Lowering the barriers to innovation
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Lowering the Barriers to Innovation. Jennifer Rexford Computer Science Department Princeton University http://www.cs.princeton.edu/~jrex. Flash Back to 1984. Fast Forward to Today. How computers work Electrical engineering degree at Princeton Making multiple computers work together

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Lowering the Barriers to Innovation

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Lowering the Barriers to Innovation

Jennifer Rexford

Computer Science Department

Princeton University


Flash Back to 1984

Fast Forward to Today

  • How computers work

    • Electrical engineering degree at Princeton

  • Making multiple computers work together

    • Parallel computing research at U. Michigan

  • Interconnecting computers via the Internet

    • Research at AT&T Labs

  • Designing the future Internet

    • Research and teaching with undergraduate and graduate students at Princeton

How the Internet Enables Innovation

Shawn Fanning

Northeastern freshman


Meg Whitman


Innovative Applications

Tim Berners-Lee

CERN Researcher

World Wide Web



Innovative Communication Media








Fiber optics

Telephone Network

Smart Network

Dumb Terminals

Plain Old Telephone Service (POTS)

  • Dumb phones

    • Dial a number

    • Speak and listen

  • Smart switches

    • Set up and tear down a circuit

    • Forward audio along the path

  • Limited services

    • Audio

    • Later, fax, caller-id, …

  • A monopoly for a long time


Dumb Network

Smart Terminals

Power at the Edge

End-to-End Principle

Whenever possible, communications operations should occur at the end-points of a system.


With programmable end hosts, new network services can be added at any time, by anyone.

And then computers became powerful and ubiquitous….

What Does the “Dumb” Network Do?

Best-Effort Packet Delivery

Internet Protocol (IP) Packet Switching

  • Much like the postal system

    • Divide information into letters

    • Stick them in envelopes

    • Deliver them independently

    • And sometimes they get there

  • What’s in an IP packet?

    • The data you want to send

    • A header with the “from” and “to” addresses

Why Packets?

  • Data traffic is bursty

    • Logging in to remote machines

    • Exchanging e-mail messages

  • Don’t waste bandwidth

    • No traffic exchanged during idle periods

  • Better to allow sharing of resources

    • Different transfers share access to same links

Why Best Effort?

  • Best-effort delivery

    • Packets may be lost, corrupted, delayed, or delivered out-of order

  • Keeps the network simple

    • No retransmission, error correction, or guarantees of packet delivery, …



IP network

Supporting Diverse Link Technologies

  • Best-effort packet delivery over most anything

    • Serial link, fiber optic link, coaxial cable, wireless

  • Even birds

    • IP Datagrams over Avian Carriers

IP over Avian Carriers was actually implemented, sending 9 packets over a distance of approximately 3 miles, each carried by an individual pigeon, and they received 4 responses, with a packet loss ratio of 55%, and a response time ranging from 3000seconds to over 6000 seconds.

Power to the User’s Computer

Overcome network limitations

  • Retransmit lost or corrupted packets

  • Put the received data back in order

  • Slow down under congestion

Run neat applications!

Operating System


The Result: Tremendous Innovation

Internet Protocol

So, What’s the Problem?

(And where do I come in?)

Misplaced Trust in the End Host

  • Security vulnerabilities

    • No strict notions of identity

    • Powerful computers

  • Many attacks

    • Denial of service

    • Spam e-mail

    • Phishing

    • Identity theft

  • How do we protectthe Internet?

Nobody is In Charge

Around 50,000 independent networks








Web server


How to manage a global federated network?

Hard to Change the Inside of the Internet

  • Internet infrastructure

    • Scalability

    • Stability

    • Reliability

    • Performance

    • Energy-efficiency

    • Security

Internet Protocol

  • Can we make the inside programmable?

    • To unleash a wave of innovation

My Research Challenge

  • A future Internet worthy of our trust

    • More secure, scalable, stable, reliable, efficient, …

    • More flexible and evolvable over time

  • Despite all the challenges

    • Greedy and malicious users

    • Networks driven by economics and politics

  • Without losing all the good stuff

    • Innovative applications

    • Innovative communication media

  • I think this will keep me busy for awhile! 

What I Love About My Job

  • Learn new stuff all the time

  • Pick the research problems I work on

  • Pick the people I want to work with

  • Have real impact on the world today

  • And (hopefully) bigger impact in the future

  • While wearing jeans to work every day!


(Any Questions?)

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