Distributed WiFi Analysis

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Distributed WiFi Analysis

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Defines media access control and physical layer for wireless network ... Kismet. Layer 2. Parsing pcap format data. Layer 3. Create Indexes. Find contention in traces ... – PowerPoint PPT presentation

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Title: Distributed WiFi Analysis

1
Distributed Wi-Fi Analysis

By Arun Chhetri

2
Index

802.11 Introduction
Problem Description
Previous Work Motivation
Proposed Solution
State Diagram
Contention Finding Algorithm
Block Diagram
Results
Acknowledgements
References

3
802.11 Introduction

Extension of IEEE 802.3 protocol (ethernet)
Defines media access control and physical layer
for wireless network
Uses CSMA/CA as compared to CSMA/CD in Ethernet
Basic Service Set - BSS (Infrastructure BSS and
Independent BSS)
Extended Service Set ESS
Data is transferred as frames with maximum size
of 2304 bytes
Bigger frames are fragmented
Three types of frame
Control Frame
Data Frame
Management Frame

802.11 Architecture
4
A familiar question

How to give best Wi-Fi experience to users ???????

5
A familiar situation

Wi-Fi is not working !! call support

Problems
Contention with nearby wireless devices
Bad AP channel assignment
Microwave Owen
Congestion
Poor choice of AP
802.11 DOS attack
.

AP
N1
N2
6
Problem Description
AP7
AP6
6
3
S2
5
AP1
AP2
1
4
6
3
3
3
S5
2
4
S1
5
5
1
4
6
4
6
AP3
2
2
2
3
AP4
3
1
1
S6
5
S3
5
S4
4
6
4
6
5
Sniffers
2
2
1
1

What will happen when all the access points
are transmitting at same channel
How one node For e.g. N1 in AP1 will behave in
time with node N3 in AP3

7
Problem Description

To analyze the relationship between different
wireless nodes present in distributed Wi-Fi
system
Contention Graph
Probability of Successful transmission
Further these reports can be used find problems
in a Wi-Fi setting
To check whether random back-off algorithm of a
wireless node is in compliance with IEEE
specification
Efficiency of nodes, upstream and downstream
data, network usage etc.

8
Previous Work and Motivation

Yeo An Accurate Technique for Measuring the
Wireless Side of Wireless Networks
Packet capturing and merging technique
Rodrig and Mahajan Measurement-based
Characterization of 802.11 in a Hotspot Setting
Packet capturing, overheads, retransmission as a
factor of signal strength and how many active
nodes are present in network
Jigsaw Solving the Puzzle of Enterprise 802.11
Analysis
Large scale deployment of sniffers
Reconstruct a global view of network activity of
802.11 network

In future work, we intend to develop a
comprehensive portfolio of analyses and use them
to drive more complex operational questions
(e.g., what are the root causes of transient
outages and performance degradations) and
research questions (e.g., how to better optimize
wireless protocols and their interactions with
other protocol layers)
We infer that the transmission from s failed to
reach r when we do not observe an ACK from r.
9
State Diagram
DCF State Diagram
NAV State Diagram
10
Contention Finding algorithm
Atomic Sequences
RTS
CTS
Frame
ACk
So, all those frames which breaks any atomic
sequence, can cause contentionIf there is
retransmission of two or more than two different
data frames which were part of two or more
different atomic sequences which overlaps in
time, then there are fair chances that they will
collided.
Two stations will exponentially back-off, due to
the loss of ack
Two Stations S1 and S2 where they both cannot
sense each other
S2 Frame z
S2 Frame z
S2
SIFS
SIFS
RTS
CTS
S1 Frame x
S1 Frame x
S1
NAV (RTS CTS)
11
Block Diagram