How the Internet Works:What happens when information is sent from your computer?

You should know

• what a protocol is.• how TCP/IP works.• how IP addresses work.• what domain names are.• the different protocols available on

the Internet.

When Computers Communicate

• When two or more computers communicate, they must have a common way in which to communicate.

• To do this computers use protocols• A protocol is an agreement by which

two or more computers can communicate.

• Transfer Control Protocol/Internet Protocol is the underlying protocol for the Internet.

TCP/IP

Three Important Concepts: TCP/IP

Internet Addressesthe Domain Name System

How TCP/IP Works

1) Transfer Control Protocol (TCP) breaks data into small pieces of no bigger than 1500 characters each. These “pieces” are called packets.

101010101001101010011010011010110101010101011010111101010111011101110110110000101110110101010101001110101001010111101000

101010101001101010011010011010110101010101011010111101010111011101110110110000101110110101010101001110101001010111101000

101010101001101010011010011

101010101001101010011010011

101010101001101010011010011

101010101001101010011010011

101010101001101010011010011

101010101001101010011010011

How TCP/IP Works

2) Each packet is inserted into different Internet Protocol (IP) “envelopes.” Each contains the address of the intended recipient and has the exact same header as all other envelopes.

101010101001101010011010011

101010101001101010011010011

101010101001101010011010011

101010101001101010011010011

101010101001101010011010011

101010101001101010011010011

131.194.83.47 131.194.83.47 131.194.83.47

How TCP/IP Works

• A router receives the packets and then determines the most efficient way to send the packets to the recipient.

• After traveling along a series of routers, the packets arrive at their destination.

• There may be more than one route available. When a message is sent, the packets may take different routes or may arrive in the wrong order.

How TCP/IP Works

• Upon arrival at the destination, TCP checks the data for corruption against the header included in each packet. If TCP finds a bad packet, it sends a request that the packet be re-transmitted.

• You can see examples of packets traveling the Internet by using the tracert command. In Windows, the tracert command can be accessed from the command line (DOS prompt).

• Using Tracert• Start your connection to the Internet• Choose Run for the Start menu• At the Open prompt, key cmd and click OK. A

command prompt will open. • At the prompt, key in tracert and the website

(e.g., tracert www.trinity.edu)

IP Addresses

• Since computers process numbers more efficiently and quickly than characters, each machine directly connected to the Internet is given an IP Address

• An IP address is a 32-bit address comprised of four 8-bit numbers (28) separated by periods. Each of the four numbers has a value between 0 and 255

IP Addresses

• Example of an IP Address:

http://131.194.83.47/CLS 344 Instructor Station

IP Addresses vs. URLs

• While numeric IP addresses work very well for computers, most humans find it difficult to remember long patterns of numbers.

• Instead, humans identify computers using Uniform Resource Locators (URLs), a.k.a. “Web Addresses.”

IP Addresses (what machines know) vs. URLs

(what humans type in)• When a human types a URL into a browser, the request is

sent to a Domain Name Server (DNS), which then translates the URL to an IP address understood by computers.

• The DNS acts like a phonebook.• A master database keeps track of what name servers are the

authority for each and every domain name. For example, if you register your own domain, part of the registration process requires that you indicate what domain name servers (DNS) will know where to look for your web site.

• Every time you use a domain name, you use the Internet's domain name servers (DNS) to translate the human-readable domain name into the machine-readable IP address.

Anatomy of a URL

http://www.cs.iupui.edu/index.html

file nameprotocoldomainname

Top Level Domain Names

.edu.edu Educational InstitutionEducational Institution

.gov.gov Governmental AgencyGovernmental Agency

.mil.mil Military EntityMilitary Entity

.com.com Commercial EntityCommercial Entity

.net.net Internet Service Internet Service ProviderProvider.org.org Non-Profit Non-Profit OrganizationOrganization

. . .and some new ones!

Internet Protocols

http://http:// World Wide WebWorld Wide Webmailto:mailto: E-mail addressE-mail addressftp://ftp:// File Transfer File Transfer ProtocolProtocoltelnet:telnet: TelnetTelnet

Terms you should know

• Backbone• Computer network• Domain Name Server• Internet• Internet Protocol (IP)• IP address• Local Area Network (LAN)• Packet-switched network• Protocol• Router• Transmission Control Protocol (TCP)