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Aloha Dr. Abramson: Could We Eat The Telco’s Lunch?

Evolution of Computer Networking

Ravi Prakash

Department of Computer Science

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Surf the Net or Net the Surf?

• 1970: network multiple University of Hawaii campuses.

• Wireless hub-and-spoke:– Source to central campus.– Broadcast received signal to destination.

• What if multiple sources transmit concurrently?

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ALOHA: Multiple Access

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From ALOHA to Ethernet

• No central relay.• Listen before speaking.• Jamming signal on collision.• Random back-off and retry.

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The Past: Circuit Switched

Request • Reservation based.– Dedicated resources.

• Guaranteed quality of service

• Resource utilization?

Time

Send entiremessage

Response

Data

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Do Computers Talk Like That?

• No, no, no, no, ………………..no, no, no, …………………., no, no, no, no, ………………………………., no, no, …..

• Kleinrock et al.: Why waste resources?– Unlearn what Ma Bell taught us.– Learn from the Post Office instead– IP Datagrams

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Towards Packet Switching

Time Time

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Statistical Multiplexing

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Routing & Packet Switching

Source

Destination

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Danger, Will Robinson!

• Packets being dropped by routers!• Packets corrupted over links!• Network becoming too big to discover

routes!

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The Reliability Question

• The TCP answer– Cerf & Kahn, 1974

• If at first you don’t succeed, try, try, try again.– Acknowledgments.– Timers.– Retransmissions.

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Too Big To Fail?Chop, chop, chopAS1

AS2

AS4

AS6

AS5

AS3X

Y

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Hierarchical RoutingAS1

AS2

AS4

AS6

AS5

AS3

IDR: Intra-domain routing

IDR

IDR

IDR

IDR

IDR

IDRStub ASStub AS

Transit AS

Transit AS

Transit AS

Inter-AS path

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The Crash of October,1986

• NSFnet backbone traffic dropped from 32 kbits/s to 40 bits/s!– Blame it on TCP.– If at first you don’t succeed, try, try, try

again…but don’t be bull-headed.• Van Jacobson (1987): congestion-

control algorithm.

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Network Congestion

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TCP’s Congestion & Flow Control

1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536373839400

20

40

60

80

100

120

140

Window Size

Slo

w S

tart

Slo

w S

tart

Congestion Avoidance

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Design Principles

• Distributed control.• Keep the network core simple.• Push all the complexity to the edge of

the network.– Fundamentally different from the Telco

approach.– Facilitates creation of new applications.– Has security implications.

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Killer (?) Applications

• Email• FTP• Web browsing & search• Voice over IP• Torrent• Streaming audio and video

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Winners and Others

Winners include:• Google• Yahoo• Amazon• Skype• Vonage• Netflix

Non-winners:• Verizon• AT&T…at&t… &at t• Time Warner• Sprint• Comcast

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Net Neutrality Debate

• Carriers/ISPs unable to share in the profits of content providers.

• Are carriers trying to stifle competition?– Deep packet inspection– Metered data transport– Bundling

• Telefonica intends to charge Google for its traffic.

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Oh What a Ride!

• Last 20 years:– 9600-baud modem to 10 Mbps FIOS at

home.– Plain text email to elaborate attachments.– Travel agents to Travelocity.– AT&T to Skype and Vonage.– $3/min to $19.95/month unlimited to India.