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Managing Chaotic Wireless Networks. David Wetherall University of Washington. Credits. UW/CSE wireless group John Zahorjan, Maya Rodrig, Charlie Reis, Ratul Mahajan, Ed Lazowska Intel Research Seattle Yatin Chawathe, Mike Chen, Brian Noble, Anthony Nicholson CMU

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Managing chaotic wireless networks

Managing Chaotic Wireless Networks

David Wetherall

University of Washington


Credits
Credits

  • UW/CSE wireless group

    • John Zahorjan, Maya Rodrig, Charlie Reis, Ratul Mahajan, Ed Lazowska

  • Intel Research Seattle

    • Yatin Chawathe, Mike Chen, Brian Noble, Anthony Nicholson

  • CMU

    • Srini Seshan et. al. for “Chaotic” wireless


Context wifi boom
Context: WiFi boom

deployments

  • Advantages: minimal infrastructure, mobility

  • Technologies: 802.11 a/b/g/n, and more

  • Deployments: hotspots, home networks

measure

cost-performance

time


Chaotic wireless networks
Chaotic Wireless Networks

Two consequences of growth:

  • Overlapping (dense) deployments

    • Compete for spectrum

    • Seen in urban areas today

  • That are independently managed

    • Limited visibility into the operation of others

    • Focus on their own goals; no central planning

      Chaotic = overlapping + independent

      Claim for chaotic environments:

  • Today’s 802.11 designs won’t fare well

  • There’s an opportunity to do much better


A single 802 11 network architecture

CSE Allen Center, 3rd floor

10 802.11b/g APs per floor, managed as a whole:

Channels 1, 6, 11

20/30 mW power

Omni-directional antennas

Site surveys, sparse deployments, and decoupling are the basis for good coverage and performance.

A single 802.11 network architecture


Adverse interactions across networks
Adverse interactions across networks

  • 802.11 won’t degrade gracefully in chaotic environments

    • Ideally CSMA/CA would provide reasonable sharing …

  • Default channel assignments

    • Crowding, non-orthogonal effects

  • Static power management

    • Wastefully high, leads to interference

  • Rate diversity

    • High rate transmissions beat out by low rates

  • Hidden terminals and capture

    • Poor access from some locations

  • Other unlicensed band transmissions

    • Don’t argue with a phone/microwave …

  • Problems increase with density, load and heterogeneity


A band aid dynamic tuning
A Band-aid: Dynamic tuning

  • One possible fix: dynamic parameter tuning

    • Each network measures environment and chooses the channel/power/routes that works best for it

  • Claim: dynamic tuning isn’t enough

    • Adaptation is necessary but not sufficient

    • There are opportunities to do much better


Pitfalls 1 you can get stuck

Top: AP conflict on channel 1 (middle two blue nodes) can’t be resolved by individual tuning

Bottom: but a solution needs only a simple switch between two adjacent nodes

Pitfalls (1) – you can get stuck

1

5

4

3

2

6

1

5

4

3

2

6


Pitfalls 2 lack of stability
Pitfalls (2) – lack of stability can’t be resolved by individual tuning

  • To avoid getting stuck, need to perturb the system, changing channels even without immediate gain

  • Q: What happens to in the configuration below?

  • A: Four APs dance around three channels

  • Tradeoff between stability and convergence

4

1

3

2


Pitfalls 3 power escalation
Pitfalls (3) – power escalation can’t be resolved by individual tuning

  • Suppose APs adjust their transmit power (between min and max) based on delivery to their clients

  • What will the APs on channel 1 do?

    • Higher power increases delivery/rate and interference

    • Potential tragedy of the commons (lose/lose)

4

1

3

2


Opportunities for coordination
Opportunities for Coordination can’t be resolved by individual tuning

  • Suppose we go beyond dynamic tuning …

    • Coordination = actively exchange information and make joint decisions (for selfish gain), rather than merely try to avoid each other

  • Claim: coordination beats tuning

    • Improves outcome for pitfalls

    • Enables new beneficial scenarios


Relaying for coverage performance
Relaying for coverage/performance can’t be resolved by individual tuning

  • Relaying can leave both networks better off

    • Use of better links allows higher rates,

    • i.e., one transmission per packet at 1 Mbps vs. two transmissions per packet, each at 55Mbps

1

AP1

C1

55

55

55

55

1

AP2

C2


Backup for reliability performance
Backup for reliability/performance can’t be resolved by individual tuning

  • Use neighbor AP for backup Internet access

    • Or always use neighbor’s surplus for performance

    • Need to consider AUP issues

Internet

Internet

X

AP1

AP2

C1

C2


Goal wireless internetworking
Goal: Wireless internetworking can’t be resolved by individual tuning

  • Wireless Internet = architecture that coordinates multiple individual wireless networks for better coverage, performance and reliability

    • Predictably allocate wireless and access bandwidths

    • Leave individual networks better off than before

  • Architectural roles:

    • Effectively allocate underlying resource

    • Allow new applications to flourish

    • IP does both; 802.11 does neither …


Research agenda
Research agenda can’t be resolved by individual tuning

  • How does wireless work in practice?

    • Predict what will happen for a given choice of channel/power/routes and protocols

  • What information is exchanged where?

    • Need to find small regions with tight coupling

  • How do we make this win-win?

    • Choices that benefit all players

  • How do we foster a grassroots effort?

    • Deployment incentives


Questions
Questions? can’t be resolved by individual tuning


Aside wifi vs cellular data
Aside: WiFi vs Cellular data can’t be resolved by individual tuning

  • WiFi

    • Local = high bandwidth, inexpensive

    • Many islands of coverage

  • Cellular data

    • Wide-area = low bandwidth, expensive

    • Build-out for good coverage “away from home”

  • So concentrate on WiFi here

    • Potential for combining the best of both worlds


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