19MAM44

DATA COMMUNICATIONS AND

NETWORKING
(UNIT – I)

Prepared by
Dr. Stanly Felix C
Assistant Professor
Department of Computing (MSc Software Systems)
Coimbatore Institute of Technology, India
Overview of Unit I
✔Introduction

✔Data Communications

✔Networks

✔The Internet

✔Protocols and Standards

✔OSI model

✔TCP / IP protocol suite

✔Addressing
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INTRODUCTION

Data:
– Consists of useful or useless information to convey.
– Forms > Text(alpha numeric and others), Image or picture, Video or motion
picture, Audio.
Communication:
– Whole sum data are to be transmitted or received between the terminals or
devices or gadgets.
– The human beings or the machines are going to make use of it.

Networking:
– Data Communication can be performed between one to one or one to many
or many to many.
– To communicate faster between the terminals, a group or multiple groups
are formed called networking.

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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:
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.
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Components: A data communications system has five components

1. Message. The message is the information (data) to be communicated. Ex: text,

numbers, pictures, audio, and video.
2. Sender. The sender is the device that sends the data message. Ex: computer,
workstation, telephone handset, video camera, and so on.
3. Receiver. The receiver is the device that receives the message. Ex: computer,
workstation, telephone handset, television, and so on.

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4. Transmission medium: The transmission medium is the physical path by which a

message travels from sender to receiver. Ex: 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:
1.TEXT data
•set of bit patterns represent alphanumeric chars is called CODE and the process is called
CODING.
•Ex: Unicode coding system – used 32 bits to represent a symbol or char.
•ASCII – represents 127 chars using 8 bit pattern.

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2. NUMERAL data
•Uses binary 0’s and 1’s to represent numbers in real-time.
•Binary, octal and hexadecimal base conversions utilized.

3. IMAGE data
•image is composed of a matrix of pixels (picture elements)
•Pixels - smallest possible picture element of a captured image, are utilized to represent as
data.
•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.
•RGB and YCM used.
•Ex: black and white color in a chess board, can be represented using 1 bit pattern. 0 for
black and 1 for white.
•Image to binary conversion is done

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4. VIDEO data
•recording or broadcasting of a picture or movie.
•produced as a continuous entity (e.g., by a TV camera) or of images, each a discrete entity,
arranged to convey the idea of motion.
•25 to 30 frames / sec and 6 to 7 MHz bandwidth / channel
•“Scanning” is performed on the received signal.
•Video and audio synchronization is essential.
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5. AUDIO data
•recording or broadcasting of sound or music
•It is continuous, not discrete.
•Audio signal > Sampling > Quantization > Binary value > storage

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Data Flow
• Communication between two devices can be performed using 3 modes: simplex,
half-duplex, or full-duplex.

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1. Simplex Mode:
• communication is unidirectional, as on a one-way street. Only oneof the two devices on
a link can transmit; the other can only receive.
• Ex: Keyboards and traditional monitors
• uses the entire capacity of the channel to send data in one direction.

2. 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.
• the entire capacity of a channel is taken over by whichever of the two devices is
transmitting at the time. Ex: Walkie-talkies and CB (citizens band) radios

3. Full duplex mode:

• both stations can transmit and receive simultaneously
• signals going in one direction share the capacity of the link with signals going in the
other direction.
• two physically separate transmission paths
• Ex: telephone network
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• Networks - interconnection of a set of devices capable of communication

• Device - can be a host (or an end system) Ex: large computer, desktop, laptop,
workstation, cellular phone, or security system
• Connecting device: Ex :– router – connects the network to other networks, switch -
connects devices together, modem (modulator-demodulator) - changes the form of data
Network Criteria:
• Performance of a network is measured using the following metrics:
• Transit time : amount of time required for a message to travel from one device to
another.
• Response time: elapsed time between an inquiry and a response.
• Throughput : the amount of data moved successfully from one place to another in a
given time period.
• Network delay: specifies the latency for a bit of data to travel across the network from
one communication endpoint to another.
• Reliability: measured by the frequency of failure, the time it takes a link to recover from
a failure.
• Security: protecting data from unauthorized access, protecting data from damage and
development, and implementing policies and procedures for recovery from breaches and
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Physical structures
Network attributes: Type of Connection 1. Point-to-Point 2. Multipoint

1. Point-to-Point connection:
• Provides a dedicated link between two devices
• Entire capacity of the link is reserved for transmission between those two devices.
• End-points are connected using cables, wires, satellite or microwave links

2. Multipoint connection: A multipoint (also called multidrop) connection is one in

which more than two specific devices share a single link.

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•the capacity of the channel is shared, either spatiallyor temporally.

•it is a spatially shared connection since several devices are using the same link
simultaneously.
•it is a timeshared connection as because of the users may take turns.

Physical Topology
•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.
•Topology: geometric representation of the relationship of all the links and linking devices
(usually called nodes) to one another.

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FOUR basic topologies are:

1.MESH
2.STAR
3.BUS
4.RING

5.MESH TOPOLOGY

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• 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.

ADVANTAGES
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.
Mesh topology is robust. If one link becomes unusable, it does not incapacitate the
entire system.
There is the advantage of privacy or security. When every message travels along a
dedicated line, only the intended recipient sees it.
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
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DISADVANTAGES
Installation and reconnection are difficult. because every device must be connected to every
other device.
Needs large amount of cabling and the number of I/O ports.
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.

APPLICATIONS
•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.

2. STAR TOPOLOGY

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• 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.
• 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
Less expensive, easy to install and reconfigure. Because, each device needs only one
link and one I/O port to connect it to any number of others.
Far less cabling needs to be housed, and additions, moves, and deletions involve only
one connection: between that device and the hub.
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.

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DISADVANTAGES
Dependency of the whole topology on one single point, the hub. If the hub goes down, the
whole system is dead.
More cabling is required in a star than in some other topologies (such as ring or bus).

APPLICATIONS
Used in local-area networks (LANs). High-speed LANs often use a star topology with a
central hub.

3. BUS TOPOLOGY

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• Bus topology is multi-point.

• A 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.
• 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
Easy installation.
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.

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DISADVANTAGES
Difficult reconnection and 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.
A fault or break in the bus cable stops all transmission, even between devices on the same
side of the problem. The damaged area reflects signals back in the direction of origin,
creating noise in both directions.

APPLICATIONS
Ethernet LANs

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4. 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.

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ADVANTAGES
Easy to install and reconfigure. Each device is linked to only its immediate neighbours
(either physically or logically).
To add or delete a device requires changing only two connections.
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.

DISADVANTAGES
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.

APPLICATIONS
Ring topology was prevalent when IBM introduced its local-area network, Token Ring.

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LOCAL AREA NETWORK (LAN)

•Privately owned and connects some hosts in a single office, building, or campus.
•Ex: LAN can be as simple as two PCs and a printer in someone’s home office.
•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.
•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.

WIDE AREA NETWORK (WAN)

•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.
•WAN is normally created and run by communication companies and leased by an
organization.

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WAN examples:
1.point-to-point WANs and
2.switched WANs

Point – to – Point WAN

•Connects two communicating devices through a transmission media (cable or air).

•It has got only two ends.
•Connecting devices may be a switch or router.

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2. Switched WAN

•Switched WAN is a network with more than two ends.

•Switched WAN is a combination of several point-to-point WANs that are connected by
switches.

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Internetwork

•When two or more networks are connected, they make an internetwork, or internet.
•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.

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Ex 2: A heterogeneous network made of four WANs and three LANs

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Difference between Hub, Switch and Router:

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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.
•TWO types of switched network:
1. circuit-switched and 2. packet-switched networks

1.CIRCUIT SWITCHED NETWORK

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Ex: Telephone networks

•The switches used in this example have forwarding tasks but no storing capability.
•Circuit-switched network is efficient only when it is working at its full capacity.
•It is inefficient because it is working at partial capacity.

2. PACKET SWITCHED NETWORK

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Ex: Computer networks

•In a computer network, the communication between the two ends is done in blocks
of data called packets.
•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.
•A router in a packet-switched network has a queue that can store and forward the
packet.
•More efficient than a circuit switched network, but the packets may encounter some
delays.

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THE INTERNET
• An internet is two or more networks that can communicate with each other.

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• 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.
• Provider networks use the services of the backbones for a fee.
• Customer networks 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).
• Backbones are often referred to as international ISPs
• Provider networks are often referred to as national or regional ISPs.

ACCESSING THE INTERNET

1. Using Telephone Networks
a. Dial-up service
Very slow, and when the line is used for Internet connection, it cannot be
used for telephone (voice) connection. It is only useful for small
residences.
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b. DSL Service – Digital Subscriber Line

Upgraded telephone wires used by DSL, faster than dial up service. It allows
the line to be used simultaneously for voice and data communication.

2. Cable Networks
A residence or a small business can be connected to the Internet by using this
service. It provides a higher speed connection, but the speed varies depending on the
number of neighbours that use the same cable.

3. Wireless Networks
A household or a small business can use a combination of wireless and wired
connections to access the Internet.

4. Direct Connection
A large organization or a large corporation can itself become a local ISP and be
connected to the Internet. This can be done if the organization or the corporation
leases a high-speed WAN from a carrier provider and connects itself to a regional ISP.

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INTERNET HISTORY
1.ARPANET(Advanced Research Projects Agency Network)
•Each host computer (not necessarily from the same manufacturer) would be attached to
a specialized computer, called an interface message processor (IMP).
•The IMPs, in turn, would be connected to each other. Each IMP had to be able to
communicate with other IMPs as well as with its own attached host.
•Software called the Network Control Protocol (NCP) provided communication between
the hosts.

2. Transmission Control Protocol (TCP) and Internet Protocol (IP)

•IP would handle datagram routing while TCP would be responsible for higher level
functions such as segmentation, reassembly, and error detection.

3. Computer Science Network (CSNET)

•It is a less expensive network; there were no redundant links and the transmission rate
was slower.

4. World Wide Web and Multimedia

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STANDARDS AND ADMINISTRATION

•Internet standard: It is a thoroughly tested specification(Internet draft) that is useful
to and adhered to by those who work with the Internet.
•Internet draft: It is a working document (a work in progress) with no official status
and a six-month lifetime.
•Upon recommendation from the Internet authorities, a draft may be published as a
Request for Comment (RFC).
•RFC is then edited, assigned a number, and made available to all interested parties.
RFCs go through maturity levels and are categorized according to their requirement
level.

MATURITY LEVELS
Six levels are there:
1.Proposed Standard
•Specification that is stable, well understood, and of sufficient interest to the Internet
community.
•At this level, the specification is usually tested and implemented by several different
groups.
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2. Draft Standard
•A proposed standard is elevated to draft standard status after at least two successful
independent and interoperable implementations.
•Barring difficulties, a draft standard, with modifications if specific problems are
encountered, normally becomes an Internet standard.

3. Internet Standard
•A draft standard reaches Internet standard status after demonstrations of successful
implementation.

4. Historic
•They either have superseded by later specifications or have never passed the necessary
maturity levels to become an Internet standard.

5. Experimental
•Describes the work related to an experimental situation that does not affect the
operation of the Internet.
•Such an RFC should not be implemented in any functional Internet service.
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6. Informational
•Contains general, historical, or tutorial information related to the Internet. It is usually
written by someone in a non-Internet organization, such as a vendor.

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REQUIREMENT LEVELS
Five levels are there:
1.Required
•An RFC is labelled required if it must be implemented by all Internet systems to
achieve minimum conformance.
•For example, IP and ICMP are required protocols.
2. Recommended
•An RFC labelled recommended is not required for minimum conformance.
•It is recommended because of its usefulness. For example, FTP and TELNET are
recommended protocols.
3. Elective
•An RFC labelled elective is not required and not recommended. However, a system can
use it for its own benefit.
4. Limited Use
•An RFC labelled limited use should be used only in limited situations. Most of the
experimental RFCs fall under this category.
5. Not Recommended
•An RFC labelled not recommended is inappropriate for general use. Normally a
historic RFC may fall under this category.
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INTERNET ADMINISTRATION

ISOC – Internet Society

•Provides support for the Internet standards process.
•Promotes research and other scholarly activities relating to the Internet.
IAB – Internet Architecture Board
•It is the technical advisor to the ISOC.
•Oversees the continuing development of the TCP/IP Protocol Suite using IETF and
IRTF.
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IETF - Internet Engineering Task Force
•It is a forum of working groups managed by the Internet Engineering Steering Group
(IESG).
•Responsible for identifying operational problems and proposing solutions.
•Develops and reviews specifications intended as Internet standards.
•The working groups are collected into areas, and each area concentrates on a specific
topic.
•The areas include applications, protocols, routing, network management next
generation (IPng), and security.

IRTF - Internet Research Task Force

•It is a forum of working groups managed by the Internet Research Steering Group
(IRSG).
•IRTF focuses on long-term research topics related to Internet protocols, applications,
architecture, and technology.

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PROTOCOLS AND STANDARDS

• 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.

Single layer protocol

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Three layer protocol

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Modularity
•Means independent layers defined in terms of a black box with inputs and outputs.

Module(layer)
•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.

Advantages of protocol layering

•It allows us to separate the services from the implementation.

Principles of protocol layering

First principle - able to perform two opposite tasks.
•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 – two objects under each layer at both sites should be identical.

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TCP / IP PROTOCOL (Transmission Control Protocol/Internet Protocol)

• It is a 5 layer protocol suite (a set of protocols organized in different layers) used in
the Internet.
• It is a hierarchical protocol made up of interactive modules, each of which provides
a specific functionality.

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LAYERS:

1.Physical layer
•Responsible for carrying individual bits in a frame across the link.
•The communication between two devices at the physical layer is still a logical
communication because there is another, hidden layer, the transmission media (cable or
wire).
•The transmission medium does not carry bits; it carries electricalor optical signals.
•The bits received in a frame from the data-link layer are transformed and sent through
the transmission media, but we can think that the logical unit between two physical
layers in two devices is a bit.

2. Data link layer

•Responsible for taking the datagram(packet) 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.
•Takes a datagram and encapsulates it in a packet called a frame.

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3. Network layer
•responsible for creating a connection between the source computer and the destination.
•There can be several routers from the source to the destination, the routers in the path
are responsible for choosing the best route for each packet.
•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 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. 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.

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4. Transport layer
•The transport layer is responsible for giving services to the application layer: to get a
message from an application program running on the source host and deliver it to
the corresponding application program on the destination host.

5. Application layer
•The logical connection between the two application layers is end to end.
•Two application layers exchange messages between each other as though there were a
bridge between the two 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.
•Supported by protocols like HTTP, SMTP, FTP, TELNET, SSH, SNMP, DNS and
IGMP

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• 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 protocols to find the
network-layer address of a computer.
• The Internet Group Management Protocol (IGMP) is used to collect membership in
a group.

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LAYERED ARCHITECTURE
Ex: Communication through an Internet

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Logical connections between layers of the TCP/IP protocol suite:

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Identical objects in the TCP/IP protocol suite:

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Encapsulation and Decapsulation:

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Multiplexing and Demultiplexing

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THE OSI MODEL

•Open Systems Interconnection
•An open system is a set of protocols that allows any two different systems to
communicate regardless of their underlying architecture.
•It is a model for understanding and designing a network architecture that is flexible,
robust, and interoperable.
•It consists of seven separate but related layers, each of which defines a part of the
process of moving information across a network.

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OSI versus TCP/IP

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Lack of OSI Model’s Success:

•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.
•Third, when OSI was implemented by an organization in a different application, it did
not show a high enough level of performance

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ADDRESSING

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