Before we take a look at how wireless networking actually works, let's take a quick look at how computers communicate on a network. For computers to communicate on a network, there must be a network architecture in place that dictates how the data moves from one computer and then over the wire (on a cabled LAN) or wireless signal (on a WLAN).
The most widely embraced network architecture is Ethernet. The Ethernet standards define how an Ethernet network adapter, Ethernet switch, Ethernet access point, and other Ethernet devices transmit data on the network. Data transmission speed is measured in bits per second (bps). A bit is one binary digit, either a 1 or a 0 (it is the smallest unit of data; 8 bits make up a byte). Ethernet provides data transmission speeds in excess of a million bits per second (Mbps). In terms of networking, bandwidth is considered the number of bits that can be sent across the network medium (such as the wired or wireless network) at a given time. So, the terms data transmission speed and bandwidth are often used interchangeably.
Ethernet got its start in 1972 at the Xerox Palo Alto Research Center (PARC). Xerox released a commercial version of Ethernet in 1975 that provided a transmission speed of 3Mbps. Ethernet has matured to the point where today we have gigabit Ethernet that provides a huge amount of bandwidth. Wireless Ethernet networks can provide up to 54Mbps of bandwidth, which is greater than what some hard-wired LANs can deliver.
Ethernet is a passive, wait-and-listen network architecture. Computers must contend for transmission time on the network medium. To receive data, computers just sit and wait, listening to the network. When they sense that a particular transmission is meant for them, they receive it on their network adapter.
Ethernet takes care of the movement of data at the hardware level. But users like us deal with software. Software that provides our method of communication with the computer's hardware. For our various computer software applications to talk over the network, there must be some software standards. These standards are communication protocols. A protocol is really software code that provides the rules for how computers communicate over the Ethernet hardware.
Protocol A set of software rules that dictate how computers and other devices communicate over a network architecture such as Ethernet.
The only network protocol we really need to discuss is the TCP/IP network protocol stack (it's a stack because it contains a number of protocols that have different jobs). A protocol stack such as TCP/IP must provide an address system and also take care of converting data we create in our software applications to a form that can be moved by Ethernet hardware as a bit stream.
TCP/IP (Transmission Control Protocol/Internet Protocol) The common language for the networking world. TCP/IP is the protocol suite (or stack) that serves as the foundation for the mega-network known as the Internet. Nearly all computer operating systems embrace TCP/IP as their default networking protocol.
To make a long story short, TCP/IP takes care of the data conversion process and also provides the addressing system for computers and other devices on the network. The addressing system consists of IP addresses. A unique IP address is assigned to each device on the network. Each piece of data sent over the network is labeled with the IP addresses of the sending device and the receiving device, allowing for the movement of data from point A to point B.
Computers and devices on a TCP/IP network can have their IP addresses configured manually or dynamically. To manually configure a computer with a static IP address (meaning an address that never changes), you configure the computer with a unique IP address and an accompanying subnet mask (the subnet mask helps other computers determine which part of the address is network information and which part is specific device information).
The alternative to manually configuring devices with an IP address and subnet mask is to use a DHCP (Dynamic Host Configuration Protocol) server on the network. The DHCP server leases IP addresses to computers and other devices on the network. Wireless routers (discussed in several chapters in this book) can act as DHCP servers, so you won't have to assign IP addresses to all the computers on your wireless networkthe router does that automatically and behind the scenes.
In Windows XP (both the Home and Professional versions), the IP address is configured in the Internet Protocol (TCP/IP) Properties dialog box. You can either configure a Windows XP computer with a static address or configure it to accept an IP address from a DHCP server on the network (such as your wireless router).
Computers running Windows XP can be configured with static IP addresses or configured to accept an IP address from a DHCP server.
We discuss IP configuration and other network settings in Configure TCP/IP Settings.
TCP/IP takes care of network communication at the software level, and Ethernet takes care of communication at the hardware level. The wireless standards used for WLANs are actually Ethernet standards. We discuss wireless Ethernet in "Understanding Wireless Networking Standards," later in this chapter.