Wednesday, February 29, 2012

Hacking Basics and Introduction(OSI Model) Part-2

OSI MODEL,

OSI defines inter-networking in terms of a vertical stack of seven layers. The upper layers represent software that implements network services like encryption and connection management. The lower layers of the OSI model implement more primitive, hardware-oriented functions like routing, addressing, and flow control.
7)  Application Layer : The application layer provider different services to the application. Example of services provided by this layer are file transfer, electronic messaging e-mail, virtual terminal access and network management.
6) Presentation Layer : The Presentation layer is responsible for protocol conversion, date encryption/decryption, Expanding graphics command and the date compression. This layer makes the communications between two host possible.
5) Session Layer : This layer is responsible for establishing the process-to-process communication between the host in the network. This layer is responsible for establishing and ending the sessions across the network. The interactive login is an example of services provided by this layer.
4) Transport Layer : This layer is responsible for end-to-end delivers of messages between the networked hosts. It first divides the streams of data into chunks or packets before transmission and  then the receiving computer re-assembles the packets. It also guarantee error free data delivery without loss or duplications.
3) Network Layer : This layer is responsible for addressing, determining routes for sending and managing network problems such as packet switching, data congestion and routines.
2) Data Link Layer : Data link layer is responsible for controlling the error between adjacent nodes and transfer the frames to other computer via physical layer.
1) Physical Layer : Physical  Layer is responsible for transmitting row bit stream over the physical cable. The physical layer defines the hardware items such as cables, cards, voltages etc.

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