EXPLAINATION OF OSI LAYER

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).