Welcome to Computer Network

8/8/2019 Welcome to Computer Network

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Understanding Computer Network:

What is computer network?

A network is group of computers interconnected with each other to exchange information or resource.

A computer network is collection of interconnected autonomous computers interconnected in a single

technology.

Two computers are said to interconnected with each other if they share some information between

them.

What are the advantages of having computer network?

1.Increased communication capabilities.

2.File sharing: Network offer quick and easy way to share files directly at a rapid speed thus saving time

and integrity of files.

3.Resouce sharing : All computers in a network can share resources like printer, scanner, modem, fax

machines, hard disk.

4. Security: Specific directories can be password protected to limit access to authorized users. Also, files

and programs on a network can be designated as "copy inhibit" so you dont have to worry about the

illegal copying of programs.

5. It is also possible to share data files across the network by creating a share on the hard drive and

allowing other people access to that information.

6.Increases the productivity.

7. You can connect all the computers which are connected through a network to the internet by using a

single line. So it means that you can save the connection cost for each computer but you internet

connection must be fast.

8. Internet connection sharing - Using a home network, multiple family members can access the

Internet simultaneously without having to pay an ISP for multiple accounts. You will notice the Internet

connection slows down when several people share it, but broadband Internet can handle the extra load

with little trouble. Sharing dial-up Internet connections works, too.

or

Connect your entire office to the Internet through one line.


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What are the disadvantages of computer network?

1.Network faults can cause loss of data.

2.Network faults could lead to loss of resources.

3.Systems open to hackers.

4.Could become inefficient.

5.Could degrade to performance.

6.Resources could be located too far from users.

7.As a work group user cannot Login from other work group machine within LAN network.

8.User also cannot login from any remote machine from WAN environment.

What are the different types of computer networks?

PAN( personal area network) : Network that is meant for one person

Eg: A wireless network connecting a computer with its mouse, keyboard, printer is PAN. Covers 1m

distance only.

LAN (local area network) : LANs are privately owned network which covers a room, building or a

campus ( 10m, 100m, 1km) of distance.

LANs are widely used in offices, companies, industries.

Characteristics:

* Lans are restricted in size

*Lans uses transmission media as cable , to which all the machine are attached.

*Lans basically uses Bus and Ring Topologies( network structure) to broadcast.

Traditional Lans runs at the speed of 100Mbps and newer Lans runs at the speed of 10Gbps.

Lans are un-switched ( they dont have routers).

MAN (metropoliterian area network): MAN covers city ( about 10Km) in distance.

The best example of Man is the CABLE TV NETWORK available .

Cable TV is not the only MAN ,development in high speed wireless internet access resulted in MAN.


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MANs are also un-switched ( i.e dont have routers)

WAN (wide area network): A wide area network covers a large geographical areas like country or a

continent ( about 100Km, 1000Km, 10,000Km)in distance.

In WAN, subnet consist of two components Transmission lines like copper cable, optical fiber ( move bits

between machines) and Switching elements or routers (specialized computers or devices that connects

3 or more transmission lines, when date arrives to incoming line, router choose an outgoing line on

which to forward them.

Hosts ( users computers) are connected to subnet.

Subnet is owned and operated by telephone company or isp.

The subnet is collection of communication lines and routers ( but not hosts).

The job of subnet is to carry message from host to host .

In most WANs , the network contains numerous transmission lines , each one connecting pair of router.

If two routers do not share a transmission line , wish to communicate they must do this indirectly via

other router .

When a packet is sent from one router to another via one or more intermediate routers, the packet is

received at each intermediate router in its entirety , stored until the required output is free, and then

forwarded.

This principle is known as store and forward or packet switched subnet.

What are the types of transmission media ?

Signals are usually transmitted over some transmission media that are broadly classified in to two

categories.

Guided Media:

These are those that provide a conduit from one device to another that include twisted-pair,

coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is

contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that

accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic

cable that accepts and transports signals in the form of light.

Unguided Media:

This is the wireless media that transport electromagnetic waves without using a physical

conductor. Signals are broadcast either through air. This is done through radio communication,

satellite communication and cellular telephony.


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Cable (Conducted media) -

y Co-axial

y Twisted Pair (UTP)

y Shield Twisted Pair (STP)

y Fiber optics

Radiated

y Infrared

y Microwave

y Radio wave

y Satellite

What are the different types of network hardware?

1. NIC ( network interface card)

2. Repeater

3. Switch

4. Router

5. Hub

6. Modem

7. Server

8. Gateways

9. Bridges

10.firewall

History of computer network

In 1969,a network called ARPANET (advanced research project agency) was created. For

transmission lines of 56kb dedicated line.

In 1970, DECNET (digital electronic corporation network) was created . For proper trait design.

In 1977-83, ETHERNET was created . Network capacity10Mhz. Support token ring topology.

In 1981, a network called TCP/IP (transmission control protocol/internet protocol) was created.To support LAN and WAN. Which lead to the beginning of INTERNET.

In 1980s , GIGA BYTE network was created. To support applications such as FTP, SMTP, HTTP,

POP3, IMAP4.


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NIC (network interface card)

Also known as Lan card ,Ethernet card, Network/Ethernet adaptor.

It is an interface between computer and network cables.

Functions of LAN card are,

*Data transfer

*Buffering data construction

*Medium access control

*Encoding and decoding

*Data transmission and reception

Lan cards are full duplex ( they can send and receive data )

Lan card can have UTP, BNC, AUI ports.

Lan card puts packet on the cable.

It contains MAC address.

What is MAC address?

MAC (media access control ) 48-bit number (6-byte).Unique to each and every Lan card , represented inhexadecimal notation.

This address is used for communication at low level.

This address comes from manufacturer.

Securities are based on MAC address.

What is an IP?

IP (Internet protocol) is a method or protocol by which data is sent from one computer to another

computer on the internet.

Each computer on the internet has at least one IP address that uniquely identifies it from all other

computer on the internet.

When you send or receive data (for example , an e-mail or web page), the message gets divided into

little chunks called packets.


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Each of these packets contains both senders internet address (IP address) and the receivers address.

Any packet is sent first to gateway computer that understands a small part of internet.

The gateway computer reads the destination address and forwards the packet to an adjacent gateway

that in turn read the destination address and so forth across the internet until one gateway recognizes

the packet as belonging to computer within its immediate neighborhood or domain.

The gateway then forwards the packet directly to the computer whose address is specified.

Because message is divided into number of packets, each packet can, if necessary , be sent by a different

route across the internet.

Packets can arrive in the different order they were sent in.

The internet protocol just delivers them. It is up to other protocol, the TCP/IP to put back in the right

order.

What is IP address?

An IP address is an address with which a computer is identified on a network (internet).

An IP address is a logical address of the network adaptor.

An IP address is a 32-bit number which has two parts network number and host number.

00001010000001110000010100000001

Computer wont have problem in understanding this number but we as human cant deal with binary.

An organization named IANA (internationally assigned numbering authority) as divided this 32-bit

number into 4-octat and has given the range from 0-255

00001010- 00000111- 00000101- 00000001

An IP address in represented in decimal notation form like,

192.168.1.1

Based on the range from 0-255 IANA has divided this 32-bit number into three classes,

Class A from 0-126

Class B from 128-191

Class C from 192-223

*127 is loopback address


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*224-255 is for research and development purpose.

To manage and maintain network again IANA has divided each class of IP address into 2 parts,

*Network portion (N/P) represented by 1s

*Host portion (H/P)- by 0s

IANA has assigned class A with single octet (8-bits) for network portion and three octet (24-bits) for host

portion.

IANA has assigned class B with two octet (16-bits) for network portion and two octets (16-bits) for host

portion.

IANA has assigned class C with three octet (24-bits) for network portion and single octet (8-bits) for host

portion.

What is HUB?

A HUB is a device which connects various machines in a network.

Its major function is to replicate data it receives from one device attached to it.

Hub is "Signal Splitter"

Operates in "Physical Layer"

Collisions will occur in hub and it listen for collision domains.

Hub is Half-duplex(can receive or forward only)

Also known as Concentrator

Types,


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Passive (splitter)

Active (signal boosting)

Intelligent (manageable)

What is Router?

A router is a device or a specialized computer which takes data

packets from incoming lines, and decides outgoing lines on which to forward them.

A router is responsible for routing the data packets towards their destination.

A router is a device, which enables communication between two different networks

or enables communication between two different series/classes of network.

A router is a internetworking device.

A router routes the packet from one logical network to other logical network.

The main job or function of router is to calculate the best path/route for the packet

to reach to its destination. Or

The main role of router is to determine the best path towards destination.

It determines where the data should go on the physical network.

It deals with, finding the way to the destination.

Types of Routers:

There are two types of routers: Fixed router and Modular router

Fixed router:

1. Parts in the router are inbuilt where modification to the interface is not possible.

2. Access layer router is the example of fixed router except 1600 and 1700 series.


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Modular Router:

1. Parts to the router can be added and removed i.e. modification to the interface is

possible.

2. Distribution and core layer router are the examples of modular router.

Cisco Routers are divided into 3 categories or layers:

1. Access Layer Router

2. Distribution Layer Router

3. Core Layer Router

Access Layer routers are used by small organizations. Also known as desktop or

company layer routers. Router that are mostly used here are, router series 800,

1000, 1600, 1700, 2500.

Distribution Layer router are used by ISPs .Also known as IS layer routers. Router

series 2600, 3200, 3600, 3700.

Core layer router is used by global ISPs .Also known as backbone routers. Router

series 6400, 7200, 7300, 7400, 7500, 7600, 10000, 12000.

What is switch?

A switch is a device which connects various systems in a network.

Switch maintains MAC address table.

Packets are directly transferred to the destination without broadcasting.

Switch is considered as an intelligent device.


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In switch, each packet gets the same speed.

A switch is Full-duplex (can forward & receive simultaneously)

Packets are filtered by switches.

No concept of collision domain or No collision as it is full duplex.

Works in Data link layer layer 2 and in layer 3

There are two types of switches,

1. Manageable switch has console port, we can make configuration

2. Unmanagable switch has no console port.

Cisco divided switches in 3 layers:

1. Access layer switches: It works in layer 2 as it understands MAC address

only. It doesnt understand IP address. Switches series 1900 & 2900

2. Distribution layer and 3.Core layer switches: It works in layer 3 because it

understands MAC address as well as IP address. Switches series 7000 &

10000.

Distribution layer and core layer switches can access millions of packets per

second - whereas - Router can access 1 lakh packets per second.

What is repeater?

Repeater is a device used to extend a network.

Extends the range of a network.

Amplifies or regenerates the data signal, in order to extend network.

Doesnt amplify noise.


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A repeater amplifies and cleans up digital signals and forwards their destination.

What is firewall?

* System that establish access control policies among network.

* They can block information from entry.

* A combination of hardware and software that protects a network from attack by

hackers that could gain access through public network, including the internet.

What is Modem?

It is a device, which converts binary code (from the computer) to the analog signal needed for

transmitting messages over telephone lines.

It does modulation-demodulation

Or

A device used to convert digital signals into analog tones that can be transmitted over the

telephone network.

Types,

*Internal Modem

*External Modem

*Card Version


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What is Ethernet?

Originally developed by Xerox Corporation, that can link up to 1024 nodes in bus network.

A networking hardware, communication and cabling standard.

A high-speed standard using a base band (single channel) communication technique.

Ethernet Provides row data transfer rate of 10 Mbps.

Ethernet uses (CSMA/CD) to prevent network failures when two devices try to access thenetwork at the same time.

What is Gateway?

A system that bridges two systems. A computer connected with various computer, wants to transfer a packet, can transfer

directly to the router by giving router address as gateway address at IP address portion. Gateways are used to connect two dissimilar LAN. Gateways work in application layer of OSI model. A gateway is required to convert data packets from one protocol format to another before

forwarding it, as it connects two dissimilar networks. Gateway Protocols: Members of TCP/IP protocol suite that routers use to determine the best route for the data

packets.

What are the different types of topologies?

* Star topology * Bus topology * Ring topology * Token ring topology * Hybrid topology * Mesh topology


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Topology means Structure of computer network or Design of computer network.

Star topology:

In star topology all the systems are connected to a central device which may be hub or

switch. Advantage: If one computer cable is broken or damage then other computers will not be

affected i.e. Network is not affected.

Disadvantage: If central device (hub or switch) stops working then whole companynetwork is blocked (any system cant communicate with each other).

Bus Topology:

In bus topology all the systems are connected to a single cable/channel or backbone .Computers are connected with this cable using BNC connector or T connector. Atthe both ends of cable Terminators are connected.

Advantage: Cheap and Easy to implement. Disadvantage: If terminators are not connected or open then data will bounce back.

Ring Topology:

In ring topology each computer is connected to each other .ie every system isconnected to their next system in form of ring .

Advantage: Easy to install and easy to troubleshoot. Disadvantage: If one of the computer goes down or if one of the cable break between two

machines then whole the network is down.Data packets cant go further.

TokenRing Topology:

In token ring toplogy, all the systems are connected to a centraldevice MSAU multiple station access unit Hub.

Token ring is 802.5 standard. Developed by IBM Has a unique token passing access method. Contains an electronic signal which constantly rotates in MSAU hub. Here if one computer needs to send a packet to other then this packet from source

machine is taken or attached to token(electronic signal) and forwarded or takes to the

destination address machine. Disadvantage: If this central device (MSAU) stops working or fails then whole the

company network is down or all the systems connected cant communicate with eachother.


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What is firewall?* System that establish access control policies among network.

* They can block information from entry.

* A combination of hardware and software that protects a network from attack

by hackers that could gain access through public network, including the

internet.

What is Modem?

It is a device, which converts binary code (from the computer) to the analog

signal needed for transmitting messages over telephone lines.

It does modulation-demodulation

Or

A device used to convert digital signals into analog tones that can be

transmitted over the telephone network.

Types,

*Internal Modem

*External Modem

*Card Version

What is repeater?

Repeater is a device used to extend a network.

Extends the range of a network.

Amplifies or regenerates the data signal, in order to extend network. Doesnt amplify noise.

A repeater amplifies and cleans up digital signals and forwards their

destination.


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What is the architecture of networking?

1. Peer to Peer (Point to Point):

Here each node acts as client as well as server.

Hard disk, cd-rom, printer can be shared.Example: windows2000, 9x

Sharing of file between two nodes

Nobody is server here

Using desktop type of OS (XP) we can use peer to peer.

2. Client/ Server:

Best example, Internet.It can support more than one processor.

Server- giving services, file sharing server, printing server.

Example: a demo video showing on server can be shared to all the machines in anetwork.

UNIX, windows, Linux dominates.

Used in large environment.One or more machine as dedicated server.

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