Module 1

Networking Principle and Layered

Architecture

Data Communications and Networking: A Communications Model – Data

Communications –Evolution of network, Requirements, Applications, Network
Topology (Line configuration, Data Flow), Protocols and Standards, Network
Models (OSI, TCP/IP)
DATA COMMUNICATIONS
• The term telecommunication means communication
at a distance.
• The word data refers to information presented in
whatever form is agreed upon by the parties creating
and using the data.
• Data communications are the exchange of data
between two devices via some form of transmission
medium such as a wire cable.
Communication Model
CHARACTERISTICS OF DATA COMMUNICATIONS

The effectiveness or requirements 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.
Components of a data communication system
Components of a data communication system

• Message
The message is the information (data) to be communicated. Popular forms of
information include text, numbers, pictures, audio, and video.
• Sender
The sender is the device that sends the data message. It can be a computer,
workstation, telephone handset, video camera, and so on.
• Receiver
The receiver is the device that receives the message. It can be a computer,
workstation, telephone handset, television, and so on.
• 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.
• 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 flow (simplex, half-duplex, and full-duplex)
Data flow - 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
• 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.
Data flow - Half-Duplex

• In half-duplex mode, each station can both transmit and receive, but not
at the same time. : When one device is sending, the other can only
receive, and vice versa
• The half-duplex mode is like a one-lane road with traffic allowed in both
directions. 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
• Walkie-talkies are examples of 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.
Data flow - Full-Duplex

• Both stations can transmit and receive simultaneously.

• 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.
• The full-duplex mode is used when communication in both directions is
required all the time
NETWORKS
NETWORKS
• A network is a set of devices (often referred to as
nodes) connected by communication links.
• A node can be a computer, printer, or any other
device capable of sending and/or receiving data
generated by other nodes on the network.
• A link can be a cable, air, optical fiber, or any
medium which can transport a signal carrying
information.
Network Criteria

 Performance
 Depends on Network Elements
 Measured in terms of Delay and Throughput
 Reliability
 Failure rate of network components
 Measured in terms of availability/robustness
 Security
 Data protection against corruption/loss of data due to:
 Errors
 Malicious users
Line Configuration – Type of Connection
Line Configuration – Point to Point
Network 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.
Categories of Network Topology
A fully connected mesh topology (five devices)
Mesh topology

• Every device has a dedicated point-to-point link to every other device.

• The term dedicated means that the link carries traffic only between the two
• devices it connects.
• 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 (see Figure 1.4) to be connected to the other n – 1
stations.
Mesh topology

Advantages
•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.
Mesh topology

Disadvantages
•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, for example, as a backbone connecting the main computers of a
hybrid network that can include several other topologies.
•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.
A star topology connecting four stations
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
Star topology

Advantages
•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.
Star topology

Disadvantages
•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)
A bus topology connecting three stations
Bus topology

• The preceding examples all describe point-to-point connections.

• A bus topology, on the other hand, 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.
Bus topology

Advantages
•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.
Bus topology

Disadvantages
•Disadvantages include 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.
•In addition, 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.
Bus topology was the one of the first topologies used in the design of early local
area networks. Traditional Ethernet LANs uses bus topology
A ring topology connecting six stations
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
Ring topology

Advantages
•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
Ring topology

Disadvantages
•However, unidirectional traffic can be a disadvantage.
•In a simple ring, a break in the ring (such as a disabled station) can disable the
entire network.
•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.
•Today, the need for higher-speed LANs has made this topology less popular.
A hybrid topology: a star backbone with three bus networks
 Categories of Networks

 Local Area Networks (LANs)

 Short distances
 Designed to provide local interconnectivity
 Wide Area Networks (WANs)
 Long distances
 Provide connectivity over large areas
 Local Area Networks (LANs)
 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.
Local Area Networks (LANs)
 Wide Area Networks (WANs)
 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
 Wide Area Networks (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. We
can say that a switched WAN is a combination of several point-to-point WANs
that are connected by switches
A heterogeneous network made of four WANs and two LANs
THE INTERNET
• Internet is composed of thousands of interconnected networks.
• Internet as several backbones, provider networks, and customer networks.
• At the top level, the backbones are large networks owned by some communication
companies.
• 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).
Evolution of Networks
Early History
•There were some communication networks, such as telegraph and telephone networks,
before 1960.
•These networks were suitable for constant-rate communication at that time, which
means that after a connection was made between two users, the encoded message
(telegraphy) or voice (telephony) could be exchanged.
ARPANET
•In 1967, Advanced Research Projects Agency presented its ideas for the Advanced
Research Projects Agency Network (ARPANET), a small network of connected computers.
•The idea was that 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.
Evolution of Networks

TCP/IP
Cerf and Kahn’s landmark 1973 paper outlined the protocols to achieve end-to-end
delivery of data
In October 1977, an internet consisting of three different networks (ARPANET, packet
radio, and packet satellite) was successfully demonstrated. Communication between
networks was now possible.
MILNET
In 1983, ARPANET split into two networks: Military Network (MILNET) for military users
and ARPANET for nonmilitary users
CSNET
In 1981, Computer Science Network (CSNET) was a network sponsored by the National
Science Foundation (NSF). The network was conceived by universities that were ineligible
to join ARPANET due to an absence of ties to the Department of Defense. CSNET was a
less expensive network; there were no redundant links and the transmission rate was
slower.
Evolution of Networks

NSFNET
With the success of CSNET, the NSF in 1986 sponsored the National Science Foundation
Network (NSFNET), a backbone that connected five supercomputer centers located
throughout the United States. Community networks were allowed access to this
backbone, with a 1.544-Mbps data rate, thus providing connectivity throughout the United
States.
ANSNET
In 1991, the U.S. government decided that NSFNET was not capable of supporting the
rapidly increasing Internet traffic. Three companies, IBM, Merit, and Verizon, filled the
void by forming a nonprofit organization called Advanced Network & Services (ANS) to
build a new, high-speed Internet backbone called Advanced Network Services Network
(ANSNET).
World Wide Web
The 1990s saw the explosion of Internet applications due to the emergence of the World
Wide Web (WWW). This invention has added the commercial applications to the Internet.
PROTOCOLS

• A protocol is synonymous with rule.

• It consists of a set of rules that govern data
communications.
• It determines what is communicated, how it is
communicated and when it is communicated.
• The key elements of a protocol are syntax, semantics
and timing
 Elements of a Protocol

 Syntax
 Structure or format of the data
 Indicates how to read the bits - field delineation
 Semantics
 Interprets the meaning of the bits
 Knows which fields define what action
 Timing
 When data should be sent and what
 Speed at which data should be sent or speed at which it is
being received.
STANDARDS AND ADMINISTRATION

Internet Standards
An Internet standard is a thoroughly tested specification that is useful to and

adhered to by those who work with the Internet.

There is a strict procedure by which a specification attains Internet standard

status.
A specification begins as an Internet draft.

An Internet draft 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).

 Each RFC is edited, assigned a number, and made available to all interested

parties.
RFCs go through maturity levels and are categorized according to their

requirement level.
STANDARDS AND ADMINISTRATION

Maturity levels of an RFC

STANDARDS AND ADMINISTRATION

Maturity Levels
Proposed Standard
A proposed standard is a 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.
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.
Internet Standard
A draft standard reaches Internet standard status after demonstrations of
successful implementation.
STANDARDS AND ADMINISTRATION

Maturity Levels
Historic
The historic RFCs are significant from a historical perspective. They either have
been superseded by later specifications or have never passed the necessary
maturity levels to become an Internet standard.
Experimental
An RFC classified as experimental describes 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.
Informational
An RFC classified as 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.
STANDARDS AND ADMINISTRATION
Requirement Levels
Required
An RFC is labeled required if it must be implemented by all Internet systems to achieve minimum
conformance. For example, IP is required protocols.
Recommended
An RFC labeled recommended is not required for minimum conformance; it is recommended
because of its usefulness. For example, FTP is a recommended protocol.
Elective
An RFC labeled elective is not required and not recommended. However, a system can use it for
its own benefit
Limited Use
An RFC labeled limited use should be used only in limited situations. Most of the experimental
RFCs fall under this category.
Not Recommended
An RFC labeled not recommended is inappropriate for general use. Normally a historic
(deprecated) RFC may fall under this category.
STANDARDS AND ADMINISTRATION
Internet Administration
STANDARDS AND ADMINISTRATION
ISOC
The Internet Society (ISOC) is an international, nonprofit organization formed in 1992

to provide support for the Internet standards process.

ISOC accomplishes this through maintaining and supporting other Internet

administrative bodies
IAB
The Internet Architecture Board (IAB) is the technical advisor to the ISOC.

The main purposes of the IAB are to oversee the continuing development of the

TCP/IP Protocol Suite and to serve in a technical advisory capacity to research

members of the Internet community.
IAB accomplishes this through its two primary components, the Internet Engineering

Task Force (IETF) and the Internet Research Task Force (IRTF).
STANDARDS AND ADMINISTRATION
IETF
The Internet Engineering Task Force (IETF) is a forum of working groups managed by the

Internet Engineering Steering Group (IESG).

IETF is responsible for identifying operational problems and proposing solutions to these

problems.
IETF also develops and reviews specifications intended as Internet standards. The working

groups are collected into areas, and each area concentrates on a specific topic. Currently nine
areas have been defined.
The areas include applications, protocols, routing, network management next generation

(IPng), and security.

IRTF
The Internet Research Task Force (IRTF) 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.

CONNECTING DEVICES
CONNECTING DEVICES
Hub & Repeater
A hub is a device that operates only in the physical layer.

Signals that carry information within a network can travel a fixed distance before attenuation

endangers the integrity of the data.

A repeater receives a signal and, before it becomes too weak or corrupted, regenerates and

retimes the original bit pattern.

The repeater then sends the refreshed signal.

In the past, when Ethernet LANs were using bus topology, a repeater was used to connect two

segments of a LAN to overcome the length restriction of the coaxial cable.

Today, however, Ethernet LANs use star topology.

In a star topology, a repeater is a multiport device, often called a hub, that can be used to serve

as the connecting point and at the same time function as a repeater.

A hub or a repeater is a physical-layer device. They do not have a link-layer address and they do

not check the link-layer address of the received frame. They just regenerate the corrupted bits
and send them out from every port.
CONNECTING DEVICES
CONNECTING DEVICES
Switch
A link-layer switch (or switch) operates in both the physical and the data-link layers. As a

physical-layer device, it regenerates the signal it receives.

As a link-layer device, the link-layer switch can check the MAC addresses (source and

destination) contained in the frame.

Router
A router is a three-layer device; it operates in the physical, data-link, and network layers.

As a physical-layer device, it regenerates the signal it receives.

As a link-layer device, the router checks the physical addresses (source and destination)

contained in the packet.

As a network-layer device, a router checks the network-layer addresses

A router can connect networks.

In other words, a router is an internetworking device; it connects independent networks to

form an internetwork.
CONNECTING DEVICES
Bridge – A bridge operates at the data link layer. A bridge is a repeater, with add on the
functionality of filtering content by reading the MAC addresses of the source and
destination. It is also used for interconnecting two LANs working on the same protocol.
It has a single input and single output port, thus making it a 2 port device.
Switch – A switch is a multiport bridge
Gateway – A gateway, as the name suggests, is a passage to connect two networks that
may work upon different networking models. They work as messenger agents that take
data from one system, interpret it, and transfer it to another system. Gateways are also
called protocol converters and can operate at any network layer.
Network Models
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, or protocol layering.
TCP/IP PROTOCOL
 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.
TCP/IP PROTOCOL
TCP/IP PROTOCOL
TCP/IP PROTOCOL
Logical connections between layers of the TCP/IP protocol suite
TCP/IP PROTOCOL
Identical objects in the TCP/IP protocol suite
TCP/IP PROTOCOL
Physical Layer
Physical layer is responsible for carrying individual bits in a frame across the link.

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

TCP/IP PROTOCOL
Data-link Layer
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

wireless WAN.
We can also have different protocols used with any link type.

In each case, the data-link layer is responsible for moving the packet through the link.

The data-link layer takes a datagram and encapsulates it in a packet called a frame.

Some link-layer protocols provide complete error detection and correction, some

provide only error correction.

TCP/IP PROTOCOL
Network Layer
The network layer is responsible for creating a connection between the source

computer and the destination computer.

Since 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 is responsible for creating a connection between the source

computer and the destination computer. The communication at the network layer is
host-to-host. However, since 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.
IP is a connectionless protocol that provides no flow control, no error control, and no

congestion control services

TCP/IP PROTOCOL
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.
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.
TCP/IP PROTOCOL
Application Layer
the logical connection between the two application layers is endto-end. 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.
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,

etc.
TCP/IP PROTOCOL
TCP/IP PROTOCOL
TCP/IP PROTOCOL
OSI MODEL

 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.
 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.
OSI MODEL
OSI MODEL
Session Layer
This layer is responsible for the establishment of connection, maintenance of sessions,

and authentication, and also ensures security.

The Functions of the Session Layer

Session establishment, maintenance, and termination: The layer allows the two

processes to establish, use and terminate a connection.

Synchronization: This layer allows a process to add checkpoints that are considered

synchronization points in the data. These synchronization points help to identify the
error so that the data is re-synchronized properly, and ends of the messages are not cut
prematurely and data loss is avoided.
Dialog Controller: The session layer allows two systems to start communication with

each other in half-duplex or full-duplex.

OSI MODEL
 Presentation Layer
 The presentation layer is also called the Translation layer. The data from the
application layer is extracted here and manipulated as per the required format to
transmit over the network.
 The Functions of the Presentation Layer are
• Translation: For example, ASCII to EBCDIC.
• Encryption/ Decryption: Data encryption translates the data into another form or
code. The encrypted data is known as the ciphertext and the decrypted data is
known as plain text. A key value is used for encrypting as well as decrypting data.
• Compression: Reduces the number of bits that need to be transmitted on the
network.
OSI MODEL
 Layer 7- Application Layer
 At the very top of the OSI Reference Model stack of layers, we find the Application
layer which is implemented by the network applications. These applications produce
the data, which has to be transferred over the network. This layer also serves as a
window for the application services to access the network and for displaying the
received information to the user.
 Example: Application – Browsers, Skype Messenger, etc.
 Note: The application Layer is also called Desktop Layer.
 The Functions of the Application Layer are
• Network Virtual Terminal
• FTAM- File transfer access and management
• Mail Services
• Directory Services