Function of WLAN Beacon Frame
Like other networks, beacon frame in WLAN is used to announce the availability of the network (i.e. Access Point Router). It is also used for maintenance of tasks. This beacon frames are transmitted at regular time periods so that mobile stations (i.e. stations or any WLAN clients such as laptop,tablet or any wifi gadgets) can find and identify the network. This helps WLAN devices match the parameters with the network and finally they will be able to join the network.
Beacon frame is transmitted by the AP(Access Point) in the case of infrastructure networks. Hence in order for stations to receive beacon frame they should be nearer to AP.
WLAN Beacon Frame fields
Fig-1 mentions fields carried by WLAN beacon frame. Not all of the fields mentioned are present in all the beacon frames. As per application and physical layer of use, frame fields may vary. FH and DS parameter sets are used based on FH or DS physical layers. Pls. note that at any one time, only one physical layer will be present in WLAN STATION or AP (either FH or DS). Table-1 below mentions fields carried by WLAN beacon frame body portion. The frame body of WLAN beacon frame is divided into mandatory and optional fields.
| WLAN Beacon Frame Body Field Information | Description(If any) |
|---|---|
| Timestamp | |
| Beacon Interval | - |
| Capability Info | - |
| SSID | - |
| FH parameter set | This WLAN information element is present when FH physical layer is used. |
| DS parameter set | This WLAN information element is present when DS physical layer is used. |
| CF parameter set | THe APs which supports PCF will have this information element embedded in the beacon frame transmitted by them. |
| IBSS parameter set | This information element is present in beacon frames transmitted by APs in IBSS network. |
| TIM | Stands for Traffic Indication Map, present only in beacon frames produced by APs. |
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