The network ”and the network of networks, the Internet ”is a combination of hardware and software that allows computers to talk with each other. Networks stack protocols. That is, they have a foundation layer with another layer stacked on top of it, and another on top of that. It's the same in your computer. It has embedded hardware, software, and device drivers; the operating system is on top of that; your application is running on top of all that; and there is a protocol for communication between your application and another one. Open Systems Interconnect (OSI) is an International Organization for Standardization (ISO) standard for worldwide communications that defines a networking framework. It specifies implementing protocols in these seven layers listed from highest to lowest :
All the protocols in the preceding list are necessary for the Internet to work. The code listings that follow demonstrate how to combine several Java network components to build interesting applications, such as a Web browser and Web server, represented by the OSI layering model. |