The application layer enables the user whether human or software to access the network. It provides user interfaces and support for services such as electronic mail, fire access and transfer access to systems resources surfing the world wide web and network management. In this part we briefly discuss some applications that are designed as a client server pair in the internet. the client sends a request for a service to the server the server responds to the client.
In this chapter we will briefly the key application layer concepts including application layer protocol clients and servers. Processes sockets and transport layer interface and full explanation of several network applications in detail including the web e mail DNS ( Domain Name Server) and P2P ( point to point) file sharing.