Before we guys going through real hacking tricks we need to know what is exactly the OSI layer.. Because everything is depend on this seven layer..As more you learn about this, as much as you will be a great hacker..
OSI Layer:
let's breakdown this definition piece by piece and then we'll move onto a thorough explanation of each layer. Standards are rules of communication between two or more machines Protocols are instances of standards that apply to communication between equal processes on different machines but on the same layer. This same layer communication is known as horizontal
communication. In an attempt to create an analogy imagine standards as Federal Laws protocols would be like State Laws.
A framework is like a blueprint, a basic design. Lastly, a network is a system of computer components that connects two or more computers.
Application Layer:-
Starting
at the top, the Application layer allows communication to take place between
two different applications on two different machines.
Different
applications have different protocols just as different file systems have
different naming conventions and other such incompatibilities are all dealt
with on the application layer.
Examples
of different applications are file transfers and e-mail..
Presentation Layer:-
Just
below the Application Layer is the presentation Layer. The basic design of the
presentation Layer is format the information to be delivered or information
received to the preferences of the two computers involved in the transaction.
These
computers agree on a transfer syntax. It is as if English and German speakers,
who both also speak French and Italian agree to communicate in French ?(Panko)
This layer is also were processes such as data compression and data encryption
also occur. This layer also causes many problems for any computer trying to
communicate with it using TCP/IP.
because
TCP/IP does not have a specific layer to serve these purposes..
Session Layer:-
The
Session Layer establishes a session between two computers.
This
session may be remotely timed, may allow file transfer, it may manage dialogue.
This dialogue can allow traffic to go in both directions at the same time or
may limit transfer so only one party may transmit at a time.
The
session can also be set up for token transfers. This token is like a talking
stick in the kindergarten. The person with the talking stick is the only one
allowed to talk at a time. When it is passed, then that person becomes the only
one allowed to talk. Another service of the Session Layer is to enable
synchronization.
This
option prevents all possibility of collision during transmission.
Examples
of Session Layer Protocols include NetBIOS, Name Pipes, Mail Slots, and RPC
(OSI Model Layers).
Transport Layer:-
The
main function of the Transport Layer is to receive data from the Session Layer,
break it up into smaller units if needed, pass them all to the network layer,
and ensure that all of the pieces arrive at the destination correctly.
The
Transport Layer establishes the correct network connection specified by the
Session Layer. The Transport Layer may create multiple network connections, to
increase throughput. Depending on the options set due to expensive transmission
costs, the Transport Layer may also multiplex many connections onto the same
network connection.
Multiplexing
is the act of breaking up the connection into sections to send more information
at once. The type of service is also determined on this layer, such as
Point-to-Point.
The
Transport Layer uses the transport header to tell the receiver what message
belongs to what connection. The final responsibility of the Transport Layer is
to establish network connections and delete them.
Examples
of protocols used on the Transport Layer are NetBIOS, TCP, and ATM (OSI Model
Layers).
Network Layer:-
I
know this is boring, but there’s only three more layers to go. The Network
Layer is next.
“The
network and transport layers of the OSI correspond closely to the internet and
transport layers of TCP/IP (Panko). The Network layer controls the operation of
the subnet.
The
Network Layer decides the route for the packets to take. This route may be “wired
into?
Such
as in a terminal session, or may be dynamic which allows for decision making
according to the current network workload.
The
Network Layer also keeps track of the amount of data sent for billing purposes.
Data Link Layer:-
The
Data Link Layer is what you could consider the organizer of the system.
The
Physical Layer accepts data with no regard for organization. The DLL (Data Link
Layer) organizes the received data into a single stream in order as described
by the frame.
The
DLL provides error control, by announcing any missing frames or damaged
ones.
The
DLL can also regulate the speed of transmission. This is necessary when the
sender is capable of sending information much faster than the receiver can take
it.
This
is critical in preventing loss of data and congestion. If the Session Layer has
allowed for transmission in both directions, the DLL must compensate for lack
of transmission capabilities by using techniques such as piggybacking.
The
protocol for this layer is the 802.1 OSI Model (OSI Model Layers).
Physical Layer:-
Finally,
the Physical Layer is the most basic of all the layers in concept. All it does
is transmit and receive data in the form of electrical pulses.
It
uses binary language to transmit. The electrical signal is in pulses, so a 0
represents off and 1 represents on.
Problems
on this layer come from use of physical transmission medium like a phone line
or a cable line or even a fiber optic line.
The
transmission protocols for the Physical Layer include IEEE 802, IEEE 802.2, ISO
2110, and ISDN (OSI Model Layers).
