15-441: Computer Networking

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15-441 Computer Networking

• Lecture 26 Where do we go from here?

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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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Google
Biggest content source
Third largest ISP
Global Crossing
Level(3)
Google
source ATLAS Internet Observatory 2009 Annual
Report, C. Labovitz et.al.
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1995 - 2007Textbook Internet
2009Rise of the Hyper Giants
source ATLAS Internet Observatory 2009 Annual
Report, C. Labovitz et.al.
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What does the network look like
ISP
ISP
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What should the network look like
ISP
ISP
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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 90s 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. (!)
• Thats 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 distance2
• Sensor ? sensor ? sensor ? base station?
• Total Tx power n (distance/n) 2 d2 / 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?

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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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Internet
City
bike
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1
Village
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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 dont 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 wont/cant 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

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Disruption Tolerant Networks
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Disruption Tolerant Networks
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Routing?
Village 2
City
Village 1
time (days)
bike
bandwidth
satellite
phone
Connectivity Village 1 City
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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