Figure 7-4 show the relationship between an organization’s information system and the Internet. A device called A border router connects an organization’s information system to the Internet. Behind the border router is the main firewall, which is either a special-purpose hardware device or software running on a general-purpose computer. The organization’s Web servers and e-mail servers are placed in a separate network, called the demilitarized zone(DMZ) because it sits outside the corporate network yet is accessible which information is allowed to enter and leave the organization’s information system. To understand how they function, it is first necessary to briefly discuss how information is transmitted on the Internet.