We're almost done with our discussion of Internet addresseswe just have one more layer to discuss: application addresses. Email, Web browsing, ICQ, and Inter-net Relay Chat (IRC) are just a few of the services that have their own application-specific addressing. When you send email, you know to use a two-part address that includes both a mailbox and a domain, such as firstname.lastname@example.org. You can't send email to wkruse, nor can you just send it to computer-forensic.comyou need to specify both in order for a message to reach a destination.
Another ubiquitous form of Internet addressing that includes both domain- and application-specific information is the Universal Resource Locators (URLs) used with Web browsers. For instance, the URL http://www.lucent.com/services provides three types of information. The letters "http://" indicate the application protocol, which in this case is Hypertext Transfer Protocol (HTTP). "http://www.lucent.com," of course, represents a specific numeric IP address, and "services" points to a specific page.