Skills required to be a wireless analysis professional
Protocols analysis - the ability to capture and analyse frames and packets to determine the problems within a network and locate areas for improvement.
Spectrum analysis - the ability to understand RF activity within an environment and its impact on 802.11 operations
Troubleshooting Methods - understanding of common procedures used to understand, analyse, and resolve problems
Foundational Elements
Protocols and Communications
The 802.11 Protocol
Using RF to Communicate
Basics of Network Frames
Troubleshooting Methods
The OSI Model
Layer 7: Application
Layer 6: Presentation
Layer 5: Session
Layer 4: Transport
Layer 3: Network
Layer 2: Data Link Layer
Layer 1: Physical Layer
Layer 2
LLC - Logical Link Control. (Upper Layer)
LSDU - Logical link control Service Data Unit
LPDU - Logical link control Protocol Data Unit
MAC - Medium Access Control (Lower Layer)
MSDU - MAC Service Data Unit
MPDU - MAC Protocol Data Unit
Layer 1
PLCP - Physical Layer Convergence Protocol
PSDU - Physical layer convergence protocol Service Data Unit
PPDU - Physical layer convergence protocol Protocol Data unit
PMD - Physical Medium Dependant
PHY = Physical Level
STA = Stations (Wireless Clients and Aps )
PHY Acronym PHY Name
DSSS Direct Sequence Spread Spectrum
HR/DSSS High Rate DSSS
OFDM Orthogonal Frequency Division Multiplexing
ERP Extended Rate PHY
HT High Throughput
S1G Sub-1 GHZ
TVHT Television Very High Throughput
DMG Directional Multi-Gigabit
VHT Very High Throughput
HEW High Efficiency Wireless
A common misconception about 802.11 WLANS is that the data rate of the MAC frame is the same rate at which the entire transmission is sent. The PHY information is sent at the lowest supported data rate in the BSS and then the MAC frame is sent at the data rate indicated. For example, the PHY information may be transmitted at 1 Mbps in 2.4Ghz networks, While the MAC frame is then sent at 144Mbps.
PLCP Header includes information need by the receiver to synchronise with the transmitter and to determine the data rate of the upper layer payload (MAC Frame).
Modulation is the process of imposing bits on the transmission medium, such as RF. Something about the medium is manipulated to represent bit values in the transmission.
PSK = Phase Shift Keying
ASK = Amplitude shift keying
MCS = Modulation and Coding Scheme
BPSK = Binary Phase Shift Keying
QPSK = Quadrature Phase Shift Keying
QAM = Quadrature Amplitude Modulation
DRS = Dynamic Rate switching
TWT = Target Wake Time
BCU = Basic Channel Units
SDU = Service Data Units
SS = Station Service
DSS = Distribution System Service
Some have mistakenly referenced TWT as Target wait time , but the standard defines it as Target Wake Time. Given that it defines the duration the STA can wait before waking, one can see where the confusion enters.
Basics Of Network Frames
Encapsulation
Services provided by Station Services (SS) are :
Authentication
Deauthentication
Data confidentiality (encryption)
MSDU Delivery
Dynamic Frequency Selection (DFS)
Transmit Power Control (TPC)
Timer synchronisation with higher layers (Quality of Service (QoS) facility only)
QoS traffic scheduling (QoS facility only)Radio measurement
Dynamic STA enablement (DSE)
Services Provided by Distribution System Service
Association
Disassociation
Distribution
Integration
Reassociation
QoS traffic scheduling (Qo Facility only)
DSE
Interworking with the DS (in a Mesh)
Control Plane.
Management Plane
Data Plane
Radio resource management covers all the Planes
Frame Aggregation
A-MSDU Multiple MSDU but one Mac
A-MPDU Multiple MPDU but one MAC
Can only be sent to one device (one Mac)
64k limit on 802.11n
1Mb limit on 802.11ac
Can adjust to make better Performance = would lower the size for VoIP with data users so they are not impacted by large data transfers and have to wait and increase latency
Troubleshooting Methods
Industry Troubleshooting method
Cisco Troubleshooting
Define a clear problem statement with symptoms and potential causes
Gather the facts to help isolate the possible causes.
Create an action plan based on the remaining potential problems and the likely cause.
Implement action plan As change is made gather results.
Analyse the results and determine whether the problem has been resolved.If the problem is not resolved, create a new action plan based on the next most likely cause and proceed with steps 5-8 . Repeat until resolved or escalated
Microsoft Troubleshooting
Phase 1: Discovery - Gather information about the problem
Phase 2: Planning - Create a plan of action
Phase 3: Problem Reproduction - Reproduce the problem or determine what that you cannot reproduce it. If you cannot reproduce the problem, then you might not have enough information to confirm that there is a problem
Phase 4: Problem Isolation - Isolate the variables that relate directly to the problem.
Phase 5: Analysis - Analyse your findings to determine the cause of the problem.
CompTIA Methodologies
A+ Objectives
Identify the Problem
Establish a theory of probable cause (question the above)
Test the theory to determine causeEstablish a plan of action to resolve the problem and implement the solution
Verify full system functionality, and if applicable implement preventive measuresDocument findings, actions, and outcomes
Network +
Identify the Problem
Establish a theory of probable cause (question the above)
Test the theory to determine cause
Establish a plan of action to resolve the problem and identify potential effects.
Implement the solution or escalate as necessaryVerify full system functionality, and if applicable implement preventive measures
Document findings, actions, and outcomes
CWAP-403 Objectives and Trouble Shooting
Define the Problem
Determine the scale of the problem
Identify Probable Cause Capture and Analyse the data
Observe the problem
Choose appropriate remediation steps
Document the problem and resolution
Chapter Summary
In this chapter, you reviewed 802.11 operations including the MAC and Phy Layers. You explored troubleshooting methodologies and looked specifically at the CWAP objectives troubleshooting actions. In the net chapter will begin exploring the details of the 802.11 MAC layer
Facts to Remember
802.11 defines operations at the MAC sublayer of the Data Link Layer and the Physical Layer
The MSDU is received by the MAC sublayer and encapsulated into an 802.11 frame as an MPDU
PPDUs are transmitted onto the RF medium. They contain one or more MPDUs
802.11 networks use both PSK and ASK modulation techniques
The Throughput for WLAN clients is always less than the connection data rate because of management overhead and other communicating STAs on the shared RF medium
802.11ax adds the OFDMA modulation to the 802.11 family of PHYs and it increases the highest modulation rate to 1024-QAM
802.11ad operates at 60GHz and 802.11ah operates below 1Ghz
To increase efficiency, All 802.11ac frames are transmitted as A-MPDUs even when the frame includes only one MPDURemember that you must clearly define the problem and the scope of the problem before you can effectively identify probably cause