UNIT 1

2 Mark Questions

Define computer network.

Computer networking refers to interconnected computing devices that can exchange data and share
resources with each other. These networked devices use a system of rules, called communications
protocols, to transmit information over physical or wireless technologies.

What are the different uses of computer network?

o It allows you to share resources such as printers, scanners, etc.

o You can share expensive software and database among network users.
o It facilitates communications from one computer to another computer.
o It allows the exchange of data and information among users through a network.

Expand TCP, UDP.

TCP: Transmission control protocol

UDP: User datagram protocol

Expand LAN, MAN, WAN.

LAN: Local area network

MAN: Metropolitan area network

WAN: Wide area network

What is peer-to-peer model?

A P2P network involves two or more computers that share individual resources, such as DVD players,
printers and disk drives. Each computer acts as both client and server and directly communicates with
other computers in the network. In a P2P network, all computers on the network can access client
devices directly connected to one specific computer on the network.

What is client-server model?

o A client and server networking model is a model in which computers such as servers provide
the network services to the other computers such as clients to perform a user based tasks. This
model is known as client-server networking model.

What are the two types of transmission technology?

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 Broadcast networks and.
 Point-to-point networks.

What is unicasting and broadcasting?

Unicast –

This type of information transfer is useful when there is a participation of a single sender and a
single recipient. So, in short, you can term it as a one-to-one transmission. For example, if a device
having IP address 10.1.2.0 in a network wants to send the traffic stream(data packets) to the device
with IP address 20.12.4.2 in the other network, then unicast comes into the picture.
Broadcasting-

In Broadcast transmission, the data is transmitted from one or more senders to all the receivers within
the same network or in other networks. This type of transmission is useful in network management
packets such as ARP (Address Resolution Protocol) and RIP (Routing Information Protocol) where all
the devices must see the data.

Differentiate connection oriented and connectionless service.

A connection-oriented service is used to create an end to end connection between the sender and the
receiver before transmitting the data over the same or different networks. In connection-oriented
service, packets are transmitted to the receiver in the same order the sender has sent them.

Connectionless service is used in the network system to transfer data from one end to another end
without creating any connection. So it does not require establishing a connection before sending the
data from the sender to the receiver. It is not a reliable network service because it does not guarantee
the transfer of data packets to the receiver, and data packets can be received in any order to the
receiver.

Differentiate OSI and TCP/IP reference model.

OSI TCP/IP

OSI represents Open TCP/IP model represents the Transmission Control Protocol /
System Interconnection. Internet Protocol.
OSI is a generic, protocol TCP/IP model depends on standard protocols about which
independent standard. It the computer network has created. It is a connection protocol
is acting as an interaction that assigns the network of hosts over the internet.
gateway between the
network and the final-
user.

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What do you mean by Half duplex mode of transmission?

In a Half-duplex channel, direction can be reversed, i.e., the station can transmit and receive the data
as well. Messages flow in both directions, but not at the same time.
The entire bandwidth of the communication channel is utilized in one direction at a time.

Example
Wireless microphones as only one user can provide information in a particular piece of time.

Differentiate circuit switching and packet switching.

Circuit Switching Packet Switching

In-circuit switching has there are 3 phases:

i) Connection Establishment.
ii) Data Transfer. In Packet switching directly data transfer takes
iii) Connection Released. place.

In-circuit switching, each data unit knows the In Packet switching, each data unit just knows the
entire path address which is provided by the final destination address intermediate path is
source. decided by the routers.

In-Circuit switching, data is processed at the In Packet switching, data is processed at all
source system only intermediate nodes including the source system.

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 5 Mark Questions

List and explain the uses of computer network.

Many organizations have a large number of computers in operation. These computers may be within
the same building, campus, city or different cities.
Even though the computers are located in different locations, the organizations want to keep track of
inventories, monitor productivity, do the ordering and billing etc.
The computer networks are useful to the organizations in the following ways:
1. Resource sharing.
2. For providing high reliability.
3. To save money.
4. It can provide a powerful communication medium.
Resource sharing
• It allows all programs, equipment and data available to anyone on the network irrespective of the
physical location of the resource and the user.
High reliability due to alternative sources of data
• It provides high reliability by having alternative sources of data. For e.g. all files could be replicated
on more than one machines, so if one of them is unavailable due to hardware failure or any other
reason, the other copies can be used.
Money saving
• Computer networking is an important financial aspect for organizations because it saves money.
• Organizations can use separate personal computer one per user instead of using mainframe
computer which are expensive.
• The organizations can use the work-group model (peer to peer) in which all the PCs are networked
together and each one can have the access to the other for communicating or sharing purpose.
Communication medium
• A computer network provides a powerful communication medium among widely separated
employees.
• Using network it is easy for two or more employees, who are separated by geographical locations
to work on a report, document or R and D simultaneously i.e. on -line.

Access to remote information

Access to remote information involves interaction· between a person and a remote database. Access
to remote information comes in many forms like:
(i) Home shopping, paying telephone, electricity bills, e-banking, on line share market etc.
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(ii) Newspaper is. On-line and is personalized, digital library consisting of books, magazines, scientific
journals etc.
(iii) World wide web which contains information. about the arts, business, cooking, government,
health, history, hobbies, recreation, science, sports etc.

Person to person communication

Person to person communication includes:

(i) Electronic-mail (e-mail)
(ii) Real time e-mail i.e. video conferencing allows remote users to communicate with no delay by
seeing and hearing each other. Video-conferencing is being used for remote school, getting medical
opinion from distant specialists etc.
(iii) Worldwide newsgroups in which one person posts a message and all other subscribers to the
newsgroup can read it or give their feedback’s.

Interactive entertainment

Interactive entertainment includes:

(i) Multi-person real-time simulation games.
(ii) Video on demand.
(iii) Participation in live TV programmes likes quiz, contest, discussions etc.

Write a note on the following:

i. Business application
ii. Home application

Computer Networks: Business Applications

Following are some business applications of computer networks:

1. Resource Sharing:
The goal is to make all programs, equipments(like printers etc), and especially data, available to
anyone on the network without regard to the physical location of the resource and the user.

2. Server-Client model:
One can imagine a company's information system as consisting of one or more databases and some
employees who need to access it remotely. In this model, the data is stored on powerful computers
called Servers. Often these are centrally housed and maintained by a system administrator. In
contrast, the employees have simple machines, called Clients, on their desks, using which they access
remote data.
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3. Communication Medium:
A computer network can provide a powerful communication medium among employees. Virtually
every company that has two or more computers now has e-mail (electronic mail), which employees
generally use for a great deal of daily communication

4. eCommerce:
A goal that is starting to become more important in businesses is doing business with consumers over
the Internet. Airlines, bookstores and music vendors have discovered that many customers like the
convenience of shopping from home.

Computer Networks: Home Applications

File sharing
The first use of a home network is file sharing among selected computers. File sharing between
computers over a home network is more convenient than traditional methods such as floppy disks or
zip drives. This is mainly because the latter is likely to be infected by malware, resulting in the
destruction of files or even the complete loss of files. Other than file sharing, a home network can be
used to store similar files or information on different computers so as to act as a backup facility in
case of any malfunction of the original computer.

Internet Use
A home network is also used in sharing the internet connection among the home computers. It is
relatively cheap for family members to access the internet by using one account of an Internet Service
Provider (ISP) rather than multiple accounts. However, it should be noted that the greater the number
of internet users sharing a home network, the slower the connection gets.

Printer Sharing
Peripheral or printer sharing is also another use of the home network. It is possible to set up several
computers to share a printer and reduce the in-house movement from one computer to another just
to access the printer. Other peripherals that can be shared over the home network include webcams
which are used for video chats and compact discs (CD) burners.

Gaming and Entertainment

Home networks are also important when it comes to entertainment purposes. Members of connected
computers can freely enjoy multiplayer games over the network. Many of these games actually
support the Local Area Network (LAN) mode to use. Additionally, connected computers are able to
watch videos online from the network and also participate in online gaming since the video games
consoles are supported too. VoIP Yet another exceptionally important aspect of a home network is
the ability of users to make a Voice over Internet Protocol (VoIP) call. This comes in handy, especially
when compared to the costs that would be similarly incurred when making the calls offline.

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Explain protocol hierarchies.

To reduce their design complexity, most networks are organized as a stack of layers or levels, each
one built upon the one below it. The number of layers, the name of each layer, the contents of each
layer, and the function of each layer differ from network to network. The purpose of each layer is to
offer certain services to the higher layers, shielding those layers from the details of how the offered
services are actually implemented. In a sense, each layer is a kind of virtual machine, offering certain
services to the layer above it.

Layer n on one machine carries on a conversation with layer n on another machine. The rules and
conventions used in this conversation are collectively known as the layer n protocol. Basically, a
protocol is an agreement between the communicating parties on how communication is to proceed.
As an analogy, when a woman is introduced to a man, she may choose to stick out her hand. He, in
turn, may decide either to shake it or kiss it, depending, for example, on whether she is an American
lawyer at a business meeting or a European princess at a formal ball. Violating the protocol will make
communication more difficult, if not completely impossible.

In reality, no data are directly transferred from layer n on one machine to layer n on another machine.
Instead, each layer passes data and control information to the layer immediately below it, until the
lowest layer is reached. Below layer 1 is the physical medium through which actual communication
occurs. In Fig.16.1, virtual communication is shown by dotted line.

Explain any 3 internetworking devices.

Switch

Switches generally have a more intelligent role than hubs. A switch is a multiport device that improves
network efficiency. The switch maintains limited routing information about nodes in the internal
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network, and it allows connections to systems like hubs or routers. Strands of LANs are usually
connected using switches. Generally, switches can read the hardware addresses of incoming packets
to transmit them to the appropriate destination.

Using switches improves network efficiency over hubs or routers because of the virtual circuit
capability. Switches also improve network security because the virtual circuits are more difficult to
examine with network monitors. You can think of a switch as a device that has some of the best
capabilities of routers and hubs combined. A switch can work at either the Data Link layer or the
Network layer of the OSI model. A multilayer switch is one that can operate at both layers, which
means that it can operate as both a switch and a router. A multilayer switch is a high-performance
device that supports the same routing protocols as routers.

Switches can be subject to distributed denial of service (DDoS) attacks; flood guards are used to
prevent malicious traffic from bringing the switch to a halt. Switch port security is important so be
sure to secure switches: Disable all unused ports and use DHCP snooping, ARP inspection and MAC
address filtering.

Router

Routers help transmit packets to their destinations by charting a path through the sea of
interconnected networking devices using different network topologies. Routers are intelligent devices,
and they store information about the networks they’re connected to. Most routers can be configured
to operate as packet-filtering firewalls and use access control lists (ACLs). Routers, in conjunction with
a channel service unit/data service unit (CSU/DSU), are also used to translate from LAN framing to
WAN framing. This is needed because LANs and WANs use different network protocols. Such routers
are known as border routers. They serve as the outside connection of a LAN to a WAN, and they
operate at the border of your network.

Router are also used to divide internal networks into two or more subnetworks. Routers can also be
connected internally to other routers, creating zones that operate independently. Routers establish
communication by maintaining tables about destinations and local connections. A router contains
information about the systems connected to it and where to send requests if the destination isn’t
known. Routers usually communicate routing and other information using one of three standard
protocols: Routing Information Protocol (RIP), Border Gateway Protocol (BGP) or Open Shortest Path
First (OSPF).

Bridge

Bridges are used to connect two or more hosts or network segments together. The basic role of
bridges in network architecture is storing and forwarding frames between the different segments that
the bridge connects. They use hardware Media Access Control (MAC) addresses for transferring
frames. By looking at the MAC address of the devices connected to each segment, bridges can
forward the data or block it from crossing. Bridges can also be used to connect two physical LANs into
a larger logical LAN.

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Bridges work only at the Physical and Data Link layers of the OSI model. Bridges are used to divide
larger networks into smaller sections by sitting between two physical network segments and
managing the flow of data between the two.

(For all the remaining questions, refer the notes uploaded for the first internals)