Tools of Web Development 1:

Internet Protocols

Goals

• Understand what a protocol is.• Understand how TCP/IP works.• Understand how IP addresses work.• Understand what domain names are.• Understand 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.

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.

101010101001101010011010011010210101010101011010111101010111011101110110110000101110110101010101001110101001010111101000

101010101001101010011010011010210101010101011010111101010111011101110110110000101110110101010101001110101001010111101000

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

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.

How TCP/IP Works

• Upon arrival at their 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.

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://134.68.140.1/The IP Address of the

Computer Science Department’s Web Server

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 vs. URLs

• 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.

Anatomy of a URL

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

file name

domainname

sub-subdomain

machinename

subdomain

protocol

What about Email Addresses?

jstudent@cs.iupui.edujstudent@cs.iupui.edu

usernameusername sub-domainsub-domain

domain namedomain namesub-sub domainsub-sub domain

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

Internet Protocols

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