Overview of 802.11 Networks

Before studying the details of anything, it often helps to get a general "lay of the land." A basic introduction is often necessary when studying networking topics because the number of acronyms can be overwhelming. Unfortunately, 802.11 takes acronyms to new heights, which makes the introduction that much more important. To understand 802.11 on anything more than a superficial basis, you must get comfortable with some esoteric terminology and a herd of three-letter acronyms. This chapter is the glue that binds the entire book together. Read it for a basic understanding of 802.11, the concepts that will likely be important to users, and how the protocol is designed to provide an experience as much like Ethernet as possible. After that, move on to the low-level protocol details or deployment, depending on your interests and needs.

Part of the reason this introduction is important is because it introduces the acronyms used throughout the book. With 802.11, the introduction serves another important purpose. 802.11 is superficially similar to Ethernet. Understanding the background of Ethernet helps slightly with 802.11, but there is a host of additional background needed to appreciate how 802.11 adapts traditional Ethernet technology to a wireless world. To account for the differences between wired networks and the wireless media used by 802.11, a number of additional management features were added. At the heart of 802.11 is a white lie about the meaning of media access control (MAC). Wireless network interface cards are assigned 48-bit MAC addresses, and, for all practical purposes, they look like Ethernet network interface cards. In fact, the MAC address assignment is done from the same address pool so that 802.11 cards have unique addresses even when deployed into a network with wired Ethernet stations.

To outside network devices, these MAC addresses appear to be fixed, just as in other IEEE 802 networks; 802.11 MAC addresses go into ARP tables alongside Ethernet addresses, use the same set of vendor prefixes, and are otherwise indistinguishable from Ethernet addresses. The devices that comprise an 802.11 network (access points and other 802.11 devices) know better. There are many differences between an 802.11 device and an Ethernet device, but the most obvious is that 802.11 devices are mobile; they can easily move from one part of the network to another. The 802.11 devices on your network understand this and deliver frames to the current location of the mobile station.