Chapter 9 Flashcards
Packets?
Data Units at the Network Layer
Frames?
Data Units at the Data Link Layer
Bits?
Binary Digits
Data Link Layer?
DLL has two sublayers
Logical Link Control (LLC)
and
Media Access Control (MAC)
Logical Link Control?
Establishing Flow Control
Maintains Flow Control
Media Access Control (MAC)
802.11 Specified Operations
Where the MAC address resides
What is MSDU?
MAC Service Data Unit
- Data portion of MAC coming from LLC
What is MPDU?
MAC Protocol Data Unit
- After encapsulation in MAC frame
Detailed MSDU?
Contains Data From Layers 3-7 and the LLC
The Data Payload
Only Data Frames Carry the MSDU
Maximum size of 2,304 bytes
Detailed MPDU?
Mac Protocol Data Unit
Encapsulates the MSDU
Is an 802.11 Frame
Physical Layer?
Has two Sub-Layers
- Physical Layer Convergence Protocol (PLCP)
- Physical Media Dependent (PMD)
PLCP Services Data Unit (PSDU)
PLCP Protocol Data Unit (PPDU)
PLCP Data Units?
PLCP Services Data Unit
- The same frame as the MPDU
PLCP Protocol Data Unit (PPDU)
- Adds Preamble and PHY Header
802.11 and 802.3 Interoperability
- 3 Frames are encapsulated within 802.11 frames for Transmisision
- 3 Standard frame Max Size = 1518 bytes
- 11 standard frame Max Size = 2347 bytes
- 11 has four addresses field in header
Possible addresses of 802.11 and 802.3
Receiver Address (RA) Transmitter Address (TA) Basic Service Set Identifier (BSSID) Destination Address (DA) Source Address (SA)
802.11 Frames
Frame Types
- Management Frame
- Control Frame
- Data Frame
Management Frames?
Association request and response. Reassociation request and response Probe request, and response Beacon ATIM Disassociation Authentication, and Deauthentication Action Action No ACK Timing advertisement
Beacon Frame Content?
Time Stamp Parameter Sets Channel Information Data Rates BSS Capabilities SSID TIM and DTIM QoS Capabilities Security Capabilities Vendor Proprietary Information
What is Passive Scanning?
Passive Scanning Stations Listen for Beacon Frames
What is Active Scanning?
Active Scanning Stations use probe request and response frames
Authentication?
Stations must authenticate to begin connection with an AP
Failed authentication is the #1 Cause of Failed Association
Many authentication methods exist:
- Open (no credentials required)
- Shared key (uses WEP key_
Association?
Occurs AFTER authentication
Requires Mutually Supported Functions
Once Associated, Stations can contend for the Medium and Pass Data onto the network
States of Authentication and Association?
State 1:
Unauthenticated
Unassociated.
State 2:
Authenticated
Unassociated
Stage 3:
Authenticated
Associated
State 1 Contains?
- Listen to Beacons
- Probe Request
- Probe Response
- Authentication Request
- Authentication Response
State 2 Contains?
- Association Request
7. Association Response
State 3 Contains?
- (Optional: EAPOL Authentication)
- (Optional: Ecrypt Data)
- Move user data
Basic and Supported Data Rates?
Basic Rates are the MANDITORY data rates of the BSS
Supported Rates are the OPTIONAL data rates of the BSS
Information is Found in the beacon management frame
Control Frame?
Power Save Poll Request To Send Clear to Send Acknowledgment (ACK) Contention Free-End CF-End + CF-ACK Block ACK Request Block ACK Control Wrapper
ACK Frame?
Acknowledgement Frame
Every unicast frame bu the Standard should be acknowledged
Used due to Inability to Detect Collisions
Provide Delivery Verification
Protection Mechanism?
Request to Send / Clear to Send Clear to Send to Self Help Combat Hidden Node Issues Allows Mixed Mode Operations Creates Additional Overhead Frames Sent at Lowest Basic Rate
Clear to Send to Self
Less overhead than RTS/CTS From the station to itself Used in Mixed Mode BSS Operations Creates Additional Overhead Frames Sent at Lowest Basic Rate
Data Frames?
Can be Pure Data
Can be Null Data
Can be combined with other functions
Contains the MSDU
Power Management?
Conserves Battery Life Require use of TIM, DTIM, or ATIM Two Modes Used - Active Mode (Always ON) - Power Save Mode (ON and OFF) Legacy Power Save Still Used WMM-PS Used on Newer Devices
