Computer network

 DATA COMMUNICATIONS AND
NETWORKS DEALS WITH DATA AND
INFORMATION TRANSMISSION.
 DATA CAN BE REPRESENTED IN AMNY
WAYS SUCH AS HUMAN VOICE,GROUP
OF NUMBERS,IMAGES,TEXT AND
SOUNDS,ETC.

An analog signal is any continuous signals
for which the time is variable of the signal.

A digital signal is a physical signal that is a
representation of a sequence of discrete
values.

IT IS THE PROCESS OF VARYING ONE OR
MORE PROPERTIES OF A PERIODIC
WAVEFORM CALLED THE CARRIER
SIGNAL WITH A MODULATION TO BE
TRANSMITTED.

 SIGNAL IS A ELECTROMAGNETIC OR
LIGHT WAVE THAT REPRESENTS DATA.
 SIGNALS ARE USED TO TRANSFER DATA
FROM ONE DEVICE TO ANOTHER
THROUGH A COMMUNICATION MEDIA.

 IN PARALLEL TRANSMISSION ONE OR MORE
BYTES OF DATA ARE SEND OVER TWO OR MORE
WIRES.
 EACH WIRE TRANSMITS ONE DIGITAL BINARY
CODE.
 THEREFORE,SENDING ONE BYTE(8 BIT)OF DATA
REQUIRES 8 WIRES.
 IN THIS TYPE OF COMMUNICATION IT IS
NECESSARY TO DETECT WHERE EACH BYTE OF
DATA IS SEPERATED FROM THE NEXT.
 NORMALLY,THIS DETECTION IS MADE ON
ELAPSED TIME BASED.

1. THE WIRE ITSELF THAT IS AT LEAST 9
WIRES ARE REQUIRED FOR SENDING
ONE BYTE,,8 WIRES FOR 8 BITS AND
ONE FOR THE CONTROL THE FLOW OF
DATA.
2. ANOTHER PROBLEM LIES IN VARY
NATURE OF BITES/VOLTAGE.

 DATA IS SEND OVER A SINGLE
WIRE,THEREFORE SENDING ONE BYTE
DOES NOT REQUIRE 8 WIRES.
 THESE ARE SENT ONE AFTER THE
ANOTHER.
 IN THIS TRANSMISSION IT IS
NECESSARY TO DETECT WHERE EACH
BIT IS SEPERATED FROM NEXT AND
WHERE EACH BLOCK IS SEPERATED
FROM THE NEXT.

 IT TAKES ATLEAST 8 TIMES LONGER TO
TRANSMIT 8 INDIVIDUAL BITS ONE
AFTER THE OTHER THAN TO TRANSMIT
THEM ALL SIMULTANEOUSLY IN
PARALLEL.
 THIS SPEED LIMIT IS INSIGNIFICANT
FOR MANY TYPICAL APPLICATIONS
 SERIAL PERIPHERAL DEVICES ARE
SLOW AT LEAST IN THE COMPARISON
OF INTERNAL SPEED OF

 IN SYNCHRONOUS TRANSMISSION BOTH
RECIEVER AND SENDER HAS AN
AGREEMENT ABOUT TIMING FOR THE
SENDING DATA AND RECEIVING DATA.
 SO THAT BOTH SENDER AND RECIEVER
CAN CO-ORDINATE THEIR DATA SIGNALS.
 SYNCHRONIZATION REFERS TO CORRECT
DETECTION BY RECEIVING EQUIPMENT AT
THE BEGINNING AND END OF THE DATA
THAT WAS SEND FROM SENDING
EQUIPMENT.

 IN ASYNCHRONOUS TRANSMISSION NO
CO-ORDINATION BETWEEN SENDER
AND RECIEVER.
 ASYNCHRONOUS TRANSMISSION IS A
START OF METHOD OF TRANSMISSION
IN WHICH A SIGN B IT IS ADDED TO THE
BEGINNING OF END OF EACH
CHARACTER IN ORDER TO DETECT THE
SEPERATION OF DATA ITEMS.

 THERE ARE THREE TYPES OF
COMMICATION:-
1. SIMPLEX
2. HALF DUPLEX
3. FULL DUPLEX

 In this type of transmission mode data can
be sent only through one direction i.e.
communication is unidirectional. We cannot
send a message back to the sender.
Unidirectional communication is done in
Simplex Systems.
 Examples of simplex Mode is loudspeaker,
television broadcasting, television and
remote, keyboard and monitor etc.

 In half duplex system we can send data in
both directions but it is done one at a time
that is when the sender is sending the data
then at that time we can’t send the sender
our message. The data is sent in one
direction.
 Example of half duplex is a walkie- talkie in
which message is sent one at a time and
messages are sent in both the directions.

 In full duplex system we can send data in
both directions as it is bidirectional. Data can
be sent in both directions simultaneously.
We can send as well as we receive the data.
 Example of Full Duplex is a Telephone
Network in which there is communication
between two persons by a telephone line,
through which both can talk and listen at the
same time.

 DEFINATION OF COMPUTER NETWORK:
A computer network often simply referred
to as a network, is a collection of hardware
components, which are interconnected by
communication channels that allow sharing
of resources and information with respect to
certain set of rules / protocols via OS /
software.

 Resource Sharing
 Hardware (Computing Resources, Disks, Printers, etc.)
 Software (Application Software)
 Information Sharing
 Easy accessibility from anywhere (Files, Databases, etc.)
 Search Capability (WWW)
 Communication
 Email
 Message Broadcasting

 MINIMUM 2 COMPUTERS.
 CABLES
 A NETWORK INTERFACE DEVICE ON
EACH COMPUTER WHICH IS CALLED AS
NETWORK INTERFACE CARF(NIC).
 SWITCH
 HUBS

 SHARING OF THE RESOURCES CAN BE
EASILY DONE.
 RELIABILITY-THAT IS THERE IS NO
CENTRAL COMPUTER,SO IF ONE
BREAKS DOWN WE CAN USE OTHERS.

1. PAN
2. LAN
3. MAN
4. WAN
5. CAN

 A Personal Area Network (PAN) is smallest network
which is very personal to a user. This may include
Bluetooth enabled devices or infra-red enabled
devices.
 PAN has connectivity range up to 10 meters.
 PAN may include wireless computer keyboard and
mouse, Bluetooth enabled headphones, wireless
printers, and TV remotes.
 For example, Piconet is Bluetooth-enabled
Personal Area Network which may contain up to 8
devices connected together in a master-slave
fashion.

 A computer network spanned inside a building
and operated under single administrative
system is generally termed as Local Area
Network (LAN).
 Usually, LAN covers an organization offices,
schools, colleges or universities. Number of
systems connected in LAN may vary from as
least as two to as much as 16 million.
 LAN provides a useful way of sharing the
resources between end users. The resources
such as printers, file servers, scanners, and
internet are easily sharable among computers.

 ADVANTAGES:
1. SPEED OF DATA TRANSMISSION
2. COST OF LAN IS LOW
3. PROVIDES AVERAGE SECURITY
4. RESPURCE SHARING

 DISADVANTAGES:
1. EXPENSIVE TO INSTALL
2. IT REQUIRES ADMINISTRATIVE TIME
3. FILE SERVER MAY FAIL
4. CABLES MAY BREAK

 The Metropolitan Area Network (MAN) generally
expands throughout a city such as cable TV
network.
 It can be in the form of Ethernet, Token-ring,
ATM, or Fiber Distributed Data Interface (FDDI).
 Metro Ethernet is a service which is provided by
ISPs.
 This service enables its users to expand their
Local Area Networks.
 For example, MAN can help an organization to
connect all of its offices in a city.

 ADVANTAGES:
1. EFFICIENCY AND SHARED ACCESS
2. ALL THE COMPUTER OWNING
RESIDENTS OF THE AREA HAVE EQUAL
ABILITY TO GO ONLINE.

 DISADVANTAGES:
1. IT CAN BE COSTLY
2. AS THE NETWORK CONSIST OF MANY
COMPUTERS OVER THE SPAN OF THE
CITY THE CONNECTION CAN LAG OR
BECOME QUITE SLOW.

 As the name suggests, the Wide Area Network
(WAN) covers a wide area which may span
across provinces and even a whole country.
 Generally, telecommunication networks are
Wide Area Network.
 These networks provide connectivity to MANs
and LANs.
 Since they are equipped with very high speed
backbone, WANs use very expensive network
equipment.

 ADVANTAGES:
1. INCREASE EFFICIENCY
2. EASE OF COMMUNICATION
3. LOWERED COST

 DISADVANTAGES:
1. SECURITY PROBLEM
2. MAINTENANCE PROBLEM

 IT IS A COMPUTER NETWORK MADE UP
OF INTERCONNECTION OF LAN WITHIN
A LIMITED GEOGRAPHICAL AREA.
 IN THIS, CASE UNIVERSAL CAMPUS IS
BASED ON CAMPUS AREA NETWORK.
 IS LIKELY TO LINK AVARIETY OF CAMPUS
BUILDING INCLUDING IT.

 DEFINATION OF TOPOLOGY:
A TOPOLOGY DEFINES ARRANGEMENT
OF NODES,CABLES AND THAT MAKE UP
THE NETWORK.
IT IS A STRUCTURE IN WHICH WE CAN
COMMUNICATE THE NODES AND OTHER
PERIPHERALS OF THE NETWORK.

1. BUS TOPOLOGY
2. RING TOPOLOGY
3. STAR TOPOLOGY
4. MESH TOPOLOGY
5. TREE TOPOLOGY
6. HYBRID TOPOLOGY

 In case of Bus topology, all devices share single
communication line or cable.
 Bus topology may have problem while multiple
hosts sending data at the same time.
 Therefore, Bus topology either uses CSMA/CD
technology or recognizes one host as Bus Master
to solve the issue.
 It is one of the simple forms of networking where a
failure of a device does not affect the other devices.
 But failure of the shared communication line can
make all other devices stop functioning.

 In ring topology, each host machine
connects to exactly two other machines,
creating a circular network structure.
 When one host tries to communicate or send
message to a host which is not adjacent to it,
the data travels through all intermediate
hosts.
 To connect one more host in the existing
structure, the administrator may need only
one more extra cable.

 All hosts in Star topology are connected to a
central device, known as hub device, using a
point-to-point connection.
 That is, there exists a point to point connection
between hosts and hub.
 As in Bus topology, hub acts as single point of
failure.
 If hub fails, connectivity of all hosts to all other
hosts fails.
 Every communication between hosts takes
place through only the hub. Star topology is not
expensive as to connect one more host, only
one cable is required and configuration is
simple.

 In this type of topology, a host is connected
to one or multiple hosts.
 This topology has hosts in point-to-point
connection with every other host or may also
have hosts which are in point-to-point
connection with few hosts only.
 Hosts in Mesh topology also work as relay
for other hosts which do not have direct
point-to-point links.

 Also known as Hierarchical Topology, this is the most
common form of network topology in use presently.
 This topology imitates as extended Star topology and
inherits properties of Bus topology.
 This topology divides the network into multiple
levels/layers of network.
 Mainly in LANs, a network is bifurcated into three types of
network devices.
 The lowermost is access-layer where computers are
attached.
 The middle layer is known as distribution layer, which
works as mediator between upper layer and lower layer.
 The highest layer is known as core layer, and is central
point of the network, i.e. root of the tree from which all
nodes fork.

 All neighboring hosts have point-to-point
connection between them.
 Similar to the Bus topology, if the root goes
down, then the entire network suffers even
though it is not the single point of failure.
 Every connection serves as point of failure,
failing of which divides the network into
unreachable segment.

 A network structure whose design contains
more than one topology is said to be hybrid
topology.
 Hybrid topology inherits merits and demerits
of all the incorporating topologies.

1. HUB
2. REPEATER
3. BRIDGES
4. SWITCH
5. ROUTER
6. GATEWAY
7. MODEM
8. FIREWALL

• A common connection point for devices in a network.
• Hubs are commonly used to connect segments of a LAN.
• A hub contains multiple ports.
• A passive hub serves simply as a conduit for the data,
enabling it to go from one device (or segment) to another.
• Active hub electrically amplify the signal as it moves from
one connected device to another.
• Support 8, 12 or 24 RJ-45 ports
• Used in star or ring topology.

 A repeater is an electronic device that receives
a weak or low-level signal and retransmits it at a
higher level or higher power, so that the signal
can cover longer distances without degradation.

 In telecommunication networks, a bridge is a product
that connects a local area network (LAN) to another
local area network that uses the same protocol (for
example, Ethernet or Token Ring).
 You can envision a bridge as being a device that
decides whether a message from you to someone
else is going to the local area network in your
building or to someone on the local area network in
the building across the street.
 A bridge examines each message on a LAN,
"passing" those known to be within the same LAN,
and forwarding those known to be on the other
interconnected LAN (or LANs).

 A switch (switching hub) in the context of networking refers to a
device which filters and forwards data packets across a network.
 Unlike a standard hub which simply replicates what it receives on
one port onto all the other ports, a switching hub keeps a record of
the MAC addresses of the devices attached to it.
 When the switch receives a data packet, it forwards the packet
directly to the recipient device by looking up the MAC address.
 A network switch can utilise the full throughput potential of a
networks connection for each device making it a natural choice
over a standard hub.
 In other words, say for instance you had a network of 5 PCs and a
server all connected with 10Mbps UTP cable, with a hub the
throughput (10Mbps) would be shared between each device, with
a switch each device could utilise the full 10Mbps connection.

 Router is a specialized network device used
to interconnect different types of computer
network that uses different protocols e.g.
Ethernet to a mainframe.

 Gateway is a device that
connects dissimilar networks.
 Establishes intelligent
connection between a local
network and external networks
with completely different
structures.
 Gateway is the ISP that
connects the user to the
internet.

 Modems are most frequently used to enable
computers to communicate with each other
across telephone lines.
 Stands for Modulation – demodulation.
 Converts digital signal to analog signal and
vice versa.
 Two types- Internal and External

 In computing, a firewall is a piece of hardware and/or
software which functions in a networked environment to
prevent some communications forbidden by the security
policy, analogous to the function of firewalls in building
construction.
 A firewall has the basic task of controlling traffic between
different zones of trust. Typical zones of trust include the
Internet (a zone with no trust) and an internal network (a
zone with high trust).
 The ultimate goal is to provide controlled connectivity
between zones of differing trust levels through the
enforcement of a security policy and connectivity model
based on the least privilege principle.

 NEED OF TRANSMISSION MEDIA:
1. FOR DATA TRANSMISSION
2. TO TRANSMIT DATA SAFELY
3. AS TRANSMISSION MEDIA DECIDES THE
PATH OF DATA TO BE TRANSMITTED
BETWEEN COMPUTERS

1. COST-UTP CABLING IS CHEAP,FIBRE IS
EXPENSIVE
2. EASE OF INSTALLATION-FIBRE REQUIRES
SPECIALLIST INSTALLATION TO RUN
CABLE AND TERMINATE THE ENDS,UTP
CABLES ARE MUCH EASIER TO HANDLE
3. SECURITY-DATA PACKETS TRAVELLING
OVER WIRELESS CAN BE EASILY
INTERCEPTED VERY EASILY,FIBRE IS THE
MOST SECURE
4. DISTANCE-LONG DISTANCES CAN BE BEST
HANDLE BY FIBRE

1. Guided Media - cables
2. Unguided media – waves through air, water
or vacuum i.e. microwaves, radiowaves and
satelites.

Following types of cables are used in networks
 Unshielded Twisted Pair (UTP) Cable
 Shielded Twisted Pair (STP) Cable
 Coaxial Cable
 Fiber Optic Cable
 Wireless LANs

 Twisted pair cabling comes in two varieties:
shielded and unshielded. Unshielded twisted
pair (UTP) is the most popular and is
generally the best option for school networks
.

 A disadvantage of UTP is that it may be
susceptible to radio and electrical frequency
interference.
 Shielded twisted pair (STP) is suitable for
environments with electrical interference;
however, the extra shielding can make the
cables quite bulky.
 Shielded twisted pair is often used on
networks using Token Ring topology.

 Coaxial cabling has a single copper
conductor at its center.
 A plastic layer provides insulation
between the center conductor and a
braided metal shield .
 The metal shield helps to block any
outside interference from fluorescent
lights, motors, and other computers.
 Outer shield provides the ground.

• Fiber optic cabling consists of a center glass core
surrounded by several layers of protective
materials.
• It transmits light rather than electronic signals
eliminating the problem of electrical interference.
• This makes it ideal for certain environments that
contain a large amount of electrical interference.
• It has also made it the standard for connecting
networks between buildings, due to its immunity to
the effects of moisture and lighting.

 Radio frequency is easier to generate and because of its
large wavelength it can penetrate through walls and
structures alike. Radio waves can have wavelength from
1mm – 100,000km and have frequency ranging from
3Hz (Extremely Low Frequency) to 300 GHz (Extremely
High Frequency).
 Radio frequencies are sub-divided into six bands.
 Radio waves at lower frequencies can travel through
walls whereas higher RF can travel in straight line and
bounce back.
 The power of low frequency waves decreases sharply as
they cover long distance.
 High frequency radio waves have more power.
 Lower frequencies such as VLF, LF, MF bands can travel
on the ground up to 1000 kilometers, over the earth’s
surface.

 Electromagnetic waves above 100MHz tend to travel
in a straight line and signals over them can be sent by
beaming those waves towards one particular station.
 Because Microwaves travels in straight lines, both
sender and receiver must be aligned to be strictly in
line-of-sight.
 Microwaves can have wavelength ranging from 1mm –
1meter and frequency ranging from 300MHz to
300GHz.
 Microwave antennas concentrate the waves making a
beam of it.
 Microwaves have higher frequencies and do not
penetrate wall like obstacles. Microwave transmission
depends highly upon the weather conditions and the
frequency it is using.

 LAYERED ARCHITECHTURE
In layered architecture of Network Model, one whole network
process is divided into small tasks. Each small task is then
assigned to a particular layer which works dedicatedly to
process the task only.
Every layer does only specific work. In layered communication
system, one layer of a host deals with the task done by or to be
done by its peer layer at the same level on the remote host.
The task is either initiated by layer at the lowest level or at the
top most level. If the task is initiated by the topmost layer, it is
passed on to the layer below it for further processing. The
lower layer does the same thing, it processes the task and
passes on to lower layer. If the task is initiated by lowermost
layer, then the reverse path is taken.

 Open System
Interconnect is an
open standard for
all communication
systems. OSI
model is
established by
International
Standard
Organization (ISO).
This model has
seven layers:

 Application Layer: This layer is responsible for providing interface to
the application user. This layer encompasses protocols which directly
interact with the user.
 Presentation Layer: This layer defines how data in the native format
of remote host should be presented in the native format of host.
 Session Layer: This layer maintains sessions between remote hosts.
For example, once user/password authentication is done, the remote
host maintains this session for a while and does not ask for
authentication again in that time span.
 Transport Layer: This layer is responsible for end-to-end delivery
between hosts.
 Network Layer: This layer is responsible for address assignment and
uniquely addressing hosts in a network.
 Data Link Layer: This layer is responsible for reading and writing data
from and onto the line. Link errors are detected at this layer.
 Physical Layer: This layer defines the hardware, cabling, wiring,
power output, pulse rate etc.

 Internet uses TCP/IP
protocol suite, also known
as Internet suite. This
defines Internet Model
which contains four
layered architecture. OSI
Model is general
communication model but
Internet Model is what the
internet uses for all its
communication. The
internet is independent of
its underlying network
architecture so is its
Model. This model has the
following layers:

 Application Layer: This layer defines the protocol
which enables user to interact with the network. For
example, FTP, HTTP etc.
 Transport Layer: This layer defines how data should
flow between hosts. Major protocol at this layer is
Transmission Control Protocol (TCP). This layer
ensures data delivered between hosts is in-order
and is responsible for end-to-end delivery.
 Internet Layer: Internet Protocol (IP) works on this
layer. This layer facilitates host addressing and
recognition. This layer defines routing.
 Link Layer: This layer provides mechanism of
sending and receiving actual data. Unlike its OSI
Model counterpart, this layer is independent of
underlying network architecture and hardware.

 IPv4 is 32-bit addressing scheme used as
TCP/IP host addressing mechanism.
 IP addressing enables every host on the
TCP/IP network to be uniquely identifiable.
 IPv4 provides hierarchical addressing
scheme which enables it to divide the
network into sub-networks, each with well-
defined number of hosts.

 IP addresses are divided into many categories:
Class A: It uses first octet for network addresses and last three
octets for host addressing.
Class B: It uses first two octets for network addresses and last
two for host addressing.
Class C: It uses first three octets for network addresses and last
one for host addressing.
Class D: It provides flat IP addressing scheme in contrast to
hierarchical structure for above three.
Class E: It is used as experimental.
 IPv4 also has well-defined address spaces to be used as
private addresses (not routable on internet), and public
addresses (provided by ISPs and are routable on internet).
Though IP is not reliable one; it provides ‘Best-Effort-Delivery’
mechanism.

 IPv6 has introduced Anycast addressing but has
removed the concept of broadcasting.
 IPv6 enables devices to self-acquire an IPv6
address and communicate within that subnet.
 This auto-configuration removes the dependability
of Dynamic Host Configuration Protocol (DHCP)
servers.
 This way, even if the DHCP server on that subnet is
down, the hosts can communicate with each other.
IPv6 provides new feature of IPv6 mobility.
 Mobile IPv6-equipped machines can roam around
without the need of changing their IP addresses.

 Switching is a mechanism by which
data/information sent from source towards
destination which are not directly connected.
 Networks have interconnecting devices,
which receives data from directly connected
sources, stores data, analyze it and then
forwards to the next interconnecting device
closest to the destination.

 When two nodes communicate with each other over
a dedicated communication path, it is called circuit
switching.
 There is a need of pre-specified route from which
data travels and no other data is permitted.
 In circuit switching to transfer the data, circuit must
be established so that the data transfer can take
place. Circuits can be permanent or temporary.
 Applications which use circuit switching may have
to go through three phases:
Establish a circuit
Transfer the data
Disconnect the circuit

 Shortcomings of message switching gave birth
to an idea of packet switching.
 The entire message is broken down into smaller
chunks called packets.
 The switching information is added in the
header of each packet and transmitted
independently.
 It is easier for intermediate networking devices
to store small size packets and they do not take
much resources either on carrier path or in the
internal memory of switches.

Packet switching enhances
line efficiency as packets
from multiple applications
can be multiplexed over the
carrier. The internet uses
packet switching technique.
Packet switching enables
the user to differentiate data
streams based on priorities.
Packets are stored and
forwarded according to their
priority to provide quality of
service

Computer network

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