Network Security at OSI Layer

Topics: OSI model, Transmission Control Protocol, Internet Protocol Suite Pages: 54 (7615 words) Published: March 25, 2014
Network Security at OSI Layers
Muhammad Muzammil
Syed Zeeshan Nasir
Department of computer science FUUAST, Islamabad

1-OSI Model:
In 1983, the International Organization for
Standardization (ISO) and the International
Telegraph and Telephone Consultative
Committee (CCITT) merged documents and
developed the OSI model, which is based on
a specific hierarchy where each layer builds
on the output of each adjacent layer.
The OSI model is a protocol stack where the
lower layers deal primarily with hardware,
and the upper layers deal primarily with
software. The OSI model’s seven layers are
designed so that control is passed down
from layer to layer. The seven layers of the
OSI model are shown:
Application support such as
File Transfer Protocol (FTP),
Telnet, and
Hypertext Transfer Protocol
Presentation Encryption, Server Message
Block (SMB), American
Standard Code
for Information Interchange
(ASCII), and formatting
Data flow control, startup,
communications, UDP and
TCP services


Data link


protocols such as IP and
Open Shortest Path
First (OSPF). Path control
and best effort at delivery
Network interface cards,
Media Access Control (MAC)
framing, formatting, and
organizing data
Transmission media such as
wireless systems,
and fiber-optic cable

1.2-Functions of OSI Model:
The OSI model functions as follows:
1. Information is introduced into the
application layer and passed down until it
ends up at the physical layer.
2. Next, it is transmitted over the physical
medium (i.e., wire, coax, or wireless) and
sent to the target device.
3. Once at the target device, it proceeds
back up the stack to the application layer.

1.3-Explanation of Layers:
The Application Layer:
Layer 7 is known as the application layer.
Recognized as the official top layer of the
OSI model, this layer serves as the window
for application services.
The Presentation Layer:
Layer 6 is known as the presentation layer.
The main purpose of the presentation layer
is to deliver and present data to the
application layer. This data must be
formatted so that the application layer can
understand and interpret it. The
presentation layer is responsible for items
such as:
• Encryption and decryption of
• Compression and deCompression of
messages, format translation
• Handling protocol conversion
The Session Layer:
Layer 5 is known as the session layer. Its
purpose is to allow two applications on
different computers to establish and
coordinate a session. It is also responsible
for managing the session while information
and data are being moved. When a data
transfer is complete, the session layer tears
down the session. Session-layer protocols
• Remote Procedure Call (RPC)
• Structured Query Language (SQL)
The Transport Layer:
Layer 4 is known as the transport layer.
Whereas the application, presentation, and
session layers are primarily concerned with
data, the transport layer is focused on
segments. Depending on the application
protocol being used, the transport layer can

send data either quickly or reliably.
Transport layer responsibilities include endto-end error recovery and flow control. The two primary protocols found on this layer
• TCP A connection-oriented protocol;
provides reliable communication
using handshake acknowledgments,
error detection, and session
• UDP A connectionless protocol;
offers speed and low overhead as its
primary advantage.
The Network Layer:
Layer 3 is known as the network layer,
which is fixed to software and deals with
packets. The network layer is the home of
the IP, which offers best effort at delivery
and seeks to find the best route from the
source to the target network. Networklayer...
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