OSI Model

  • It stand for open system intercommunication and it defines protocols or rules which must be followed by each networking vendor.
  • It is a seven layered architecture where each layer plays a significant role when a devices communicates.
  • One of the key advantages of this model is that it allows different vendors network to inter operate that is possibility of communication between devices of different vendors.
  • With modular approach it makes the design, deployment, debugging easy for networks.
  • It prevents making change of one layer affecting the other layer, that is loose coupling between each layers.

Sever layers present are:

  • Application Layer
  • Presentation Layer
  • Session Layer
  • Transport Layer
  • Network Layer
  • Data link Layer
  • Physical Layer

Brief about each layer:

Application Layer:

It is the top most layer and acts as an interface between the application used and the underlying network infrastructure.

It identifies the communication partner and determine the resource availability needed for communication.

Common Protocol: HTTP, HTTPS, FTP

Presentation Layer:

This layer determines the format in which the data need to be presented before the end user. This is responsible for data compression, encryption, decryption.

Some of the common format are JPEG, MP3. Common protocols: SSL, HTML, Telnet.

Session Layer: This layer is responsible for maintaining the session that is creating, managing and then terminating the session between two end users.

It keeps the data separate for each application that is session is created on the basis of five tuples, those are: Source IP address, Destination IP address, Source port, Destination port and protocol in use.

It provide communication which is either simple, duplex or half duplex.

Common Protocols: RPC, SQL, NFS(Network File system)

These three layer together that is application, presentation and session layer are called Upper half layer or also known as host layer.

Transport Layer:

This layer is responsible for end to end communication between an application of two ends. This can be either reliable or unreliable that is either TCP protocol or UDP protocol respectively.

In this layer data are referred as segment

Two Protocols are:

  • TCP: Transport control protocol
  • UDP: User datagram protocol.

Network Layer:

This layer is responsible for inter network communication that is making the communication possible between two different networks. It makes possible host to host communication

This is possible because of device which operates in this layer called router.

In this layer data are referred as packets

Common protocols: IP both IPv4 and IPv6 and routing protocols like BGP, stating routing

Data link layer:

This layer is responsible for physical transmission of data, error notification and flow control. This is again divided into two layers:

  • LLC: Logical link control
  • MAC: Media access control

In this layer data are referred as frames.

Common protocols: Ethernet, Token ring, WAN

Physical layer:

It consist of physical medium like cables used for communication. In this layer data are referred as bits that is 1’s and 0’s

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Categories: Networking

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