network.
It is a group of computers and other computing hardware devices.
They are linked together through communication channels
Networking computer devices are used to originate, route and terminate the data
They are known as network nodes.
These nodes are such as personal computers, phones, servers and networking hardware.

Computer Network:
Computer Networks are used to:
Provide communication through email, video conferencing, instant messaging etc.
Enable sharing of a single hardware device like a printer or scanner among multiple users.
Enable file sharing across the network
Allow sharing of software or operating programs on remote systems.
Make information easier to access and maintain among network users.

Computer Network:

Evolution of Computer network:
1940 : George Stibitz used a teletype machine model at Dartmouth College and complex number calculator in New york to send and receive instruction.
1950 : Early networks was the military radar system SAGE
1962 : ARPA link the output systems like teletypewriters to computers and when J.C.R. licklider was hired he named it as intergalactic computer network.
1965 : the General Electric and Bell Labs used a computer to route and manage telephone connections

SAGE : Semi- Automatic Ground Environment
SABRE : Semi Automatic Business research environment
1960 : The commercial airline reservation system SABRE went online with two connected mainframes.

Computer Network:

Evolution of Computer network:
1991 : Home Broadband created
1996 : The 56k modem was invented by Dr. Brent Townshend
2000 : Cisco became the single most valuable corporation in the world as “Fortune 1” company.
2010 : 100 GE introduced in the market with full standardization.

1965 : Thomas Marill and Lawrence G. Roberts created the first wide area network (WAN).
2015 : Terabit optical ethernet center are aiming for 1 Terabit Ethernet over optical fiber (1 tbps)
2020 : the goal is to enable 100 tbps terabit ethernet.

Computer Network:

Types of network:
Public network :
A public network is a network that is accessible to the public.
This network is owned by a service provider such as ISPs
They offers service to any individual or organization that pays the subscription fee.
This network follow strict rules and regulation of government.

to protect communication from unintended snooping . Example of Public network are: Internet a large scale public network, Public wifi and other internet access such as wired connection offered by a network.

Computer Network:

Types of network:
Private Network :
A Private network are controlled by one particular network.
It is a connection within a specified network.
This type of network is configured in such a way that devices outside the network cannot access it.
Example LAN connectivity in offices or college campus.
Only a selected set of devices can access this type of network depending on the settings encoded in the network routers and access points. \

Computer Network:

Types of network:
Private Network :
Further Private network is connected to four categories:
SOHO (Small Office/ Home Office)
SMB (Small to Medium Business)
Large Enterprise

Computer Network:

Types of network:
Private Network :
Consumer: least expensive forms of private network consists of a network owned by an individual
Small Office/Home Office (SOHO): A SOHO network is slightly larger than a consumer network.

A typical SOHO network connects two or more computers, one or more printers, a router that connects the office to the Internet, or other devices, such as a cash register or credit card verification machine.

Computer Network:

Types of network:
Private Network :
Small-to-Medium Business (SMB): This network connect many computers in multiple offices in a building, and also include computers in a production facility (e.g., in a shipping department).
Large Enterprise: This network provide IT infrastructure for major business corporation. Enterprise networks usually include both wired and wireless technologies.

A typical large enterprise network connects several geographic sites with multiple buildings at each site, uses many network switches and routers, and has two or more high-speed connections to the global Internet

Computer Network:

Communication involves at least two entities:
One that sends information : Sender
Another that receives information : Receiver

Interoperability: is the ability of two entities to communicate efficiently.
Network communication protocol: refer to specification of rules and regulations for network communication.

GE Gigabit ethernet

Growth of

What is Internet?
Resource sharing and communication
Text to multimedia
Personal computer to cloud computing

Internet is a networking infrastructure that provides services to distributed applications.
It uses TCP/IP to transmit data via various types of media.
The nuts and bolts of internet is basic hardware and software.


Changes in Internet due to its growth -
Resource sharing to communication:
Communication speeds increased dramatically
New applications invented which represent broad cross section of society.

Two technological shift the usage of internet from resource sharing to new applications. This is due to ,higher communication speeds which enable applications to transfer large volumes of data quickly. And due to the the advent of powerful, affordable, personal computers which provide high computational power .

Transformation in data send on internet:
Text to multimedia:
Text Graphic Video High Definition
ImagesClip Movies

Internet communication initially send textual data. Example, email messages By the 1990s, computers had color screens capable of displaying graphics that allow users to transfer images easily. By the late 1990s, users began sending video clips, and downloading larger videos By the 2000s, Internet speeds made it possible to download and stream high-definition movies.

Transition in network technologies:
Telephone System - Move from analog to Voice over IP (VoIP)
Cable Television - Move from analog delivery to Internet Protocol (IP)
Cellular - Move from analog to digital cellular service (4G)
Internet Access - Move from wired to wireless access (Wi-Fi)
Data access - Move from centralised to distributed services (P2P)

Trends in computer:
Personal computer to Cloud Computing
The High-speed Internet connections allow companies to use computation and data storage services
This is less expensive than the same services that is implemented by a system where each user had their own computer.

The idea is straightforward: a cloud provider builds a large cloud data center that contains many computers and many disks all connected to the In- ternet.

Layer Model

Internetworking model
TCP/IP layers

Layer Model:
Internetworking Models:
Internetworking models are used to make communication between two devices flexible.
Before the invention of these models, the computer communicate with other computer if they are from same manufacturer.

Layer Model:
TCP/IP Protocol Suite:
The TCP/IP protocol suite is a collection of protocols that define the Internet.
It was developed by Department of Defence's Project Research Agency
The main aim to design this model is to provide end to end data communication.
It also specify how data is packetized, addressed, transmitted , routed and received in the network.

TCP/IP stands for Transmission Control Protocol and Internet Protocol
DARPA Defense Advanced Research Projects Agency
It is a project of network interconnection to connect remote machines.

Layer Model:
TCP/IP Protocol Suite:
TCP/IP is a two-layer structure:
The higher layer represent Transmission Control Protocol which manages the assembling of a message into smaller packets that are transmitted over the Internet.
The lower layer represent Internet Protocol which add the IP or MAC address to packets so that it gets to the right destination.

TCP/IP uses the client/server model of communication in which a client user requests and server provide a service in the network.

Layer Model:
TCP/IP Protocol Suite:
The TCP/IP model consist of 5 layers:
Application Layer
Transport Layer
Network/Internet Layer
Data Link Layer
Physical Layer/Network interface layer

Each layer in TCP/IP model corresponds to one or more layers of the 7-layer of Open Systems Interconnection (OSI) model.

Layer Model - TCP/IP:

Layer Model:
TCP/IP Protocol Suite: Application Layer
The Application layer provides interface between the applications and protocols.
It represent ability to access the services of the other layers and defines the protocols that applications use to exchange data.
The most widely-known Application layer protocols are HTTP, FTP, SMTP and telnet
Example: Web browsing, video conferencing and smartphone applications

The Hypertext Transfer Protocol (HTTP) is used to transfer files that make up the Web pages.
The File Transfer Protocol (FTP) is used for file transfer.
The Simple Mail Transfer Protocol (SMTP) is used for the transfer of mail messages and attachments.
Telnet, a terminal emulation protocol, is used for logging on remotely to network hosts.

Layer Model:

TCP/IP Protocol Suite: Transport layer
The Transport layer is responsible for end to end delivery of data packets.
The protocols of the Transport layer are TCP and UDP.
It perform functions such as multiplexing, segmenting or splitting of data
Transport layer adds header information to the data and arrange the packets to be sent, in sequence.

It is also known as Host to Host Transport Layer.

Layer Model:
TCP/IP Protocol Suite: Network Layer
The Network layer perform basic functions such as addressing, packaging, and routing of data packets.
This layer holds the whole architecture together and helps the packet to travel independently to the destination.
The protocol used by network layer are IP, ARP, ICMP etc

It is also known as Internet Layer.
The protocols used at Network layer are:
The Internet Protocol (IP) is responsible for IP addressing, routing, and the fragmentation and reassembly of packets.
The Address Resolution Protocol (ARP) is responsible for the resolution of the IP address to the Network Interface layer address such as a MAC address.
The Internet Control Message Protocol (ICMP) is responsible reporting errors due to the unsuccessful delivery of IP packets.

Layer Model:
TCP/IP Protocol Suite: Data Link Layer
This layer perform functions such as :
Data Framing
Error Detection and Correction
means encapsulating data messages into frames that are sent over the network at the physical layer.
means adding MAC address with data message.
layer handles errors that occur at the lower levels of the network stack by using cyclic redundancy check (CRC) method.

Layer Model:
TCP/IP Protocol Suite: Physical Layer
Protocols are used to connect host to host and network to network.
This layer is responsible for sending and receiving TCP/IP packets on the network medium.
These include LAN technologies and WAN technologies.

It is also known as network interface layer and Network access Layer.

Layer Model

OSI layers

Layer Model:
OSI reference Model:
Created in late 1970’s to be used in networking.
It contain set of rules and regulations created by ISO and ITU as competitor of internet protocol.
OSI model helps the vendors to create interoperable network devices and softwares in the form of protocols. So that different vendor’s devices could work with each other.

It stands for Open system interconnection
(International Organisation for standardization)
ITU international telecommunication union
Why we need this OSI reference model?
To make communication possible between two devices which are manufactured by different vendors.
To implement rules and regulations which are used by every device in the network while communicating.
Basically,OSI model make communication flexible.

OSI Model Architecture

Layer Model:
OSI reference Model : Application Layer
It provide an interface between network applications and network protocols.
Network applications such as web browser, gmail, Dropbox etc
Network protocols such as http, ftp, smtp, pop3 etc which carry request to the application
Example: Gmail , chrome etc
It provide interface where user actually communicate with the devices.It is a software present in computers or devices

Layer Model:
OSI reference Model :Presentation Layer
This layer is responsible for data formatting.
It indicate the destination system about the type of file being sent to it by sender.
Example: .mp3 file, .jpg file, .txt file, .docx file etc

As it name suggest, it present data to the upper layer i.e. Application Layer

Layer Model:
OSI reference Model : Session Layer
It establish, maintain and terminate the connection between two devices.
It also check whether the destination system is available or not.
Session Layer perform synchronization.

Connection may be a simplex, half duplex or full duplex.

Layer Model:
OSI reference Model : Transport Layer
Transport layer function is to support end to end delivery of packets in network.
It perform functions such as
Segmentation of message into packets,
Adding sequence number,
Assigning transmission protocol such as TCP or UDP ,
Assigning logical port number such as http=80,ftp=21,smtp=25

Layer Model:
OSI reference Model : Network Layer
The main function of network layer is to do wrapping of segments to form packets.
Layer add source and destination IP address or Logical address with packets.
At this layer, Router is used to route the packets in the network.

Layer Model:
OSI reference Model : Data Link Layer
The main function of data link layer is wrapping of packets to form frame.
Wrapping is done by adding MAC address or Physical address to the packets.
LLC(Logical Link Control)- perform error checksum/correction,frame synchronization and also check network layer protocol i.e IPv4 or IPv6 .
MAC(Media Access Control)- This layer is used to add source and destination MAC address

At this Layer,Switch is used to forward packet in the network.

Layer Model:

OSI reference Model : Physical Layer
This layer provide the physical connectivity between the devices via transmission medium such as coaxial wire, optical fiber and wireless.
It is used to send the digital bits through transmission medium.
It handle the bit flow transmission.
NIC (network interface card) or Hub are used at this Layer.

Client and Server

Connectionless and connection oriented service
Client Server Model
Client and Server software
How client identify server?
Concurrent server
P2P network
Difference between P2P network and Client/Server network

Client Server Model:
Connectionless Service:
Packets are sent without establishing a connection
Packets are numbered at sender and reassemble at destination
Packets may be delayed, lost or arrive out of sequence
Example UDP
Connection Oriented Service:
First Connections is established between sender and receiver.
After data transfer , connection is terminated.
Packets are send in sequence
Example : TCP and SCTP
Stream Control Transmission Protocol

Client Server Model:
Client Classification:
Client start after the server in communication.
It know to which server it want to contact
It initiates the contact whenever there is need of communication

Server Classification:
Server start first during communication
It does know which clients is going to contact it
Server wait passively for the client contact

Client Server Model:
Client Classification:
It communicates with the server by sending and receiving data.
Client may terminate after interacting with a server.
Server Classification:
It communicate with the clients by sending and receiving data.
It stay online after servicing one client and wait for another.

Client Server Model:
Client Software:
Consists of an various application program.
It becomes a client temporarily whenever remote access is needed.
It runs locally on a user’s computer or device .
It actively initiates contact with a server.
Can access various services, but can contact one remote server at a time.
Does not require powerful hardware.

Client Server Model:

Server Software:
Server consists of a special-purpose, privileged program.
It is invoked automatically when a system boots, and continues to execute through many sessions.
It runs on a dedicated computer system.
It waits for contact from different remote clients.
It require powerful hardware and operating system.
It can accept connections from many clients at the same time, but (usually) only offers one service

Client Server Model:
Client Server Characteristics:
Client runs on a standard computer.
Server runs in a server class computer.
Information can flow in either or both directions between a client and server.
Client sends a request to the server for communication and server send the response for the request.

Client Server Model:

How client identify a server?
The Internet protocols divide identification into two pieces:
An identifier that specifies the computer on which a server runs
An identifier that specifies a particular service on the computer
Identifying A Computer: Each computer in the Internet is assigned a unique identifier known as an Internet Protocol address (IP address)†. When it contacts a server, a client specify the server’s IP address. To make server identification easy for humans, each computer is also assigned a name, and the Domain Name System which is used to translate a name into an address. Thus, a user specifies a name such as rather than an integer address.
Identifying A Service: Each service available in the Internet is assigned a unique 16-bit identifier known as a protocol port number (often abbreviated port number). For example, email is assigned port number 25, and the World Wide Web is assigned port number 80.

Client Server Model:

Concurrent Server:
A concurrent server uses threads of execution to handle requests from multiple clients at the same time.
It means a client does not have to wait for a previous client to finish.
Concurrent server code is divided into two pieces:
Main program (thread)
The main program accepts contact from a client, and creates a thread of control to handle the client. Each thread of control interacts with a single client, and runs the handler code.
After handling one client, the thread terminates. Meanwhile, the main thread keeps the server alive — after creating a thread to handle a request, the main thread waits for another request to arrive.

Client Server Model:

P2P network:
In a P2P network, the "peers" are computer systems which are connected to each other via the Internet.
The files are shared directly between systems on the network without using central server.
Common P2P software programs are Kazaa, Limewire, BearShare, Morpheus, and Acquisition.
In other words, each computer on a P2P network becomes a file server as well as a client
The only requirements for a computer to join a peer-to-peer network are an Internet connection and P2P software.

Client Server Model:
Client/Server network:
It is designed for the end users called clients, to access resources from a central computer called server.
In this network, server is a centralized and a powerful computer.
Server’s sole purpose is to serve its clients.
Peer to peer network:
Peer to peer network is created by connecting two or more computers and they share their resources with each other in the network.
Each computer will act as server and client.
This network is less expensive as compared to client/server network.
C/S :such as files, songs, video collections or some other services

Client Server Model:

Client Server Model:

Socket API: is a interface of an application which is use to specify internet communication.
An application creates a socket for Internet communication, the operating system returns a small integer descriptor that identifies the socket.
In many operating systems, socket descriptors are integrated with other I / O descriptors for read and write operations.
Application Programming Interface
the API is available for many operating systems, such as Microsoft’s Windows systems, Apple’s OS-X, Android, and various UNIX systems, in- cluding Linux.
The application then passes the descriptor as an argument when it calls functions to perform an operation on the socket

Part 1

Application Layer Protocol
Web Protocol
Electronic mails

Internet Applications:
Application Layer Protocol:
A programmer create applications that communicate over a network by defining,
The syntax and semantics of messages
Who will initiate the communication client or server
Actions to be taken if an error arises
How the two sides know when to terminate communication

Internet Applications:
Application Layer Protocol:
Data Representation: Syntax of data items that are exchanged, specific from used during transfer, translation of integers, characters and files sent between computers
Data Transfer: Interaction between clients and server, message syntax and semantics, valid and invalid exchange, error handling and termination of interaction
Two aspects of interaction

Internet Applications:
WWW Protocol:
HTML - used to specify the contents and layout of a web page.
URL - specifies the format and meaning of web page identifiers. For example : protocol:// computer_name:port/ document_name? parameters
HTTP - specifies how a browser interacts with a web server to transfer data
XML - is a markup language that defines a set of rules for encoding documents
HTTP - Hypertext markup language
URL - Uniform resource locator
HTTP - Hypertext transfer protocol
XML Extensible markup language

HTML use a textual representation to describe web pages that contain multimedia. It provide markup specifications it also permit a hyperlink to be embedded in an arbitrary object.

URL :where protocol is the name of the protocol used to access the document, computer_name is the domain name of the computer on which the document resides, :port is an optional protocol port number at which the server is listening, document_name is the optional name of the document on the specified computer, and ?parameters is optional parameters for the page.

HTTP : use textual control messages, transfer binary data files, Can download or upload data, incorporates caching

XML : in a format that is both human-readable and machine-readable.

Internet Applications:
WWW Protocol:
Caching : Browser reduce download times significantly by saving a copy of each image in a cache on the user’s disk and using the cached copy.
The most of the sites consist of large images that use GIF or JPEG standards.
Such images contain backgrounds that do not change frequently.

Browsing: Much of the content at a given site consists of large images that use the Graphics Image Format (GIF) or Joint Photographic Experts Group (JPEG) standards. Such images often contain backgrounds or banners that do not change frequently.

Internet Applications:
WWW Protocol:
Transfer different type of File Contents
Bidirectional Transfer
Authentication And Ownership
Ability To Browse Folder
Exchange of Textual Control Messages between Client and Server
Accommodates Heterogeneity
FTP can transfer any type of data, including documents, images, music, or stored video.
FTP can be used to download files (transfer from server to client) or upload files (transfer from client to the server)
FTP allows each file to have ownership and access restrictions, and honors the restrictions.
FTP allows a client to obtain the contents of a directory (i.e., a folder).
Like many other Internet application services, the control messages exchanged between an FTP client and server are sent as ASCII text.
FTP hides the details of individual computer operating systems, and can transfer a copy of a file between an arbitrary pair of computers.

Internet Applications:

It is a method of exchanging messages and attachments over the internet. This is a free service which is offered by ISP.
It provide a quick way for people to communicate with one another.
Email servers accept, forward, deliver and store messages.
Web based services providing access to email are Google’s Gmail, Microsoft Windows live Outlook, Yahoo! Mail
E-Mail or Electronic Mail play a major part in internet revolution.

Internet Applications:

E-Mail: Protocols used by E-mail program are: SMTP,POP3 and IMAP4
Simple Message Transfer Protocol (SMTP): SMTP protocol is used by a client to send mail .It use TCP/IP port 25.
Post Office Protocol Version 3 (POP3): POP3 protocol is used to receive email from SMTP server. It use TCP/IP port 110.
Internet Message Access protocol version 4 (IMAP4): it is used to retrieve an email from email server. It use TCP/IP port 143. It also support some extra features.
POP3 : This protocol is not used now.
IMAP4 is an alternative to POP3.

Internet Applications:
Email :
Two email representations have been standardized:
RFC2822 Mail Message Format
Multi-purpose Internet Mail Extensions (MIME)
RFC 2822: define by IETF standards document Request For Comments 2822. The format is straightforward: a mail message is represented as a text file and consists of a header section, a blank line, and a body.

MIME : The MIME standard inserts extra header lines to allow non-text attachments to be sent within an email message. An attachment is encoded as printable letters, and a separator line appears before each attachment.

Part 2

DNS Server
DNS Terms
How DNS Server work?
DNS Security Extension

Internet Application:
Domain Name System (DNS) is a powerful, extensible and flexible system use for resolving name over an entire internet.
DNS use TCP port 53 and UDP port 53.
This technology make easier for the people to remember the words rather than numbers.
For example, As we want to open a web page, we type instead of typing its ip address as http://2001:4860:4860::8844

Domain Name System is a name resolution protocol.
Need of DNS is more in IPV6

Internet Application:
DNS Server:
DNS server is a collection of computers that want to join domain name system.
They work as a team and collectively known as DNS root servers.
The internet name of this computer team is “.” (“dot”).
DNS servers are organized in a hierarchical form.
DNS root servers are the top level domain servers

which include top level domain name such as com, org, net, edu and gov etc.
It includes a complete database of internet domain names and their corresponding IP addresses.
Low level DNS servers are owned by businesses and Internet service Provider (ISP).

Internet Application:
DNS Terms:
Domain Namespace:
The naming system on which DNS is based is a hierarchical and imaginary tree structure called the domain namespace.
It includes all the possible names that could be used within a single system.
Each node in the DNS tree represent a DNS name.

Internet Application:
Domain namespace
Hierarchy diagram:
TLD are controlled by ICANN Internet Corporation for Assigned Names and Numbers (ICANN) Some TLDs are generic, which means they are generally available. Other TLDs are restricted to specific groups or government agencies.
Example org for organisation, biz for business, coop for cooperative association, mil - US military travel- travel and tourism

Internet Application:
DNS Terms:
Name Server:
It include:
DNS name server: is a computer that has DNS software installed on it. It is specifically designed for managing the different domain names.
Zone: is a container which holds the records of a single domain.
Record: is a line in a data contained by zone which maps an FQDN (fully qualified domain name) to an IP address.

A simple network has one DNS server for entire network.
A single domain name can use more than one DNS server. For example: is a busy domain so it need multiple DNS servers to support all the incoming DNS queries.

Internet Application:

DNS Terms:
Name Server:
IPv6 defined the two type of record type:
Quad A - AAAA type record : RFC 3596
A6 type record - RFC 2874

Designed to make renumbering of network and prefix changes easier for the network administrator
Other dns record types are NS records and PTR records they remain unchanged… only these two are supporting the changes for IPv6 network

Internet Application:
DNS Terms:
Name Resolution:
Name Resolution means successfully mapping a DNS domain or hostname to an IP address.
DNS can resolve name in three ways:
By Broadcasting (Small Network)
By locally consulting the locally stored hosts text file.
By contacting a DNS server.
Software to perform the translation is known as a name resolver (or simply resolver).

Internet Application:
How DNS server will work?
DNS act as the central part of internet, as it provide a way to match website name or computer name to their IP addresses.
A user type the name of website in search engine. Which generate a query and is send over the internet.
Let suppose the user query first goes to the recursive resolver (which is operated by its ISP)
The recursive resolver know where to send the query in the network.
Then recursive resolver talk with the root DNS server about the IP address of website.
Then root DNS server search for its particular top level domain(TLD) by analysing the domain name of website.
Query is send to the particular TLD. where TLD servers stores the address information for second level domains within TLD.
Then TLD server gives the IP address of particular DNS which knows about the IP address of website to the recursive resolver.
Then recursive resolver sends the query to the DNS. As DNS know about the IP address of full domain. It tells the IP address of the website.
Recursive resolver send IP address of website to user. Thus website appears.
Now user can browse the website and retrieve the content using IP address

DNS Security Extension:
DNS security extension (DNSSEC) is an authentication and authorization protocol to provide security to DNS server.
The DNSSEC is a suite of Internet Engineering Task Force (IETF) specifications.
DNSSEC is implemented through (Extension mechanism for DNS) EDNS

Security are added to protect DNS from unauthorized user.



Importance of Data Communication
Signal types
Converting Analog to Digital signal
Data Compression

Data Communication:
Data communication is a combination of ideas and approaches from:
Physics : draws ideas about electric current, light, radio waves and EM waves.
Mathematics : includes theories and various forms of analysis of data communication
Electrical Engineering : use technology developed by data communication.

Data Communication:

Data Communication:
Information Source: A source of information can be either analog or digital.
Source Encoder and Decoder: The digitized information is represented in digital form and transformed and converted to other form.
Encryptor and Decryptor: used to protect information and keep it confidential.
Channel Encoder and Decoder: Channel coding is used to detect and correct transmission errors.
IS : Important concepts include characteristics of signals, such as amplitude, frequency, and phase. Classification is either periodic (occurring regularly) or aperiodic (occurring irregularly).
Encryptor is used before transmission and decryptor upon reception.
It include methods to detect and limit errors, and practical techniques like parity checking, checksums, and cyclic redundancy codes that are employed in computer networks.

Data Communication:

Multiplexer and Demultiplexer: Multiplexing refers to the way information from multiple sources is combined for transmission across a shared medium.
Modulator and Demodulator: Modulation refers to the way EM wave are used to send information.
Physical Channel and Transmission: it includes transmission media and transmission modes.
known as modems that perform the modulation and demodulation. Concepts include both analog and digital modulation schemes, and devices
Important concepts include bandwidth, electrical noise and interference, and channel capacity, as well as transmission modes, such as serial and parallel.

Data Communication:

Signal Types:
Analog and Digital signal:
The analog signals contain information which is translated into electric pulses of varying amplitude.
In digital signals ,translation of information is into binary format where each bit is representative of two distinct amplitudes.

Data Communication:
Periodic and Aperiodic Signals:
A signals that repeats its pattern over a period is called periodic signal.
A signal which does not repeat itself after a specific interval of time is called aperiodic signal.

Data Communication:

Signal Types:
Sine Waves:
The four important characteristics of signals that relate to sine waves are:
Sine waves are fundamental to input processing because many natural phenomena produce a signal that corresponds to a sine wave as a function of time.

Data Communication:
Frequency: the number of oscillations per unit time (usually seconds)
Amplitude: the difference between the maximum and minimum signal heights
Phase: phase of the wave is defined as the distance between the first zero-crossing and the point in space defined as the origin
Wavelength: the length of a cycle as a signal propagates across a medium

Data Communication:

Signal Types:
Composite Signals:
A composite signal is a signal that is composed of other signals.
It is decomposed into set of simple sine waves.
A mathematical method discovered by Fourier allows a receiver to decompose a composite signal into constituent parts.

Data Communication:

Two methods are used to convert signal from analog to digital:
Pulse Code Modulation (PCM) : refers to a technique where the level of an analog signal is measured repeatedly at fixed time intervals and converted to digital form.
Delta Modulation : sends one quantization value followed by a string of values that give the difference between the previous value and the current value.
It consist of steps such as sampling, quantizing and encoding.
PCM is a encoder decoder
DM is Modulator

Data Communication:

Compressing signals:
Data compression is a technique that reduces the number of bits required to represent data.
Two methods are used :
Lossy — Some information is lost during compression.
Lossless — All information is retained during compression.
reducing the number of bits used to represent data reduces the time required for transmission.
Lossy compression is generally used with data that a human consumes, such as an image, a segment of video, or an audio file. compression schemes such as JPEG (used for images) or MPEG-3 (abbreviated MP3 and used for audio recordings) employ lossy compression.
Lossless compression preserves the original data without any change. Thus, loss- less compression can be used for documents or in any situation where data must be preserved exactly.

Media -
Electrical Energy

Guided and Unguided Medium
Forms of energy
Twisted Pair Cable
Coaxial Cable

Transmission Media:
Guided Medium :
In guided medium, the signals are confined within the wire and do not propagate outside of the wire.
E.g. Copper Unshielded Twisted Pair (UTP), Copper Shielded Twisted Pair (STP), Copper Co-axial cables, Fiber Optic Cables.
Electrical and optical signals passed through a solid medium like cable.
The signals is guided by the size, shape and length of the wire.

Transmission Media:

Unguided Medium:
In this, information is transmitted by sending EM signals through free space.
The signals are not guided in any specific direction or inside any specific medium.
Antennas are used that are of different shape and sizes.
Example: Wifi, Wimax and 4G

Transmission Media:

Form of energy:
Energy type:
Electrical Energy Light EnergyEM Waves
Twisted PairOptical FiberTerrestrial radio
Coaxial CableInfraredSatellite

Transmission Media:

Electrical Energy:
The forms of wiring that help reduce interference from electrical noise are:
Twisted Pair Cable
Unshielded Twisted Pair (UTP)
Shielded Twisted Pair (STP)
Coaxial Cable

Transmission Media:

Electrical Energy:
Twisted Pair Cable:
Twisted pair cables consist of two conductors, each with its own plastic insulation and they are twisted together.
One wire is used to send signals to the destination and second wire is used as ground reference.
They are twisted together to reduce crosstalk and EMI from external source.

EMI : Electromagnetic Interference
At the receiver side there will be no signal difference because unwanted signals are cancelled out.
It is used to transmit analog and digital signals and frequency signals ranges from 100 Hz to 5MHz.
Types of Twisted Pair cables are UTP and STP.

Transmission Media:

Unshielded Twisted Pair:
These cables don’t have an outer protection.
These cables have covering jacket made of PVC or FEP plastics.
These Cables are less immune to external noise or interference.

Shielded Twisted Pair:
These cables has a metal foil which cover each pair of insulating conductor.
It have a outer layer cover made of PVC or FEP plastics.
More immune to external noise and interference due to presence of metallic shield.

Polyvinyl chloride and Fluorinated ethylene propylene
UTP: This cable is used in computer network as ethernet cables.
UTP cables are also known as CAT cable (Category Rating)
STP : This cable are used in factories with large electronics equipments.

Transmission Media:
Unshielded Twisted Pair Cable
Shielded Twisted Pair Cable

Transmission Media:

Variety of CAT cables:
CAT ratingFrequencyBandwidthUsed For
CAT 1<1 MHz-Voice only
CAT 24 MHz4 mbpsData
CAT 316 MHz16 mbpsData
CAT 420 MHz20 mbpsData
CAT 5100 MHz100 mbpsData
CAT 5e100 MHz1 gbpsData
CAT 6250 MHz10 gbpsData
CAT 6a500 MHz10 gbpsData

Transmission Media:

Electrical Energy:
Co axial Cables:
Coaxial cable or coax is a type of cable in which inner conductor is surrounded by plastic jacket with a braided shield over it.
Copper shield is covered by using PVC (Polyvinyl Chloride) or FEP (Fluoroethylene Propylene) plastic.
For a High Frequency electrical signals it provide an interference-free transmission path. Example: Thinnet,Thicknet,Television Cable

RG6 and RG59 are the coaxial cable grades used for home video devices such as TV.
RG59 used for short distance communication and RG6 is expensive cable used for long distance transmission.

Coaxial Cables
It include one physical channel that carries the signal and it is surrounded by another concentric physical channel, both running along the same axis. That’s why it known as “coaxial”.

Media -
Light energy

Light Energy
Optical Fiber
Infrared Transmission
Laser communication

Transmission Media:

Light Energy:
Three forms of media use light energy to carry information:
Optical fibers
Infrared transmission
Point-to-point lasers

Transmission Media:
Light Energy:
Optical Fiber :
Optical fiber is a cylindrical non-conducting waveguide that transmit the light along its axis.
It consist of core and cladding layer and refractive index of core is greater than cladding.
It transfer the light signal to a longer distance.
It follow the principle of total internal reflection (TIR) to transmit the light through glass medium.

Transmission Media:
Single mode Optical fiber:
This fiber has a small diameter of core and only one mode of light will travel through it.
The diameter of core is 9 microns and cladding is of 125 microns.
Launching of light in this fiber is difficult.
Multimode optical fiber:
This fiber can support multiple light rays to travel through it.
The diameter of core/ cladding is 50/125 and 62.5/125 microns.
Launching of light in this fiber is easy.
It is further of two types.
There are 2 types of optical fiber cable.
SMF It is used in long distance communication with high bandwidth links
MMF This fiber contain large side of core as compared to single mode optical fiber.

Transmission Media:
Single Mode Optical Fiber and Multimode Optical Fiber

Transmission Media:
Step Index Fiber:
In this fiber, the refractive index of the core is uniform.
But the interface of core and cladding the refractive index change abruptly.
It is used in short distance communication.

Graded Index optical fiber:
In this fiber, the refractive index of core is non-uniform.
The refractive index decreases gradually from the axis of the fibre to its surface.
It is also used for long distance transmission of signals.

SIF The size of core is large so it can support multiple modes.
The diameter of core/cladding is 200/380 microns
GIF Light rays propagate in the form of skew rays or helical rays.This fiber reduce the modal dispersion .

Transmission Media:
Step Index Multimode Fiber and Graded Index Multimode fiber

Transmission Media:

Light Energy:
How is light sent and received on a fiber?
The Light is sent and received by using devices:
Transmission: Light Emitting Diode (LED)
Injection Laser Diode (ILD)
Reception: Photosensitive cell

LEDs and photosensitive cells are used for short distances and slower bit rates with multimode fiber.
Single mode fiber, used over long distances with high bit rates and it use ILDs and photodiodes.

Transmission Media:
Light Energy:
Infrared Transmission:
Infrared communication technology mostly used indoors.
It is used when the path between sender and receiver is short and free from obstruction.
IrDA-SIR Slow-speed Infrared 0.115 Mbps
IrDA-MIR Medium-speed Infrared 1.150 Mbps
IrDA-FIR Fast-speed Infrared 4.000 Mbps
This signals can be reflect from a smooth, hard surface, and an opaque object.
as thin as a sheet of paper can block the signal, as does moisture in the atmosphere.

Transmission Media:

Light Energy:
Point to Point Laser Communication:
Laser technology is used to create a point-to-point communications system.
As, Laser emits a narrow beam of light, the transmitter and receiver are aligned precisely such on the roof of a building.
Laser beams advantage is it is suitable for outdoors use, and can span greater distances than infrared.

Transmission Media:
Electromagnetic Communication:
EM waves are waves that are created as a result of vibrations between an electric field and a magnetic field.
These waves depend on the frequency.
Spectrum define the range of possible frequencies which is allocated by governments around the world
RF frequencies are spread approximately 3 KHz to 300 GHz.
These frequencies are used for radio and television broadcast as well as satellite and microwave communications.

They sets rules for how frequencies are allocated, and sets limits on the amount of power that communication equipment can emit at each frequency.
RF transmission has advantage over light that RF energy can traverse long distances and penetrate objects such as the walls of a building.

Transmission Media:
Electromagnetic Communication:
Classification Range
Low Frequency < 2 MHz
Medium Frequency 2 to 30 MHz
High Frequency > 30 MHz

Wave follows earth’s curvature, but can be blocked by unlevel terrain
Wave can reflect from layers of the atmosphere, especially the ionosphere
Wave travels in a direct line, and will be blocked by obstructions

Media -

Types of satellites
Selection of transmission medium
Performance factors

Transmission Media:
A satellite is an object in space that orbits or circles around a bigger object like earth.
Kepler’s Law govern the motion of an satellite or other objects
There are two kinds of satellites:
Natural Satellite - such as the moon orbiting the Earth.
Artificial Satellite - such as the International Space Station orbiting the Earth.

Transmission Media:
Types of artificial satellite based on distance from earth:
Low Earth Orbit (LEO)
Medium Earth Orbit (MEO)
Geostationary Earth Orbit (GEO)
Advantage is that it provide information with low delay, Disadvantage does not with match rotation of earth so Tracking is difficult because satellites move rapidly
An elliptical orbit used to provide communication at the North and South Poles
Advantage is that the satellite remains at a fixed position with respect to a location on the earth’s surface, whereas disadvantage is that satellite is far away
HEO: This orbit is made for satellites that do not revolve in circular orbits, only a very few satellite are operating in this orbit.

Transmission Media:
Low Earth Orbit (LEO) :
Low earth orbits (LEO) are satellite systems used in telecommunication.
It orbit between 400 and 1,000 miles above the earth's surface.
They are used for data communication such as email, video conferencing and paging.
They move at extremely high speeds and are not fixed in space in relation to the earth.

Transmission Media:
Medium Earth Orbit (MEO) :
A medium earth orbit satellite orbit within the range from a few hundred miles to a few thousand miles above the earth's surface.
These satellites orbit higher than low earth orbit (LEO) satellites, but lower than geostationary satellites.
The orbital periods of MEO satellites range from about two to 12 hours.
Some MEO satellites orbit in near perfect circles, and therefore have constant altitude and travel at a constant speed. Other MEO satellites revolve in elongated orbits.

Transmission Media:
Geostationary Earth Orbit (GEO) :
It is an earth-orbiting satellite
It is placed at an altitude of approximately 35,800 kilometers (22,300 miles) directly over the equator.
It revolves in the same direction the earth rotates (west to east).
It named as geostationary because satellite appears nearly stationary in the sky as seen by a ground-based observer.
Some MEO satellites orbit in near perfect circles, and therefore have constant altitude and travel at a constant speed. Other MEO satellites revolve in elongated orbits.

Transmission Media:
Geostationary Earth Orbit (GEO) :
The three satellites are used to provide coverage to entire planet.
Each satellite is separated by 120 degrees of longitude
A geostationary satellite is accessed using a directional antenna, usually a small dish.
These antennas are aimed at the spot in the sky where the satellite appears to hover.
Some MEO satellites orbit in near perfect circles, and therefore have constant altitude and travel at a constant speed. Other MEO satellites revolve in elongated orbits.

Transmission Media:

Transmission medium are selected on the basis of:
Data rate
Signals quality
materials, installation, operation, and maintenance
number of bits per second that can be sent
time required for signal propagation or processing
attenuation and distortion
susceptibility to interference and electrical noise
susceptibility to eavesdropping

Transmission Media:

Transmission medium performance measurement:
Propagation Delay: the time required for a signal to traverse the medium
Channel Capacity: the maximum data rate that the medium can carry


Transmission error
Channel Coding Technique
Block Error Codes
Convolutional Error Codes
16 bit Checksum
Cyclic Redundancy Codes (CRC)

Channel Coding:
The error caused in transmission are:
Interference : means the disruption of signal as it travel along the source and destination. For example : EMI , CCI , ACI etc
Attenuation : refers to the reduction of signal strength as it travel to a long distance.
Distortion : means the alternation of original signal or waveform . For example : Dispersion of pulse signal

EMI : electromagnetic interference
CCI : Co channel interference
ACI : Adjacent channel interference
Although transmission errors are unavoidable, error detection mechanisms add overhead. Therefore, a designer must choose exactly which error detection and compensation mechanisms will be used.

Channel Coding:

Effects of these transmission error on signals:
Single Bit Error
Burst Error
A single bit in a block of bits is changed and all other bits in the block are unchanged (often results from very short-duration interference)
Multiple bits in a block of bits are changed (often results from longer-duration interference)
(Ambiguity) The signal that arrives at a receiver is ambiguous and does not clearly correspond to either a logical 1 or a logical 0 (can result from distortion or interference)

Channel Coding:

Channel Coding Technique:
Forward Error Correction (FEC) mechanisms : is a digital signal processing technique used to enhance data reliability.
Block Error Codes
Convolutional Error Codes
Automatic Repeat request (ARQ) mechanisms : is a protocol for error control in data transmission. This is used to enhance data integrity.
This technique is used by introducing redundant data, called error correcting code, so before data transmission or storage. FEC provides the receiver with the ability to correct errors without a reverse channel to request the retransmission of data.
When the receiver detects an error in a packet, it automatically requests the transmitter to resend the packet. This process is repeated until the packet is error free. ARQ is sometimes used with Global System for Mobile (GSM) communication to guarantee data integrity.

Channel Coding:
Forward Error Correction technique:
Block Error Code :
A block code divides the data which is to sent, into a set of blocks.
In this technique, the code is attach having extra information known as redundancy code.
These codes are memoryless.
Examples of block codes are Reed–Solomon codes, Hamming codes, Hadamard codes, Expander codes, Golay codes, and Reed–Muller codes.
in the sense that the encoding mechanism does not carry state information from one block of data to the next.

Channel Coding:
Forward Error Correction technique:
Convolutional Error Code :
A convolutional code treats the data as a series of bits.
It computes a code over a continuous series.
Convolutional codes are said to be codes with memory.

Thus, the code computed for a set of bits depends on the current input and some of the previous bits in the stream.
When implemented these codes into software, it is seen that convolutional error codes require more computation than block error codes. so, convolutional codes often have a higher probability of detecting problems.

Channel Coding:
16 Bit Checksum:
16 bit checksum channel coding scheme plays a key role in the Internet.
This code consists of a 16-bit 1’s complement checksum.
The Internet checksum treats data in a message as a series of 16-bit integers.
It is known as the Internet checksum,
The Internet checksum does not impose a fixed size on a dataword. Instead, the algorithm allows a message to be arbitrarily long, and computes a checksum over the entire message.

Channel Coding:
Cyclic Redundancy Codes (CRC):
It is used in high-speed data networks.
The term cyclic is derived from a property of the codewords.
The key features of CRC are:
Arbitrary Length Message
Excellent Error detection
Fast Hardware Implementation

a circular shift of the bits of any codeword produces another codeword.