07. Application Layer of OSI Model (Layer7)

The last layer of OSI Model, the Application Layer is responsible for End user Network Applications. It is the 7th & highest Layer in the 7Layer OSI Model. This is the layer where real traffic data is generated in most of the cases. This could be a web request generated from HTTP protocol, a command from telnet protocol, a file download request from FTP protocol etc.

OSI Model divides the network communication processes into seven layers in order to simplify it. Each layer performs specific functions to support the layers above it. The 7x Layer model starts from Physical till Application Layer as in below fig:

OSI Model Layers Waqas Karim

 

Functions/Duties of Application Layer

Each Layer in OSI Model Performs some important duties. Important functions performed by Network Layer are listed here:

  • Application Layer manages applications software running on a computer or terminal. This is the most important function of Applications Layer.
  • Application Layer supplies Network Services to End User It works like an interface between Network Services & Applications.
  • Application Layer is also responsible for End User Processes Management.
  • Application Layer also provides miscellaneous other services including Naming Services (e.g. DNS), Mail Services (e.g. SMTP/POP3), Remote Login Services (e.g. Telnet/SSH), Remote Host Mgmt (e.g. SNMP) ,…

 

Application Layer Protocols

The OSI Model provides a conceptual framework for communication between computers, but the model itself is not a method of communication. Actual communication is made possible by using communication protocols. Each layer on the OSI Model has some protocols associated with it. Some important protocols on Physical layer are listed in below:

OSI Model Application Layer Waqas Karim Pic1

 

Network Equipment/Components at Application Layer

Similar to protocols, each layer has associated equipment with it. Some important Equipment that operate at Physical Layer of OSI Model are listed in below:

OSI Model Application Layer Waqas Karim

 

Summary

  • 7th Layer in OSI 7 Layer Model
  • It performs important functions like Applications Management, End User Processes Mgmt & Miscellaneous other services like DNS, DHCP, SMTP, Telnet, …
  • Important Protocols at Application Layer include HTTP, DNS, DHCP, FTP, Telnet, POP3/IMAP, BOOTP, Bitcoin …
  • Equipment operating at Application Layer include End Devices, Firewalls, Gateways, Load Balancers.

 

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