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Welcome to my Welcome to my Lecture Lecture

ononData CommunicationData Communication

M. Mozammel Hoque ChowdhuryM. Mozammel Hoque Chowdhury

Associate ProfessorAssociate Professor

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Chapter 1

Introduction

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1-1 DATA COMMUNICATION1-1 DATA COMMUNICATION

Data communication is the exchange of data between two devices via some form of transmission medium such as a wire cable.---or---Data Communication is the process of transporting data using computer devices from one point to another.

Figure 1.1 Five components of data communication

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Data Transmission Modes (Ways)

The way of data transfer is called transmission mode.

● Simplex (Ex. Data transmission from computer to monitor)● Half Duplex (Ex. Data transmission through Walkie-talkie)● Full Duplex (Ex. Data transmission through

Telephone/cable)

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Communication Channel Communication channel is the link or path between sender and receiver.

Communication Channels are grouped into three basic categories: Narrowband Voice Band BroadbandNarrowband channels range in speed from 45 to 300 bps (bits per second). This channel is used mainly for telegraph line and low-speed terminals.Voice band channels can transmit data at speeds up to 9600 bps. It is so called because its major application is for ordinary telephone voice communication. Broadband/wideband channels are used when large volumes of data is to be transmitted at high speed. This system provides data transmission rate of 1 million bps or more. These channels are used for high speed computer-to-computer data communication.

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Channel Capacity/Bandwidth

Bandwidth defines the volume of signals that can be transmitted through a communication channel.

So, it defines how much data/information can be transmitted

in one second. It is usually measured in Hertz (Hz) - cycle per second.

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1-2 COMPUTER NETWORK1-2 COMPUTER NETWORK

► A computer network is a set of computers, printers, and/or other devices capable of sending and receiving data connected via communication links.

The computer or other devices are often referred as nodes.

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The Uses of a Computer Network Simultaneous access to data

Data files are shared Shared files stored on a server Software can be shared

Shared peripheral device Printers and faxes are common shares Reduces the cost per user Devices can be connected to the network Print servers control network printing

Personal communication Email

Instantaneous communication Conferencing

Tele conferencing Videoconferencing Audio-conferencing Data-conferencing

Voice over IP Phone communication over network wires

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An overview of Computer Network

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Network Types Local Area Network (LAN)

Designed in one office or building of up to a few of kilometers. An organization may have several LANS Share printers, faxes, computers and servers. Traditional LANs run at speeds of 10 – 100 Mbps, newer LANs

can operate at higher speeds, up to hundreds of Mbps

Wide Area Networks (WAN) Two or more LANs connected over a large geographic area Typically use public or leased lines

Phone lines Satellite

The Internet is an example of WAN.

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Network Types… Campus Area Networks (CAN)

A LAN in one large geographic area Resources related to the same organization Each department shares the LAN

Metropolitan Area Network (MAN) Large network that connects different

organizations Shares regional resources A network provider sells time

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How Networks Are Structured Server based network

Node is any network device Servers control what the node accesses Users gain access by logging in Server is the most important computer

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How Networks Are Structured Client/Server network

Nodes and servers share data roles Nodes are called clients Servers are used to control access Database software

Access to data controlled by server Server is the most important computer

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How Networks Are Structured Peer to peer networks (P2PN)

All nodes are equal Nodes access resources on other nodes Each node controls its own resources

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The History about Computer Network

1966 Terms, packets and packet switching, are coined out. A project was funded to create an experimental network.

1969 The project evolves into Advanced Research Projects Agency Network (ARPANET).The first four nodes of ARPANET were: – BBN (Bolt, Beranek and Newman), a consulting company– SRI (Stanford Research Institute)– The Univ. of California– The Univ. of Utah

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The History about Computer Network…1971 ARPANET has 15 sites, 23 hosts1972 FTP is outlined in 1972;

E-mail is created in 1972 by Ray Tomlinson of BBN; Telnet protocol is proposed in his year.

1974 Vinton Cerf, propose the Transmission Control Protocol (TCP) in the paper, “A Protocol for Packet Network Internetworking”, which introduce the term Internet.

1977 The first wireless gateway is connected to ARPANET, which transmits packet over radio waves.

1978 Vinton Cerf, launch the plan for Internet Protocol (IP), which is proposed as a routing function that is separated from TCP.

1982 TCP and IP are adopted as the main protocol suite for ARPANET

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The History about Computer Network…1983 ARPANET reaches 500 and becomes a truly civilian-

based network, which marks the arrival of Internet1988 The Internet grows to 60,000 hosts

Europe & North America are linked by fiber-optic cableInternet Worm, the 1st internet virus, impacts 10% of the internet computers

1993 > 2 million hosts, 17 countries in Africa, Asia, …, joined Internet

1999 > 16 million hosts, US law establishes domain names as property, US Internet backbone reach the speed at 2.5Gbps

2000 IPv6 is used for internet, The push to implement wireless communication is on.

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Network Topologies Topology

Logical layout of wires and equipment Several different types

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Network Topologies Bus topology

Also called linear bus One wire connects all

nodes Terminator ends the

wires Advantages

Easy to setup Small amount of wire

Disadvantages Slow Easy to crash

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Network Topologies Star topology

All nodes connect to a hub Packets sent to hub Hub sends packet to

destination Advantages

Easy to setup One cable can not crash

network Disadvantages

One hub crashing downs entire network

Uses lots of cable Most common topology

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Network Topologies Ring topology

Nodes connected in a circle Tokens used to transmit

data Nodes must wait for

token to send Advantages

Time to send data is known

No data collisions Disadvantages

Slow Lots of cable

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Network Topologies Mesh topology

All computers connected together

Internet is a mesh network

Advantage Data will always be

delivered Disadvantages

Lots of cable Hard to setup

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Tree Topology

Advantage:When one hub breaks only stations connected to the broken hub will be affected.

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Hybrid Topology

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Network Hardware Network linking devices

Connect nodes in the network Cable runs from node to device Crossover cable connects two

computers

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Network Hardware Hubs

Center of a star network All nodes receive transmitted packets Slow and insecure

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Network Hardware Switches

Replacement for hubs Only intended node receives

transmission Fast and secure

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Network Hardware Bridge

Connects two or more LANs together Packets sent to remote LAN cross

Other packets do not cross Segments the network on MAC

addresses

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Network Hardware Router

Connects two or more LANs together Packets sent to remote LAN cross Network is segmented by IP address Connect internal networks to the Internet Need configured before installation

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Bridge vs. Router

The purpose of both bridge and router is to connect two or more LANs of the same type.

Bridge forwards data from one network to all other networks connected to it with desired and no-desired networks.

On the other hand, router sends data to the desired machine on the desired network.

So, in case of bridge, network traffic jam occurs, but which is not applicable for router.

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Network Hardware Gateway

Connects two dissimilar networks Most gateways contained in other

devices

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Network Interface Cards

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Network Protocols

Language of the network Rules of communication Error resolution Defines collision and collision recovery Size of packet Naming rules for computers

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Network Protocols

TCP/IP Transmission Control Protocol/Internet Protocol Most popular protocol Machines assigned a name of 4 numbers

IP address 209.8.166.179 is the White House’s web site

Dynamic Host Configuration Protocol (DHCP) Simplifies assignment of IP addresses

Required for Internet access

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Why IPv6 IPv6 is a new version of IP (128 bits) IPv4 – the current IP is going to run out of address

Internet growing too fast, Also have some waste : half of B Class networks have

less 50 hosts. To provide more support to new requirements,

like Better support to real time services, such as video on

demand Support roaming without change IP Will be more security

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Other Network Protocols IPX/SPX

Internet Packet Exchange/Sequenced Packet Exchange

Older protocol Associated with Novell Netware Replaced by TCP/IP

NetBEUI Network BIOS Extended User Interface Used by Windows to name computers Transmission details handled by TCP/IP

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ISO’s OSI Reference Model ISO:

International Standards Organization A voluntary organization founded in 1946. Its members are the national standards

organizations like, ANSI(US), BSI (British), IEEE (Institute of Electrical and Electronics Engineers)

OSI Reference Model: Open System Interconnected Reference Model

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OSI Reference Model

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THE INTERNETTHE INTERNET

The Internet has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use.

• Internet is a worldwide system of interconnected computer networks, which is also called a network of networks interconnected through regional and national backbone connections.

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Internet related Terms WWW: The World Wide Web, commonly known as

the Web, is a system of interlinked hypertext documents accessed via the Internet.

With a web browser (e.g. Internet Explorer, Mozilla Firefox etc.), one can view web pages that may contain text, images, videos, and other multimedia and navigate between them by using hyperlinks.

E-mail: Electronic mail, is a method of exchanging digital messages.

Facebook: Facebook is a social utility that connects people with friends and others who work, study and live around them. People use Facebook to keep up with friends and others.

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Internet related Terms…● Intranet : An internal corporate or

government network that uses Internet tools, such as Web browsers, and Internet protocols.

Extranet: A network that uses the Internet to link multiple intranets.

DNS (Domain Name System) address Domain name: nub.edu Sub-domain: cse.nub.edu

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Terms Abbreviation WWW World Wide Web HTTP Hyper Text Transfer Protocol

ISP Internet Service Provider HML Hyper Text Markup Language URL Uniform Resource Locator FTP File Transfer Protocol IRC Internet Relay Chat DNS Domain Name System

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Role of MODEM in Data Communication

Modulation – the process of converting digital signals to analog signals Demodulation – the reverse process of modulation, i.e. converting

analog signals back to digital signals.

MODEM : comes from MOdulator (who performs Modulation) and DEModulator (who performs Demodulation)

MODEM performs digital modulation and demodulation.

Why Modulation is Necessary Modulation is a scheme under which the signal is first modified

to suitable form and mixed with the carrier for transmission. To transfer the message signal from one site another site over

a long distance without any interference and loss for that we are using modulation.

Modulation is important due to following basic reasons: Low frequency signals can't be transmitted for long distance.

That's why we are modulating the information signals.  Need of bandwidth: suppose many people are talking at the

same time, we just cant make out the difference who is talking what, so bandwidth is provided to each wave and it is done over high frequency to save the quality of signal.

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Why Modulation is Necessary…. Height of antenna: when we want to transmit electrical signal over

an antenna, through free space, it must be converted into electro-magnetic waves. Only electro-magnetic waves have the property to travel through space (vacuum) at the speed of light.

For better transmission the height of antenna should be quarter half of the wavelength of wave to be transmitted. so, frequency is increased (wavelength decreased) to make it practically possible.Now suppose we want to transmit, an electric signal having frequency 3 kHz (voice frequency) over an antenna. Then what happens:

It means that we need height of antenna equal to 100 km! This is practically impossible!

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