Computer Networks - Unit 1 PPT

KARPAGAM INSTITUTE OF TECHNOLOGY
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
1
Karpagam Institute of Technology
4/5/2022
Course Code with Name : CS8591/Computer
Networks
Staff Name / Designation : Mrs.C.Kalpana / AP
Department : CSE
Year/Semester : III/V

4/5/2022 Karpagam Institute of Technology 2

Course Objective
 To understand the protocol layering and
physical level communication.
 To analyze the performance of a network.
 To understand the various components required
to build different networks.
 To learn the functions of network layer and the
various routing protocols.
 To familiarize the functions and protocols of the
Transport layer.

UNIT I INTRODUCTION AND
PHYSICAL LAYER
Networks – Network Types – Protocol Layering –
TCP/IP Protocol suite – OSI Model – Physical
Layer: Performance – Transmission media –
Switching – Circuit-switched Networks – Packet
Switching.

Why do we need computer
networks?
Computer networks help users on the
network to share the resources and in
communication.
Can you imagine a world now without
emails, online newspapers, blogs, chat and
the other services offered by the internet?

Data Communication
When we communicate, we are sharing
information. This sharing can be local or remote.
Between individuals, local communication usually
occurs face to face, while remote communication
takes place over distance.

Characteristics of data
communication
 Delivery- the system must deliver the
data to the correct destination
 Accuracy-the system must deliver the
data accurately.
 Timelines- the system must deliver data
in timely manner
 Jitter-It refers to the variation in the
packet arrival time.

Components of data communication

Components of data communication
 Message- it is the information to be
communicated
 Sender-it is the device that sends the
message
 Receiver-it is the device that receives the
message
 Transmission Medium- it is physical path
through the data travels from the sender to
the reciver.
 Protocol-it is set of rules that govern data
communications.

Data representation
Information today comes in different forms
such as
 text
 numbers
 images
 audio and
 video.

Data Flow
 Communication between two devices can
be simplex, half-duplex, or full-duplex

Simplex mode
 In simplex mode, the communication is
unidirectional, as on a one-way street.
Only one of the two devices on a link can
transmit; the other can only receive (see
Figure a). Keyboards and traditional
monitors are examples of simplex devices.

Half-duplex
 In half-duplex mode, each station can both
transmit and receive, but not at the same
time. When one device is sending, the
other can only receive, and vice versa .
The half-duplex mode is like a one-lane
road with traffic allowed in both
directions.

Full -Duplex
 In full-duplex both stations can transmit
and receive simultaneously.
 One common example of full-duplex
communication is the telephone network.
When two people are communicating by a
telephone line, both can talk and listen at
the same time.

Computer Networks
 A network is a set of devices (often
referred to as nodes) connected by
communication links. A node can be a
computer, printer, or any other device
capable of sending and/or receiving data
generated by other nodes on the network.

Distributed Processing
 Most networks use distributed processing,
in which a task is divided among multiple
computers. Instead of one single large
machine being responsible for all aspects
of a process, separate computers (usually
a personal computer or workstation)
handle a subset.

Network criteria
 A network must be able to meet a certain
number of criteria. The most important of
these are performance, reliability, and
security.

Performance
Performance can be measured in many ways,
including transit time and response time.
 Transit time is the amount of time required
for a message to travel from one device to
another.
 Response time is the elapsed time between
an inquiry and a response.
 The performance of a network depends on a
number of factors, including the number of
users, the type of transmission medium, the
capabilities of the connected hardware, and
the efficiency of the software..

Reliability
 network reliability is measured by the
frequency of failure, the time it takes a
link to recover from a failure, and the
network's robustness in a catastrophe.

Security
 Network security issues include protecting
data from unauthorized access, protecting
data from damage and development, and
implementing policies and procedures for
recovery from breaches and data losses.

Physical structures
 For communication to occur, two devices
must be connected in some way to the
same link at the same time. There are two
possible types of connections: point-to-
point and multipoint.

Point to point
 A point-to-point connection provides a
dedicated link between two devices. The
entire capacity of the link is reserved for
transmission between those two devices.
 When you change television channels by
infrared remote control, you are
establishing a point-to-point connection
between the remote control and the
television's control system.

Multipoint
 A multipoint (also called multidrop)
connection is one in which more than two
specific devices share a single link.
 In a multipoint environment, the capacity
of the channel is shared, either spatially or
temporally.
 If several devices can use the link
simultaneously, it is a spatially shared
connection. If users must take turns, it is a
timeshared connection.

Topology
 A Network Topology is the arrangement
with which computer systems
or network devices are connected to each
other.
 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.

Physical Topology
 Physical topology refers to the way in
which a network is laid out physically.
One or more devices connect to a link;
two or more links form a topology.

Mesh Topology
 In a mesh topology, every device has a
dedicated point-to-point link to every
other device.
 The term dedicated means that the link
carries traffic only between the two
devices it connects.
 In other words, we can say that in a mesh
topology, we need n(n -1) /2 duplex-mode
links.

Advantages
 The use of dedicated links guarantees that each
connection can carry its own data load, thus eliminating
the traffic problems that can occur when links must be
shared by multiple devices.
 A mesh topology is robust. If one link becomes
unusable, it does not incapacitate the entire system.
 Third, there is the advantage of privacy or security.
When every message travels along a dedicated line, only
the intended recipient sees it.

Disadvantages
 The amount of cabling because every device must be
connected to every other device, installation and
reconnection are difficult.
 Second, the sheer bulk of the wiring can be greater than
the available space (in walls, ceilings, or floors) can
accommodate. Finally, the hardware required to connect
each link (I/O ports and cable) can be prohibitively
expensive.

Star Topology
 Each device has a dedicated point-to-point
link only to a central controller, usually
called a hub.
 The devices are not directly linked to one
another. Unlike a mesh topology, a star
topology does not allow direct traffic
between devices.
 The controller acts as an exchange: If one
device wants to send data to another, it sends
the data to the controller, which then relays
the data to the other connected device .

Advantages
 It is easy to install and reconfigure. Far less cabling
needs to be housed, and additions, moves, and deletions
involve only one connection: between that device and
the hub.
 Other advantages include robustness. If one link fails,
only that link is affected. All other links remain active.
This factor also lends itself to easy fault identification
and fault isolation. As long as the hub is working, it can
be used to monitor link problems and bypass defective
links.

Disadvantages
 The dependency of the whole topology on one single
point, the hub. If the hub goes down, the whole system
is dead.
 Although a star requires far less cable than a mesh, each
node must be linked to a central hub. For this reason,
often more cabling is required in a star than in some
other topologies (such as ring or bus).

Bus Topology
 A bus topology, on the other hand, is multipoint.
One long cable acts as a backbone to link all the
devices in a network running between the device
and the main cable.

 Nodes are connected to the bus cable by
drop lines and taps.
 A drop line is a connection running
between the device and the main cable.
 A tap is a connector that either splices into
the main cable or punctures the sheathing
of a cable to create a contact with the
metallic core.

Advantages & Disadvantages
 Ease of installation. Backbone cable can
be laid along the most efficient path, then
connected to the nodes by drop lines of
various lengths. In this way, a bus uses
less cabling than mesh or star topologies.
 Disadvantages include difficult
reconnection and fault isolation.

Ring Topology
 In a ring topology, each device has a dedicated point-to-
point connection with only the two devices on either
side of it.
 A signal is passed along the ring in one direction, from
device to device, until it reaches its destination. Each
device in the ring incorporates a repeater.

 When a device receives a signal intended
for another device, its repeater regenerates
the bits and passes them along.
 A ring is relatively easy to install and
reconfigure. Each device is linked to only
its immediate neighbors (either physically
or logically).

Advantages
 To add or delete a device requires changing
only two connections.
 The only constraints are media and traffic
considerations (maximum ring length and
number of devices).
 In addition, fault isolation is simplified.
Generally in a ring, a signal is circulating at
all times.
 If one device does not receive a signal within
a specified period, it can issue an alarm. The
alarm alerts the network operator to the
problem and its location

Disadvantage
 However, unidirectional traffic can be a
disadvantage. In a simple ring, a break in
the ring (such as a disabled station) can
disable the entire network.

Hybrid Topology
 A combination of two or more topology is
known as hybrid topology. For example a
combination of star and mesh topology is
known as hybrid topology.

Advantages
 We can choose the topology based on the
requirement for example, scalability is our
concern then we can use star topology instead of
bus technology.
 Scalable as we can further connect other
computer networks with the existing networks
with different topologies.

Disadvantages
 Fault detection is difficult.
 Installation is difficult.
 Design is complex so maintenance is high
thus expensive.

MAC Address
 MAC Address: MAC addresses are assigned directly by
the hardware manufacturer, they are also referred to as
hardware addresses. With Microsoft Windows, the MAC
address is referred to as the physical address.
 MAC addresses in LAN or WLAN networks consist of 6
bytes (48 bits) and are written in hexadecimal notation.
The use of separators such as hyphens or colons between
two bytes increases readability.

IP Address
 An IP address identifies a device on the global
internet. An IPv4 address consists of 32 bits,
usually written as four decimal numbers, or a
dotted quad.
 Possible values range from 000.000.000.000
through 255.255.255.255, although many
possible addresses are disallowed or reserved for
specific purposes.

Network Terminologies
 Repeater- A repeater operates at the
physical layer.
 Its job is to regenerate the signal over the
same network before the signal becomes
too weak or corrupted so as to extend the
length to which the signal can be
transmitted over the same network.

 Hub – A hub is basically a multiport
repeater.
 A hub connects multiple wires coming
from different branches, for example, the
connector in star topology which connects
different stations.
 Hubs cannot filter data, so data packets
are sent to all connected devices.

 Bridge – A bridge operates at data link
layer.
 A bridge is a repeater, with add on the
functionality of filtering content by
reading the MAC addresses of source and
destination.
 It is also used for interconnecting two
LANs working on the same protocol.
 It has a single input and single output port,
thus making it a 2 port device.

 Switch – A switch is a multiport bridge with a
buffer and a design that can boost its
efficiency(a large number of ports imply less
traffic) and performance.
 A switch is a data link layer device. The switch
can perform error checking before forwarding
data, that makes it very efficient as it does not
forward packets that have errors and forward
good packets selectively to correct port only.
 In other words, switch divides collision domain
of hosts, but broadcast domain remains same.

 Routers – A router is a device like a switch that
routes data packets based on their IP addresses.
 Router is mainly a Network Layer device.
Routers normally connect LANs and WANs
together and have a dynamically updating
routing table based on which they make
decisions on routing the data packets.
 Router divide broadcast domains of hosts
connected through it.

 Gateway-It is a passage to connect two networks
together that may work upon different
networking models.
 They basically work as the messenger agents
that take data from one system, interpret it, and
transfer it to another system.
 Gateways are also called protocol converters
and can operate at any network layer. Gateways
are generally more complex than switch or
router.

Categories of networks
 LAN(Local Area Network)
 WAN(Wide Area Network)
 MAN(Metropolitan Area Network)

Local Area Network
 Local area networks, generally called LANs, are
privately-owned networks within a single building or
campus of up to a few kilometres in size.
 They are widely used to connect personal computers and
workstations in company offices and factories to share
resources (e.g., printers) and exchange information.
 LANs are distinguished from other kinds of networks by
three characteristics: (1) Their size, (2) Their
transmission technology, and (3) Their topology

 Local Area Network is a group of computers connected
to each other in a small area such as building, office.
 LAN is used for connecting two or more personal
computers through a communication medium such as
twisted pair, coaxial cable, etc.
 It is less costly as it is built with inexpensive hardware
such as hubs, network adapters, and ethernet cables.
 The data is transferred at an extremely faster rate in
Local Area Network. Local Area Network provides
higher security.

Metropolitan Area Network
 A metropolitan area network, or MAN,
covers a city. The best-known example of
a MAN is the cable television network
available in many cities.

 A metropolitan area network is a network that covers a
larger geographic area by interconnecting a different
LAN to form a larger network.
 Government agencies use MAN to connect to the
citizens and private industries.
 In MAN, various LANs are connected to each other
through a telephone exchange line.
 The most widely used protocols in MAN are RS-232,
Frame Relay, ATM, ISDN, OC-3, ADSL, etc.It has a
higher range than Local Area Network(LAN).

Uses of MAN
 MAN is used in communication between
the banks in a city.
 It can be used in an Airline Reservation.
 It can be used in a college within a city.
 It can also be used for communication in
the military.

Wide Area Network
 A wide area network, or WAN, spans a large
geographical area, often a country or continent. It
contains a collection of machines intended for running
user (i.e., application) programs. These machines are
called as hosts. The hosts are connected by a
communication subnet, or just subnet for short.

 A Wide Area Network is a network that extends over a large
geographical area such as states or countries.
 A Wide Area Network is quite bigger network than the LAN.
 A Wide Area Network is not limited to a single location, but it
spans over a large geographical area through a telephone line,
fibre optic cable or satellite links.
 The internet is one of the biggest WAN in the world.
 A Wide Area Network is widely used in the field of Business,
government, and education.

Why Protocol is needed?
 consider the process of mailing a letter. On the envelope,
addresses are written in the following order: name, street
address, city, state, and zip code.
 If an envelope is dropped into a mailbox with the zip
code written first, followed by the street address,
followed by the state, and so on, the post office won't
deliver it.
 There is an agreed-upon protocol for writing addresses
in order for the postal system to work. In the same way,
all IP data packets must present certain information in a
certain order, and all IP addresses follow a standardized
format.

Protocols
 A protocol is a set of rules that govern
data communications. A protocol defines
what is communicated, how it is
communicated, and when it is
communicated.
 The key elements of a protocol are syntax,
semantics, and timing.

Syntax
 The term syntax refers to the structure or
format of the data, meaning the order in
which they are presented.
 For example, a simple protocol might
expect the first 8 bits of data to be the
address of the sender, the second 8 bits to
be the address of the receiver, and the rest
of the stream to be the message itself.

Semantics
 Semantics. The word semantics refers to
the meaning of each section of bits.
 How is a particular pattern to be
interpreted, and what action is to be taken
based on that interpretation?
 For example, does an address identify the
route to be taken or the final destination of
the message?

Timing
 The term timing refers to two
characteristics: when data should be sent
and how fast they can be sent.
 For example, if a sender produces data at
100 Mbps but the receiver can process
data at only 1 Mbps, the transmission will
overload the receiver and some data will
be lost.

Internet
 The Internet is the global system of
interconnected computer networks that
use the Internet protocol suite (TCP/IP) to
link devices worldwide.

Internet, Intranet and Extranet
 Internet is global communication
accessed through the Web.
 Intranet is shared content accessed by
members within a single organization.
 Extranet is shared content accessed by
groups through cross-enterprise
boundaries.

Intranet
 An intranet is a private computer network
that uses Internet protocols, network
connectivity, and possibly the public
telecommunication system to securely
share part of an organization’s information
or operations with its employees.

Extranet
 An extranet is an intranet that can be
partially accessed by authorized outside
users, enabling businesses to exchange
information over the Internet securely.

Internet Protocol
 Internet Protocol (IP) – a set of rules that
dictate how data should be delivered over the
public network (Internet).
 The Internet Protocol (IP) is a protocol, or
set of rules, for routing and addressing
packets of data so that they can travel across
networks and arrive at the correct
destination.
 Data traversing the Internet is divided into
smaller pieces, called packets.

TCP-Transmission Control
Protocol
 TCP is a connection oriented protocol and offers end-to-
end packet delivery. It acts as back bone for connection.
 TCP is a reliable and connection oriented protocol.
 TCP ensures reliability by sequencing bytes with a
forwarding acknowledgement number that indicates to
the destination the next byte the source expect to
receive.
 It retransmits the bytes not acknowledged with in
specified time period.

UDP-User Datagram Protocol
 UDP is connectionless and unreliable
protocol.
 It doesn’t require making a connection
with the host to exchange data.
 Since UDP is unreliable protocol, there is
no mechanism for ensuring that data sent
is received.