Planning around Technology

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Planning around Technology

• Prof. Eric A. BrewerUC Berkeley
• ICT for Developing Regions
• September 17, 2003

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Todays Focus

• How to think about technology
• Not very technical
• Goal map applications into technology options
• Architecture
• Networking
• Devices and Sensors

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General Architecture
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Data Centers

• Best place to store persistent data
• (device is second best)
• Can justify backup power, networking, physical
  security
• Cheapest source of storage/computer per user
• 100-1000x less than a personal device (!)
• Factors shared resources, admin cost, raw costs
  (power, disks, CPUs)
• Need at least two for disaster tolerance
• Plan about 3 in urban centers (for one region)
• Berkeley will be the data center for our early
  work

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Networking

• The key enabler distribution for information.
• Focus on wireless
• Vastly cheaper to deploy
• Wide range of options
• Packets allow efficient use of media
• multiplexing
• IP Internet Protocol
• Global names for every device
• Way to route packets to names

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Basics

• Bandwidth data/sec
• Modem 56 kilobits/sec
• DSL 384 kilobits/sec
• Latency transmission delay in seconds
• Ethernet milliseconds
• Satellite ¼ second
• Power should be mostly tied to transmission
• Double distance gt quadruple power
• Sequence of short hops usually lower power(but
  higher latency)

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Communication Attributes

• Directional or Omnidirectional
• Broadcast or Unicast
• Wireless is always broadcast
• Shared or Single User
• Wireless is always shared
• Synchronous or Asynchronous
• Cellular is synchronous full-time two-way
  connection
• E-mail is asynchronous send now, receive later

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Understanding Range

• Range costs power (squared)
• Long distances best covered with directional
  antennas
• 10x difference in range for low cost
• Point-to-point links
• Can go 50km at reasonable cost
• User density matters
• Range also limited by total users
• Urban areas thus use short-range wireless
• Rural areas need long-range
• Claim need islands of coverage (with
  point-to-point)
• Islands are the dense areas (e.g. villages)

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Example India

• Mumbai (Bombay)

Chennai (Madras)
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Mumbai
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Broadcast vs. Unicast

• Broadcast same data to everyone
• TV, radio, newspaper
• Unicast data to one person
• Web page, e-mail
• Wireless broadcast is cheap
• Easy to reach many users with one transmission
• Example satellite TV
• Claim we will need to exploit broadcast
• Broadcast common data even for unicast
  applications
• Example common web content
• Goal minimize unicast data

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Synchronous vs. Asynchronous

• Synchronous two-way communications
• Low latency, e.g. Phone ¼ sec or less
• Expensive dedicated resources along whole path
• Examples phones, games, web browsing
• Async One-Way e.g. TV, Internet movie
• Delay allowed e.g. buffering for Real Player
• Hides losses resend data before it is missed
• Typical delay is 10 seconds
• Good fit for broadcast
• Examples Streaming, Market Prices, Weather
  alerts

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Sync vs. Async (2)

• Async Two-Way e.g. e-mail request
• Delay in getting response ( two async one-way)
• Semi-interactive, but potentially much cheaper
• Savings
• No need for dedicated resources
• Can store-and-forward data (like real mail)
• Can hide problems (e.g. power out) by waiting
• Examples e-mail, correspondence classes, medical
  diagnosis (non-emergency), coordinating money
  transfers, e-commerce (e.g. catalogs)
• Open Questions
• How much cheaper? How much more reliable?
• When is async good enough?

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Intermittent Networking

• Physical
• Low-earth orbit satellites connect only while
  they are overhead
• Mules moving basestation collects data
• Basestation could be on a bus
• Weather, e.g. some places only get radio on clear
  nights
• Overloaded network may delay transmission
• Extended coverage
• User may periodically enter the coverage area
• E.g. coverage only near market or school

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The Case for Intermittent

• Pros
• Cost better use of resources, more tolerant of
  problems
• Reliability delay hides transient problems
• Ease of deployment can be more ad hoc, less
  coordination than a synchronous system
• Coverage Intermittent coverage gtgt full time
  coverage
• Cons
• Not really interactive, or only interactive in
  some areas
• Need to design apps around this (new) model
• Dont know what delay is OK (depends on the app)

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Cellular Phones

• Advantages
• User interface works well (no need for literacy)
• High demand for voice, but some data provided
• High-volume phones and basestations
• Disadvantages
• Hard and expensive technically
• Voice may be inefficient use of bandwidth
• Poor fit for rural users (low density of users)
• Typical data rate lt 9600 baud

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Example Cellular Standards
System Cell Range Cost Bandwidthbits/sec Simult. Users
GSM 10 km 100K 9600 800
PHS 100-300 m 3K 9600 200
MiniGSM 35 km ? 9600 800
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Satellites

• Pros great for broadcast, coverage
• Cons limited shared bandwidth, mostly one-way,
  high latency
• GEO (geostationary stays in one place)
• 35000 km up, very high latency
• Mostly one-way due to power
• LEO (low-earth orbit), lt1000 km up
• Intermittent coverage (only when overhead)
• Better latency and power, cheaper
• Need lots of satellites (800?)

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Two-way using Satellites

• Option 1 transmit up to the satellite
• Very high power required, and large antenna
• Very low bandwidth (9600 or less)
• Option 2 use a different network
• Telephone is most common, could use wireless
• Tricky but possible to do TCP
• Variation upload data later when convenient
  (intermittent)
• Good for mostly broadcast applications, coverage

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WiFi 802.11

• Made for wireless local-area network
• Three variations
• b 1 Mb/s, oldest and cheapest, 5/chipset
• Best for long-distance links
• a 11 Mb/s, shorter range
• g 54 Mb/s, shorter range, more channels
• Best for omni coverage of local area (if cheap)
• Decent for long distance (802.11b)
• Special directional antennas alignment,
  (20-200)
• 30km seems easy, 88km is current record
• Longer distances need towers, 40 typical

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WiMax (802.16)

• New standard for metro areas
• Target is 30km radius, 20K for basestation
• Cost should come down (as with 802.11)
• High bandwidth, low density
• Receiver per village, not per person
• 100 villages per basestation plausible
• Probably requires licensing (not free for all)
• Complements 802.11 for local coverage
• Expect this combo to be very popular

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Proxies and Basestations

• Cellular gt one basestation per cell
• Proxies are similar locally shared
  computing/storage
• 10x less than devices (per user!)
• Target cost 200 or about 20 per user
• Good way to share computing, storage
• Relay point for networking
• Typically stationary, may be solar powered
• Mules are mobile proxies
• Easy to upgrade in place (like Tivo)
• Not good for long-term storage (persistent
  data)
• No backup plan, unreliable power and security

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Example Proxy Tasks

• Caching of frequently used data
• Such data can be broadcast to proxies
• Temporary storage
• Packets waiting for LEO
• Transactions in progress
• Computation-intensive tasks
• Speech recognition
• Sensor data analysis
• Process data for dumb device
• Can double as big device, e.g. Internet kiosk

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Devices

• Wide range of devices are possible
• Two broad classes
• General-purpose computer (Simputer, PDA, laptop)
• Task specific water testing, telephone, camera
• Claim task specific is a better choice
• Much simpler to use (and train for)
• Can be more cost effective
• Volume should be high enough to justify

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Shared Devices

• Sharing reduces the cost per user
• Village phones have 4-8x better cost/performance
• May only need one per village (water testing)
• Some design issues
• Does behavior depend on which user?
• E-mail does, telephone does not
• Need for authentication, accounting?
• Claim Most projects should start with shared
  devices
• Can move to personal devices if demand warrants

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Device Costs

• Big costs
• Packaging
• Screen color is gt3x monochrome
• Battery
• UI keyboard, buttons, touch screen,
• General driver too many components
• Solution better integration into silicon
• Silicon is free (marginal cost)
• We are working on real details of costs

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How to think about devices

• Sharing is good (but design for it)
• Task-specific is good (simpler and cheaper)
• UI and size have a lot to do with cost
• Dependence on infrastructure is good
• Reduces cost (and theft)
• Can push work into infrastructure as needed
• Increases extensibility, decreases obsolescence
• but requires thought about disconnected
  operation

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Sensors

• Sensors on silicon gt very cheap
• Basic temp, humidity, pressure, moisture, light
• Moderate acceleration, magnetic, position
• Simple chemical gases, smoke
• Complex biological toxic agents
• Actuators control environment as well
• Much harder usually want human in the loop

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Sensor Applications

• Environmental monitoring
• Water testing
• Weather warnings?
• Aid to Infrastructure
• Electrical grid loss/theft
• Water distribution loss/theft/quality
• Commerce
• Butterfat testing for milk pricing
• Health
• Home environment
• Human tests? (or animal)

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Example Great Duck Island

• Monitoring petrels on an island in Maine
• About 50 sensors
• Some in burrows, detect occupancy
• Some to track environmental conditions
• Fits architecture
• Data center in Berkeley
• Network local wireless in patches, satellite to
  UCB
• Proxies process/manage data collection
• Mix of sensors
• Intermittent connectivity (to save power)

1.25 inch
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Summary

• Decide on the task
• Not about internet access (per se), about
  applications
• Drives UI, leads to simplicity, lower cost
• Long-term single chip per app is ideal
• Wide range of devices can share infrastructure
• Intermittent networking may be sufficient
• Greater coverage, much lower cost, more reliable
• Not always interactive
• Share, share, share
• Data centers are big shared resources, gt100x
  savings
• Proxies are locally shared resources, gt10x
  savings
• Share devices as well