TCP/IP Model

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TCP/IP was developed by the DoD (Department of Defense) of the United States and DARPA
(Defense Advanced Research Project Agency) in the 1970s. TCP/IP was designed to be an
open standard that anyone could use to connect computers together and exchange
information between them. Ultimately, it became the basis for the Internet.


The TCP/IP model defines four totally independent layers into which it divides the process of
communication between two devices. The layers through which it passes information
between two devices are:



The application layer is the layer nearest the end user. This is the layer that is in charge of
translating data from applications into information that can be sent through the network.
The basic functions of this layer are:

  • Representation
  • Codification
  • Dialog Control
  • Application Management


The transport layer establishes, maintains and finishes virtual circuits for information transfer. It
provides control mechanisms for data flow and allows broadcasting, and it provides
mechanisms for the detection and correction of errors. The information that arrives at this
layer from the application layer is divided into different segments. Information that comes to
the transport layer from the internet layer is delivered back to the application layer through

The basic functions of this layer are:

  • Reliability
  • Flow Control
  • Error Correction
  • Broadcasting


This layer divides the segments of the transport layer into packets and sends the packets
across the networks that make up the Internet. It uses IP, or internet protocol addresses to
determine the location of the recipient device. It does not ensure reliability in the
connections, because this is already taken care of by the transport layer, but it is responsible
for selecting the best route between the originating device and the recipient device.

Network Access:

This layer is in charge of sending information at both the LAN level and the physical level. It
transforms all the information that arrives from the superior layers into basic information (bits)
and directs it to the proper location. At this level, the destination of the information is
determined by the MAC, or media access control, address of the recipient device.

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