Radio Cards – the MAC functionality is found here, as well as the signalling for the physical layer. A radio card is termed an “802.11 station”.
Access Points – the MAC and physical layer functions are here as well. The AP generally contains an ethernet interface for connection to the wired LAN. Some APs offer multiple card slots, allowing the administrator to mix ‘n’ match his choice of radios in the AP.
Antennas – the device that actually creates the radio waves. The book states that “air” is the medium, which is not correct, I don’t believe. Air is not necessary – you can send a radio wave through a vacuum. But I know what the author is getting at. Antennas can be omnidirectional (broadcasting RF in all directions equally) or directive (RF focused more in one direction than others). Directive antennas are typically used to cover longer distances.
Repeaters – receives 802.11 data frames and then rebroadcasts them on the same channel. Repeaters have the disadvantage of the spectrum being used to say the same thing twice, thus reducing bandwidth.
Bridges – using wireless technology to connect 2 different networks. A nice way to connect cross-town, if you’ve got line of sight. Good for a few miles, or as much as 20 – 30 miles with the right antennas. From my own experience, line of sight is the single most important element of a long-haul wireless bridge. If you have to go through vegetation or other buildings, then you’re chances for a reliable link and/or high throughput will be reduced.
Routers – referring to the wireless all-in-one solutions you can get at Best Buy, where the device is a broadband router, NAT box, DHCP server, firewall AP, ethernet switch and coffee maker all in one. Not a bad home or SOHO solutions, but not what enterprise networks typically deploy.
Radio Frequency Peripherals – refers to ways you can monkey with the signal. Split to 2 different antennas, run the signal through an amplifier, etc.