Contents

• General Web Concepts
• DNS
• Client - Server Architecture
• Ports and Sockets
• Web vs Application Server
• Network Protocols
• HTTP protocol & status codes
• Session and cookies
• CORS

General Concepts

• URL (UNIFORM RESOURCE LOCATOR) - The address of a World Wide Web page
• WWW - the universe of network-accessible information, an embodiment of human knowledge.
• Internet - A global collection of computer networks that are linked together by routers and use a common set of protocols for data transmission known as TCP/IP
  • ​How does it work?
• Browser - A software on your computer that allows you to access the World Wide Web
  • ​How does it work?

How does A Browser work?

1. Resource Gathering - fetching all the assets
2. Parse HTML & Create DOM tree
3. Create Render Tree from DOM Tree - applying styles
4. Layout - Position and give size (boxes)
5. Painting - using UI backend - (overlapping happens here)

Client Server Architecture

DNS

• The Domain Name System
• Used to resolve human-readable hostnames like www.example.com into machine-readable IP addresses like 93.184.216.34
• When you visit a domain, your computer follows a series of steps to turn the human-readable web address into a machine-readable IP address.
• Steps
  • Step 1: Request information
  • Step 2: Ask the recursive DNS servers
  • Step 3: Ask the root nameservers

  • Step 4: Ask the TLD nameservers

  • Step 5: Ask the authoritative DNS servers

  • Step 6: Retrieve the record

  • Step 7: Receive the answer

Ports & Sockets

• The network port identifies the application or service running on the computer.
• A port number is a 16-bit unsigned integer, thus ranging from 0 to 65535.
• The use of ports allows computers/devices to run multiple services/applications.
• A socket is the combination of IP address plus port. A connection between two computers uses a socket.​ 

Network Protocols

Web Vs Application Server

• A Web server exclusively handles HTTP requests, whereas an application server serves business logic to application programs through any number of protocols.
• Web Server is mostly designed to serve static content, though most Web Servers have plugins to support scripting languages like Perl, PHP, ASP, JSP etc.

HTTP

• Follows Client-server Model
• It's an Application layer protocol - HTTP uses TCP as its transport layer protocol
• Stateless protocol - one request is not dependent on any other request
• HTTP methods - GET / POST
• Supports Headers (Request and Response Headers)
  • Content-Type​ - text, image etc.
  • Cache-Control
  • WWW-Authenticate
• Status Codes
  • OK - 200
  • Not Found - 404
  • Unauthorised - 401
  • Unprocessable Entity - 422
  • Internal Server Error - 500

Session & Cookies

• A cookie is a small piece of text stored on a user's computer by their browser. Common uses for cookies are authentication, storing of site preferences, shopping cart items, and server session identification.
• A cookie is a great way of linking one page to the next for a user's interaction with a web site or web application.
• A session can be defined as a server-side storage of information that is desired to persist throughout the user's interaction with the web site or web application.
• A session id is passed to the web server every time the browser makes an HTTP request (ie a page link or AJAX request).

CORS

• Cross Origin Resource Sharing

• Access-Control-Allow-Origin headers

Questions?

References

• https://dyn.com/blog/dns-why-its-important-how-it-works/
• http://www.steves-internet-guide.com/tcpip-ports-sockets/
• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers
• https://www.youtube.com/watch?v=WjDrMKZWCt0
• https://www.youtube.com/watch?v=kYv0Q4vFdfs

Thank You