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Chapter 7 Telecommunications, the Internet, and Wireless Technology 289

Protocol (IP) address, which currently is a 32-bit number represented by four
strings of numbers ranging from 0 to 255 separated by periods. For instance, the
IP address of www.microsoft.com is 207.46.250.119.
When a user sends a message to another user on the Internet, the message is
first decomposed into packets using the TCP protocol. Each packet contains its
destination address. The packets are then sent from the client to the network
server and from there on to as many other servers as necessary to arrive at a
specific computer with a known address. At the destination address, the pack-
ets are reassembled into the original message.

The Domain Name System
Because it would be incredibly difficult for Internet users to remember strings
of 12 numbers, the Domain Name System (DNS) converts domain names
to IP addresses. The domain name is the English-like name that corresponds
to the unique 32-bit numeric IP address for each computer connected to the
Internet. DNS servers maintain a database containing IP addresses mapped
to their corresponding domain names. To access a computer on the Internet,
users need only specify its domain name.
DNS has a hierarchical structure (see Figure 7.6). At the top of the DNS
hierarchy is the root domain. The child domain of the root is called a top-level
domain, and the child domain of a top-level domain is called is a second-
level domain. Top-level domains are two- and three-character names you are
familiar with from surfing the Web, for example, .com, .edu, .gov, and the
various country codes such as .ca for Canada or .it for Italy. Second-level
domains have two parts, designating a top-level name and a second-level
name—such as buy.com, nyu.edu, or amazon.ca. A host name at the bottom
of the hierarchy designates a specific computer on either the Internet or a
private network.

FIGURE 7.6 THE DOMAIN NAME SYSTEM

Domain Name System is a hierarchical system with a root domain, top-level domains, second-level
domains, and host computers at the third level.

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