CNS Model Answers Unit 1
CNS Model Answers Unit 1
CNS Model Answers Unit 1
Unit 1
Computing devices connected by link for exchange of data and sharing of hardware & software
resources with each other.
Components of computer network:
Advantage of network
A) Sharing of computing resources ( H/W & S/W)
• Resource sharing – using network-connected peripheral devices like printers, scanners
and copiers, or sharing common software between multiple users. So saves money.
• Sharing a single internet connection – Instead of having separate internet connection to
every device . So saves money.
• Increasing storage capacity – by having network-attached storage devices shared by all
devices.
B) Sharing of information
• File sharing – you can easily share data between different users,
• centralized network administration: thus less IT support is required
• one centralized database : You can reduce errors and improve consistency :because
all staff work from information Stored at single place
• The most common LAN topologies are bus, ring, and star
• Example of protocol : wireless LANs called IEEE 802.11, popularly known as WiFi
• example of a MAN: is the part of the telephone company network that can provide a
high-speed DSL line to the customer.
• Another example is the cable TV network can also be used for connection to the Internet
in addition to TV channels
• example of Protocols : IEEE 802.16 popularly known as WiMAX.
Wide are network (WAN)
• Spans over large geographic areas that may comprise a country, a continent, or even the
whole world
Personal area network (PAN)
Owned by a single person for communicating between different devices such as PC, keyboard,
mouse, printer , sound box etc
Network software
is defined as a wide range of software that streamlines the operations, design, monitoring, and
implementation of computer networks
Traditional networks were hardware-based and comprised elements such as routers and switches
with embedded software.
Functions of network software
• User management allows administrators to add or remove users from the network.
• File management lets administrators decide the location of data storage and control user
access to that data.
• Access enables users to allow uninterrupted access to network resources.
• Network security systems assist administrators in looking after security and preventing
data breaches.
What is protocol?
protocols
A protocol is a set of rules that govern data communications.
It represents an agreement between the communicating devices. Without a protocol, two devices
may be connected but not communicating, just as a person speaking French cannot be
understood by a person who speaks only Japanese. our human protocol, there are specific
messages we send, and specific actions we take in response to the received reply messages or
other events.
Eg .
Explain ISO OSI model wrt list of functions of each layer, addresses used in each layer ,
three examples of protocols in each layer
International Standards Organization (ISO) developed the standard for network communications
called the Open Systems Interconnection (OSI) model. It was introduced in the 1977
Open system is a set of protocols that allows any two different systems to communicate
regardless of their underlying architecture or changing it. i.e. interoperable
OSI is not protocol but a model .
It has 7 layers .
Each layer has a set of functions different from other layers.
Layer 1,2,3 are called network support layers deals with physicaly moving of data from one
device to next.
Layers 5,6,7 are called host or user support layers allows interoperability among different
software systems.
Between each pair of adjacent layers is an interface which defines which services the lower
layer gives to the upper layer.
At each layer a header is added as data units from upper layers are moved from upper layers to
lower at sender ( Tx) side
Headers and trailers are used( interpreted) by corresponding layer in receiver (Rx) and then they
removed before passing the data to upper layer
Functions of each layer
is responsible for moving frames from one node to the next node. ( i.e. hop to hop)
is responsible for the delivery of individual packets from the source host(node) to the
destination host(node) connected in different networks
Here each device is given address called IP address.
Related Functions of NL
1. Logical addressing: ( DLL uses physical address, but across different networks a logical
address is required) which is called Internet Protocol (IP) address
2. Routing: protocols to decide to which path a packet has to be sent so that it reaches RX
3. Connection model: connection-oriented and connectionless communication
Eg of devices : router , gateway , end devices ( PC, laptop , mobile phone etc)
Analogy :
The TCP/IP protocol suite was developed before the OSI model & used in internet.
Internet layer
Transport layer
functions of TCP :
• connection oriented ,
• Reliable ( provides error control)
• ordered delivery ( sequencing of segments at Receiver).
• Flow control the rate at which data are exchanged and to reduce network traffic
congestion.
applications of TCP : email , browsing
TCP UDP
Transmission control protocol User Datagram Protocol
Protocol used in transport layer Protocol used in transport layer
connection oriented , Connection less
Reliable Unreliable
Slower Faster
Supports only unicast ( one to one) Supports unicast , multicast ( one to many ) &
broadcast ( one to all)
applications of TCP : email , browsing Use : Domain Name System (DNS), streaming
media applications such as IPTV, Voice over
IP (VoIP), Trivial File Transfer Protocol
(TFTP) and many online games
Compare ISO-OSI with TCP/IP
ISO-OSI TCP/IP
It has 7 layers ( APSTNDP) It has 4 layers (ATIN)
Presentation & session layer combined with
application layer. Data link & physical layer are
combined as host to network layer( or network
access layer )
Developed by ISO in 1977 Derived from ARPANET in 1960s & already being
used in internet
OSI is a reference used as a guidance tool. TCP/IP model is, implementation of the OSI
More commonly used as teaching aid. model.
Follows vertical approach. Follows horizontal approach. (Adjacent Layers
(Corresponding Layers communicate) communicate)
The model came first, and the protocols The protocols came first, and the model later was
later really just a description of the existing protocols.
OSI is a reference model as a guidance TCP/IP model is, in a way implementation of the
tool. More commonly used as teaching OSI model.
aids.
defines services, interfaces and protocols services, interfaces and protocols are not clearly
very clearly defined
Describe various addresses used in networking wrt name of layer where it is used , size , how to
find address , how to modify address etc
Four levels of address are used in an internet employing the TCP/IP protocols:
Specific address
It is just another representation for IP address . Since it is Difficult for us to remember IP address
which consists of just numbers, so they are represented by user-friendly address.
Eg: www.abc.com
When we enter this URL , it is converted back to IP for actual communication , Which is done
by DNS
Topology
(In Greek language , topos means "place", and logis means "study")
Topology is the mathematical study of shapes.
Two basic categories of network topologies :
1) physical topologies
2) logical topologies.
Physical topology: refers to the way in which a network is laid out physically. The topology of a network
is the geometric representation of the relationship of all the links and linking devices(usually called
nodes)to one another.
Logical topology : is the way that the data passes through the network from one device to the next. It has
no relation which physical topology is being used
A network's logical topology is not necessarily the same as its physical topology.
Bus star
Ring Mesh
Transmission media is anything that can carry info from source to destination in form of EM
signal. Different media has different properties and used for particular applications
Co axial
Distance ( based on Long; few hundred Moderate ;50 to 80km Short ;few meters
frequency used) Km
Obstacles Pass through they are reflected by metal; they Can’t Pass through
Obstacles pass through glass, paper, Obstacles
plastic, and similar materials;
and they are absorbed by foods.
Applications in AM , FM radio, TV, Mobile telephones, Remotes for gadgets
wireless sea ,police , military WiFi ( WLAN ), Bluetooth like TV, mouse,
,aviation keyboard, printer etc
communication
communication
Explain twisted pair media wrt subtypes, operation, range of frequencies, attenuation ( loss) ,
delay & repeater spacing
Explain co-axial media wrt subtypes, operation, range of frequencies, attenuation ( loss) , delay
& repeater spacing
Explain fiber optic cable media wrt subtypes, operation, range of frequencies, attenuation ( loss) ,
delay & repeater spacing
List the name of the frequency range & their applications of EM spectrum.
In the client-server architecture, when the client computer sends a request for data to the server
through the internet, the server accepts the requested process and deliver the data packets
requested back to the client. Clients do not share any of their resources with server.
Servers provides various services to the client that include access for specific applications,
storage of data, sharing of files & the computing power of the server
Examples of Client-Server Model are web server ,Email server ,file server, DNS , etc.
How the browser interacts with the servers ?
There are few steps to follow to interact the server with a client.
• User enters the URL(Uniform Resource Locator) of the website or file. The Browser then
requests the DNS(DOMAIN NAME SYSTEM) Server.
• DNS Server lookup for the address of the WEB Server.
• DNS Server responds with the IP address of the WEB Server.
• Browser sends over an HTTP/HTTPS request to WEB Server’s IP (provided by DNS
server).
• Server sends over the necessary files of the website.
• Browser then renders the files and the website is displayed. This rendering is done with
the help of DOM (Document Object Model) interpreter, CSS interpreter and JS Engine
collectively known as the JIT or (Just in Time) Compilers.
Advantages of Client-Server model:
• Centralized system with all data in a single place.
• Cost efficient because less maintenance cost.
• The capacity of the Client and Servers can be changed separately.
Disadvantages of Client-Server model:
• Clients are attacked by viruses, Trojans and worms if present in the Server
• Server can be affected by Denial of Service (DOS) attacks.
• Data packets may be spoofed ( modified ) during transmission by hackers
• Phishing or capturing login credentials or other useful information of the user are
common and MITM(Man in the Middle) attacks are common.
Client-Server Architecture Types:
• 1 Tier Architecture
• 2 Tier Architecture
• 3 Tier Architecture
• N Tier Architecture
1 Tier Architecture:
• This architecture contains all types of settings on a single device
2 Tier Architecture:
In this the user interface is on the client device and the related database is stored on the server
device.
3 Tier Architecture:
A middleware lies in between the client and the server machines
• Presentation layer (Users’ Tier) in client machine
• Application layer (Business Tier) in the middleware
• Database Tier (Data Tier) in server machine
N Tier Architecture:
• The approach is also named “Multi-tier architecture”.
This architecture has each function as an isolated layer
Describe switch
It is layer 2 device ( Data link layer & physical layer).
Used to connect PCs to form a LAN in star topology.
switch has many ports (each station is connected to one port) .
There is a dedicated link between PC & switch . therefore run in full duplex with no collisions.
Subtypes : Unmanaged & managed
Unmanaged : No settings of switch can be changed ( plug & play)
managed : settings can be changed such as Turn particular port ON or OFF, Link speed and
duplex settings, VLAN setting etc.
Describe bridge
It is layer 2 device ( Data link layer & physical layer)
It divides LAN into two or more segments & we get more BW per segment.
Eg
In single segment , frame sent by one station travels in whole network ( one collision domain) ,
but bridge limits it to individual segments( many collision domains) thus further increasing
improved speed.
Bridge has filtering capability
It either forwards or drops a frame depending upon destination address .i.e. if destination is on
same side from where frame came, it drops and if not ,then it is forwarded to other side.
Bridge will forward frame from source in segment1 to segment 2 if destination is in segment2
else blocks it . Similarly Bridge will forward frame from source in segment2 to segment 1 if if
destination is in segment 1 else blocks it.
Subtypes :
Transparent bridging : self learning based on traffic
Source route bridging: source machines tell the bridge where to forward a frame. But not used
now a days.
Now a days bridges are replaced by switches.
Explain Router
It is a three layer device also called as 3 layer switch.
which connects LANs and WANs in the internet. (LAN to Wan or WAN to WAN)
It forwards the packets based on their logical addr(IP addr) and routing table.
Router structure
It has 4 parts
1. i/p ports 2. o/p ports 3. Processor 4. switching fabric
The tracert command displays all the routes from your station to station with specified IP or
domain name eg tracert google.com
Netstat (network statistics) is a command line tool for monitoring network connections both
incoming and outgoing as well as viewing routing tables, interface statistics etc.
Subtypes of routers:
SOHO : small offices and home offices.
Subscriber Edge Router: Located at the edge of the subscriber's network,
Inter-provider Border Router: Interconnecting ISPs
Core router: A router that is within the middle or in the backbone of the
LAN network rather than at its periphery
Explain Gateway
Also called as protocol converter.
Works at all 7 layers of OSI or 4 layers of TCP/IP
But the gateway can connect two networks having different protocols 9 (e.g. AppleTalk to
TCP/IP)
A gateway can be implemented in hardware, software or both, but they are usually implemented
by software installed within a computer or router
Thus gateway converts one protocol stack into another. i.e. equipped for interfacing with
another network that uses different protocols, by performing the required protocol
conversions.
In the network for an company, a computer server acting as a gateway node is also does
additional functions as a proxy server and a firewall server.
Some people use the terms router and gateway interchangeably ( Which is wrong)
Bridge Switch
Layer in OSI layer 2 ( data link layer) layer 2 ( data link layer) with more
model but with few ports ports ( one port for each station )
connects two LANs or two Connects stations of same LAN,
segments of same LAN , There
Basic function/
gives more BW to each is one collision domain per station (
application
station by increasing the each station has dedicated individual
number of collision domains connection to switch.)
i) Unmanaged , managed
transparent , source routing, ii) smart, enterprise, store & forward
Subtypes
remote bridges &
cut through
Router Gateway
Has functions of
which layers of layer 3 Layer 7
OSI model
protocol conversion when
routing of packets from source
basic function connecting two networks which
to destination station
are using different protocols
Subscriber Edge Router, Inter
Subtypes provider Border Router & Core ---
router
proxy server , firewall server ,
other
--- NAT ( network address
applications
translation)
AP is a networking hardware device that allows other WiFi devices to connect to a wired
network
An access point is a device that creates a wireless local area network, or WLAN, usually in an
office or large building. An access point connects to a wired router, switch, or hub via an
Ethernet cable, and projects a Wi-Fi signal to a designated area.
IEEE has defined the specifications for a wireless LAN called IEEE 802.11,
The standard defines two kinds of services:
1. the basic service set (BSS) and
2. the extended service set (ESS).
ESS
Access point supports both standards ethernet ( to connect to wired switch )& Wifi ( to connect
to wireless devices
Subtypes of AP
◼ Standalone access point
provides the same functionality as a switch in the wired network.
◼ Multifunction Access Point
is the combination of many devices, so no need to buy separate devices. Eg .wireless router
which combines an access point, a regular Ethernet switch and a router.
Data need to converted to electromagnetic signal before sending through to transmission media.
When digital data is converted to digital signal , it is called as line coding.
Advantages : receiver can easily synchronise , since each bit has a compulsory transistion. (self
clocking)
Disadvantage: There is at least one transition per bit time so bandwidth of Manchester and
differential Manchester is 2 times that of other codings which use level
Application : used in standard Ethernet ( 10 Mbps)
Explain Differential Manchester
In this Data is represented by change in signal level (i.e., transitions) rather than levels
Rule :
▪ if next bit is 1 , no inversion
▪ if next bit is 0 , there is inversion
Advantages : receiver can easily synchronise , since each bit has a compulsory transistion. (self
clocking)
Disadvantage: There is at least one transition per bit time so bandwidth of Manchester and
differential Manchester is 2 times that of other codings which use level
Explain DSSS.
It is Direct sequence spread spectrum . it is type of spread spectrum used for provide protection
against eavesdropping and jamming.
message bits are modulated by a pseudorandom bit sequence known as a spreading sequence.
Also known as a chip.
Eg here one station is assigned a chip 10110111000 . Data is converted to polar format ( bit 1 is
positive voltage & bit 0 is -negative voltage ) and multiplied by chip. Since in one bit period
there are 11 chips bits, the spread signal has 11 times the rate of original signal rate and hence
the BW too.
Application of DSSS:
1. code-division multiple access (CDMA) method,
2. the IEEE 802.11b specification used in Wi-Fi networks, and
3. the Global Positioning System ( GPS)
Explain FHSS
frequency-hopping spread spectrum
It is type of spread spectrum used for provide protection against eavesdropping and jamming.
It transmits radio signals by rapidly changing the carrier frequency among many distinct
frequencies occupying a large spectral band. The changes are controlled by a code known to only
to transmitter and receiver.
signals are difficult to intercept since the frequency-hopping pattern is not known to any one
other than transmitter and receiver.
Application :
1.Bluetooth uses FHSS which hops between 79 different 1 MHz-wide channels.
2. in military radio app