1. Addresses on the Web

2. The Internet vs. the Web Internet—networked computers
World Wide Web—a service for sharing information over the Internet
The Internet is a physical infrastructure, made from computers connected via copper wires, glass fiber optic cables, and radio wave signals like mobile (like 4G) and WiFi (like N).
The Web is one way to share information over the Internet. Many other Internet services like are independent of the Web, even though many people access their through the Web.
The Web is a service offered over the HTTP or hypertext transfer protocol.
The Internet began with Department of Defense projects in the 1960s. The Web was new in 1995.

3. Web servers respond to web clients
Many clients can make requests of one server
Common clients: Firefox, Chrome, etc.
Server
Server holds data/web content
Common web server program: Apache
Your computer runs a client, also called a browser. The browser requests a web page from a server and the server responds.

4. Web server sends web page Web page = HTML, CSS, JavaScript
Request
Server
Response often contains HTML, CSS, JavaScript
The response from the server might be a file, like a Word document, a JPG image, or a PDF file. Most commonly, the response is written in a combination of the three web languages: HTML for content, CSS for styling and appearance, and JavaScript for interaction with the user.
Client

5. Every computer has an IP address
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Every computer has an IP address
IP addresses like
Many computers also have a domain name like
Domain names are coordinated by ICANN, the Internet Corporation for Assigned Names and Numbers. Names are in a hierarchy, forming a tree. At the top of the tree is the root.

6. Domain names are in a hierarchy
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Domain names are in a hierarchy
ICANN = Internet Corporation for Assigned Names and Numbers
(root)
Domain names are coordinated by ICANN, the Internet Corporation for Assigned Names and Numbers. Names are in a hierarchy, forming a tree. At the top of the tree is the root.
.com
.org
.us
fun.org
example.org

7. Domain names are in a hierarchy
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Domain names are in a hierarchy
ICANN delegates to top-level domain owners
Top-level
domains
(root)
ICANN is a non-profit organization. Together with governments, universities, and other organizations, they control the root. But they do not keep a centralized control on domain names. They delegate the authority to create new domain names to the owners of top-level domains like .com and .org.
.com
.org
.us
fun.org
example.org

8. Domain names are in a hierarchy
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Domain names are in a hierarchy
Domain owners can create subdomains
(root)
The owner of a domain has the authority to create as many subdomains as they wish. In this diagram the owner of .org has created two subdomains: fun.org and example.org.
.com
.org
.us
fun.org
example.org

9. URLs URL = address of a resource on the web
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
URLs
URL = address of a resource on the web
URL (uniform resource location)
URI (uniform resource identifier)
Example:
Scheme
Domain name or IP address
Path
http
:// /
docs/e-web/predictions/17_Great_Challenges.pdf
https
pltworg
technews.acm.org
././archives.cfm
URLs consist of a scheme, a domain name, and a path. There may also be a port number and a query string, as we'll see in a bit. The scheme might be HTTP, for example. Another scheme is HTTPS, with the S indicating that the communication is encrypted, though the fact that you are communicating with a domain name's owner is public. The domain name is between the colon-slash-slash and the very next slash. The end of the domain name is what is important, so this address is controlled by acm.org and has nothing to do with technews.org. The path is everything after that next slash, up to a question mark, if there is one. None of these examples have a question mark, so that path is just the rest of the URL after that slash. Paths often end with a filename of a web page or with the filename of a program that runs on the web server to create the web page for you. The first part of the path often gives a directory path, and can inform you about the web page's author or the author's intentions.
Test yourself: Is this address from PLTW?

10. Domain name or IP address
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Query String
Keyword = value pairs
Scheme
Domain name or IP address
Path
Keyword #1
Value #1
Keyword #2
Value #2
http
:// /
sch/i.html ?
_nkw =
shirt
&
_sacat
facebook.com.net
signin
secure
true
Sometimes URLs have a query string. This comes after a question mark and usually has pairs of text providing information to the web server. Each pair has a keyword. This is like a variable name. Each pair has a value. This is the value of the variable being sent to the web server.

11. DNS request, then web request
Server
DNS
Server
HTTP
Request
DNS
Response 3 1 2
DNS
Request
When a web page fails to load, understanding the process can help you troubleshoot. First, your computer asks a domain name system server to look up the IP number of the domain name. The DNS server responds with an IP number. Your computer sends a message to that IP address, asking for the URL, and the web server responds. 4
HTTP
Response
Client

12. The Browser Status Bar
Most browsers have a status bar that reports the progress as a page loads. The status bar is in the lower-left corner of several common browsers. Which steps of the process do you think have already occurred based on this status bar? Step 1 has occurred, and your computer is waiting on the DNS response.

13. The Browser Status Bar
Which steps of the process do you think have already occurred based on this status bar? Steps 1, 2, and 3 have occurred.

14. Before entering personal information in a web page
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Before entering personal information in a web page
HTTPS
Strangers can see data sent by HTTP
Domain name is correct
Mismatch indicates a fraud
Never assume a link in is legitimate
Enter the URL in the location bar or use a bookmark login pages directly from a browser
Take extra care with your name, address, personal details, usernames, and passwords when working in a browser. Before typing the first character of any personal information, check for the "S" in HTTPS and a domain name that ends with the website name you think you are communicating with.

15. Certificates are specific to domain names
Presentation Name
Course Name
Unit # – Lesson #.# – Lesson Name
Certificates are specific to domain names
This browser warned its user: you're not guaranteed to be communicating with facebook.org. This occurred because VeriSign (a certificate authority) issued the certificate to the owner of facebook.com, a different domain name. Even though facebook.com is the correct domain name for the company Facebook, the certificate doesn't match the domain name entered in the location bar.