Internet Reference Models - Internet Technologies

What is Reference Model?

Reference Model is acceptable everywhere as a means of standardization as the computer network is located over a wide physical range and has heterogeneous architecture.

OSI and TCP/IP reference model are the two types of reference models. Even though OSI model is a hypothetical one, TCP/IP is a practical model.

OSI Model

International Organization of Standardization (ISO) developed ISO model and is acronym of Open System Interface. Hence it is also referred as ISO-OSI model.

Below diagram shows the OSI model. It has seven layers each having a specific function.


Physical Layer

This layer is responsible for the activities below:

  • Activation, maintenance and deactivation of the physical connection.
  • Transmission voltages and data rates are defined.
  • Electrical signal is converted to digital bits.
  • Choosing what the connection type should be simplex, half duplex or full duplex.

Data Link Layer

This layer does the following functions:

  • The data transmitted over the physical link is synchronized and error control is done.
  • Error detection bits are added to the data for transmission.

Network Layer

Below are the functions of Network Layer:

  • Routing the signals via many channels to the other end.
  • It functions as the network controller by choosing the route the data should take.
  • It combines incoming packets into messages and divide the outgoing messages into packets for higher levels.

Transport Layer

Following are the functions performed by Transport layer-

  • Decision for transmitting data over parallel path or single path is done in this layer.
  • Slitting and Multiplexing is performed.
  • Data groups are broken down into small units and pass it over to network layer so that they can handle it efficiently.
  • This layer guarantees the data transmission from one end to other end.

Session Layer

This layer performs the below functions-

  • Messages are managed and the conversations are synchronized between two different applications.
  • User Identification, Billing and Session management is controlled.

Presentation Layer

The Presentation layer does below functions:

  • It makes sure that the data is presented in understandable way in the end.

Application Layer

The Application layer does below functions:

  • Manipulation of data, retransferring the files of information, distributing the results etc. is the services this layer provides.
  • It performs LOGIN or password checking.

TCP/IP Model

TCP/IP is the acronym of Transmission Control Protocol and Internet Protocol and is a practical model used in the internet.

This layer is the combination of Physical and Data Link layer i.e. Host-to-Network layer. Below diagram shows the different types of TCP/IP model-


Application Layer

Similar to OSI model and below are its functions.

  • Different services such as manipulation of information in several ways, retransferring the files of information, distributing the results etc. are performed.
  • LOGIN or password checking is done by the application layer.
  • TELNET, FTP, SMTP, DN, HTTP, NNTP are the protocols employed in this layer.

Transport Layer

Similar to OSI model and below are the key points-

  • TCP and UDP protocol for end to end transmission is used.
  • TCP protocol is most reliable and connection oriented protocol.
  • Flow control is handled by TCP.
  • The UDP is not reliable and a connection less protocol also does not perform flow control.
  • TCP/IP and UDP protocols are used in this layer.

Internet Layer

In this layer, host is allowed to insert packets into network and they are travelled independently to the destination. Though the packets are sent in an order, at the receiving end, the order is not guaranteed.

  • Internet Protocol (IP) is employed in Internet layer.

Host-to-Network Layer

  • It is the lowest layer in the TCP/IP model. The host has to connect to network using some protocol, so that it can send IP packets over it. This protocol varies from host to host and network to network.
  • ARPANET, SATNET, LAN, packet radio are the protocols employed in this layer.

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