OSI Model
                     The Open System Interconnection (OSI) Model provides an abstract description of the network communication process. International Organization for Standard (ISO) develops it to provide a road map for non-proprietary protocol development. The OSI model is just a reference model and many of OSI protocols are no longer in use. There are seven layers in OSI Model. Those are as follows:

Layer 7 -  Application
                        Performs services for the application used by the end users.

Layer 6 -  Presentation
                       Provides data format information to the application.

Layer 5 -  Session
                      Manages session between users.

Layer 4 -  Transport
                     Defines data segments and numbers them at the source, transfers the data, and reassembles the data at the destination.

Layer 3 -  Network
                    Creates and addresses packets for end-to-end delivery through intermediary devices in other network.

Layer 2 - Data Link
                    Creates and addresses frames for host-to-host delivery on the local LANs and between WAN devices.

Layer 1 - Physical
                    Transmits binary data over media between devices. Physical layer protocols define media specifications.

TCP/IP Model
                    TCP / IP is an open standard. The rules and implementation of the TCP/IP model were cooperatively developed by members of the industry using Request for Comments (RFC) documents. There are four layers in TCP/IP Model. Those are as follows:

Layer 4 -  Application
                   Represents application data to the user.

Layer 3 - Transport
                Supports communication between devices and performs error correction.

Layer 2 - Internet
                   Finds the best path through the network.

Layer 1 - Network access
                  Controls hardware devices and media.


Comparison of OSI and TCP / IP Model

  7.  Application     4. Application
  6.  Presentation
  5.  Session
  4.  Transport
   3. Transport
  3.  Network    2.  Internet
  2.  Data Link    1. Network Access
  1.  Physical

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