Elias C. Efstathiou Mobile Multimedia Lab Computer Science Department Athens University of Economics...

Elias C. Efstathiou

Mobile Multimedia LabComputer Science Department

Athens University of Economics and BusinessAthens 10434, Greece

[email protected] - http://mm.aueb.gr

Authors: P. Antoniadis, C. Courcoubetis, E. C. Efstathiou, G. C. Polyzos, and B. StruloIST Project MMAPPS - Market Management of Peer-to-Peer Services

(RTD No IST-2001-34201)

IST Mobile and Wireless Summit 2003, Aveiro, Portugal

The Case forPeer-to-Peer Wireless LAN Consortia

(PWC)

A P2P Approach to WLAN Roaming

2 / 14AUEB Mobile Multimedia Lab – http://mm.aueb.gr

Introduction (1 of 2)

Ubiquitous Internet Access a Necessity

• However, WISPs are facing difficulties

• WISP roaming practically non-existent

• Many under-exploited private WLANs do exist

The Peer-to-Peer Wireless LAN Consortium (PWC):

• A Framework for uniting all WLANs in one global group

• A Community of WLAN Administrative Domains that offer wireless Internet access to each other’s registered users

• The PWC is a P2P network of Domain Agents (DAs)• DAs are physical nodes that represent one domain each

• Their purpose is to eliminate the overhead of roaming agreements

• Instead, DAs obey a simple token-exchange rule


Introduction (2 of 2)

Domain Independence: a PWC Distinctive Characteristic

• DAs make autonomous decisions concerning the amount of resources they provide to visitors

• Key difference from other roaming schemes

PWC Simplicity

• No central entity controls the PWC or the interactions of its participants

• No cost of entry for domains

• PWC subsystems leverage its P2P nature: no external servers are required


Background

Motivation

• Existing under-exploited WLANs

• IEEE 802.11 simplicity

• Next-generation portable devices

WLAN Roaming Today

• Practically non-existent• Hotspot aggregation (e.g. Boingo Inc.) is not WLAN roaming

• Limitations of WISP associations (e.g. Pass-One)• Service-mark logic• Insufficient privacy• Insufficient autonomy• Administrative overhead and complexity

The PWC as a P2P System

• Shared good: bandwidth

• Autonomous peers: independent domain agents

• Free-riding: domains that may not provide access to visitors

• Incentives and rules: token-exchange rule


PWC Requirements

1. Domain Independence

• The peers make autonomous decisions• Concerning their contribution level• Concerning their participation status

2. Domain Reciprocal Behavior

• Free-riding must be minimized

• PWC system rule: token-exchange• This rule “guides” domain behavior

3. Easy-to-Join

• No administrative overhead

• Similar to joining a P2P file-sharing network• Assuming the domain WLAN infrastructure is already in place

4. PWC Self-Sufficiency

• PWC subsystems rely only on the PWC peers themselves

5. Decentralization

• No central entities

• No central authority manages the PWC


PWC Entities

Domain Agents (DAs)

• The PWC is a P2P network of DAs

• DAs are nodes running the PWC DA software

• Exactly one DA per PWC administrative domain

• Each DA has a unique logical name:• aueb.gr, cometa.net• The_Aveiro_Smith_Family

Users

• Registered with one (or more) DAs

• Each has a unique identifier (user_name@logical_domain_name)

Bandwidth

• The PWC ‘good’ - 802.11 bandwidth and bandwidth to the Internet

Tokens

• Unforgeable virtual currency

• Exchanged between DAs

• Represent the value, which DAs ascribe to their consumed bandwidth


PWC High-Level View

WLAN viewWLAN view P2P viewP2P view

AP : WLAN Access Point

: User

DA : PWC Domain Agent

AP

AP

AP

AP

AP A

P

AP

AP A

P

DA‘White’

DA‘Gray’

DA‘Black’


PWC Domain Agent Modules

1. Name-service

• Maps logical domain names to DA IP addresses

• Uses a Distributed Hash Table (DHT)

2. Authentication

• Maintains a database of registered users• Along with their security

credentials

3. Traffic Policing

• Logs and shapes egress and ingress Internet traffic

• Allocates specific amounts of bandwidth to visitors

4. WLAN

• Firewall, DHCP, DNS, NAT/NAPT, WLAN control

5. Distributed Accounting

• Secure storage of PWC accounting information

• Also uses a DHT

6. Consumer Strategy

• Regulates the consumption actions of the domain’s roaming users

7. Provider Strategy

• Regulates contribution to visitors

• Dynamically assigns “prices” to consumed resources

8. Privacy Enhancement

• Ensures PWC user anonymity and untraceability


PWC Security Issues

PWC security is a superset of WLAN security

• The usual confidentiality, integrity, and availability problems apply

• The following three issues are PWC-specific:

1. Traffic Logging by Untrustworthy Providers

• User traffic completely visible to the visited Domain Agent

• Encryption does not hide useful metadata (e.g. remote-party address)

• SOLUTION: Tunnel (encrypt and route) through the home DA

2. Identity Privacy: PWC Pseudonyms

• User name visible to the visited DA

• SOLUTION: Use algorithmically updated user aliases

3. Anonymity and Untraceability: PWC Mixes

• User name and home domain name visible to the visited DA

• Home domain name required for PWC accounting

• SOLUTION: Use PWC privacy enhancement modules (PWC mixes)


PWC Mixes

DA‘P’

(Provider)

DA‘A’

(First mix)

DA‘B’

(Second mix)

DA‘C’

(Consumer)

user_X@C

“My PWC user ID is alias_X@A”

(Appends real ID and a mix chain, all encrypted using layered public-key encryptions)

P, A, and B cannot know if the domain on the right is the real consuming domain or a mix

A, B, and C cannot know if the domain on the left is the real providing (visited) domain or a mix

Blue arrows

represent

token flow


Open PWC Issues

1. Secure Distributed Accounting

• Maintains PWC accounting history

• Must be fault-tolerant, scalable, hack-proof

2. Tokens and Token Generation

• Cryptographically secure, unforgeable tokens

• Generated, perhaps, by a PWC internal distributed bank

• Distributed to new PWC entrants

3. Domain Heterogeneity

• Domains covering areas diverse in size and location

• Domains may have completely uneven populations of registered users

• Small domains may receive only very few requests (and thus tokens)

4. “Offline” Domains

• Domain Agent autonomy may mean a DA is unreachable/offline

• Who “pays” for a roaming user of that domain?• The roaming user? Another domain?


Deploying the PWC

Domain Agent Administrative Interface

• Must hide PWC complexity from Domain Agent administrators

• DAs must require a minimum number of input parameters:1. A list of registered users and their security credentials

2. The domain’s aggregate egress and ingress Internet bandwidth

3. A “map” of WLAN cells and local traffic bottlenecks

4. The average WLAN load (local registered users and visitors)

5. The average PWC usage by roaming users of the domain

• Some of these parameters will be administrator’s ‘best-guesses’

PWC Profit Opportunities

1. Vendors of PWC Domain Agents

2. Vendors of PWC support modules

3. PWC domain aggregators

4. “Pay-as-you-go” domains


PWC Domain Agent Prototype

We’ve built two prototype PWC Domain Agents• Running on PCs with Red Hat Linux 9 (2.4.20 kernel)

• Developed using C, Java, and Python

• Each DA is also a WLAN router, connected to the Internet and to a Cisco Aironet 1200-series WLAN AP

Modules completed:• Authentication

• Using IEEE 802.1X• Using a custom web-based login function (and the iptables firewall)

• Traffic Policing• Using the libpcap library and the tc utility

• WLAN• Using Linux IP masquerading (for NAT/NAPT) and standard Linux DHCP, DNS, and

routing functionality

• Strategy (using a very simple P2P token-exchange rule)

Still needed:• Unforgeable tokens, secure DHT (for distributed accounting and name-

service), more complex strategy algorithms, PWC mixes


Concluding Remarks

• The PWC is a simple alternative to existing roaming schemes

• The PWC is designed around organic growth

• PWC strategic agents replace static roaming agreements

• Although, by design, the PWC cannot provide any strong guarantees, it could become a suitable vehicle for achieving ubiquitous, low-cost, Internet access

• PWC autonomy and privacy considerations could make it more socially acceptable

• Real-world regulations could, however, affect PWC growth

• More analysis and simulations are needed to assist in designing optimal PWC rules

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