A wireless network consists of two basic components: a radio card and a network card (typically Ethernet). A radio cards operates in one of two modes: Basic Service Set (BSS) and Independent Service Set (ISS).

BSS and IBSS Modes
In the BSS mode, a hardware component known as the "access point" (AP) provides wireless-to-Ethernet bridging. It receives the packets from the clients and passes them on to the physical network connection, after performing the necessary authentication and conversions. Similarly, an AP collects outgoing traffic from the physical network, converts them to radio waves, and transmits them to the clients. Before a client gains access to the network, it must first establish connection with a local AP, which identifies and authenticates it. Networks that are large enough may contain several APs. Such networks often support Extended Service Set (ESS). ESS enables APs to communicate with each other and hand over roaming clients.

Under the IBSS mode, no APs are used. Instead, any network node within range can communicate with any other node, after performing a basic handshake process. This networking model is called "ad-hoc peer-to-peer networking". If one of those nodes is connected to a wired network, other nodes may use it to access that network.

Additional AP Services
An AP bridges between a wired network and wireless clients. However, it often provides additional services:

• MAC address filtering. To avoid unauthorized access to a network, an AP may check clients' MAC addresses and grant access only to clients whose MAC address is listed on an internal table.
• Closed networks. By default, a client may connect to any available AP. In closed networks, a client must specify the target network to which it wishes to connect.
• Link quality monitoring, statistics, and performance analysis.

Peer-to-Peer Linux Hardware
Most 802.11b cards today are PCMCIA cards. They cost between $70-$200. Laptop computers often have a PCMCIA slot so they can be ideal candidates for building a wireless network. However, if your machine doesn't have a PCMCIA slot you can use ISA or PCI converters to fit a wireless card to it.

In addition to the wireless adapter, you will need a second PCMCIA slot for a network interface. In a desktop or rack mount machine, an Ethernet card is your likely choice. On a laptop, a built-in modem can serve as your network interface.