The application layer is the topmost layer of the TCP/IP protocol. It also performs the role of the session layer and presentation layer in TCP/IP model.
This layer allows people to use the network services and establish network-based applications.
The protocols of this layer are Hypertext transfer protocol (HTTP), File transfer protocol (FTP), TELNET, simple network management protocol, Domain name system protocol and simple mail transfer protocol (SMTP).
This layer promotes the user to utilize the utilities of the network. It gives users utilities like user log in, initializing messages, emails and transmission of files.
2. Transport Layer
This layer is designed for the purpose to allow computers on the source side and destination side to start a communication.
The transport layer regulates the flow of the bits through a flow regulate mechanism or control mechanism, and it gives a reliable and error-free connection between two or more devices.
The protocols of these layers are Transmission control protocol (TCP), User datagram protocol (UDP) and Stream control transmission protocol (SCTP).
The transport layer gives an interface for the operators to the primary network.
3. Internet Layer
This layer defines the protocol that are responsible for the logical transfer of data across the globe.
The protocols of this layers are internet protocol (i.e., responsible for delivering packets), internet control message protocol (i.e., responsible for allowing hosts with data regarding network errors) and Addressing resolution protocol (i.e., responsible for finding the hardware address of a host from a special IP address).
This layer deals with the error in the transmission of data packets and displacements of data packets.
The purpose of this layer is to inject data packets into any network to move independently from source to destination.
4. Network Access Layer
This layer is the combination of the physical layer and data link layer.
It relates to physical layer functions such as bits and the medium used to carry bits and also relates to data link layer functions like converting bits into MAC addresses and ethernet frames.
The network access layer is allocated an address from the internet layer because of this, it can connect with computers on another network.
This layer checks out for hardware addressing, and the protocols of this layer permit the actual transmission of bits.