The Internet!!

The Internet is not the only network! Can connect a bunch of computers without connecting to the Internet, and those computers can communicate with each other SCU has a local network “Novell” An internet is a network of networks – The Internet is an internet You can be connected to more than one network at the same time!

The www is not the whole Internet! It’s a series of tubes! is not always web-based – Thunderbird, outlook not web-based, use the Internet to send s as data Your Netflix streaming through your Blu-Ray player is not the web, but it uses the Internet to send movies as data Xbox Live Ssh uses the Internet to send commands as data The web uses the Internet to send webpages as data

“The World Wide Web (abbreviated as WWW or W3, [2] commonly known as the web), is a system of interlinked hypertext documents accessed via the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia, and navigate between them via hyperlinks.” [2]systemhypertextInternetweb browserweb pagesmultimedianavigatehyperlinks

What is the Internet? Not magic  Mainly, a bunch of cables Mostly privately owned You pay your access ISP (Internet Service Provider) And they make arrangements with other (higher-tier) ISPs to use their cables to get your traffic where it’s going Tier_1_network

What is the Internet? Yes, even across the ocean! These are also privately owned; AT&T, etc g.gif g.gif The.com bubble of the late 1990s led to an excess of bandwidth Where no cable: Satellite (slow, expensive, unreliable)

How do I connect to the Internet? Computer/device  access point (for wireless)  ISP connects you to “the Internet”  Routers send your traffic along different cables (that belong to ISPs your ISP is friends with)  The computer out there that you’re trying to connect to

What is this other computer I’m connecting to? Usually, a server (web (wikipedia), data (netflix streaming), )

If Jane is in Sunnyvale, and Bob is in Germany And Jane sends Bob an from her address to Bob’s address When Bob reads the message, what can you say about the path the bits have taken to get to him?

How does the Internet know how to find everything?!?!? Addresses! Every device connected to the Internet has a unique address that looks something like (Google “What is my IP?”) You’ll notice that it changes – usually you’re assigned a new IP (Internet Protocol) address every time you connect But not servers – The Internet needs to be able to find them, so they have static IPs IP address has meaning; different ISPs control different blocks of IP addresses – This is how routers know where to send your packet so it eventually reaches its destination – 500 El Camino Real, Santa Clara, CA, USA

What does have to do with ? I wouldn’t want to have to type every time I wanted to go to the SCU webpage! is the human-readable name that maps to the static IP address of SCU’s web server (Something like ) So how does get translated into ? You must register this correspondence with the Domain Name System servers Servers whose sole purpose is to translate URLs (uniform resource locator, aka web address) into IP addresses

Regional Internet Registires Managed by ICANN Each allocates blocks of IP addresses to local ISPs

Domain Name System (DNSs) Root_name_server Root_name_server When you try to go somewhere on the www, the first thing is a DNS lookup to get the IP address – DNS Server not found error Then you can establish a connection with the web server at that IP address What if these servers go down?!?!?!

Anatomy of a URL There is a web server for That web server is responsible for getting you anywhere that ends in.scu.edu math.scu.edu/~linnell

What is sent and how? And what does this have to do with security? Once you find the computer you want to connect to, you negotiate a connection – Authentication Then the information to be sent is broken up into packets, each of which has information about where it came from, where it’s going, and who sent it. – Encryption, https