Wireless Networks

By Roddy Knight, Chris Zeiders, and Sanjay Ginde

Survey of Wireless Networks

Public Access Networks User groups Commercial services Universities

Technical aspects of Wi-Fi networks 802.11 standard Privacy and authentication in Wi-Fi

Importance of Wi-Fi

Ubiquitous internet Mobile users benefit No strings attached

Architectural Advantages Transfer speeds up to 11 Mbps

Rich media possible Hardware encryption

Rapid Growth Quarterly shipments

of Wi-Fi equipment doubled from last year

Dell ships all new laptops with Wi-Fi cards

Intel plans to embed Wi-Fi functionality in new processor dubbed Banias

Networks (public/private)

User groups provide non-commercial wireless access

Telecom companies provide commercial networks in hotels and cafes

Commercial networks offer more reliability and coverage for a price

User Groups Loose assortment of

broadband customers with publicly accessible hotspots

Publish status of available hotspots on web

Provide online forum for debate of public access issues

Survivors of 9/11 utilized NYC wireless nodes to spread word about relief efforts at ground zero

Municipal Initiatives Wireless networks are funded by

municipalities to attract high-tech entrepreneurs

Pittsburgh Public Wireless Internet Project plans network to cover 4-square-mile area of downtown Pittsburgh

Jackonsonville, FL hopes free wireless networks in shopping malls will increase pedestrian traffic and revitalize economically depressed areas

University Networks Duke has 45 hotspots across

campus and plans to eliminate current authentication hassle

Dartmouth has 500 hotspots that cover 200 acres of campus

UNC incorporates Wi-Fi into course work Students share drafts in English class

ISP Resistance Time Warner Cable has

mailed threatening notices to customers ordering them to terminate public wireless access for personal liability reasons

Most cable modem customers share common upstream pipe unlike DSL users

DSL providers sell equipment directly to customers because they perceive Wi-Fi as opportunity

Cellular Carrier Dilemma Carriers have spent $6 billion upgrading

networks for high-speed internet access Wi-Fi networks require a fraction of the

infrastructure cost and offer greater bandwidth

Carriers scrambling to join commercial Wi-Fi market by placing nodes at airports, hotels, Starbucks

T-Mobile charges $30/month or $2.99/minute

National Wi-Fi Network

Cometa plans coverage for top 50 metropolitan cities with 20,000 hotspots

Company resells service through ISPs Service priced around $50/month Backed by IBM, AT&T, and Intel Nodes installed in hotels, coffee

shops, and public venues

Wireless Protocols

Competing Standards 802.11, 802.15, 802.16, HomeRF, Bluetooth

802.11 Standard Wireless equivalent to Ethernet Known as “Wi-Fi” First WLAN specification adopted by

commercial vendors

802.11 Protocol

Physical and Data-Link Layer of OSI Network

Transmitting Data

Infrared Radio Waves – A double-edged

sword Spread Spectrum Technology

FHSS DSSS

Unique Wireless Problems

Hidden Nodes Problem Exposed Nodes Problem

Undetected Collision

Unnecessarily blocked to transmit

802.11 Solution

Virtual Collision Detection (VCD)

RTS

CTS

CTS not sent to D, so waits to transmit

?

D Hears RTS, but not CTS, so free to transmit

Access Points

Necessary for widespread public wireless networks

APs connected to a Distributed System

802.11 does not define how the Distributed System works

802.11 does specify “scanning” and “roaming”

Packet Routing

Wireless user has no “stable” network it is associated with

Packet routing using IP is impossible

Mobile IP Two addresses: Home address and “care-

of” address Each user has a static home address with a

“home agent” User sends a “care-of” address to home

agent when it connects to a foreign network Packets sent to home address via TCP,

home agent re-routes data to care-of address

Security Goals

Privacy Open connection

Authentication Authorization

Why Is Privacy Important?

Use by business men and woman Need at least the same level that

an a direct cabled connection would provide

Wired Equivalent Privacy (WEP) standard for 802.11b

Wired Equivalent Privacy

C = P RC4(v,k)

Graphic from:

Gast, Matthew S. 802.11 Wireless Networks.

More WEP

Graphic from:

Gast, Matthew S. 802.11 Wireless Networks.

Problems with WEP

Manual key management Automation needed with unknown

users Wireless roaming

Need to manually enter keys at new AP

Only protects outside attacks Unknown users at AP

WEP Keystream Reuse Difficult key management = rare

rekeying Cipher Analysis

If C1 = P1 RC4(v,k) and C2 = P2 RC4(v,k)

then C1 C2 = (P1 RC4(v,k)) (P2 RC4(v,k))

= P1 P2

Collisions Relatively small IV space

Graphic from:

Gast, Matthew S. 802.11 Wireless Networks.

Is Authentication Important?

ALS Scan Inc. v. RemarQ Communities Inc. ISP potentially liable for illegal activity

Wi-Fi and Terrorism

Authentication

802.11b uses MAC addresses Inflexible

Extensible Authentication Protocol (EAP) Supports different authentication

methods Free public wireless providers Wireless roaming

Virtual Private Networking

Standard for remote access security More secure privacy Supports different authentication

methods Average user set off by technicality

BOINGO software Need for authentication servers

Summary We covered Wi-Fi networks from

social standpoint Commercial and free deployments

Surveyed key issues involved in implementation of wireless network

802.11 addresses issues Unique security issues related to

wireless networks

Future Research

Analyze the 9 task groups in IEEE 802.11 working group

Compare WLANs to competing wireless protocols for broadband access such as 3G