The seventh and the top most Layer in the Open Systems Interconnection (OSI) Model, the application layer is also a part of the Transmission Control Protocol and Internet Protocol (TCP/IP).
The main focus of this layer is to provide process to process communication, meaning; to deliver messages from the source host to the destination host. Its is also the only layer which hold a communication line with the end user.
Categorically, it is an abstract layer which ensures the working details of a subsystem is well hidden and allows the facilitation of the separation of concerns (separation of a computer program into different section so that each section can handle a different responsibility) and platform independence.
It is necessary to distinguish between the application layer and an actual application. While an application is a type of software under the wide umbrella term ‘Software,’ an application layer is merely a component inside it designed to establish and hold together a communication channel over a network. Unlike the other layers, it works independently and doesn’t need to interoperate with any of them.
Some of the services provided by the application layer:
- Simple Mail Transfer Protocol
- File Transfer, access and management
- Web surfing
- Mail service
- Directory services
- Exchange of messages
- Web chat
- Virtual terminals
- Network Virtual Terminal
Alongside these services, application layer ensures that the receiving device is identified and is within the reach to receive data while detecting the Ethernet or Wi-Fi as the interface for the necessary communication.
An agreement from both devices is important for the process of data recovery and privacy which is reached through this layer.
The Protocols in the application layer are:
- Hyper Text Transfer Protocol (HTTP) for the transfer of the texts
- Hyper Text Transfer Protocol Secure (HTTP) for a more secure service of text transfer
- File Transfer Protocol (FTP) for the transfer of the files
- Trivial File Transfer Protocol (TFTP) for the file as well as mail transfer and also to read those mails
- Post Office Protocol v3 (POP3)
- Internet Message Access Protocol (IMAP)
- Telecommunication Network (TELNET)
- Network File System (NFS) to view, store and update files pn a remote computer or any other device
- Simple Mail Transfer Protocol (SMTP)
- Line Print Daemon to connect a device with a printer
- Simple Network Management Protocol (SNMP)
- Domain Name Service (DNS)
- Dynamic Host Configuration Protocol (DHCP)
Download Application Layer in OSI Model in pdf – Click here