How does the Internet work ?

1. How does the Internet work ? By: Angus Macaulay All though the Internet is a young technology, it's hard to imagine life without it. Each and every year, engineers create more devices to integrate with the Internet. These “computers” connect to the Internet via a tremendous array of communications mediums including phone lines, coaxial television cable, fiber optic cable, serial lines, short-range (in-building) wireless signals and long-range (cellular) wireless signals and protocols. One of the greatest things about the Internet is that nobody really owns it. It is a global collection of networks, both big and small. These networks connect together in many different ways to form the single entity that we know as the Internet. In fact, the very name comes from this idea of interconnected networks. But How Does It Work?

2. Internet History The Internet is a global network of interconnected computers, enabling users to share information along multiple channels. http://en.wikipedia.org/wiki/Internet • Started in 1969 as ARPANET funded by DARPA (Defense Advanced Research Projects Agency) • Build as packet switching network to recover from a nuclear attack by automatically rerouting data through surviving links “When I took office, only high energy physicistshad ever heard of what is called the World WideWeb... Now even my cat has it's own page.” -Bill Clinton

3. The User Perspectivehave little laptop at home in NJ • want to exchange information with big server in California (or Japan or wherever…)

4. Basic SetupEach computer must have a unique identifier • IP number and IP name • Computers must be able to exchange data (electrons, photons, drum beats) • Wireless cards, fiber optics, or Ethernet connections • Unit of data is “bit” (“zero” or “one”, on/off, 2 states) • Everyone involved must speak the same language • TCPIP (Transmission Control Protocol/Internet Protocol) • Every computer on the Internet has at least one unique identifier, usually two: • IP Number: #.#.#.#, where # is an 8 bit number • IP Name for easy reference Network Member Identifier

5. Router A Router B ISP DHCP fiber optic lines www.google.com DNS ISP: Internet ServiceProvider DHCP: Dynamic HostConfigProtocol DNS:Domain Name Server

7. The Data: IP Packet www.google.com(66.102.1.147) Thousands even Millions of Packets can make up a single message. Packets of a message can take different routes. Can arrive at receiving destination in any order. Receiving destination reassembles packets into message. (149.150.254.102) Packets

8. Postal Service/Internet Postal ServiceInternet • A letter is sent from 318 Elm Street in Raleigh, NC. Data is sent from 209.178.41.76. • Elm Street's Postal Service worker carries the letter to Raleigh Post Office. The 209.178.41 gateway sends the data to its router. • The Raleigh Post Office sends the letter to the Washington Sorting Facility. The router sends the data to a larger/important router. • The Washington Sorting Facility sends the letter to the Springfield Post Office. A larger/important router sends the data to 64.54 router. • The Springfield Post Office gives letter to Oak Street's Postal Service worker. The 64.54 router sends the data to the 64.54.23 gateway. • Oak Street's Postal Service worker delivers the letter to 318 Oak Street. The 64.54.23 gateway delivers the data to 64.54.23.198. While these examples are very simplified representations of both the United States Postal Service and the Internet, they demonstrate how data is sent through the Internet. In the "real world" of the Internet, there are the following differences: • There are generally more "stops" along the way at various routers. • The data is generally broken up by the source computer into several smaller "packets" that are each treated as individual “letters". The destination computer will reconstruct the data from the packets.

9. The Protocol A mutually agreed-upon convention or standard that controls or enables the connection, communication, and data transfer between computing endpoints. http://en.wikipedia.org/wiki/Protocol_(computing) • Regulates the data exchange and interpretation • Defines who says what at which time • Defines how to interpret data that is exchanged • Regulates what constitutes an error and what to do if one occurs

10. Client – Server Model • Communication on the Internet usually takes place between a client and a server program/computer: • Server program: program without a user interface running on a “large” computer with access to many resources (also called the server computer) • Client program: a program with extensive interface capabilities but few resources running on a “small” computer (also called the client computer) • One server computer usually run several server programs, each of which can service multiple client programs simultaneously

11. Client – Server: Telnet A Telnet client is built into Windows: • Click on “Start” • Pick “Run …” and type “cmd” • Type “telnet” if you get error message in Vista, open Control Panel, select “Programs”, click “Turn Windows features on or off”, and check “Telnet client” (not “Telnet server”). Then try again. • To open a connection to www.shu.edu, type: open www.shu.edu • Optional: to save a log of your session, type: set logfile log.txt

12. Telnet’ing to a Web Server • Start “telnet” and type: open www.lcc.edu 80 • Next type carefully and without errors (you might not see what you type on the screen – type anyway, including the empty line and capitals): GET / HTTP/1.0↵↵ • You have issued a request according to the Hypertext Transfer Protocol, version 1.0, for the root web page

13. How email works Email systems have two parts, and consequently work with two server programs and two protocols: • Retrieving email uses either pop3 (Post Office Protocol version 3 on port 110) or IMAP (Internet message access protocol on port 143) • Sending email uses smtp (simple mail transport protocol on port 25)

14. An smtp Conversation

15. Protection ISP Firewall Protection SPAM Protection • Every packet transported over the Internet contains the protocol (port), sender address, and destination address • A firewall is a device that inspectsevery incoming (and outgoing) packet and includes rules to block data depending on the port, sender, or destination • A firewall is typically integrated into a home wireless router • Most firewalls do not check the content of a packet • Every Internet packet contains the port, sender, destination, and content (data) – usually unencrypted • A SPAM filter is a device that inspectsall email packets and includes rules to block messages depending on the content of the email. • A SPAM filter is typically integrated into you ISP or email provider • SPAM filters typically read your email!

16. Privacy/Content Protection ISP • All Internet traffic is public! • To protect content, the data portion of IP packets must be encrypted • To protect data between your wireless router and your laptop, use e.g. WPA wireless encryption • To protect data after it leaves your router, you must use encrypted services (https instead of http or sftp instead of ftp) • Note: no standard encryption for email! Sending email is like passing a postcard along a chain of hundreds of people with a note: “to Jane – do not read if you’re not Jane”

17. References A.Macaulay: Artifact 3, Bus 101 LCC; How Does the Internet Work? Images: Google and Dogpile Content: Wikipedia http://www.theshulers.com/whitepapers/internet_whitepaper/index.html http://computer.howstuffworks.com/internet/basics/internet.htm http://pirate.shu.edu/~wachsmut/Teaching/CSAS-WebProg/lecture01-Internet