963cbe79-8554-4130-a03e-adb5bf9449ca (1).pptx

COMPUTER COMMUNICATION NETWORKS
Data Communications
Module 1
18EC71
Faculty:
Mrs. Jyothi H
Assistant Professor, Dept. of ECE, SJBIT
||Jai Sri Gurudev||
Sri Adichunchanagiri Shikshana Trust (R)
SJB INSTITUTE OF TECHNOLOGY
(Affiliated to Visvesvaraya Technological University, Belagavi & Approved by AICTE, New Delhi)
No. 67, BGS Health & Education City, Dr. Vishnuvardhan Road, Kengeri, Bengaluru-560060.

Prescribed & Reference Books:
Sl.
No.
Particulars Book Title Book Author Book
Publication
s
1 Prescribed
Books
Data
Communication
& Networking
Behzad
Forouzan
5th Ed, 2016,
TMH
2 Reference
Books
Computer
Networks
James F.
Kursoe,
Keith W. Ross
2nd Ed, 2013,
Pearson
3 Introduction to
Data
communication &
Networking
Wayne Tomasi 2007, Pearson

Module-1
• Introduction: Data Communications:
Components, Representations, Data Flow,
Networks: Physical Structures, Network Types:
LAN, WAN, Switching, Internet.
• Network Models: Protocol Layering: Scenarios,
Principles, Logical Connections, TCP/IP Protocol
Suite: Layered Architecture, Layers in TCP/IP
suite, Description of layers, Encapsulation and
Decapsulation, Addressing, Multiplexing and
Demultiplexing, The OSI Model: OSI Versus
TCP/IP.

Introduction
• Data communications and networking have changed
the way we do business and the way we live. Business
decisions have to be made ever more quickly, and
• the decision makers require immediate access to
accurate information.
• Data communication and networking have found their
way not only through business and personal
communication, they have found many applications in
political and social issues.
• People have found how to communicate with other
people in the world to express their social and political
opinions and problems.
• Communities in the world are not isolated anymore.

DATA COMMUNICATIONS
• 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.
• The term telecommunication, which includes
telephony, telegraphy, and television, means
communication at a distance (tele is Greek for
“far”).

• Data communications are the exchange of data
between two devices via some form of
transmission medium such as a wire cable.
• the communicating devices must be part of a
communication system made up of a
combination of hardware (physical equipment)
and software (programs).
• The effectiveness of a data communications
system depends on four fundamental
characteristics:
• delivery, accuracy, timeliness, and jitter.

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.

Components
• A data communications system has five
components

1.Message.
The message is the information (data) to be communicated. Popular
forms of information include text, numbers, pictures, audio, and video.
2. Sender.
The sender is the device that sends the data message. It can be a
computer, workstation, telephone handset, video camera, and so on.
3.Receiver.
The receiver is the device that receives the message. It can be a
computer, workstation, telephone handset, television, and so on.
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, just as a person speaking French cannot be understood
by a person who speaks only Japanese.

Data Representation
Information today comes in different forms such as
text, numbers, images, audio, and video.
• Text
In data communications, text is represented as a bit
pattern, a sequence of bits (0s or1s). 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.
• Numbers
Numbers are also represented by bit patterns. the
number is directly converted to a binary number to
simplify mathematical operations.

• 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.
• For example, an image can be divided into 1000 pixels or 10,000
pixels. In the second case, there is a better representation of the
image (better resolution), but more memory is needed to store the
image.
• After an image is divided into pixels, each pixel is assigned a bit
pattern. The size and the value of the pattern depend on the image.
• There are several methods to represent color images. One method
is called RGB, so called because each color is made of a
combination of three primary colors: red, green, and blue. The
intensity of each color is measured, and a bit pattern is assigned
to it.
• Another method is called YCM, in which a color is made of a combination
of three other primary colors: yellow, cyan, and magenta.

• Audio
• Audio refers to the recording or broadcasting
of sound or music. It is continuous, not discrete.
Even when we use a microphone to change
voice or music to an electric signal, we create a
continuous signal.
• Video
• Video refers to the recording or broadcasting of
a picture or movie. Video can either be
produced as a continuous entity (e.g., by a TV
camera), or it can be a combination of images,
each a discrete entity, arranged to convey the
idea of motion.

Data Flow
• Communication between two devices can be simplex, half-duplex,
or full-duplex as shown in Figure
• Simplex
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. The keyboard can only introduce input; the monitor can
only accept output.
• The simplex mode can use the entire capacity of the channel to
send data in one direction.

• 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 (see Figure b).
• The half-duplex mode is like a one-lane road with traffic allowed
in both directions. When cars are traveling in one direction, cars
going the other way must wait.
• In a half-duplex transmission, the entire capacity of a channel is
taken over by whichever of the two devices is transmitting at the
time.
• Ex: Walkie-talkies are half-duplex systems.
• The half-duplex mode is used in cases where there is no need for
communication in both directions at the same time; the entire
capacity of the channel can be utilized for each direction.

• Full-Duplex
• In full-duplex mode (also called duplex), both stations can transmit and receive
simultaneously (see Figure c).
• The full-duplex mode is like a two-way street with traffic flowing in both directions
at the same time.
• In full-duplex mode, signals going in one direction share the capacity of the link
with signals going in the other direction. This sharing can occur in two ways: Either
the link must contain two physically separate transmission paths, one for sending
and the other for receiving; or the capacity of the channel is divided between
signals traveling in both directions.
• 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.
• The full-duplex mode is used when communication in both directions is required all
the time. The capacity of the channel, however, must be divided between the two
directions.

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

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.

• Performance is often evaluated by two
networking metrics: throughput and delay.
• We often need more throughput and less delay.
However, these two criteria are often
contradictory. 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.

• 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
• Type of Connection
A network is two or more devices connected
through links.
A link is a communications pathway that
transfers data from one device to another.
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 connections 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.
• Most point-to-point connections use an actual
length of wire or cable to connect the two ends.
• When we change television channels by infrared
remote control, we are establishing a point-to-point
connection between the remote control and the
television’s control system.

• Multipoint
• A multipoint (also called multi drop) 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.

Physical Topology
• The term physical topology refers to the way in which
a network is laid out physically.
• Two or more devices connect to a link;
• two or more links form a topology.
• 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.
• There are four basic topologies possible:
Mesh
 star
Bus
ring

Mesh Topology
• In a mesh topology, every device has a dedicated point-to-point link
to every other device. To find the number of physical links in a fully
connected mesh network with n nodes,
 we first consider that each node must be connected to every other
node.
 Node 1 must be connected to n – 1 nodes,
 node 2 must be connected to n – 1 nodes,
 And finally node n must be connected to n – 1 nodes.
 We need n (n – 1) physical links.
 However, if each physical link allows communication in both
directions (duplex mode), we can divide the number of links by 2.
• In other words, we can say that in a mesh topology, we need n (n –
1) / 2 duplex-mode links.
• To accommodate that many links, every device on the network must
have n – 1 input/output (I/O) ports to be connected to the other n – 1
stations.

• A mesh offers several advantages over other network topologies.
• First, 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.
• Second, 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. Physical boundaries prevent other users from gaining access to
messages.
• Finally, point-to-point links make fault identification and fault
isolation easy. Traffic can be routed to avoid links with suspected
problems. This facility enables the network manager to discover the
precise location of the fault and aids in finding its cause and solution.

• The main disadvantages of a mesh are related to the
amount of cabling and the number of I/O ports
required.
• First, 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.
• For these reasons a mesh topology is usually
implemented in a limited fashion
• One practical example of a mesh topology is the
connection of telephone regional offices in which each
regional office needs to be connected to every other
regional office.

Star Topology
• In a 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

• A star topology is less expensive than a mesh
topology.
• In a star, each device needs only one link and one
I/O port to connect it to any number of others.
• This factor also makes it 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.
• One big disadvantage of a star topology is 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).
• The star topology is used in local-area networks (LANs).
• High-speed LANs often use a star topology with a central
hub.

Bus Topology
• A bus topology, is multipoint. One long cable acts as a
backbone to link all the devices in a network
• 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.
• As a signal travels along the backbone, some of its energy is
transformed into heat. Therefore, it becomes weaker and
weaker as it travels farther and farther.
• For this reason there is a limit on the number of taps a bus
can support and on the distance between those taps.

• Advantages of a bus topology include 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.
• In a star, for example, four network devices in the same room
require four lengths of cable reaching all the way to the hub.
• In a bus, this redundancy is eliminated. Only the backbone cable
stretches through the entire facility. Each drop line has to reach
only as far as the nearest point on the backbone.

• Disadvantages :
 difficult reconnection
 fault isolation.
• A bus is usually designed to be optimally efficient at
installation. It can therefore be difficult to add new devices.
• Signal reflection at the taps can cause degradation in
quality. This degradation can be controlled by limiting the
number and spacing of devices connected to a given length
of cable.
• Adding new devices may therefore require modification or
replacement of the backbone.
• In addition, a fault or break in the bus cable stops all
transmission. The damaged area reflects signals back in the
direction of origin, creating noise in both directions.
• Bus topology was the one of the first topologies used in the
design of early local area networks. Traditional Ethernet
LANs can use a bus topology

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).
• 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

• 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. This weakness can be solved by
using a dual ring or a switch capable of closing off the break.
• Ring topology was prevalent when IBM introduced its local-area
network, Token Ring.
• (A token ring network is a local area network (LAN) in which all
computers are connected in a ring or star topology and pass one
or more logical tokens from host to host. Only a host that holds a
token can send data, and tokens are released when receipt of the
data is confirmed. Token ring networks prevent data packets from
colliding on a network segment because data can only be sent by
a token holder and the number of tokens available is controlled)
• Today, the need for higher-speed LANs has made this topology
less popular.

1.Multipoint topology is
• Bus
• Star
• Mesh
• Ring
2. In mesh topology, devices are connected via
• Multipoint link
• Point to point link
• No Link
• None of above
3. Bus, ring and star topologies are mostly used in the
• LAN
• MAN
• WAN
• Internetwork
QUIZ TIME

4. combination of two or more topologies are called
• Star Topology
• Bus Topology
• Ring topology
• Hybrid
5. It can be a simple 2 personal computers and a printer or
could contain dozens of computers, workstations, and
peripheral devices.
• Local area network
• Metropolitan area network
• Wide area network
• Global area network
6. ________________ a network that provides connections
between countries around the entire globe.

7. ____________________________ is an organization
dedicated to worldwide agreement on internations
standards in a variety of fields which was created in
1947 with 82 industrialized nations as representative
bodies.
8 It is the simplest and most common method of
interconnecting computers.
• Star topology
• Hybrid topology
• Mesh topology
• Bus topology
9. ____________________ is a computer network that
spans a relatively small area within one building.

10. These are the oldest type of data communications
network that provide relatively slow-speed, long-
distance transmission of data, voice, and video
information over relatively large and widely dispersed
geographical areas.
• Local area network
• Metropolitan area network
• Wide area network
• Global area network
11. It is a network connection that normally carries traffic
between departmental LANs within a single company.
• Building backbone
• Campus backbone
• Enterprise network

Ans.
• 1. bus
• 2. point to point
• 3. LAN
• 4. hybrid
• 5. local area network
• 6. global area network
• 7.ISO
• 8.bus topology
• 9. LAN
• 10. wide area network
• 11.campus back bone

NETWORK TYPES
• two types of networks: LANs and WANs
• Local Area Network:
• A local area network (LAN) is usually privately owned
and connects some hosts in a single office, building, or
campus.
• Depending on the needs of an organization, a LAN can
be as simple as two PCs and a printer in someone’s
home office, or it can extend throughout a company
and include audio and video devices.
• Each host in a LAN has an identifier, an address, that
uniquely defines the host in the LAN. A packet sent by
a host to another host carries both the source host’s
and the destination host’s addresses.

• 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

• Today, 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.
• The switch alleviates the traffic in the LAN and
allows more than one pair to communicate
with each other at the same time if there is no
common source and destination among them.

Wide Area Network
• A wide area network (WAN) is also an interconnection of
devices capable of communication.
• However, there are some differences between a LAN and a
WAN.
• A LAN is normally limited in size, spanning an office, a building,
or a campus;
• a WAN has a wider geographical span, spanning a town, a
state, a country, or even the world.
• A LAN interconnects hosts; a WAN interconnects connecting
devices such as switches, routers, or modems.
• A LAN is normally privately owned by the organization that
uses it; a WAN is normally created and run by communication
companies and leased by an organization that uses it.
• two distinct examples of WANs today:
 point-to-point WANs and
 switched WANs.

Point-to-Point WAN
• A point-to-point WAN is a network that
connects two communicating devices through
a transmission media (cable or air).

• Switched WAN
• A switched WAN is a network with more than
two ends. A switched WAN is used in the
backbone of global communication today.
• switched WAN is a combination of several point-
to-point WANs that are connected by switches.

Internetwork
• Today, it is very rare to see a LAN or a WAN in isolation; they are connected to one
another. When two or more networks are connected, they make an internetwork, or
internet.
• As an example, assume that an organization has two offices, one on the east coast and
the other on the west coast. Each office has a LAN that allows all employees in the
office to communicate with each other. To make the communication between
employees at different offices possible, the management leases a point-to-point
dedicated WAN from a service provider, such as a telephone company, and connects
the two LANs.
• Now the company has an internetwork, or a private internet (with lowercase i).
Communication between offices is now possible

• When a host in the west coast office sends a
message to another host in the same office,
the router blocks the message, but the switch
directs the message to the destination.
• On the other hand, when a host on the west
coast sends a message to a host on the east
coast, router R1 routes the packet to router
R2, and the packet reaches the destination.

• Figure shows another internet with several
LANs and WANs connected. One of the WANs
is a switched WAN with four switches.

Switching
• An internet is a switched network in which a
switch connects at least two links together. A
switch needs to forward data from a network
to another network when required.
• The two most common types of switched
networks are
 circuit-switched and
packet-switched networks.

Circuit-Switched Network
• In a circuit-switched network, a dedicated connection,
called a circuit, is always available between the two
end systems; the switch can only make it active or
inactive.
• Figure 1.13 shows a very simple switched network that
connects four telephones to each end. We have used
telephone sets instead of computers as an end system
because circuit switching was very common in
telephone networks in the past, although part of the
telephone network today is a packet-switched network

• the four telephones at each side are connected to
a switch. The switch connects a telephone set at
one side to a telephone set at the other side. The
thick line connecting two switches is a high-
capacity communication line that can handle four
voice communications at the same time; the
capacity can be shared between all pairs of
telephone sets. The switches used in this example
have forwarding tasks but no storing capability.

Packet-Switched Network
• In a computer network, the communication
between the two ends is done in blocks of data
called packets.
• In other words, instead of the continuous
communication we see between two telephone
sets when they are being used, we see the
exchange of individual data packets between the
two computers.
• This allows us to make the switches function for
both storing and forwarding because a packet is an
independent entity that can be stored and sent
later.

• Figure 1.14 shows a small packet-switched
network that connects four computers at one
site to four computers at the other site.

• A router in a packet-switched network has a queue
that can store and forward the packet.
• Now assume that the capacity of the thick line is
only twice the capacity of the data line connecting
the computers to the routers.
• If only two computers (one at each site) need to
communicate with each other, there is no waiting
for the packets. However, if packets arrive at one
router when the thick line is already working at its
full capacity, the packets should be stored and
forwarded in the order they arrived.
• The two simple examples show that a packet-
switched network is more efficient than a circuit
switched network, but the packets may encounter
some delays.

• The figure shows the Internet as several backbones,
provider networks, and customer networks.
• At the top level, the backbones are large networks owned
by some communication companies such as Sprint,
Verizon (MCI), AT&T, and NTT.
• The backbone networks are connected through some
complex switching systems, called peering points.
• At the second level, there are smaller networks, called
provider networks, that use the services of the backbones
for a fee.
• The provider networks are connected to backbones and
sometimes to other provider networks.
• The customer networks are networks at the edge of the
Internet that actually use the services provided by the
Internet. They pay fees to provider networks for receiving
services.

• Backbones and provider networks are also
called Internet Service Providers (ISPs).
• The backbones are often referred to as
international ISPs; the provider networks are
often referred to as national or regional ISPs.

• IEEE 802.11 – WLAN
• IEEE 802.12 – high speed lan
• IEEE 802.14 - MAC
• IEEE 802.15 – WPAN(zigbee, bluetooth)
• IEEE 802.16 - WiMax

Topics
• Protocol Layering: Scenarios, Principles,
Logical Connections
• TCP/IP Protocol Suite: Layered Architecture,
Layers in TCP/IP suite, Description of layers,
Encapsulation and Decapsulation, Addressing,
Multiplexing and Demultiplexing
• The OSI Model: OSI Versus TCP/IP.

Introduction
• Two models have been devised to define
computer network operations:
the TCP/IP protocol suite and
the OSI model
PROTOCOL LAYERING
• In data communication and networking, a protocol
defines the rules that both the sender and
receiver and all intermediate devices need to
follow to be able to communicate effectively.

• 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, or protocol layering.
• 2.1.1 Scenarios
• First Scenario
• In the first scenario, communication is so simple that
it can occur in only one layer.

• Assume Maria and Ann are neighbors with a lot of
common ideas. Communication between Maria and
Ann takes place in one layer, face to face, in the
same language
• First, Maria and Ann know that they should greet
each other when they meet.
• Second, they know that they should confine their
vocabulary to the level of their friendship.
• Third, each party knows that she should refrain
from speaking when the other party is speaking.
• Fourth, each party knows that the conversation
should be a dialog, not a monolog: both should
have the opportunity to talk about the issue.
• Fifth, they should exchange some nice words when
they leave.

• Second Scenario
• In the second scenario, we assume that Ann is offered a
higher-level position in her company, but needs to move to
another branch located in a city very far from Maria.
• The two friends still want to continue their communication
and exchange ideas because they have come up with an
innovative project to start a new business when they both
retire.
• They decide to continue their conversation using regular mail
through the post office.
• they do not want their ideas to be revealed by other people if
the letters are intercepted.
• They agree on an encryption/decryption technique. The
sender of the letter encrypts it to make it unreadable by an
intruder;
• the receiver of the letter decrypts it to get the original letter.

Now we can say that the communication between Maria and Ann takes place
in three layers, as shown in Figure
Protocol layering enables us to divide a complex task into several smaller and
simpler tasks.

Modularity
• if Maria and Ann decide that the encryption/
decryption done by the machine is not enough to
protect their secrecy,
• they would have to change the whole machine. In
the present situation, they need to change only the
second layer machine; the other two can remain the
same. This is referred to as modularity.
• Modularity in this case means independent layers. A
layer (module) can be defined as a black box with
inputs and outputs,

• ADVANTAGES OF PROTOCOL LAYERING:
• One of the advantages of protocol layering is that it
allows us to separate the services from the
implementation. A layer needs to be able to receive
a set of services from the lower layer and to give the
services to the upper layer; we don’t care about how
the layer is implemented.
• If two machines provide the same outputs when
given the same inputs, they can replace each other.
For example, Ann and Maria can buy the second
layer machine from two different manufacturers.
• As long as the two machines create the same cipher
text from the same plaintext and vice versa, they do
the job.

• Another advantage of protocol layering, is that
communication does not always use only two
end systems; there are intermediate systems
that need only some layers, but not all layers.
• If we did not use protocol layering, we would
have to make each intermediate system as
complex as the end systems, which makes the
whole system more expensive.

Principles of Protocol Layering
• First Principle
• The first principle dictates that if we want
bidirectional communication, we need to make
each layer so that it is able to perform two
opposite tasks, one in each direction.
• For 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
• The second principle is that the two objects under
each layer at both sites should be identical.
• For example, the object 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.

Logical Connections
• This means that we have layer-to-layer communication.
• Maria and Ann can think that there is a logical
(imaginary) connection at each layer through which
they can send the object created from that layer.

TCP/IP PROTOCOL SUITE
• TCP/IP is a protocol suite (a set of protocols organized in
different layers) used in the Internet today.
• It is a hierarchical protocol made up of interactive
modules, each of which provides a specific functionality.
• The term hierarchical means that each upper level
protocol is supported by the services provided by one or
more lower level protocols.
• The original TCP/IP protocol suite was defined as four
software layers built upon the hardware.
• Today, however, TCP/IP is thought of as a five-layer model.

963cbe79-8554-4130-a03e-adb5bf9449ca (1).pptx

Layered Architecture
• To show how the layers in the TCP/IP protocol
suite are involved in communication between
two hosts, we assume that we want to use the
suite in a small internet made up of three LANs
(links), each with a link-layer switch. also assume
that the links are connected by one router

• Let us assume that computer A communicates with
computer B.
• we have five communicating devices in this
communication:
• source host (computer A), the link-layer switch in link 1,
the router, the link-layer switch in link 2, and the
destination host (computer B).
• Each device is involved with a set of layers depending on
the role of the device in the internet.
• The two hosts are involved in all five layers; the source
host needs to create a message in the application layer
and send it down the layers so that it is physically sent to
the destination host.
• The destination host needs to receive the communication
at the physical layer and then deliver it through the other
layers to the application layer.

• The router is involved in only three layers; there is
no transport or application layer in a router as long
as the router is used only for routing.
• The router is involved in three links, but the message
sent from source A to destination B is involved in
two links. Each link may be using different link-layer
and physical-layer protocols;
• the router needs to receive a packet from link 1
based on one pair of protocols and deliver it to link 2
based on another pair of protocols.
• A link-layer switch in a link, however, is involved only
in two layers, data-link and physical. Although each
switch in the above figure has two different
connections, the connections are in the same link,
which uses only one set of protocols.

Layers in the TCP/IP Protocol Suite

• As the figure shows, the duty of the application,
transport, and network layers is end-to-end.
• the domain of duty of the top three layers is the
internet, and the domain of duty of the two lower
layers is the link.
• In the top three layers, the data unit (packets)
should not be changed by any router or link-layer
switch. In the bottom two layers, the packet
created by the host is changed only by the routers,
not by the link-layer switches.

second principle discussed previously
for protocol layering

• although the logical connection at the
network layer is between the two hosts,
• we can only say that identical objects exist
between two hops in this case because a
router may fragment the packet at the
network layer and send more packets than
received

Physical Layer
• the physical layer is the lowest level in the TCP/IP
protocol suite,
• the communication between two devices at the
physical layer is still a logical communication
because there is another, hidden layer, the
transmission media, under the physical layer.
• Two devices are connected by a transmission
medium (cable or air).
• We need to know that the transmission medium
does not carry bits; it carries electrical or optical
signals. So the bits received in a frame from the
data-link layer are transformed and sent through
the transmission media

Data-link Layer
• We have seen that an internet is made up of
several links (LANs and WANs) connected by
routers. There may be several overlapping sets of
links that a datagram can travel from the host to
the destination. The routers are responsible for
choosing the best links.
• when the next link to travel is determined by the
router, the 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 wirelessWAN.

• The data-link layer is responsible for moving the
packet through the link.
• TCP/IP does not define any specific protocol for
the data-link layer.
• It supports all the standard and proprietary
protocols.
• The data-link layer takes a datagram and
encapsulates it in a packet called a frame.
• Each link-layer protocol may provide a different
service. Some link-layer protocols provide
complete error detection and correction, some
provide only error correction.

Network Layer
• The network layer is responsible for creating a
connection between the source computer and the
destination computer.
• The communication at the network layer is host-to-
host & routing the packet through possible routes.
 One reason, as we said before, is the separation of
different tasks between different layers.
 The second reason is that the routers do not need the
application and transport layers. Separating the tasks
allows us to use fewer protocols on the routers.

• The network layer in the Internet includes the main
protocol, Internet Protocol (IP), that defines the format of
the packet, called a datagram at the network layer.
• IP also defines the format and the structure of addresses
used in this layer.
• IP is also responsible for routing a packet from its source
to its destination, which is achieved by each router
forwarding the datagram to the next router in its path.
• IP is a connectionless protocol that provides no flow
control, no error control, and no congestion control
services. This means that if any of theses services is
required for an application, the application should rely
only on the transport-layer protocol.
• The network layer also includes unicast (one-to-one) and
multicast (one-to-many) routing protocols.

• The network layer also has some auxiliary protocols
that help IP in its delivery and routing tasks.
• The Internet Control Message Protocol (ICMP) helps
IP to report some problems when routing a packet.
• The Internet Group Management Protocol (IGMP) is
another protocol that helps IP in multitasking.
• The Dynamic Host Configuration Protocol (DHCP)
helps IP to get the network-layer address for a host.
• The Address Resolution Protocol (ARP) is a protocol
that helps IP to find the link-layer address of a host
or a router when its network-layer address is given.

Transport Layer
• The logical connection at the transport layer is also end-
to-end.
• 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 sends it, through the logical
(imaginary) connection, to the transport layer at the
destination host.
• The reason is the separation of tasks and duties, The
transport layer should be independent of the application
layer.
• In addition, we will see that we have more than one
protocol in the transport layer, which means that each
application program can use the protocol that best
matches its requirement.

• The main protocol, Transmission Control Protocol
(TCP), is a connection-oriented protocol that first
establishes a logical connection between transport
layers at two hosts before transferring data.
• It creates a logical pipe between two TCPs for
transferring a stream of bytes.
• TCP provides flow control (matching the sending
data rate of the source host with the receiving data
rate of the destination host to prevent
overwhelming the destination),
• error control (to guarantee that the segments arrive
at the destination without error and resending the
corrupted ones), and
• Congestion control to reduce the loss of segments
due to congestion in the network.

• User Datagram Protocol (UDP), is a connectionless
protocol that transmits user datagrams without first
creating a logical connection.
• In UDP, each user datagram is an independent entity
without being related to the previous or the next one
(the meaning of the term connectionless).
• UDP is a simple protocol that does not provide flow,
error, or congestion control.
• Its simplicity, which means small overhead, is attractive
to an application program that needs to send short
messages and cannot afford the retransmission of the
packets involved in TCP, when a packet is corrupted or
lost.
• A new protocol, Stream Control Transmission Protocol
(SCTP) is designed to respond to new applications that
are emerging in the multimedia.

Application Layer
• The two application layers exchange messages
between each other as though there were a bridge
between the two layers. However, we should know
that the communication is done through all the layers.
• 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.
• The application layer in the Internet includes many
predefined protocols, but a user can also create a
pair of processes to be run at the two hosts.

• The Hypertext Transfer Protocol (HTTP) is a vehicle for
accessing the World Wide Web (WWW).
• The Simple Mail Transfer Protocol (SMTP) is the main
protocol used in electronic mail (e-mail) service.
• The File Transfer Protocol (FTP) is used for transferring files
from one host to another.
• The Terminal Network (TELNET) and Secure Shell (SSH) are
used for accessing a site remotely.
• The Simple Network Management Protocol (SNMP) is used
by an administrator to manage the Internet at global and
local levels.
• The Domain Name System (DNS) is used by other protocol
to find the network-layer address of a computer.
• The Internet Group Management Protocol (IGMP) is used to
collect membership in a group

Encapsulation and Decapsulation
we show the encapsulation in the source host, decapsulation in the destination host,
and encapsulation and decapsulation in the router.

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,.
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-toend
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.

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
• At the destination host, 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.
• It is necessary to say that decapsulation in the
host involves error checking.

Addressing
• Any communication that involves two parties
needs two addresses: source address and
destination address.
• Although it looks as if we need five pairs of
addresses, one pair per layer, we normally have
only four because the physical layer does not
need addresses; the unit of data exchange at the
physical layer is a bit, which definitely cannot
have an address

• At the application layer, we normally use names
to define the site that provides services, such as
someorg.com, or the e-mail address, such as
somebody@coldmail.com.

• At the transport layer, addresses are called port
numbers, and these define the application-layer
programs at the source and destination.
• Port numbers are local addresses that distinguish
between several programs running at the same
time.
• At the network-layer, the addresses are global, with
the whole Internet as the scope.
• A network-layer address uniquely defines the
connection of a device to the Internet.
• The link-layer addresses, sometimes called MAC
addresses, are locally defined addresses, each of
which defines a specific host or router in a network
(LAN or WAN).

Multiplexing and Demultiplexing

• Since the TCP/IP protocol suite uses several
protocols at some layers, we can say that we
have multiplexing at the source and
demultiplexing at the destination.
• Multiplexing means that a protocol at a layer
can encapsulate a packet from several next-
higher layer protocols (one at a time);
• demultiplexing means that a protocol can
decapsulate and deliver a packet to several
next-higher layer protocols (one at a time).

Cntd..
• To be able to multiplex and demultiplex, a protocol
needs to have a field in its header to identify to
which protocol the encapsulated packets belong.
• At the transport layer, either UDP or TCP can accept
a message from several application-layer protocols.
• At the network layer, IP can accept a segment from
TCP or a user datagram from UDP.
• IP can also accept a packet from other protocols
such as ICMP, IGMP, and so on.
• At the data-link layer, a frame may carry the payload
coming from IP or other protocols such as ARP

THE OSI MODEL
• Established in 1947, the International
Organization for Standardization (ISO) is a
multinational body dedicated to worldwide
agreement on international standards
• An ISO standard that covers all aspects of
network communications is the Open Systems
Interconnection (OSI) model.
• It was first introduced in the late 1970s.

OSI MODEL
•The OSI model is a layered framework for the design of network systems that
allows communication between all types of computer systems.
• It consists of seven separate but related layers, each of which defines a part of
the process of moving information across a network

• An open system is a set of protocols that allows
any two different systems to communicate
regardless of their underlying architecture.
• The purpose of the OSI model is to show how
to facilitate communication between different
systems without requiring changes to the logic
of the underlying hardware and software.
• The OSI model is not a protocol; it is a model
for understanding and designing a network
architecture that is flexible, robust, and
interoperable.
• The OSI model was intended to be the basis for
the creation of the protocols in the OSI stack.

OSI versus TCP/IP
• we find that two layers, session and presentation,
are missing from the TCP/IP protocol suite.
• The application layer in the suite is usually
considered to be the combination of three layers in
the OSI model

• First, TCP/IP has more than one transport-
layer protocol. Some of the functionalities of
the session layer are available in some of the
transport-layer protocols.
• Second, the application layer is not only one
piece of software. Many applications can be
developed at this layer.
• If some of the functionalities mentioned in
the session and presentation layers are
needed for a particular application, they can
be included in the development of that piece
of software.

Lack of OSI Model’s Success
• The OSI model appeared after the TCP/IP protocol suite. Most
experts were at first excited and thought that the TCP/IP
protocol would be fully replaced by the OSI model.
• First, OSI was completed when TCP/IP was fully in place and a
lot of time and money had been spent on the suite; changing
it would cost a lot.
• Second, some layers in the OSI model were never fully
defined. For example, although the services provided by the
presentation and the session layers were listed in the
document, actual protocols for these two layers were not
fully defined, nor were they fully described, and the
corresponding software was not fully developed.
• Third, when OSI was implemented by an organization in a
different application, it did not show a high enough level of
performance to entice the Internet authority to switch from
the TCP/IP protocol suite to the OSI model.

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