Computer Networking: Internet Protocols in Action

Chapter 5.3. Wireless LANs

INTRODUCTION

Today, it seems that wireless LANs are available everywhere—in homes, hotels, airports, coffee shops and office buildings. The IEEE 802.11 standards define the technology underlying this increasingly ubiquitous convenience.

In an 802.11 wireless LAN, client nodes associate with a wireless Access Point (AP) to form a Basic Service Set or BSS. A wireless AP is the center of a local area network segment that is shared by many clients. Access points can then connected to the rest of the Internet, often through wired connections to a switch or router.

In many ways, wireless access points are similar to the Ethernet hubs we discussed in Exercise 5.2. However, in an Ethernet network, the hub itself creates the shared medium and in the wireless case, the shared medium, a range of frequencies, is already present. As a result, the IEEE 802.11 standards also allow for a BSS in which no access point is present. These BSS are called Independent Basic Service Sets or ad-hoc networks. These ad-hoc networks provide connectivity between a set of local machine but do not provide a link to the rest of the Internet.

Figure 5.3.1. Basic Service Sets

In some environments, a client has multiple access points available in range. When a client wants to associate to an access point, it will hop through all available channels looking for "beacons" sent out by the wireless ...