How the Internet Works .

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How the Web Functions. Jennifer Rexford Software engineering Office Shawn Fanning, Northeastern green bean Napster. Tim Berners-Lee CERN Scientist Internet. Meg Whitman E-Straight. How Is It Conceivable?. Maybe (Previous) Representative Ted Stevens Knows
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How the Internet Works Jennifer Rexford Computer Science Department

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Shawn Fanning, Northeastern green bean Napster Tim Berners-Lee CERN Researcher World Wide Web Meg Whitman E-Bay How Is It Possible?

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Perhaps (Former) Senator Ted Stevens Knows… The Internet is not something you simply dump something on. It\'s not a truck . It\'s a progression of tubes . What\'s more, on the off chance that you don\'t comprehend, those tubes can be filled. Furthermore, on the off chance that they are filled, when you put your message in, it gets in line and it will be postponed by anybody that puts into that tube colossal measures of material, gigantic measures of material.

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No Truck, Yes Tubes What the hell is going ahead in the Senate?

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So, I Went to Wikipedia… The Internet is the around the world, freely open system of interconnected PC organizes that transmit information by parcel exchanging utilizing the standard Internet Protocol (IP). It is a "network of networks" that comprises of a huge number of littler household, scholastic, business, and government systems, which together convey different data and administrations ,, for example, electronic mail, online talk, record exchange, and the interlinked Web pages and different reports of the World Wide Web.

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Key Ideas Underlying the Internet

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Idea #1: The ascent of the moronic system

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Telephone Network Smart Network Dumb Terminals

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Telephone Network Dumb telephones Dial a number Speak and listen Smart switches Set up and tear down a circuit Forward sound along the way Limited administrations Audio Later, fax, guest id, … A syndication for quite a while

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Internet Dumb Network Smart Terminals

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Power at the Edge End-to-End Principle Whenever conceivable, interchanges convention operations ought to be characterized to happen toward the end-purposes of a correspondences framework. Programmability With programmable end has, new system administrations can be included whenever, by anybody . And after that end has turned out to be capable and omnipresent… .

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Idea #2: Going Postal

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Internet Protocol (IP) Packet Switching Much like the postal framework Divide data into letters Stick them in envelopes Deliver them autonomously And now and then they arrive What\'s in an IP parcel? The information you need to send A header with the "from" and "to" locations

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Why Packets? Information activity is bursty Logging into remote machines Exchanging email messages Don\'t squander data transmission No movement traded amid sit out of gear periods Better to permit multiplexing Different exchanges share access to same connections tube

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Why Packets? Bundles can be conveyed by most anything Serial connection, fiber optic connection, coaxial link, remote Even winged animals RFC 1149: IP Datagrams over Avian Carriers IP over Avian Carriers was really actualized, sending 9 parcels over a separation of around 5km (3 miles), each conveyed by an individual pigeon, and they got 4 reactions, with a parcel misfortune proportion of 55% , and a reaction time running from 3000 seconds to more than 6000 seconds .

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Idea #3: Never saying you\'re sad

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Best-Effort Packet-Delivery Service Best-exertion conveyance Packets might be lost Packets might be ruined Packets might be conveyed out of request source goal IP arrange

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IP Service Model: Why Best-Effort? I never guaranteed you a rose garden No mistake location and redress Don\'t recollect from one bundle to next Don\'t save transmission capacity and memory Easier to survive disappointments Transient interruptions are alright amid failover … in any case, applications do need proficient, precise move of information all together, in an opportune manner Let the end have deal with that!

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What if Packets are Lost or Delayed? Issue: Lost or Delayed Data GET index.html Internet Solution: Timeout and Retransmit GET index.html GET index.html Internet GET index.html Waiting for an affirmation…

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What if Packets are Corrupted? Sender processes a checksum Sender aggregates up the majority of the bytes And sends the whole to the get Receiver checks the checksum Received entireties up the majority of the bytes And looks at against the checksum GET index.html GET inde y. html Internet 134 + 212 = 346 134 + 21 6 = 350

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What if the Data is Out of Order? Issue: Out of Order ml inde GET x.htindeml Solution: Add Sequence Numbers ml 4 inde 2 3 GET 1 GET index.html

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What if the Receiver is Out of Space? Recipient keeps up a window estimate Amount of information it can support Advertises window to the sender Amount sender can send without affirmation Ensures that sender doesn\'t send excessively While sending however much as could be expected ?

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What if Too Many Hosts Send on the double? A few people need to back off…

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Idea #4: Think comprehensively, act locally

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Congestion Too many hosts sending bundles on the double Some parcels need to hold up in line Eventually the line comes up short on space And a few parcels gets dropped on the floor

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Sharing the Limited Resource Reserve assets Room for ten telephone calls Block the 11 th call Sub-separate assets Tell the 11 exchanges to each utilization 1/11 of the data transfer capacity How???? Neighborhood adjustment Each exchange backs off Voluntarily, for more prominent great

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Congestion Control What if excessively numerous people are sending information? Senders consent to back off their sending rates … because of their bundles getting dropped For more prominent\'s benefit

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Congestion Control Detecting blockage My parcel was lost Reacting to clog I deliberately decrease my sending rate (by 2X) Testing the waters I step by step increment my sending rate (directly) sending rate

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Transmission Control Protocol (TCP) Runs on the end have Puts information into bundles and sends them Congestion control Speeds up and backs off Ordered solid byte stream Sender retransmits lost bundles Receiver disposes of ruined parcels Receiver reorders out-of-request bundles Reliable administration on a problematic system

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Key thought #5: Standing on the shoulders of monsters

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Layering: A Modular Approach Sub-isolate the issue Each layer depends on administrations from layer underneath Each layer trades administrations to layer above Interface between layers characterizes communication Hides usage subtle elements Layers can change without aggravating different layers Application-to-application channels Host-to-host network Link equipment

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Application-Layer Protocols Messages traded between applications Syntax and semantics of the messages between hosts Tailored to the particular application (e.g., Web, email) Messages exchanged over transport association (e.g., TCP) Popular application-layer conventions Telnet, FTP, SMTP, NNTP, HTTP, … GET/index.html HTTP/1.1 Client Server HTTP/1.1 200 OK

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IP Ethernet interface Ethernet interface Ethernet interface Layering in the Internet have HTTP message HTTP TCP portion TCP switch IP bundle IP parcel IP bundle IP Ethernet interface SONET interface SONET interface

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UDP TCP The Narrow Waist of IP Applications FTP HTTP NV TFTP TCP UDP Waist IP Data Link NET 1 NET 2 … NET n Physical The Hourglass Model The midriff encourages interoperability

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Idea #6: A rose by some other name

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Separating Naming and Addressing Host names Mnemonic name increased in value by people Variable length, alpha-numeric characters Provide nearly nothing (assuming any) data about area Examples: and IP addresses Numerical address increased in value by switches Fixed length, double number Hierarchical, identified with host area Examples: and

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Separating Naming and Addressing Names are less demanding to recollect versus Addresses can change underneath Move to Name could guide to various IP addresses to numerous copies of the Web webpage Map to various addresses in better places Address of a close-by duplicate of the Web website E.g., to lessen dormancy, or return distinctive substance Multiple names for a similar address E.g., nom de plumes like and

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Domain Name System (DNS) Hierarchy Distributed "telephone directory" Multiple inquiries to make an interpretation of name to address Small number of "root servers" Tell you where to look into ".com" names Larger number of "top-level spaces" Tell you where to look into "" names .com root .edu

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Idea #7: You scratch my back…

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Network of Networks Autonomous Systems 4 3 5 2 6 7 1

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Autonomous Systems Currently around 40,000 ASes. Level 3: 1 MIT: 3 Harvard: 11 Yale: 29 Princeton: 88 AT&T: 7018, 6341, 5074, … UUNET: 701, 702, 284, 12199, … Sprint: 1239, 1240, 6211, 6242, …

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Inside an AS: Abilene Internet2 Backbone

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Cooperation and Competition Traffic moves through numerous ASes 4 3 5 2 6 7 1 Web server Client

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Problems With the Internet: Cheaters do win

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No Strict Notions of Identity Leads to Spam Spoofing Denial-of-administration

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Nobody in Charge Traffic navigates numerous Autonomous Systems Who\'s blame is it when things turn out badly? How would you redesign usefulness? Understood trust at last host What if a few hosts disregard clog control? Anybody can include any application Whether or not it is lawful, moral, great, and so on. No one knows how enormous the Internet is No worldwide registry of the topology Spans numerous nations So no administration can be in control

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The Internet of the Future Can we settle what troubles the Internet Security Performance Upgradability Managability <your most loved complain here> Without tossing out the infant no sweat of including new has Ease of including new administrations Ease of including new li

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