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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

Lowering the Barriers to Innovation

Jennifer Rexford

Computer Science Department

Princeton University


Fast forward to today
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

Innovative applications

Shawn Fanning

Northeastern freshman


Meg Whitman


Innovative Applications

Tim Berners-Lee

CERN Researcher

World Wide Web



Innovative communication media
Innovative Communication Media








Fiber optics

Telephone network
Telephone Network

Smart Network

Dumb Terminals

Plain old telephone service pots
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
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

What Does the “Dumb” Network Do?

Best-Effort Packet Delivery

Internet protocol ip packet switching
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
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
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
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
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


So what s the problem

So, What’s the Problem?

(And where do I come in?)

Misplaced trust in the end host
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
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
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
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
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?)