1. WLAN

2. Wireless LAN
A wireless LAN or WLAN is a wireless local area network that uses radio waves as its carrier.
WLAN Reference Architecture
The terminology and some of the specific features are unique to this standard and are not reflected in all commercial products.
However, it is useful to be familiar with the standard since its features are representative of the Wireless LAN capabilities required.

3. Reference Architecture of WLANs
Station (STA)
terminal with access mechanisms to the wireless medium and radio contact to the access point
Basic Service Set (BSS)
Group of stations using the same radio frequency
Access Point (AP)
station integrated into the WLAN and the distribution system
Portal
bridge to other (wired) networks
Distribution System
Interconnect network to form one logical network (ESS: Extended Service Set) based on several BSS
STA1
BSS1
Portal
Access
Point
Distribution System
Access
Point
BSS2
STA2
STA3
ESS 9

4. Reference Architecture
The smallest building block of a WLAN is a basic service set (BSS), which consists of some number of stations executing the same MAC protocol and competing for access to the same shared medium.
A BSS may be isolated or it may connect to a backbone distribution system through an access point.
The access point functions as a bridge.
The BSS generally corresponds to what is referred to as a cell in the literature.

5. Reference Architecture
An extended service set (ESS) consists of two or more BSSs interconnected by a distribution system.
Typically, the distribution system is a wired backbone LAN.
The ESS appears as a single logical LAN to the logical link control (LLC) level.
The standard defines three types of stations based on mobility: No transition BSS transition ESS transition

6. Reference Architecture
No transition: A station of this type is either stationary or moves only within the direct communication range of the communicating stations of a single BSS.
BSS transition: This is defined as a station movement from one BSS to another BSS within the same ESS. In this case, delivery of data to the station requires that the addressing capability be able to recognize the new location of the station.
ESS transition: This is defined as a station movement from a BSS in one ESS to a BSS within another ESS. This case is supported only in the sense that the station can move.

7. WLAN Configuration Infrastructure Network Ad-hoc Network BSS BSS BSS
AP: Access Point AP AP
Distributed System AP
BSS
BSS
Ad-hoc Network
IBSS
IBSS

8. Ad hoc Network
In an ad hoc WLAN, wireless nodes, or stations, transmit directly to each other via wireless NICs without an intervening connectivity device.
An ad hoc arrangement would not work well for a WLAN with many users or whose users are spread out over a wide area, or where obstacles could stand in the way of signals between stations.

9. Infrastructure Network
WLANs use the infrastructure mode depends on an intervening connectivity device called an access point (AP).
The AP accepts wireless signals from multiple nodes and retransmits them to the rest of the network.
AP may also be known as base stations.

10. Infrastructure Network
To cover its intended range, an access point must have sufficient power and be strategically placed so that stations can communicate with it.
It’s common for a WLAN to include several access points.
The number of access points depends on the number of stations. The maximum number of stations each access point can serve varies from 10 to 100, depending on the wireless technology used.

11. WLAN and Wired LAN
WLANs operate in almost the same way as wired LANs, using the same networking protocols and supporting the most of the same applications.
WLANs support the same protocols (for example, TCP/IP) as wired LANs.
This compatibility ensures that wireless and wired transmission methods can be integrated on the same network.

12. How are WLANs Different?
They use specialized physical and data link protocols

13. They integrate into existing networks through AP which provide a bridging function
fixed
terminal
mobile terminal
infrastructure
network
access point
application
application
TCP
TCP IP IP
LLC
LLC
LLC
MAC
MAC
802.3 MAC
802.3 MAC
PHY
PHY
802.3 PHY
802.3 PHY