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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