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WiFiProfiler: Cooperative Diagnosis in Wireless LANs. Ranveer Chandra, Venkat Padmanabhan, Ming Zhang Microsoft Research. Wireless Woes. Users often wonder why: “My machine says: wireless connection unavailable” “I get poor performance on wireless”

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Wifiprofiler cooperative diagnosis in wireless lans l.jpg

WiFiProfiler: Cooperative Diagnosis in Wireless LANs

Ranveer Chandra, Venkat Padmanabhan, Ming Zhang

Microsoft Research


Wireless woes l.jpg
Wireless Woes

  • Users often wonder why:

    • “My machine says: wireless connection unavailable”

    • “I get poor performance on wireless”

    • “My wireless card keeps trying to authenticate”

    • “Is it just me?”


Wireless woes3 l.jpg
Wireless Woes

  • Users often wonder why:

    • “My machine says: wireless connection unavailable”

    • “I get poor performance on wireless”

    • “My wireless card keeps trying to authenticate”

    • “Is it just me?”

  • Many places have no/minimal network admin

    • Hotspots: cafes, airports

    • Transient networks: conferences, IETF meetings


Prior work operator view l.jpg
Prior Work: Operator View

  • Infrastructure-based monitoring (Aruba, DAIR)

    • Focuses on operator perspective (e.g., rogue APs)

  • Monitoring at clients (e.g., [Adya 2004])

    • Fault diagnosis using infrastructure support

    • Also focuses on operator perspective

  • Correlate client observations at AP (MOJO)

    • Detect PHY level anomalies


Wifiprofiler goal user view l.jpg
WiFiProfiler Goal: User View

Enable clients to diagnose network failures without requiring admin/infrastructure support:

  • Reduce user frustration

  • Reduce load on admin, when there is one

Help users help themselves


State of the art local diagnosis l.jpg
State of the Art: Local Diagnosis

  • Wireless Connection Manager, WZC

    • Reasonable detection, Poor diagnosis

Bad NIC

MAC

Filtering

Bad WEP

Key

Cannot Associate

Bad AP


Wifiprofiler l.jpg
WiFiProfiler

  • Based on two key observations:

    • Clients form Information Plane with peers

      • Even when client cannot connect to AP

    • Extent of problem indicates cause

Diagnose faults by correlating peers’ health


Wifiprofiler overview l.jpg
WiFiProfiler Overview

Healthy Client

Req. Health

Health Info.

(WEP key info)

Dissatisfied Machine

(Cannot connect to

WEP-enabled AP)

Create Information

Plane

Access Point

Health Info.

(WEP key info)

Req. Health

Diagnose Problem:

Same WEP key?

Healthy Client

Diagnose range of problems across layers!


Faults and some causes l.jpg
Faults and Some Causes

Location

No AP Detected

H/w or s/w

No Association

Security

DHCP Server

No IP Address

Firewall/proxy

End-to-End Failure

WAN Disconnect

WAN congestion

Poor Performance

Wireless problem


Outline l.jpg
Outline

  • Introduction

  • WiFiProfiler Overview

  • WiFiProfiler Design

  • Evaluation

  • Summary


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WiFiProfiler Design Goals

  • Transparency:

    • Minimal user impact/involvement

  • Deployability:

    • Work with off-the-shelf cards and unmodified drivers

  • Scalability:

    • Work with a large number of clients

  • Security:

    • Prevent compromise of clients and AP


Wifiprofiler architecture l.jpg
WiFiProfiler Architecture

  • Sensing: What is monitored?

  • Communication: How is it shared?

  • Diagnosis: How are faults diagnosed?


Sensing l.jpg
Sensing

  • Monitor health of client’s connectivity

    • Static info (e.g., NIC type)

    • Dynamic info (e.g., assoc. success/failure)

Sensed Info

Some Causes

Fault

NIC Model, Make,

Driver version

H/w or s/w

No Association

Auth/Encryption

setting, key info

Security


Sensed information l.jpg
Sensed Information

  • User-level service (daemon) polls various layers

    • Wireless: NIC, BSSID, RSSI, Beacon Loss, 1-way hash of key, Interface Queue

    • IP: IP Address, DHCP, DNS

    • Transport: Failed connections, Server Ports

    • Application: Web proxy settings

  • Snapshot obtained once every second

    • Summarized information < 1200 bytes


Communication l.jpg
Communication

802.11 NICs can connect to only one network at a time

Challenges:

  • Discovery: How does H know that D needs help?

  • Parallelism: How does H send packets to D?

Req. Health

H

D

Sensed Info

Establishing the Information Plane


Discovery l.jpg
Discovery

  • D initiates ad hoc network with distinct SSID

    • Special SSID format denotes request for help

    • H receives beacon even when associated to AP

SSID:

Help:169.254.10.125:5000

D

H

169.254.10.125

Port: 5000


Parallelism using virtualwifi l.jpg
Parallelism using VirtualWiFi

Details: Infocom ’04

Approach: Virtualize card, buffer packets, switch b/w networks

Application Layer

User-level

Kernel-level

TCP/IP, Network Stack

VirtualWiFi Layer

Virtual Interface 1

Virtual Interface 2

Virtual Interface 3

Wireless Card


Communication protocol l.jpg
Communication Protocol

  • WiFiProfiler uses 2 (virtual) adapters:

    • Primary adapter activated in normal use

    • Helper adapter dedicated for WiFiProfiler

      • Activated only when needed

SSID:

Help:169.254.10.125:5000

D

H

Primary VNIC

169.254.10.125

Port: 5000

Helper VNIC

Scalability and Security discussions in paper


Diagnosis l.jpg
Diagnosis

  • Initiated by user

  • Correlate peers’ info and infer likely cause

    • Rule-based techniques instead of black-box

  • Suggest steps for problem resolution

    • Change configuration settings

      • e.g. local DNS server, web proxy, WEP key

    • Change location, contact admin

  • Diagnose faults across layers of network stack


Diagnosing association failure l.jpg
Diagnosing Association Failure

If another peer has successfully associated with the AP:

Similar card

Associated?

Is Sec.

config

Same?

Is BLR

much

higher?

YES

NO

NO

YES

YES

NO

Bad Sec. setting

(Fix it)

Bad signal

(change location)

MAC Filtering

(contact admin)

S/w or H/w config

(change NIC or

update driver)


Diagnosis features l.jpg
Diagnosis Features

  • Inherent uncertainty in some cases

    • Need info from AP to confirm MAC filtering

  • Conflicting info from peers

    • Used to eliminate branches in diagnosis procedure, e.g. NIC type

  • Vulnerability to bogus info from attackers

    • Use information from large number of peers

    • Susceptible to Sybil attack


Outline22 l.jpg
Outline

  • Introduction

  • WiFiProfiler Architecture

    • Sensing

    • Communication

    • Diagnosis

  • Evaluation

  • Summary


Evaluation l.jpg
Evaluation

  • Sensing: Low overhead

    • (used < 1% CPU on 1.33 GHz laptop)

  • Communication using VirtualWiFi:

    • Healthy clients spend < 2 sec sending info

    • Sick clients get information within 30 seconds

      • Much of the delay in discovery (scanning delays)


Little impact on healthy clients l.jpg
Little Impact on Healthy Clients

Extra 0.5 to 3 seconds!


Effectiveness of wifiprofiler l.jpg
Effectiveness of WiFiProfiler

Relevant diagnosis at all clients within 30 seconds!


Wifiprofiler summary l.jpg
WiFiProfiler Summary

  • Enables cooperative diagnosis in WLANs

    • Without infrastructure support, low overhead

  • Working system on Windows XP

  • Future work:

    • Security: Privacy, Sybil Attacks, Passive Mode

    • Long-term Profiling


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