Transcript Office of Communications - The University of Texas at Dallas

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
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No central relay.
Listen before speaking.
Jamming signal on collision.
Random back-off and retry.
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The Past: Circuit Switched
• Reservation based.
– Dedicated resources.
Time
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Send entire
future
message
• Guaranteed quality of
service
• Resource utilization?
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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
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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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AS1
Too Big To Fail?
Chop, chop, chop
AS3
X
AS5
Y
AS2
AS6
AS4
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Hierarchical Routing
Stub AS
AS1
Stub AS
IDR
IDR
AS3
AS5
IDR
AS2
Transit AS
Transit AS
Inter-AS path
IDR
AS6
IDR
IDR: Intra-domain routing
AS4
IDR
Transit AS
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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): congestioncontrol algorithm.
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Network Congestion
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TCP’s Congestion & Flow
Control
140
120
100
80
Window Size
60
40
20
0
1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031323334353637383940
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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:
Non-winners:
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•
•
•
•
•
•
•
•
•
•
Google
Yahoo
Amazon
Skype
Vonage
Netflix
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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.
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