Application Layer

The application layer is the topmost layer of the OSI Model. As shown in the figure below, the upper three layers of the OSI model (application, presentation, and session) describe the functions of the single TCP/IP application layer. The application layer enables humans or software to get access to the network. It also serves as the source and destination of communications across data networks.

Application Layer 1

The application layer applications, services, and protocols enable humans to interact with the data network in a way that is useful. The applications are computer software programs with which the user interacts and start the data transfer process at the request. The services are programs that run in the background and give the link between the application layer and the lower layers.

The Protocols give a structure of rules that make sure services running on a particular device, and can send and receive data from a range of different network devices. The client should request from the server, the delivery of data packets over the network. In the case of a P2P network, the affiliation of client/server establishes, according to the source device and which the destination device is at that time of establishes. The conversions are exchanged between the application layer services at both end devices in accordance with the terms of the protocol to set up and use these relations.

TCP/IP Application Layer Protocols

The end devices usually require application layer protocols. For example, the end devices receive web pages using HTTP (hypertext transfer protocol) application, which is one of the widely used application protocols.

HTTP is the base for the World Wide Web. When a browser requests a web page, the protocol sends the name of the required page to the server. The server then sends the requested page to a client. For example, the servers SMTP (simple mail transfer protocol), IMAP(internet messaging access protocol), and POP (post office protocol) keep up sending and receiving the email. SMB(server message block),  FTP (file transfer protocol) and TFTP(trivial file transfer protocol)  allow clients to share files.

P2P applications make it easier to share media in a distributed fashion. DNS (domain name system) resolves the IP address and name address for better human understanding. Clouds are remote locations that host applications and store data so that end-users do not need as many local resources, and the users can effortlessly access content from a different place.

The TCP/IP application protocols show the format and control information required for many general Internet communication functions.  Both source and destination devices use the application layer protocols during a communication session. The application layer also enables hosts to work and play over the Internet. The figure below illustrates the application layer for both the OSI and TCP/IP models.

Application Layer 2