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Millions of users browse the Internet from mobile devices every day, many without a second thought as to how wireless data transfer works. Though wireless service providers make surfing the Internet seem like a seamless extension of the cell phone, wireless delivery of Internet data follows a long and complex technological path.
To end users, the cell phone is the most visible part of wireless Internet service. The phone is essentially a handheld personal computer; it contains a processor, memory, storage and software designed for accessing and using the Internet. Unlike a typical computer, though, cell phones also include radio transceivers that encode data for wireless transmission and decode data received over the air. When a user browses the Internet from a cell phone, all of these components work together to accept the user’s input, establish a connection with the wireless data network and connect to the Internet.
The Cell Tower
Cell towers facilitate the connection between cell phones and the wireless network. When users connect to the Internet, the cell phone collects data, breaks it into small, encoded pieces known as packets, labels each packet with the Internet Protocol address of the destination server and transmits the packets to the cell tower. The cell tower decodes the incoming data, then passes it on to the rest of the network. At the same time, the cell tower receives data destined for the cell phone, encodes it into packets, labels the packets with the cell phone’s unique identifying information and uses radio waves to transmit the packets to the phone.
The IWF
As the wireless carrier’s network receives data packets from cell phone users, it must connect those packets with the Internet. To accomplish this task, service providers use a device known as the Interworking Function, or IWF. This device, which consists of both hardware and software, accepts data packets from the cell tower, determines that they are destined for the Internet and relays the packets to an attached high-speed Internet connection. The IWF also receives data packets from the Internet, determines the cell tower most capable of connecting them with the cell phone, and routes them accordingly.
The Internet
When data packets arrive at the carrier’s Internet connection, the network uses the IP address assigned by the cell phone to route the packets to the destination server. Depending on the destination, the data packets may pass through dozens of different computers, known as nodes, as they travel between the wireless network and the server. Each of these nodes interprets the destination IP address and forwards the packet to the next node, ultimately delivering it to the destination server. The server responds by sending its own data packets, each carrying the cell phone’s IP address, back out to the Internet for delivery to the wireless network. By exchanging hundreds or even thousands of data packets, cell phones can access and retrieve information from almost any Internet device.