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WIFI 802.11

| Reference | {{:mywiki:standards:802.11:ieee-802.11overview.ppt|}} | {{:mywiki:standards:802.11:80211_powermanage.ppt|}} |

====== Terms ======

| DTIM | delivery traffic indication map | Informs the clients about the presence of buffered multicast/broadcast data \\ on the access point. It is generated within the periodic beacon at a frequency \\ specified by the DTIM Interval. \\ Normal DTIMs that are present **in every beacon** are for signaling the presence of buffered unicast data. \\ **After a DTIM, the access point will send the multicast/broadcast data** on the channel following the normal channel access rules (CSMA/CA). \\ The 802.11 standards define a power-save mode for client devices. In power-save mode, a client device may choose to sleep for one or more beacon intervals waking for beacon frames that include DTIMs. When the DTIM period is 2, a client device in power-save mode will awaken to receive every other beacon frame. Upon entering power-save mode, a client device will transmit a notification to the access point, so that the access point will know how to handle unicast traffic destined for the client device. The client device will begin to sleep according to the DTIM period. \\ The higher the DTIM period, the longer a client device may sleep and therefore the more power that particular client device may potentially save. \\In the present standards, an access point is able to store only a single DTIM period |
|  Beacons |  | Are packets sent by an access point to synchronize a wireless network |
| BSS | Basic Service Set |
| IBSS | Infrastructure BSS |
| ESS | Extended Service Set |
| DS | Distribution System |
| NAV | Network Allocation Vector |


====== Power Management Example ======
In this example, DTIM is configured to 2, ie, there is one DTIM for every two beans. This can be used to send broadcast/multicast packet with need ACK. 

{{:mywiki:standards:802.11:wifi_power_management.png?700}}

  *   Allow idle station to go to sleep: stations power save mode stored in AP
  *   AP buffers packets for sleeping nodes: 
  *     *  AP announces which station have frames buffered
  *     *  TIM sent with every Beacon
  *   Power Saving stations wake up periodically
  *   - - listen for Beacons
  *   TSF assures AP and Power save stations are synchronized
  *   - - TSF timer keeps running when stations are sleeping

====== Architecture ======
{{:mywiki:standards:802.11:wifi_architecture.png|}}

====== DCF ======
{{:mywiki:standards:802.11:wifi_dcf.png|}}

====== Frame Types ======
{{:mywiki:standards:802.11:wifi_frame_types.png|}}

{{:mywiki:standards:802.11:wifi_sub_frame_types.png|}}