WLANs are flexible data communications systems implemented as an extension or as an alternative for wired LANs. Using radio frequency (RF) technology, WLANs transmit and receive data over the air, minimizing the need for wired connections. Thus, WLANs combine data connectivity with user mobility.

WLANs can be built with either of the following topologies:

• Peer-to-peer (ad-hoc) topology
• Access point based topology
• Point-to-multipoint bridge topology

1. LAN Adapter:

i. For any LAN, Wire or Wireless, a LAN adapter is always needed.

ii. In a WLAN, it provides the interface between network operating system and an antenna to create a transparent connection to the network.

iii. Thus, the mobile device (end user) can access the network.

iv. Wireless adapters are in same basic form as their wired counter parts: PCMCIA, Card bus, PCI, and USB.

2. Peer-to-peer topology:

i. The devices communicate to each other directly.

ii. Each device is a client. There is no fixed topology (ad hoc).

Fig4. Peer to Peer Topology (Ad hoc network)

3. Access Point (AP):

i. It transmits, buffers and receives data between the WLAN and the wired network, supporting a group of wireless user devices.

ii. APs have a range from 20 to 500 meters. A single AP can support between 15 to 250 users, depending on technology, configuration and use.

4. Access point based topology:

i. It user an AP which has either wired or wireless network in its backbone. The AP

ii. provides a wireless device an access to the network in its backbone.

iii. It is easier to scale such network by deploying more APs. It needs handoff but it reduces network congestion and enlarges coverage area.

iv. AP- based topology is more common and it demonstrates that WLAN does not completely replace wired LAN. It only extends connectivity to mobile devices.

Fig5. Access point based topology

v. In the above figure, communications between station 1 and station 4 actually flow from station 1 to AP1 and then from AP1 to AP2 and then from AP2 to AP4 and finally AP4 to station 4.

vi. An AP performs a bridging function and connects multiple WLAN cells or channels, and connects WLAN cells to a wired enterprise LAN.

5. Point-to-multipoint bridge topology:

i. This topology is used to connect LAN in one building to LANs in other building even if they are miles apart.

ii. This topology uses an outdoor WLAN bridge to connect along with line-of-sight directional antennas.

iii. WLAN bridges support high data rates. And ranges of several miles. But the range depends on type of bridge, type of antenna and environmental conditions.