How a network transmits data
To view a Web page, the user opens a Web browser, such as Internet Explorer, and enters a Web address, such as http://www.microsoft.com.
The computer translates the Web address into an Internet Protocol, or IP address.
TCP/IP adds the hardware address of the default gateway and sends the data to the computer’s network interface card. In this example, the default gateway is an asymmetric digital subscriber line (ADSL) router, but it can also be a cable modem or a dial-up analog modem.
The network interface card sends the data in single or multiple packets over a wired or wireless network. In this example, the ADSL router is connected directly to the Internet through your Internet service provider (ISP).
TCP/IP sends the data, or network packet, to the local computer’s network interface card, which then passes the packet to the ADSL router. The ADSL router retrieves the packet and passes it to TCP/IP.
TCP/IP examines the packet and decides where to send the data next. TCP/IP replaces the hardware address with the hardware address of the next router and passes the data to the network interface card for transmission on the network.
The data may pass through several routers before it reaches the destination host, or Web server. At every router, the packet is examined and TCP/IP decides where to send the data next.
When the packet reaches the Web server, the application retrieves the requested data (in this case, the Web page) and sends it back to the requesting computer.
The network interface card on the computer receives the data and passes the information to TCP/IP. TCP/IP examines the packet and passes the data to Internet Explorer, which then displays the page. In this example, the computer and ADSL router represent a local area network, or LAN, because they are physically close together.
The Internet is an example of a wide area network, or WAN, because the routers on the Internet typically connect different networks that are geographically separated. In an office environment, when a user requests a Web page, the packet may pass through several hubs, switches, or routers on the office LAN before it reaches the Web server on the Internet.