UNIT II
COMPUTER NETWORKS
● Evolution
of Networking: ARPANET, Internet, Interspace Different ways of sending
data across the network with reference to switching techniques (Circuit and Packet
switching).
● Data
Communication terminologies: Concept of Channel, Bandwidth (Hz, KHz, MHz)
and Data transfer rate (bps, Kbps, Mbps, Gbps, Tbps).
● Transmission
media: Twisted pair cable, coaxial cable, optical fiber, infrared, radio
link, microwave link and satellite link.
● Network
devices: Modem, RJ45 connector, Ethernet Card, Router, Switch, Gateway,
WiFi card.
● Network
Topologies and types: Bus, Star, Tree, PAN, LAN, WAN, MAN.
● Network
Protocol: TCP/IP, File Transfer Protocol (FTP), PPP, HTTP, SMTP, POP3,
Remote Login (Telnet) and Internet, Wireless / Mobile Communication protocol such
as GSM, GPRS and WLL.
● Mobile
Telecommunication Technologies: 1G, 2G, 3G, 4G and 5G; Mobile
processors;
Electronic mail protocols such as SMTP, POP3, Protocols for Chat and Video
Conferencing: VoIP, Wireless technologies such as Wi-Fi and WiMax

Network Security Concepts:
Threats and prevention from Viruses, Worms, Trojan horse, Spams Use of Cookies,
Protection using Firewall, https;
India IT Act, Cyber Law, Cyber Crimes, IPR issues, hacking.
● Introduction To Web services: WWW, Hyper Text Markup Language (HTML),
Extensible Markup Language (XML); Hyper Text Transfer Protocol (HTTP); Domain
Names; URL; Website, Web browser, Web Servers; Web Hosting, Web Scripting –
Client side (VB Script, Java Script, PHP) and Server side (ASP, JSP, PHP), Web 2.0
(for social networking)
● E-commerce
payment transactions using online banking, mobile banking, payment
apps and services.
● Evolution
of Networking: ARPANET, Internet, Interspace Different ways of sending
data across the network with reference to switching techniques (Circuit and Packet
switching).
NETWORK
A network is any collection of independent computers that communicate with one
another over a shared network medium. A computer network is a collection of two or
more computers linked together for the purpose of sharing information and resources.
Computers joined in a network, can share files and peripherals such as modems,
printers, backup drives, or CD-ROM drives. Each computer on the network is called a
node a network is a series of points or nodes interconnected by communication paths
(transmission media).A network can be small with two computers that share a printer
or as complex like, the Internet.
Example: in computer labs, one printer is connected to only one computer, serving to
the needs of all the computers in the lab. all your lab's computers and peripherals are
forming a network. They are interconnected with each other enabling you to send and
receive data from one computer to another. Hence it can be said that two computers
are interconnected if they are able to exchange information.
NEED FOR NETWORKING / ADVANTAGES OF NETWORKING:
1. Resource sharing - files and peripherals
a. Sharing of files and software
b. Sharing Peripherals
c. Sharing storage
2. Improving communication
3. Access to remote database
1. Resource sharing - files and peripherals
a) Sharing of files and software:
Users can share data files with each other in a network. E.g. an organization with
departments which are physically separated, can store their data in a central
computer. Backup of files can be maintained.
b) Sharing Peripherals :
All most all peripheral devices are quite expensive. Networks enable us to share such
resources and hence reduce the operational cost of any organization. For e.g. a
company with about fifty computers can share resources such as printers, scanners,
hard disks etc. Audio and video content can also be streamed to multiple devices.
c) Sharing storage :
Storage can be distributed and thus database load can be shared on the network.
On a network, one can access data from any machine. Hence this is cost effective. A
file can even have copies on two or three machines.
2. Improving communication:
Network provide a powerful, fast and reliable communication medium among the
users on the network. Physically separated people can access the same thing at same
time. With the help of internet communication is made easy eg, mails, sms, chats etc.
4. Access to remote database:
Any one can access a remote database. E.g. airline reservation system, database of
trains, hotels etc.
DISADVANTAGES OF NETWORKING:
1. Threat to data
A computer network may be used by unauthorized users to steal or corrupt the data.
One can generate a computer viruses or computer worms on the network. File
security has to be taken care of.
2. Difficult to set up
The systems on a network are more sophisticated and complex to run. Setting up a
network, is a difficult task and costly, hard to maintain. If systems are badly
managed services can become unusable.
ARPANET:
Advanced Research Project Agency NETwork – first network in 1969 - to connect
computers at different universities and U.S. defense.
In mid 80s, the National Science Foundation created a new high capacity network
called NSFnet which allowed only academic research on its network. So many private
companies built their own networks, which were later interconnected along with
ARPANET and NSFnet to form Internet - a network formed by linking two or more
networks.
INTERNET:
A network of networks spread across the globe, all of which are connected to each
other. Internet is a system of linked networks that are worldwide in scope and
allows all the computers to exchange information with each other through a common
set of rules for communication. These rules are called protocols and the internet uses
Transmission Control Protocol/Internet Protocol (TCP/IP). Programs such as web
browsers, File Transfer Protocol (FTP) clients, and email clients are some of the most
common ways through which the users work on the Internet.
INTERSPACE :
It is a client/server software program that allows multiple users to communicate
online with real time audio, video and text chat in dynamic 3D environments. It
provides the most advanced form of communication technology available today. It is a
vision of what internet will become tomorrow. The users will be able to communicate
in multiple ways and from multiple sources instantly.
REQUIREMENTS OF A NETWORK :
Every network includes:
 At least two computers - Server or Client workstation.
 Network Interface Cards (NIC)


A connection medium
Network Operating system software
NODE – each computer in a network is called a node / workstation.
SERVER - A computer that facilitates sharing of data, software and hardware
resources on the network is known as the server. A network can have more than one
server. Each server has a unique name by which it is identified by all the nodes on the
network.
Servers can be of two types:
a) Dedicated and
b) Non dedicated servers
a) Dedicated server :
One computer is reserved for server's job. It helps all nodes access data, software and
hardware resources. Since it does not double up as a workstation but only manages
the network, so it is known as a dedicated server and such type of networks are called
master- slave networks. These are generally used on big network installations.
b) Non-dedicated servers:
A workstation can double up as a server. These servers are known as non dedicated
servers. The small networks using such a server are known as Peer to Peer networks.
These are generally used in small networks.
NETWORK INTERFACE UNIT (NIU) - A network interface unit is a device that is
attached to each of the workstations and the server which helps to establish
communication between the server and workstations. Every node needs an NIC
to establish connection with the network. This is also known as Terminal Access Point
(TAP) or Network Interface card(NIC).The NIC manufacturer assigns a unique physical
address to each NIC card and this physical address is known as the MAC address.
SWITCHING TECHNIQUES :
Switching techniques are used to efficiently transmit data across the network. The
two types of switching techniques :
a) Circuit switching
b) Packet switching
a) Circuit Switching :
A dedicated route is established between the source and the destination and the
entire message is transferred through it. A dedicated and complete physical
connection is established between two nodes and through this dedicated
communication channel, the nodes may communicate. The circuit guarantees the full
bandwidth of the channel and remains connected for the duration of the
communication session. Even if no communication is taking place in a dedicated
circuit, that channel still remains unavailable to other users (idle channels).
e.g. early analogue telephone network. When a call is made from one telephone to
another, switches within the telephone exchange create a continuous wire circuit
between the two telephones, for as long as the call lasts.
Phases of Circuit Switch Connection

Circuit Establishment : In this phase, a dedicated circuit is established from
the source to the destination through a number of intermediate switching
centres. The sender and receiver transmits communication signals to request
and acknowledge establishment of circuits.

Data Transfer : Once the circuit has been established, data and voice are
transferred from the source to the destination. The dedicated connection
remains as long as the end parties communicate.

Circuit Disconnection : When data transfer is complete, the connection is
relinquished. The disconnection is initiated by any one of the user.
Disconnection involves removal of all intermediate links from the sender to the
receiver.
Packet Switching
Packet switching is a switching technique in which packets (discrete blocks of data of
fixed size and of any content, type or structure) are routed between nodes over data
links shared with other traffic. Each packets is of about 200 bytes (on average),
which are then sent out onto the network. Each packet contains a "header" with
information necessary for routing the packet from source to destination. Each packet
in a data stream is independent. The main advantage of packet-switching is that the
packets from many different sources can share a line, allowing for very efficient use
of the communication medium. With current technology, packets are generally
accepted onto the network on a first-come, first-served basis. If the network becomes
overloaded, packets are delayed or discarded ("dropped"). This method of data
transmission became the fundamental networking technology behind the internet and
most Local Area Networks method of data transmission became the fundamental
networking technology behind the internet an most Local Area Networks.
Packet Switching transmits data across digital networks by breaking it down into
blocks or packets for more efficient transfer using various network devices. Each time
one device sends a file to another, it breaks the file down into packets so that it can
determine the most efficient route for sending the data across the network at that time.
The network devices can then route the packets to the destination where the receiving
device reassembles them for use.
Packet switching is the transfer of small pieces of data across various networks. These
data chunks or “packets” allow for faster, more efficient data transfer.
Often, when a user sends a file across a network, it gets transferred in smaller data
packets, not in one piece. For example, a 3MB file will be divided into packets, each
with a packet header that includes the origin IP address, the destination IP address, the
number of packets in the entire data file, and the sequence number.
DIFFERENCE BETWEEN CIRCUIT & PACKET SWITCHING:
CIRCUIT SWITCHING
1.Guaranteed capacity – reservers the
entire bandwidth in advance
2.Capacity is wasted if data is bursty
3.Path is established before sending data
between source and destination
4.All data in a single flow follow one path
5.No reordering, no packet drops
6.Always have a constant delay
7.Bandwidth wastage
PACKET SWITCHING
1.No guarantees
2.More efficient
3.Data is send immediately
4.Different packets may follow different
paths
5.Packets may be reordered or dropped
6.Delay time varies
7.No bandwidth wastage
QUESTIONS:
1. …………… is a network of physical objects embedded with electronics, software, sensors
and network connectivity.
internet
2. Name the first network
ARPANET
3. Expand ARPANET, NSFnet, TCP/IP
4. What do you meant by a protocol? Explain the protocol used by internet.
5. ……………….. is a client/server software program that allows multiple users to
communicate with real time systems
interspace
6. Computers that are attached to a network is called as ………………. Node/workstation
7. A computer that facilitates the sharing of resources on the network is termed as a
…………..
server
8. What are servers? What are the different type of servers?
9. Differentiate between the two types of servers
10. What do you meant by a peer-to-peer network?
11. What do you meant by a master/slave network?
12. A ………………… is an interpreter that helps to establish communication between the
server and workstation
13. ………….. refers to the physical address assigned by NIC manufacturer.
14. Define a network. What is its need?
15. Write two advantages and disadvantages of networks.
16. What is MAC address
17. Define : i) node
ii) server
iii) NIU
iv) Dedicated server
18. What do you meant by switching technique
19. Differentiate between circuit switching and packet switching
20. What do you meant by idle channels?
21. What are dropped packets?
● Data
Communication terminologies: Concept of Channel, Bandwidth (Hz, KHz, MHz)
and Data transfer rate (bps, Kbps, Mbps, Gbps, Tbps).
CHANNEL:
A communication channel is a medium that is used in the transmission of a message
from one point to another. It is a pathway over which data is transferred between
remote devices. It may refer to the entire physical medium, such as a telephone line,
cables.
Depending on their speed, we have three broad categories of communication
channels:
- narrow band - which is slow and used for telegraph lines and low speed terminals.
- voice band - used for ordinary telephone communication and
-broad band - which is fastest and is used for transmitting large volumes of
data at high speeds.
BANDWIDTH :
the frequency range over which a signal is transmitted. It is one way of describing
the maximum amount of information that the channel can carry. It is expressed as the
difference in Hertz(Hz) between the highest frequency and the lowest frequency.
For example , a typical voice signal has a bandwidth of approximately 3KHz. Wider
the bandwidth of a communication system, greater is the capacity and hence greater
is the amount of data that can be transmitted over a period of time.
Bandwidth is the difference between the upper and lower frequencies in a continuous
band of frequencies.
DATA TRANSFER RATE :(DTR) is the amount of data in digital form that is moved
from one place to another in a given time on a network. greater the bandwidth of a
given medium, the higher is the data transfer rate. This can also be referred to as
throughput. Data transfer rate is often measured in bits per second (bps),
the unit baud , which is one bit per second is also used. It is commonly used to
measure how fast data is transferred from one location to another.
For example, your ISP may offer an Internet connection with a maximum data
transfer rate of 4Mbps.
In data communications, bits per second (abbreviated bps or bit/sec) is a common
measure of data speed for computer modems and transmission carriers. The speed
in bps is equal to the number of bits transmitted or received each second.
One
One
One
One
kilobit per second (abbreviated Kbps = 1,000 bps.
megabit per second (Mbps) = 1,000,000 bps or 1,000 Kbps.
gigabit per second (Gbps) = 1,000,000,000 or 1000Mbps
terabits per second (Tbps) = 1000 Gbps.
● Transmission
media: Twisted pair cable, coaxial cable, optical fiber, infrared, radio
link, microwave link and satellite link.
TRANSMISSION MEDIA / COMMUNICATION CHANNEL.:
carries a signal from one computer to another. The medium which connect two or
more work stations in a network.
Communication media are of two categories:
a) Guided / wired media – include cables for transmission
a. Twisted Pair Cables
b. Coaxial cables
c. Optical Fibre
b) Unguided/ wireless media – transmits waves through air, water and vaccum
a. Microwave
b. Radio wave
c. Infrared waves
d. Satellite
a.a) TWISTED PAIR CABLE :
This is the most common wiring used. It consists of two identical wires wrapped
together in a double helix. All twisted pair cables have two characteristics in common
- The wires come in pairs
- The pairs of wires are twisted around each other.
e.g. internal office telephone wiring – Voice Grade Medium (VGM)
LAN applications – Data Grade Medium (DGM)
Need of twisting : twisting reduces crosstalk.
- Protects signal from internal crosstalk
- Protects from external forms of signal interference
Crosstalk - the bleeding of a signal from one wire to another which can corrupt
signals and cause network errors.
Advantages :
 Simple
 Easy installation and maintenance
 Physically flexible
 Low weight
 Inexpensive
 Can be connected easily
Disadvantages :
 It causes high attenuation, so cannot carry signal over long distances without
repeaters
 It has low bandwidth capability, so cannot be used for broadband applications.
Twisted Pair Cables are of two types :
1. Unshielded Twisted Pair cable (UTP) – can have maximum segment length of
100 m. This type doesn’t have a shield covering each twisted pairs.
2. Shielded Twisted Pair cable(STP) - have a shield surrounding individual pair
of wires. It also has segment length of 100m. Only difference with UTP is added
protection from external interference and crosstalk. It is heavier, costlier than
UTP and requires proper grounding at both ends.
a.b) COAXIAL CABLES:
This has an inner solid wire core surrounded by one or more foil or wire shields, each
layers separated by a plastic insulator. Inner core carries signal, shield provides
grounding. It is widely used in television signal (CATV) and for building security
systems.
Advantages :
 Better data transmission characteristics than TPC
 Used as the basis of shared cable network
 Used for broad band transmission (several channels transmitted simultaneously)
 Offer high bandwidth upto 400 MBPS.
Disadvantages :
 Expensive compared to TPC
 Are not compatable with TPC.
There are two types of coaxial cables :
1. Thicknet - supports segment length upto 500 m long. Thicker
2. Thinnet – maximum segment length of 185 m. Thinner
a.c) OPTICAL FIBERS:
The inner core is made of glass or glass like material, that is so constructed that they
can carry light from source at one end to a detector at other end. The light source
may be an LED (Light Emitting Diode) or an LD (Laser Diode). Frequency modulation
technique is used to modulate data onto light beam.
LED bandwidth ranges between 20 and 150 mbps
LD have high rates.
Fiber cable has three parts :
1. The core – glass or glass like material through which light travels
2. The cladding – covering of the core that reflects light back to core
3. protective coating - protects cable form external factors.
Advantages:
 it is not affected by electrical and magnetic interference.
 Not affected by noise as data is in modulated light beam
 Suitable for harsh industrial environment
 Secure transmission
 High transmission capacity
 Suitable for broadband transmission - several channels are handled in parallel
 Tapping is impossible as its noise immune
Disadvantages:
 Installation problem – fiber optic cable is quite fragile, difficult to solder
 Connecting two fibers together or two light sources together is a difficult
process
 Light ma y reach the receiver out of phase
 Most expensive
WIRELESS TECHNOLOGIES / UNBOUNDED MEDIA / UNGUIDED MEDIA :
Signals are transmitted through air, water or vaccum. This uses electromagnetic
waves without using a physical conductor medium. Signals are broadcasted through air
or water. So signal is available to anyone who has device capable of receiving.
1) Infrared waves :
IR is a frequency of light that is not visible to human eye. It ranges from NearIR to
FarIR. farIR are thermal that is why feel heat from sunlight, fire , radiator. NearIR are
used by TV remotes.
IR communication needs a transceiver at both ends. Transceiver is a combination of
transmitter and receiver. It follows line-of-sight transmission, so it’s sensitive to
atmospheric conditions like fog, rainfall etc. it can’t penetrate solid objects.
Advantages :
1. Follows line of sight transmission, so it have short range hence its secure mode.
2. No need of government licence
3. Quite inexpensive
Disadvantage:
1. At a time only two devices can communicate
2. Cannot cross solid objects
3. Performance drops with longer distance
2) Bluetooth :
is a wireless technology used for creating personal network operational with in range
of 10 meters. Bluetooth can connect upto 8 devices at a time.
3) Microwaves :
Uses high frequency radio signals to transmit data through space. This can penetrate
solid obstacles like buildings. They also follow line of sight between transmitter and
receiver. Repeaters are required for longer distance transmission.
Advantages:
1. Cables are not needed.
2. Ease of communication in terrains like hilly areas.
Disadvanatges :
1. Not so secure
2. Attenuation of signal occurs, so repeaters are needed, which makes it
expensive
3. High maintenance
4. Weather conditions affect microwave propogation.
4) Radio waves :
Signals are modulated to high speed radio waves using amplitude, frequency, phase.
Communication ranges from few meters to cities eg: walkie talkie. This is easy to
generate and can travel long distances.
Advantages:
1. This supports mobility and cover large span of areas.
2. Propogate in all directions
3. Can penetrate solid
4. Transmitter and receiver need not be in line of sight.
Disadvantages :
1. Expensive
2. Insecure
3. Susceptible to weather conditions
4. Permission from authorities are required.
5) Satellite link:
Satellite uses a special type of microwave transmission system. Satellite is placed
exactly at 36000 km above equator, where satellite orbit speed exactly matches the
earth rotation speed. So satellite stays in aligned with earth at same point with
respect to earth. Transmitting of data from antenna to satellite is called uplink and
receiving of data is called downlink. Three satellites are needed to cover entire
earth.
Advantages:
1. Secure, uninterrupted, high quality transmission.
2. No restriction of line of sight
Disadvantages:
1. Very expensive
2. Legal permissions are needed
3. Complex structure
● Network
devices: Modem, RJ45 connector, Ethernet Card, Router, Switch, Gateway,
WiFi card.
MODEM (MODULATOR – DEMODULATOR):
Modem is a peripheral device that enables a computer to transmit data over a
telephone or cable line. Computer operates digitally using binary language, but
transmission medium are analogue. Modem modulates an analogue signal to encode
digital information and also demodulates a carrier signal to decode transmitted
information, hence the name Modulator Demodulator.
NIC/ NIU/ TAP:
NETWORK INTERFACE UNIT (NIU) - A network interface unit is a device that is
attached to each of the workstations and the server which helps to establish
communication between the server and workstations. Every node needs an NIC
to establish connection with the network. This is also known as Terminal Access Point
(TAP) or Network Interface card(NIC).The NIC manufacturer assigns a unique physical
address to each NIC card and this physical address is known as the MAC address.
MAC address: is of 6 bytes (This 48-bit address space) .seperated by colon.
_ _ : _ _ : _ _ : _ _: _ _: _ _
first three corresponds to manufacturer id and last three to NIC number.
MAC Address
IP Address
Definition
MAC Address stands for Media
Access Control Address.
IP Address stands for Internet Protocol
Address.
Usage
MAC Address ensure that physical
address of the computer is unique.
IP Address is a logical address of the
computer and is used to uniquely
locate computer connected via a
network.
Format
MAC Address is of six byte
hexadecimal address.
IP Address is of 4 bytes or of 16 bytes.
Access
Protocol
MAC Address can be retrieved
using ARP protocol.
IP Address can be retrieved using
RARP protocol.
Provider
Chip maker manufacturer provides
the MAC Address.
Internet Service Provider, ISP provides
the IP Address.
REPEATER :
A repeater is an electronic device that receives a signal amplifies it and retransmits it
on to network, so signal covers longer distance. When an electrical signal is
transmitted via a channel, it gets attenuated depending upon the nature of the
channel or the technology. This poses a limitation upon the length of the LAN or
coverage area of cellular networks. This problem is alleviated by installing repeaters
at certain intervals. Repeaters amplifies the attenuated signal and then retransmits
it.
HUB / CONCENTRATOR :
a hub is a hardware device used to connect several computers together.
Hubs are of two types:
1) Passive hub : allows signals to pass from one to other without any change.
2) Active hub : amplifies the signal as it moves from one node to other. These
acts as repeaters as well.
Hubs can support 8, 12, 24 RJ45 ports.
a hub has many ports in it. A computer which intends to be connected to the network
is plugged in to one of these ports. When a data frame arrives at a port, it is
broadcast to every other port, without considering whether it is destined for a
particular destination or not.
SWITCH :
A switch is a device that is used to break a network into subnetwork called Subnet/
Lan segment. Switch prevents traffic overloading on network. Switch performs
filtering of data and is a intelligent hub. Switch supports any packet protocol.
Like a hub, a switch also has many ports, to which computers are plugged in.
However, when a data frame arrives at any port of a network switch, it examines the
destination address and sends the frame to the corresponding device(s). Thus, it
supports both unicast and multicast communications.
Differences between Hub and Switch
Hub
Switch
They operate in the physical layer of the OSI
model.
They operate in the data link layer of the OSI
model.
It is a non-intelligent network device that
sends message to all ports.
It is an intelligent network device that sends
message to selected destination ports.
It primarily broadcasts messages.
It is supports unicast, multicast and
broadcast.
Transmission mode is half duplex.
Transmission mode is full duplex.
Collisions may occurs during setup of
transmission when more than one computers
place data simultaneously in the
corresponding ports.
Collisions do not occur since the
communication is full duplex.
They are passive devices, they don’t have
any software associated with it.
They are active devices, equipped with
network software.
They generally have fewer ports of 4/12.
The number of ports is higher – 24/48.
ROUTER :
They are responsible for receiving, analysing, and forwarding data packets among the
connected computer networks. When a data packet arrives, the router inspects the
destination address, consults its routing tables to decide the optimal route and then
transfers the packet along this route.

It connects different networks together and sends data packets from one network
to another.

A router can be used both in LANs (Local Area Networks) and WANs (Wide Area
Networks).

It transfers data in the form of IP packets. In order to transmit data, it uses IP
address mentioned in the destination field of the IP packet.

Routers have a routing table in it that is refreshed periodically according to the
changes in the network. In order to transmit data packets, it consults the table
and uses a routing protocol.
The functioning of a router depends largely upon the routing table stored in it. The
routing table stores the available routes for all destinations.
GATEWAY :
A gateway is a network node that forms a passage between two networks operating
with different transmission protocols.gate way connect dissimilar networks.

Gateway is located at the boundary of a network and manages all data that
inflows or outflows from that network.

It forms a passage between two different networks operating with different
transmission protocols.

● Network
Topologies and types: Bus, Star, Tree, PAN, LAN, WAN, MAN.
The way in which devices are interconnected to form a network is called
network topology.
BUS TOPOLOGY:
Data network with bus topology has a linear transmission cable, usually coaxial, to
which
many network
devices and workstations are
attached
along
the
length. Server is at one end of the bus. When a workstation has to send data, it
transmits packets with destination address in its header along the bus.
The data travels in both the directions along the bus. When the destination terminal
sees the data, it copies it to the local disk.
Advantages of Bus Topology
These are the advantages of using bus topology −
 Easy to install and maintain
 Can be extended easily
 Very reliable because of single transmission line
Disadvantages of Bus Topology
These are some disadvantages of using bus topology −
 Troubleshooting is difficult as there is no single point of control
 One faulty node can bring the whole network down
 Dumb terminals cannot be connected to the bus
STAR TOPOLOGY :
In star topology, server is connected to each node individually. Server is also called
the central node. Any exchange of data between two nodes must take place through
the server. It is the most popular topology for information and voice networks as
central node can process data received from source node before sending it to the
destination node.
Advantages of Star Topology
These are the advantages of using star topology −
 Failure of one node does not affect the network
 Troubleshooting is easy as faulty node can be detected from central node
immediately
 Simple access protocols required as one of the communicating nodes is always
the central node
Disadvantages of Star Topology
These are the disadvantages of using star topology −
 Long cables may be required to connect each node to the server
 Failure of central node brings down the whole network
TREE TOPOLOGY:
Tree topology has a group of star networks connected to a linear bus backbone
cable. It incorporates features of both star and bus topologies. Tree topology is also
called hierarchical topology.
Advantages of Tree Topology
These are some of the advantages of using tree topology −
 Existing network can be easily expanded
 Point-to-point wiring for individual segments means easier installation and
maintenance
 Well suited for temporary networks
Disadvantages of Tree Topology
These are some of the disadvantages of using tree topology −
 Technical expertise required to configure and wire tree topology
 Failure of backbone cable brings down entire network
 Insecure network
 Maintenance difficult for large networks
TYPES OF NETWORKS:
Networks can be categorized depending on size, complexity, level of security, or
geographical range.
PAN :
PAN is the acronym for Personal Area Network. PAN is the interconnection between
devices within the range of a person’s private space, typically within a range of 10
metres. If you have transferred images or songs from your laptop to mobile or from
mobile to your friend’s mobile using Bluetooth, you have set up and used a personal
area network.
A person can connect her laptop, smart phone, personal digital assistant and
portable printer in a network at home. This network could be fully Wi-Fi or a
combination of wired and wireless.
LAN:
LAN or Local Area Network is a wired network spread over a single site like an office,
building or manufacturing unit. LAN is set up to when team members need to share
software and hardware resources with each other but not with the outside world.
Typical software resources include official documents, user manuals, employee
handbook, etc. Hardware resources that can be easily shared over the network
include printer, fax machines, modems, memory space, etc. This decreases
infrastructure costs for the organization drastically.
A LAN may be set up using wired or wireless connections. A LAN that is completely
wireless is called Wireless LAN or WLAN.
MAN :
MAN is the acronym for Metropolitan Area Network. It is a network spread over a
city, college campus or a small region. MAN is larger than a LAN and typically spread
over several 5 -50 kilometres. Objective of MAN is to share hardware and software
resources, thereby decreasing infrastructure costs. MAN can be built by connecting
several LANs.
The most common example of MAN is cable TV network.
WAN :
WAN or Wide Area Network is spread over a country or many countries. WAN is
typically a network of many LANs, MANs and WANs. Network is set up using wired or
wireless connections, depending on availability and reliability.
The most common example of WAN is the Internet.
PAN
LAN
MAN
AREA COVERED 10 meters
10 kms
A city
100kms
Media used
Ethernet, wifi
Optical fiber, satellite
radio
wave,
microwave
Bluetooth,
cables, wifi
WAN
upto Entire country
where to place server ?
ans : in the building where there is highest number of computers.
When are repeaters required?
Ans: when the distance between components are more than 100 ms
Where to place switch/hub?
Ans: all buildings where number of computer is more than 2
Suggesting cable layout ?
Ans: minimum distance first
Suggesting LAN, MAN, PAN, WAN
Ans:
PAN
LAN
MAN
WAN
Distance in below 10 mts
Distance below 1 km
Distance between 5 – 50km
Between two countries - satellite
Selecting media of transmission ?
Ans :
High speed
Connecting each computers in a building
● Network
Optical Fibre
Coaxial cable/ Ethernet cable
Protocol: TCP/IP, File Transfer Protocol (FTP), PPP, HTTP, SMTP, POP3,
Remote Login (Telnet) and Internet, Wireless / Mobile Communication protocol such
as GSM, GPRS and WLL.
Network Protocols are a set of rules governing exchange of information in an easy,
reliable and secure way. Rules applicable to a network for communication. Each
network follows different protocol, but shares the same physical cabling. This
common physical medium allow multiple protocols to work together over a network.
This allows network to use common hardware for different protocols. This is called
protocol independence.
TCP/IP :
TCP/IP stands for Transmission Control Protocol/Internet Protocol. TCP/IP is a set
of layered protocols used for communication over the Internet. The communication
model of this suite is client-server model. A computer that sends a request is the
client and a computer to which the request is sent is the server.
These are two protocols used together. This forms the backbone of internet.
TCP: breaks the data into packets that network can handle and is transmitted over
network. At destination computer TCP reassembles the arriving packets in correct
order. Data packets can be lost in the transit. So to overcome that TCP adds support
mechanisms to detect error, data lost and then asks for retransmission until data is
received in correctly and completely.
IP: handles the addressing of each packets. Destination IP address is added to header
of each packet by the IP. Each gateway computer on the network checks the address
to know the destination and hence where the packets have to be forwarded. Even
the packets of same message follows different path the reassembled at destination.