lec16 - 15.053 April 12, 2007 An Application of Network...

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15.053 April 12, 2007 An Application of Network flow Models: Mapping at Akamai The lecture is intended to illustrate a great application of network optimization. This lecture is not intended as a promotion for Akamai, but I do think it has some very cool technology. Truth in advertising. I bought a small amount of stock in Akamai this year for my daughter. This purchase is no way affects this lecture; however, had the stock price gone down a lot, perhaps it would have affected the lecture . I think that the truth in advertising comment is expected by MIT. The Institute is careful about managing all potential conflicts of interest. In this case, the potential conflict of interest is very small. 1
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Overview z Background The Internet and WWW Akamai z Multicommodity Flows and Minimum Cost Flows z Network Modeling in Practice z The Stable Marriage Problem and its relationship to Akamai’s problem 2
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3 On accessing web sites DNS = domain name system User Types web.mit.edu Browser requests IP address for web.mit.edu DNS returns IP address Browser requests HTML MIT server returns HTML Browser obtains IP address for domain of embedded objects of MIT page. Browser requests embedded objects MIT server returns embedded objects MIT server DNS End User The point of this slide is that there is a lot going on in the background when we access a web site. A user ends up accessing the “domain name system” twice and the server at least once, and there is two-way communication each time. Anything Akamai can do to speed up this process or cut down on a step will be useful.
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4 Information is sent as “packets” router router router router End User This is to point out that information is not sent as a “steady stream”. Rather, information is broken down into packets and sent from one site to another, passing through a sequence of intermediate points. The routers are in charge of directing this flow of traffic. In the picture, you can see “dropped packets”. Typically, lots of information is sent to each router. The routers have limited capacity for storing information. So, any information beyond their “buffer size” is dropped. This sounds stupid at first, but it helps make the Internet work. If information is not dropped, then an acknowledgment is sent to the last sender of the information. If the acknowledgment is not received by the first sender of the information, then a new packet is sent. At the same time, the network protocol TCP/IP will adjust the rate that information is sent: downwards if the packets are not received and upwards if packets are received. I find it all pretty magic that the protocol could be designed when the traffic on the network was not very large, but it still works when the traffic is 100 times greater.
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A Challenge from Tim Berners-Lee 1995 “The father of the Web foresaw the congestion that is now very familiar to Internet users, and he challenged colleagues at MIT to invent a fundamentally new and better way to deliver
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This note was uploaded on 01/17/2012 for the course MGMT 15.053 taught by Professor Jamesorli during the Spring '07 term at MIT.

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lec16 - 15.053 April 12, 2007 An Application of Network...

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