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How Do You Describe What the Internet Is?
Its Functions It Structures
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Introduction and Overview of Network and Telecommunications
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Image you are setting up a wireless network at home.
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How much do you have to think about the whole structure of the Internet?
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How much do you have to be worried about the compatibility of the gears you need to buy?
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Internet Model Modularized Internet
The whole Internet is broken into thousands of small networks
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For A Single Network Connected to the Internet
A modularized network Several independent and interconnected layers! An analogy: think about a post system Sending a letter to another country Programs,tools (Browser, App) Transport protocol software Routers, Internet Protocol software Network interface cards, switches Cable, fiber optics, wifi signals
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A More General Model: OSI
Open Systems Interconnection Developed by the ISO International Organization for Standardization Seven layers -
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A More General Model: OSI
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Layering Dividing a task into pieces at different layers and then solving each piece independently Establishing a well defined interface between layers.
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Modularization Is Useful.
Help to manage complex systems Houses, cars, roads, etc. Different contractors/professionals to deal with different parts of work. Education Different grades Healthcare systems Hospitals, testing labs, pharmacies, insurance companies (?), etc. As long as modules are well coordinated!
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OK, We Know the Internet Model and Structure
OK, We Know the Internet Model and Structure. How Does the Internet Really Work, Say Sending Information Around?
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A Simple Example http://zhang.ist.psu.edu/helloworld.html
What is really happening behind the wall?
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An Analogy The Internet works like a post system.
Documents/information: mails Each computer/phone: houses with address The Internet: delivering documents based on computer/phone addresses through mailmen.
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It is more complicated. Two ends could be quite far away!
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Many "mailmen" have to be involved.
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When you type in a URL on your mobile phone to visit a web page, what really happens between your phone and the server you try to visit? Can you sketch a diagram to illustrate through what a path your phone gets information?
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Cellular Tower Internet Gateway (Phone Company) Server Maps Server
Wireless Router Cable Modem Internet Gateway (Map Service Company) Map Data Internet Gateway (Cable Company)
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It is more complicated. Documents could be huge!
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Can Post Offices Deliver This?
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We need to find a way to handle all kinds of documents, any type and any size. But How?
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Recall the Video Warriors of the Net
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An example <HTML><BODY>Hello World
An example <HTML><BODY>Hello World!</BODY></HTML>
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} } sender receiver Packets
<HTML><BODY>Hello World!</BODY></HTML> <HTML><BODY> Hello World! </BODY></HTML> Packets TCP </BODY></HTML> sender IP TCP </BODY></HTML> TCP </BODY></HTML> IP MAC LAN } MAC IP TCP </BODY></HTML> IP TCP </BODY></HTML> TCP </BODY></HTML> receiver </BODY></HTML> <HTML><BODY>Hello World! </BODY></HTML>
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Some Key Points Data is transmitted as packets.
Small data pieces. Packets are handled by equipments at different layer. Data are wrapped up at each layer. Each layer has its own protocols to follow. Different ways to wrap up. New information, or header, is added or removed before sending to the next layer.
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Why Using Packets? use the connection effectively and efficiently
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The Internet Diversification of the use of the Internet Contents
Resource sharing Communication Entertainment Contents Text multimedia
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Imagine This Scenario Your roommate is watching a 2-hour long, HD movie. You are submitting a homework assignment with a deadline in 5 minutes. What is the best way to use the network by you two?
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Do You Like This Truck Ahead of You?
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The Network Is Shared by Many Computers!
use the connection effectively and efficiently
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Connections between Computers
Overhead Telephone and Telegraph Wires in Broadway, 1890 From Book of Old New York. Henry Collins Brown. 1913
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Switch Model: Reducing the Mess
Analogy Airport hubs
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Switch Model: Reducing the Mess
Analogy Airport hubs
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Challenges TCP/IP Packets Destinations Size Timing Sequence
Fair opportunity Destinations Identification of each computer TCP/IP
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TCP: Transmission Control Protocol IP: Internet Protocol TCP/IP
Tolerating heterogeneous network data Implementation at both software and hardware levels Led to the Internet
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Friday Work on your first group assignment.
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