15-441: Computer Networking
Lecture 26: Where do we go from here?
Overview
• Content is king
• Billions of devices
• The next billion users
• “Nothing is permanent but change”
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Named Data Networking
• In the beginning...– First applications strictly focused on host-to-host
interprocess communication:• Remote login, file transfer, ...
– Internet was built around this host-to-host model.– Architecture is well-suited for communication between pairs
of stationary hosts.• ... while today
– Vast majority of Internet usage is data retrieval and service access.
– Users care about the content and are oblivious to location. They are often oblivious as to delivery time:• Fetching headlines from CNN, videos from YouTube, TV from Tivo• Accessing a bank account at www.bank.com.
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To the beginning...
• What if you could re-architect the way “bulk” data transfer applications worked• HTTP• FTP• Email• etc.
• ... knowing what we know now?
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Biggest content source
Third largest ISP
source: ‘ATLAS’ Internet Observatory 2009 Annual Report’, C. Labovitz et.al.
Level(3) GoogleGlobalCrossing
Google…
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1995 - 2007:Textbook Internet
2009:Rise of theHyper Giants
source: ‘ATLAS’ Internet Observatory 2009 Annual Report’, C. Labovitz et.al.
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ISP
ISP
What does the network look like…
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ISP
ISP
What should the network look like…
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Communication vs. Distribution
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Overview
• Content is king
• Billions of devices
• The next billion users
• “Nothing is permanent but change”
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Sensor Networks – Smart Devices
• First introduced in late 90’s by groups at UCB/UCLA/USC
• Small, resource limited devices• CPU, disk, power, bandwidth, etc.
• Simple scalar sensors – temperature, motion• Single domain of deployment
• farm, battlefield, bridge, rain forest
• for a targeted task • find the tanks, count the birds, monitor the bridge
• Ad-hoc wireless network
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Sensor Example – Smart-Dust
• Hardware• UCB motes• 4 MHz CPU• 4 kB data RAM• 128 kB code• 50 kb/sec 917 Mhz radio• Sensors: light, temp.,
• Sound, etc.,
• And a battery.
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Sensors, Power and Radios
• Limited battery life drives most goals
• Radio is most energy-expensive part.
• 800 instructions per bit. 200,000 instructions per packet. (!)
• That’s about one message per second for ~2 months if no CPU.
• Listening is expensive too. :(
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Sensor Nets Goals
• Replace communication with computation
• Turn off radio receiver as often as possible
• Keep little state (limited memory).
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Power
• Which uses less power?• Direct sensor base station Tx
• Total Tx power: distance^2
• Sensor sensor sensor base station?• Total Tx power: n * (distance/n) ^2 =~ d^2 / n
• Why? Radios are omnidirectional, but only one direction matters. Multi-hop approximates directionality.
• Power savings often makes up for multi-hop capacity• These devices are *very* power constrained!
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Example: Aggregation
• Find average temperature in GHC 8th floor.• Naïve: Flood query, let a collection point compute avg.
• Huge overload near the CP. Lots of loss, and local nodes use lots of energy!
• Better:• Take local avg. first, & forward that.
• Send average temp + # of samples
• Aggregation is the key to scaling these nets.
• The challenge: How to aggregate.• How long to wait?• How to aggregate complex queries?• How to program?
Overview
• Content is king
• Billions of devices
• The next billion users
• “Nothing is permanent but change”
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Example Routing Problem
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Village
Internet
City
bike
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3 1
Unstated Internet Assumptions
• Some path exists between endpoints• Routing finds (single) “best” existing route
• E2E RTT is not very large• Max of few seconds• Window-based flow/cong ctl. work well
• E2E reliability works well• Requires low loss rates
• Packets are the right abstraction• Routers don’t modify packets much• Basic IP processing
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New Challenges
• Very large E2E delay• Propagation delay = seconds to minutes• Disconnected situations can make delay worse
• Intermittent and scheduled links• Disconnection may not be due to failure (e.g.
LEO satellite)• Retransmission may be expensive
• Many specialized networks won’t/can’t run IP
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What about TCP?
• Reliable in-order delivery streams
• Delay sensitive [6 timers]:• connection establishment, retransmit, persist,
delayed-ACK, FIN-WAIT, (keep-alive)
• Three control loops:• Flow and congestion control, loss recovery
• Requires duplex-capable environment• Connection establishment and tear-down
Disruption Tolerant Networks
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Disruption Tolerant Networks
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Routing?
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time (days)bike (data mule) intermittent high capacity
Geo satellite medium/low capacity
dial-up link low capacity
City
Village 1
Village 2
Connectivity: Village 1 – City
ban
dw
idth
bikesatellitephone
Overview
• Content is king
• Billions of devices
• The next billion users
• “Nothing is permanent but change”
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Other Issues
• Security
• Mobility as the common case
• Clouds and replicated services
• Evolution support…
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Now for a message from the sponsors…
• Interested in this type of stuff?• Networking group often takes students during
the semester or summer • Stop by office hours or email to chat
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