Networking Fundamentals

This chapter explains the different design principles used in an enterprise network. It also differentiates hardware and software switching mechanisms. The origin of many networking myths can be traced back to the Open Systems Interconnection (OSI) reference model developed by Charles Bachman of Honeywell and formalized by the International Organization for Standardization (ISO). The ISO intended the OSI model to be a standard framework for data networks. It describes a set of “activities necessary for systems to interwork using communication media” (ISO/IEC 7498-4). One thing that has always been clear about the OSI model is that the Application layer includes application data and application protocols. The Hypertext Transfer Protocol (HTTP) is an application protocol that a web browser uses for communicating with web servers. Application data would be an HTTP GET request that the browser sends to a web server. Likewise, the web page that the server sends in response would also be application data. In short, application data is whatever the application sends or receives over the network. Incidentally, an application can use more than one protocol. For example, when a web browser uses the Hypertext Transfer Protocol Secure (HTTPS) protocol to send a request to a web server, it's making use of two protocols: HTTP and Transport Layer Security (TLS). Despite the latter's confusing name, both are application protocols.