Addresses on the Web

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 802.11N). The Web is one way to share information over the Internet. Many other Internet services like e-mail are independent of the Web, even though many people access their e-mail 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.

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.

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

Every computer has an IP address Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Every computer has an IP address IP addresses like 210.54.78.10 Many computers also have a domain name like www.pltw.org 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.

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

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 www.fun.org

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

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: http://www.ebay.com/rpp/fashion-main Scheme Domain name or IP address Path http :// www.elon.edu / docs/e-web/predictions/17_Great_Challenges.pdf https www.twitter.com 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?

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 :// www.ebay.com / 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.

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

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.

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.

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 e-mail 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.

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.