Module_1 Final.pptx _Behrouz A. Forouzan, Data Communications and Networking, 5th Edition, Tata McGraw-Hill,2013

COMPUTER NETWORKS
(BCS502)
Swathy J
Asst. Professor CSE
Cambridge Institute of Technology

Textbook
• Behrouz A. Forouzan, Data Communications and Networking, 5th
Edition, Tata McGraw-Hill,2013
Reference Books:
1. Larry L. Peterson and Bruce S. Davie: Computer Networks – A
Systems Approach, 4th Edition, Elsevier, 2019.
2. Nader F. Mir: Computer and Communication Networks, 2nd
Edition, Pearson Education, 2015.
3. William Stallings, Data and Computer Communication 10th
Edition, Pearson Education, Inc., 2014

Data Communications
• Data communications are the exchange of data between two devices via some form of
transmission medium such as a wire cable
• Four fundamental characteristics of Data Communication are:
1. Delivery: The system must deliver data to the correct destination. Data must be received by the intended device or user and only
by that device or user.
2. Accuracy: The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are
unusable.
3. Timeliness: The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio,
timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay.
This kind of delivery is called real-time transmission.
4. Jitter: Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For
example, let us assume that video packets are sent every 30 ms. If some of the packets arrive with 30-ms delay and others with 40-
ms delay, an uneven quality in the video is the result.

Data Communications- Components

Data Communications- Components(Contd...)
1. Message: The message is the information (data) to be communicated. Popular
forms of information include text, numbers, audio, and video.
2. Sender: The sender is the device that sends the data message. It can be a computer,
workstation etc
3. Receiver: The receiver is the device that receives the message. It can be a
computer, workstation etc.
4. Transmission medium: The transmission medium is the physical path by which a
message travels from sender to receiver. Some examples of transmission media
include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
5. Protocol: 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

Data Communications- Data Representation
1. Text:
• Text is represented as a bit pattern, a sequence of bits (0s or 1s)
• Different sets of bit patterns have been designed to represent text symbols. Each set is called a code, and the
process of representing symbols is called coding.
2. Numbers:
• Numbers are also represented by bit patterns and the number is directly converted to a binary number.
3. Images:
• Images are also represented by bit patterns
• In its simplest form, an image is composed of a matrix of pixels (picture elements), where each pixel is a small
dot. The size of the pixel depends on the resolution
• After an image is divided into pixels, each pixel is assigned a bit pattern.
• If the image made only on black and-white dots (0 or 1)
• In the case of Gray scale
• black pixel - 00
• dark gray- 01
• light gray - 10
• white pixel -11

Data Communications- Data Representation
• RGB : Each color is made of a combination of three primary colors: red,
green, and blue
• YCM : color is made of a combination of three other primary colors: yellow,
cyan, and magenta
4. Video:
• Video refers to the recording or broadcasting of a picture or movie
• It may be a continuous entity or combination of images, each a discrete entity, arranged to convey
the idea of motion
5. Audio :
• Audio refers to the recording or broadcasting of sound or music.
• It is continuous, not discrete

Data Communications-Data Flow
• Simplex :
• Half-duplex

Data Communications-Data Flow
• Full duplex

NETWORKS
• A network is the interconnection of a set of devices capable of communication
• Device can be a host : large computer, desktop, laptop, workstation, cellular
phone, or security system etc
• Connecting device :
• router- which connects the network to other networks
• switch- which connects devices together
• modem (modulator-demodulator)- which changes the form of data
• Devices in a network are connected using wired or wireless transmission media
such as cable or air

NETWORKS - Network Criteria
• A Network must be able to meet a certain number of criteria
1. Performance
• It measures based on transit time and response time
• Performance is often evaluated by two networking metrics: throughput and delay
• If we try to send more data to the network, we may increase throughput but we
increase the delay because of traffic congestion in the network
2. Reliability
• The frequency of failure, the time it takes a link to recover from a failure
3. Security
• Security issues include protecting data from unauthorized access, protecting data from
damage and development

NETWORKS -Network attributes (Physical Structures)
1. Type of Connection:
• Point-to-Point
• Dedicated link between two devices
• Multipoint or multidrop

NETWORKS -Network attributes (Physical Structures)
• Physical Topology : The actual or the physical layout of a network
 Four basic topologies:
 Mesh Topology
 Find the number of physical links in a fully connected mesh network with n node is n (n – 1)
 If the network

Advantages:
1. Dedicated links
2. Robust
3. Privacy or security
4. Fault identification
Disadvantages:
5. Amount of cabling and the number of I/O ports
6. Installation and reconnection
7. Hardware required to connect each link is expensive

NETWORKS -Network attributes (Physical
Structures)
 Star Topology

• Advantages:
1. less expensive than a mesh topology, easy to install and
reconfigure and less cabling needed
2. If one link fails, only that link is affected
• Disadvantage
1. The dependency of the whole topology on one single point,
the hub. If the hub goes down, the whole system is dead.

Bus Topology
• Traditional Ethernet LANs

• Advantages:
1. Ease of installation , bus uses less cabling than mesh or
star topologies
2. Redundancy is eliminated
• Disadvantage
1. Reconnection and fault isolation
2. Fault or break in the bus cable stops all transmission
3. The damaged area reflects signals back in the direction of
origin, creating noise in both directions.

• Advantages:
1. Ease of installation , bus uses less cabling than mesh or
star topologies
2. Redundancy is eliminated
• Disadvantage
1. Unidirectional traffic
2. A break in the ring (such as a disabled station) can disable
the entire network
This weakness can be solved by using a dual ring or a
switch capable of closing off the break

Network Types- LAN ( Local Area Network)
 In the past, all hosts in a network were connected
through a common cable, which meant that a packet
sent from one host to another was received by all
hosts
 The intended recipient kept the packet; the others
dropped the packet
 Most LANs use a smart connecting switch, which is
able to recognize the destination address of the packet
and guide the packet to its destination without sending
it to all other hosts

Network Types- WAN ( Local Area Network)
• WAN has a wide geographical
span, spanning a town, a state, a
country, or even the world
• WAN interconnects connecting
devices such as switches, routers,
or modems.
• WANs today:
• point-to-point WANs
• switched WANs
point-to-point WAN
Switched WAN

Network Types- Internetwork
• Two or more networks are
connected, they make an
internetwork, or internet

PROTOCOL LAYERING
• When communication is simple, we may need only one simple protocol;
when the communication is complex, we may need to divide the task
between different layers, in which case we need a protocol at each layer
Scenarios:
First Scenario:

PROTOCOL LAYERING
• Second Scenario :

Principles of Protocol Layering
• First Principle :
• Example: the third layer task is to listen (in one direction) and talk (in the other
direction). The second layer needs to be able to encrypt and decrypt. The first layer needs
to send and receive mail
• Second Principle :
• Example : Under layer 3 at both sites should be a plaintext letter. The object under layer
2 at both sites should be a ciphertext letter. The object under layer 1 at both sites should
be a piece of mail

TCP/IP PROTOCOL SUITE (Transmission
Control Protocol/Internet Protocol )
• It is a hierarchical protocol made up of interactive modules, each of
which provides a specific functionality
Layered Architecture:

Description of Each Layer
Application Layer:
• Communication at the application layer is between two processes (two programs running at
this layer).
• To communicate, a process sends a request to the other process and receives a response.
• Process-to-process communication is the duty of the application layer
• Protocols:
• Hypertext Transfer Protocol (HTTP) - Accessing the World Wide Web (WWW)
• Simple Mail Transfer Protocol (SMTP) - Electronic mail (e-mail) service
• File Transfer Protocol (FTP) - Used for transferring files from one host to another
• Terminal Network (TELNET) and Secure Shell (SSH) - Accessing a site remotely
• Simple Network Man_x0002_agement Protocol (SNMP) - used by an administrator to
manage the Internet at global and local levels
• Domain Name System (DNS) : Used by other protocols to find the network-layer address of
a computer
• Internet Group Management Protocol (IGMP) :Used to collect membership in a group

• Transport Layer:
• The transport layer at the source host gets the message from the application layer,
encapsulates it in a transport layer packet (called a segment or a user datagram in
different protocols) and send
• Protocol:
• Transmission Control Protocol (TCP) - connection-oriented protocol that first
establishes a logical connection between transport layers at two hosts before
transferring data
• TCP provides :
• Flow control
• Error Control
• congestion control

• Protocol:
• User Datagram Protocol (UDP) :
• connectionless protocol that transmits user datagrams without first creating a logical
connection
• UDP does not provide
• flow, error, or congestion control
• Stream Control Transmission Protocol (SCTP)
• Designed to respond to new applications that are emerging in the multimedia

Network Layer:
• Creating a connection between the source computer and the destination computer
• Communication at the network layer is host-to-host
• several routers from the source to the destination, the routers in the path are
responsible for choosing the best route for each packet
• Protocols :
• Internet Protocol (IP) :
• Defines the format of the packet
• IP is also responsible for routing a packet from its source to its destination
• IP is a connectionless protocol that provides no flow control, no error control, and no congestion control
services
• Internet Control Message Protocol (ICMP) : Helps IP to report some problems
when routing a packet
• Internet Group Management Protocol (IGMP) : Helps IP in multitasking

• Protocols :
• Dynamic Host Configuration Protocol (DHCP) : Helps IP to get the network-
layer address for a host
• Address Resolution Protocol (ARP): Helps IP to find the link-layer address of a
host or a router when its network-layer address is given
• Data-link Layer:
• Data-link layer is responsible for taking the datagram and moving it across the
link. The link can be a wired LAN with a link-layer switch, a wireless LAN, a
wired WAN, or a wireless WAN
• The data-link layer takes a datagram and encapsulates it in a packet called a frame
• TCP/IP does not define any specific protocol for the data-link layer.

• Physical Layer:
• Physical layer is responsible for carrying individual bits in a frame across
the link
• Bits received in a frame from the data-link layer are trans_x0002_formed
and sent through the transmission media

Encapsulation and Decapsulation

Video1-https://www.youtube.com/watch?v=0y6FtKsg6J4
Video2 https://www.youtube.com/watch?v=aaJ1KcCDz-c

• Encapsulation at the Source Host:
1. At the application layer, the data to be exchanged is referred to as a message. A message
normally does not contain any header or trailer, but if it does, we refer to the whole as the
message. The message is passed to the transport layer
2. The transport layer takes the message as the payload, the load that the transportlayer
should take care of. It adds the transport layer header to the payload, which contains the
identifiers of the source and destination application programs that want to
communicate plus some more information that is needed for the end-to-end delivery of
the message, such as information needed for flow, error control, or congestion control.
The result is the transport-layer packet, which is called the segment (in TCP) and the
user datagram (in UDP). The transport layer then passes the packet to the network layer.

• Encapsulation at the Source Host:
3. The network layer takes the transport-layer packet as data or payload and adds its
own header to the payload. The header contains the addresses of the source and
destination hosts and some more information used for error checking of the
header, fragmentation information, and so on. The result is the network-layer
packet, called a datagram. The network layer then passes the packet to the data-link
layer.
4. The data-link layer takes the network-layer packet as data or payload and adds its
own header, which contains the link-layer addresses of the host or the next hop
(the router). The result is the link-layer packet, which is called a frame. The frame is
passed to the physical layer for transmission.

• Decapsulation and Encapsulation at the Router
1. After the set of bits are delivered to the data-link layer, this layer decapsulates the
datagram from the frame and passes it to the network layer
2. The network layer only inspects the source and destination addresses in the datagram
header and consults its forwarding table to find the next hop to which the datagram is
to be delivered. The contents of the datagram should not be changed by the network
layer in the router unless there is a need to fragment the datagram if it is too big to be
passed through the next link. The datagram is then passed to the data-link layer of the
next link
3. The data-link layer of the next link encapsulates the datagram in a frame and passes it
to the physical layer for transmission.

• Decapsulation at the Destination Host:
1. Each layer only decapsulates the packet received, removes the
payload, and delivers the payload to the next-higher layer protocol
until the message reaches the application layer

Multiplexing and Demultiplexing

THE OSI MODEL (Open Systems
Interconnection)

Switching: Packet Switching and its types
• Packet Switching: If the message is going to pass through a packet-switched
network, it needs to be divided into packets of fixed or variable size
• In packet switching, there is no resource allocation for a packet. This means
that there is no reserved bandwidth on the links, and there is no scheduled
processing time for each packet. Resources are allocated on demand
• The allocation is done on a first come, first-served basis
• Two types of Packet Switchings are
• Datagram Networks
• Virtual-Circuit Networks

Packet Switching -Datagram Networks
/connectionless network

Routing Table
A switch in a datagram network
uses a routing table that is based
on the destination address
• Destination Address:
• The destination address in the
header of a packet in a datagram
network remains the same
during the entire journey of the
packet
• Efficiency

TRANSMISSION MEDIA
A transmission medium can be broadly defined as anything that can carry
information from a source to a destination.

TRANSMISSION MEDIA-GUIDED MEDIA
• Types of Guided Media:
• Twisted-pair cable
• Coaxial cable
• Fiber-optic cable
• Twisted-Pair Cable:
• A twisted pair consists of two conductors (normally copper), each with its own
plastic insulation, twisted together

Unshielded Versus Shielded Twisted-Pair
Cable

Unshielded Twisted-Pair Cable -Categories

Unshielded Twisted-Pair Cable-
Connectors
RJ - Registered Jack

Unshielded Twisted-Pair Cable-
Connectors

Twisted-Pair Cable- Performance

Twisted-Pair Cable -Applications
• Twisted-pair cables are used in telephone lines to provide voice and data
channels

Guided Media - Coaxial Cable - Standards

Guided Media - Coaxial Cable -
Connectors
• To connect coaxial cable to devices,
we need coaxial connectors
• Most common type of connector is
Bayonet Neill-Concelman (BNC)

Connectors
BNC T BNC
Connector

Performance
• Coaxial cable has a much higher
bandwidth the signal weakens
rapidly and requires the frequent
use of repeaters

Applications
• Coaxial cable was widely used in analog telephone networks where a
single coaxial network could carry 10,000 voice signals
• Digital telephone networks where a single coaxial cable could carry
digital data up to 600 Mbps
• Cable TV networks also use coaxial cables.
• Traditional Ethernet LANs
• Coaxial cable in telephone networks has largely been replaced today
with fiberoptic cable.

Guided Media - Fiber- Optic Cable
• Fiber-optic cable is made of glass
or plastic and transmits signals in
the form of light
• Light travels in a straight line as
long as it is moving through a
single uniform substance
• If a ray of light traveling through
one substance suddenly enters
another substance(of a different
density), the ray changes direction

Guided Media - Fiber- Optic Cable
• I - Angle of incidence

Fiber- Optic Cable - Propagation Modes

Fiber- Optic Cable - Fiber Size

Fiber-Optic Cable Connectors
• Subscriber channel (SC) connector -
• Used for cable TV
• uses a push/pull locking system
• Straight-tip (ST) connector
• used for connecting cable to
networking devices
• uses a bayonet locking system and is
more reliable than SC
• MT-RJ is a connector that is the same
size as RJ45

Fiber-Optic Cable - Performance

Fiber-Optic Cable - Applications
• Fiber-optic cable is often found in backbone networks because its wide
bandwidth is cost-effective
• cable TV companies use a combination of optical fiber and coaxial cable
• Local-area networks such as 100Base-FX network (Fast Ethernet) and
1000Base-X also use fiber-optic cable

Fiber-Optic Cable - Advantages
Higher bandwidth: Fiber-optic cable can support higher bandwidths (and hence data
rates) than either twisted-pair or coaxial cable. Currently, data rates and bandwidth
utilization over fiber-optic cable are limited not by the medium but by the signal
generation and reception technology available
Less signal attenuation: Fiber-optic transmission distance is significantly greater than
that of other guided media. A signal can run for 50 km without requiring regeneration.
We need repeaters every 5 km for coaxial or twisted-pair cable
Immunity to electromagnetic interference: Electromagnetic noise cannot affect fiber-
optic cables.
 Resistance to corrosive materials : Glass is more resistant to corrosive materials than
copper. Light weight. Fiber-optic cables are much lighter than copper cables.
Greater immunity to tapping: Fiber-optic cables are more immune to tapping than
copper cables. Copper cables create antenna effects that can easily be tapped.

Fiber-Optic Cable - Disadvantages
Installation and maintenance: Fiber-optic cable is a relatively new
technology. Its installation and maintenance require expertise that is not
yet available everywhere
Unidirectional light propagation: Propagation of light is
unidirectional. If we need bidirectional communication, two fibers are
needed.
 Cost : The cable and the interfaces are relatively more expensive than
those of other guided media. If the demand for bandwidth is not high,
often the use of optical fiber cannot be justified.

UNGUIDED MEDIA: WIRELESS
• Unguided medium transport electromagnetic waves without using
a physical conductor
Types are:
• Radio Waves
• Microwaves
• Infrared
Electromagnetic spectrum for wireless communication

Electromagnetic spectrum for wireless communication

• Unguided signals can travel from the source to the destination in several
ways • Ground propagation: radio waves travel through the lowest
portion of the atmosphere
• Sky propagation: higher-frequency radio waves radiate upward
into the ionosphere where they are reflected back to earth
• line-of-sight propagation: very high-frequency signals are
transmitted in straight lines directly from antenna to antenna
• Very high-frequency signals are transmitted in straight
lines directly from antenna to antenna
• Antennas must be directional, facing each other, and
either tall enough or close enough together not to be
affected by the curvature of the earth

UNGUIDED MEDIA: Radio Waves
• Waves ranging in frequencies between 3 kHz and 1 GHz
• Radio waves, particularly those of low and medium frequencies, can
penetrate wall
Omnidirectional Antenna:

• Antenna transmits radio waves, they are propagated in all directions
• Sending and receiving antennas do not have to be aligned
• Sending antenna sends waves that can be received by any receiving
antenna

• Antenna transmits radio waves, they are propagated in all directions
• Sending and receiving antennas do not have to be aligned
• Sending antenna sends waves that can be received by any receiving
antenna
Applications:
Radio waves are used for multicast communications, such as radio and
television, and paging systems

UNGUIDED MEDIA: Microwaves
• Frequencies between 1 and 300 GHz
• Microwaves are unidirectional
• Sending and receiving antennas need to be aligned
• Very high-frequency microwaves cannot penetrate walls. This
characteristic can be a disadvantage if receivers are inside buildings
• High data rate is possible

UNGUIDED MEDIA: Microwaves
• Unidirectional Antenna:
Applications:
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and
wireless LANs

UNGUIDED MEDIA: Infrared
• Frequencies from 300 GHz to 400 THz can be used for short-range
communication
• Having high frequencies, cannot penetrate walls
Advantages:
• A short-range communication system in one room cannot be affected
by another system in the next room
• We use our infrared remote control, we do not interfere with the use
of the remote by our neighbors.

UNGUIDED MEDIA: Infrared
• Disadvantages:
We cannot use infrared waves outside a building because the sun’s
rays contain infrared waves that can interfere with the communication.
Applications:
Infrared signals can be used for short-range communication in a closed
area using line-of-sight propagation

Module_1 Final.pptx _Behrouz A. Forouzan, Data Communications and Networking, 5th Edition, Tata McGraw-Hill,2013

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