er in the ISO/OSI model it is also referred to as L7. The application layer manages commu- nication between applications and handles issues like network transparency and resource allocation. In addition to providing network access as the key functional- ity, the application layer also offers services for user applications. Let us consider how the application layer offers services for user applications with an example of World Wide Web (www). The Web browser is an application that runs on a machine to display Web pages and it makes use of the services offered by a protocol that operates at the application layer. Viewing the vast collec- tion of hypertext-based files available on the Internet as well as providing quick and easy retrieval of these files using a browser is made possible using the application layer protocol called hyper text transfer protocol (HTTP). Some of the other popular application layer protocols include simple mail trans- fer protocol (SMTP) that gives electronic mail functionality to be implemented in applications through which all kinds of data can be sent to other users of the Internet as an electronic postal system and file transfer protocol (FTP) is used to transfer files between two machines. The network management protocol SNMP is Seven-Layer Communication Model also an application layer protocol as it provides interfaces for network management applications to collect network data. A program that implements the interfaces provided by the application layer protocol is required in the machine. That is, an FTP client should be running on the machine to transfer files from the FTP server and an SNMP agent should be running on the network element to source data to a network manager using the SNMP protocol. The user application can operate without an application layer using protocol modules that initialize communication with other application, set up the presenta- tion context, and transfer messages. In this mode of operation the application will interact directly with the presentation layer.