Service Sets

A service set is a term used to describe the basic components of a fully operational wireless LAN. In other words, there are three ways to configure a wireless LAN, and each way requires a different set of hardware. The three ways to configure a wireless LAN are:

• Basic service set

• Extended service set

• Independent basic service set

Basic Service Set (BSS)

When one access point is connected to a wired network and a set of wireless stations, the network configuration is referred to as a basic service set (BSS). A basic service set consists of only one access point and one or more wireless clients, as shown in Figure 7.9. A basic service set uses infrastructure mode - a mode that requires use of an access point and in which all of the wireless traffic traverses the access point. No direct clientto-client transmissions are allowed.

Each wireless client must use the access point to communicate with any other wireless client or any wired host on the network. The BSS covers a single cell, or RF area, around the access point with varying data rate zones (concentric circles) of differing data speeds, measured in Mbps. The data speeds in these concentric circles will depend on the technology being utilized. If the BSS were made up of 802.11b equipment, then the concentric circles would have data speeds of 11, 5.5, 2, and 1 Mbps. The data rates get smaller as the circles get farther away from the access point. A BSS has one unique SSID.


Extended Service Set (ESS)

An extended service set is defined as two or more basic service sets connected by a common distribution system, as shown in Figure 7.10. The distribution system can be either wired, wireless, LAN, WAN, or any other method of network connectivity. An ESS must have at least 2 access points operating in infrastructure mode. Similar to a BSS, all packets in an ESS must go through one of the access points.


Other characteristics of extended service sets, according to the 802.11 standard, are that an ESS covers multiple cells, allows – but does not require – roaming capabilities, and does not require the same SSID in both basic service sets.


Independent Basic Service Set (IBSS)

An independent basic service set is also known as an ad hoc network. An IBSS has no access point or any other access to a distribution system, but covers one single cell and has one SSID, as shown in Figure 7.11. The clients in an IBSS alternate the responsibility of sending beacons since there is no access point to perform this task.


In order to transmit data outside an IBSS, one of the clients in the IBSS must be acting as a gateway, or router, using a software solution for this purpose. In an IBSS, clients make direct connections to each other when transmitting data, and for this reason, an IBSS is often referred to as a peer-to-peer network.