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PLCP Protocol data unit (PPDU)
- The PLCP adds a preamble and PHY header to the PSDU.
- The Preamble is used for synchronization between transmitting and receiving 802.11 radios.
PLCP service data unit (PSDU)
- its a view of the MPDU from ether side.
- MAC side its MPDU
- Physical layer its PSDU
MAC protocol data unit (MPDU)
- The LLC send the MSDU to the MAC sublayer the MAC header information is assed to the MSDU to identify it.
- Its an 802.11 frame
MAC service data unit (MSDU)
The data payload that contains the IP packet plus some LLC data.
- Make up a majority of frames in WLAN. (802.11)
- Used by wireless stations to join and leave the network. It does not carry upper layer information
- There is no MSDU encapsulated in the MMPDU frame body, which carries only layer 2 info field and info elements
- Help with the delivery of data frames.
- Control frames must be able to be heard by all stations, they must be transmitted at one of the basic rates.
- Control frames are alo used to clear the channel acquire the channel and provide unicast frame ack.
- They contain layer 2 header
- carry the actual data that is passed down from the higher layer protocols
- some carry no data but have specific purpose within the BSS
- there are 15 data frame subtypes
Beacon Management Frames (Beacon)
- They are essentially the heartbeat of the wireless network.
- They are sent only by the access point of a basic service set.
- Client stations trans,it becons only when participating in an IBSS also know as an AD HOC mode
- Each beason contains a time stamp.
Beacon Management Frames (Beacon)
- time stamp- synchronization info
- spread spectrum parameter sets- FHSS, DSSS, ERP
- channel info- channel used by the AP or IBSS
- Data rates- basic and supported rates
- service set capabilities- extra BSS or IBSS parameters
- SSID- Logical WLAN name
- Traffic indication map (tim)- field used during power save process
- QoS capabilities- quality of service and EDCA info
- security capabilities- TKIP or CCMP cipher
- vendor propriety info- vender unique or vendor specific info.
open system authentication
- Provides authentication without preforming any-type of client verification.
- It exchanges hellos between the client and the access point.
shared key authentication
- more complex
- uses WEP to authentication client station and requires that a static WEP key be configured on both station and the access point.
- Will not work if keys dont match
- It includes a challenge and response between the AP and Client station.
- It first needs to discover an AP
- Is one method that stations use to discover access points.
- The station and the access point will exchange probe requests and probe response to establish the capabilities of the basic service set.
involves the client station listening for the beacon frames that are continuously being set by the access point.
- 802.11 management frame that is transmitting during active scanning.
- A client station that is looking for an SSID sends a probe request.
- Access point that hears the request will send a probe response notifying the clients presence.
after a client station sends a probe request, access points that hear the probe request will send a probe response notifying the client of the access points presence
- is the verification of user identity and credentials.
- Use passwords or digital certificates
- associate with the access point
- When a client station associates it becomes a member of a basic service set.
- The client station can send through the access point and on to the distribution system medium.
when a client station decides to roam to a new access point, it will send a reassociation request frame to the new access point
notification frame used to terminate an association.
a notification frame used to terminate an authentication
Traffic indication map (TIM)
- is used when stations have enabled Power saved modes.
- Is a list of all station that have undelivered data buffered on the access point waiting to be delivered
Delivery traffic indication message (DTIM)
a type of TIM that is used to ensure that all stations are awake when multicast or broadcast traffic is sent.
Announcement traffic indication message (ATIM)
- a unicast frame that is used in an IBSS network when power save mode is on
- If a station has buffere data for another station, it will send an ATIM frame to the other station informing it that it must stay awake untill the next ATIM window so that it can receive the buffer data
Wi-fi multimedia power save (WMM-PS)
- is to have client spend more time in a doze state and consume less power.
- designed to minimize latency for time sensitive applications such as voice during the power management process
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