What is the Internet? Acknowledgment and Disclaimer: This presentation is supported in part by the National Science Foundation under Grant Any opinions, findings, and conclusions or recommendations expressed in these materials are those of the authors and do not necessarily reflect the views of the National Science Foundation.

The Internet, a Big Idea ● The Internet is one of the 7 big ideas of Computer Science ● Key Questions: o What is the Internet, how is it built, and how does it work? o What aspects of the Internet’s design and development have enabled it to grow so large and be so influential? o How does cybersecurity affect what we do on the Internet?

Computer Networks ● A computer network is a group of two or more computers that are linked together ● Each type of network will have its protocols (rules) that determine how computers communicate Token Ring Protocol Ethernet Protocol Wifi Protocol

Local Area Network (LAN) ● A local area network (LAN) connects computers within a school or home ● An ethernet network uses wires to connect computers

Wifi: A Wireless LAN ● A Wifi network uses radio waves to connect devices (computers, smart phones, printers)

Wide Area Network (WAN) ● A wide area network (WAN) connects devices over a broad geographic region, 2 or more local area networks ● The largest WAN is the Internet

● A protocol is a system of rules that govern the behavior of some system Diplomatic protocol or etiquette governs how diplomats should behave Communication Protocol

● A protocol is a system of rules that govern the behavior of some system ● All devices connected on a network use the same communications protocol

Analogy Diplomatic protocol or etiquette governs how diplomats should behave Digital protocol determines how digital devices should behave

R R R R The internet ● An internet (small ‘i’) is a collection of disparate networks that are connected together via gateways or routers (R) A router (R) is a device that transmits data between two different networks

R R R R Internetwork Analogy Think of an internet as the collection of different language communities around the globe, with the translators from one language to another being analogous to internet routers Hello world Hallo welt 你好世界 привет мир

Routers ● Transmits data between different networks A home router connects local devices to a cable modem A cable or DSL modem connects your home to your Internet Service Provider (ISP) An enterprise-level router connects the ISP to the core Internet backbone routers

How’s it Sent? Connecting new devices to the Internet is enabled by assignment of an Internet protocol (IP) address. An IP address is an identifier for a computer or device Networks using the TCP/IP protocol route messages based on the IP address of the destination Domain name servers translate domain names like a phonebook

Name servers on campus mercer$ whois arizona.edu Domain Name: ARIZONA.EDU Registrant: University of Arizona Computer Center Tucson, AZ UNITED STATES... Name Servers: MAGGIE.TELCOM.ARIZONA.EDU PENNY.UITS.ARIZONA.EDU OPTIMA.CS.ARIZONA.EDU PENDRAGON.CS.PURDUE.EDU NS-REMOTE.ARIZONA.EDU Domain record activated: 23-Jan-1986 Domain record last updated: 08-Aug-2012 Domain expires: 31-Jul-2015

Data moves in Packet The Internet is a packet-switched system through which digital data is sent by breaking the data into blocks of bits called packets Packets contain both the data being transmitted and control information for routing the data This is an IPv4 packet header (before the data and CRC)

Internet Enables Collaboration

Applications in the cloud Not just on your computer

Internet (upper case I) wikipedia The Internet is a global system of interconnected computer networks using the Transmission Control Protocol/Internet Protocol (TCP/IP) to link several billions of devices

Internet wikipedia The Internet is a global system of interconnected computer networks using the Transmission Control Protocol/Internet Protocol (TCP/IP) to link several billions of devices A network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless, and optical networking technologies

Internet (upper case I) wikipedia The Internet is a global system of interconnected computer networks using the Transmission Control Protocol/Internet Protocol (TCP/IP) to link several billions of devices A network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless, and optical networking technologies The Internet carries an extensive range of information resources and services, such as the inter-linked hypertext documents and applications of the World Wide Web, the infrastructure to support , and peer-to peer networks for file sharing and telephony

Internet Connectivity ● The world is connected ● Internet users as % of country’s population

Growth of the Internet ● The number of computers on Internet has grown exponentially since its inception in 1984 (94-14 here)

A Picture of the Internet A partial map of the Internet based on 2005 data produced by the Opte projectthe Opte project Each line is drawn between nodes or addresses on the Internet. The colors represent different top-level domains, such as.com,.edu and.org

A Common Misconception ● The World Wide Web (WWW) is not the same as the Internet ● The WWW is the set of applications that runs on the Internet ● The WWW is a collection of documents, images, and resources that are stored on the Internet ● The WWW is NOT a network Internet != WWW

WWW is an Application Service ● The WWW is the set of application services that run on the Internet ● Other application services include: o Simple Mail Transfer Protocol (SMTP) or Post Office Protocol (POP) o Secure Shell (SSH) to log into another computer over the network (we can no longer use ftp) o Instant Messaging: Internet Relay Chat (IRC) o Telephony: Voice Over IP (VoIP) ● These are distributed applications because they run on a network, not on a single computer

Sir Tim Berners-Lee ● The WWW was invented by Tim Berners-LeeTim Berners-Lee ● Who, instead of patenting his invention, made his idea freely available without royalties ● In his view, the WWW brought the Internet to a higher level of abstraction "I just had to take the hypertext idea and connect it to the Transmission Control Protocol and domain name system ideas and—ta-da!—the World Wide Web... Creating the web was really an act of desperation, because the situation without it was very difficult when I was working at CERN later. Most of the technology involved in the web, like the hypertext, like the Internet, multifont text objects, had all been designed already. I just had to put them together. It was a step of generalising, going to a higher level of abstraction, thinking about all the documentation systems out there as being possibly part of a larger imaginary documentation system."Transmission Control Protocoldomain name system

Open Standards ● HTTP is one of many examples of the open standards that characterize the Internet Why open? “The Internet is fundamentally based on the existence of open, non-proprietary standards. They are key to allowing devices, services, and applications to work together across a wide and dispersed network of networks.” Internet Society

Open Standards Standards: HTTP, SMTP, IP, etc. Standard - Draft Public CommentRevisions Standard - Final

The HTTP Protocol ● WWW resources are accessed using the HyperText Transfer Protocol (HTTP) ● Resources are accessed by their Uniform Resource Identifiers (URIs) o ● Resources are accessed by browsers o Firefox, Chrome, Safari, IE Spartan ● Web resources are hosted by Web servers that respond to HTTP requests

The Client/Server Model ● Client computers request services from a server located on the internet ● Gmail stores messages on Google’s servers (or for CatMail, here on campus) and processes requests to send/retrieve messages

The HTTP Client/Server Model Client Browser requests an HTML document User clicks: 1

The HTTP Client/Server Model Request: User clicks: 2 Client Browser requests an HTML document

The HTTP Client/Server Model Client Browser requests an HTML document Request: User clicks: Listen at Port 80 for HTTP requests Web Server fetches and returns the requested document 3

The HTTP Client/Server Model Client Browser requests an HTML document Request: User clicks: Listen at Port 80 for HTTP requests Web Server fetches and returns the requested document page.html smiley.png Server’s Disk Drive 4

The HTTP Client/Server Model Client Browser requests an HTML document Request: User clicks: Listen at Port 80 for HTTP requests Web Server fetches and returns the requested document page.html smiley.png Server’s Disk Drive My Page Hi! This is my home page. page.html:The requested HTML document 5

The HTTP Client/Server Model Client Browser requests an HTML document Request: User clicks: Listen at Port 80 for HTTP requests Web Server fetches and returns the requested document page.html smiley.png Server’s Disk Drive My Page Hi! This is my home page. page.html:The requested HTML document 6

The HTTP Client/Server Model Client Browser requests an HTML document Request: User clicks: Listen at Port 80 for HTTP requests Web Server fetches and returns the requested document page.html smiley.png Server’s Disk Drive My Page Hi! This is my home page. page.html:The requested HTML document Browser renders HTML Hi! This is my home page 7