Computer Networking

What is Computer ?

Computer: Commonly Operated Machines Purposely Used In Technical And Educational Research

Networking: Networking refers to the practice of connecting computers and other devices to share resources, exchange data, and communicate. It involves the use of both hardware and software technologies to link multiple systems, enabling them to interact and work together efficiently

Important Terminologies

1) Internet: The Internet is a global network of interconnected computers that communicate through a standardized set of protocols

2)World Wide Web(www): The www is a system of interlinke hypertext documents and multimedia accessed via the internet

3)Browser: A Browser is a software application used to access and view websites

4)URL(Uniform Resource Locator): A URL is the address used to access resources on the internet

5)IP Address: An IP address is a unique string of numbers separated by periods(IPv4) or colons (IPv6) that identifies each computer using the Internet Protocol to communicate over a network.

6)Domain Name: A domain name is the human-readable address of a website (Low Level Domain. Second Level Domain. Top Level Domain)

7)HTTP(HyperText Transfer Protocol): HTTp is the protocol used for transmitting web pages over the internet

8)HTTPS(HyperText Transfer Protocol Secure): HTTPS is an extension of HTTP that uses encryption to secure data transfers

9)DNS(Domain Name System): DNS is the system that translates domain names into IP address

10)CDN(Content Delivery Network): A CDN is a network of servers distributed across various geographic locations to deliver content to users more efficiently.CDNs reduce latency and improve load times for websites and online services

What Happens When You type google.com ?

When you type www.google.com into your web browser's address bar and press Enter, a series of events occur behind the scenes to retrieve and display the Google homepage. Here’s a step-by-step explanation of what happens:

1. DNS Resolution

• Step 1: The browser checks its cache to see if it already has the IP address for www.google.com.

• Step 2: If the IP address is not in the browser’s cache, it checks the operating system’s cache.

• Step 3: If the IP address is not in the OS cache, a DNS query is made to the configured DNS server (often provided by your ISP or set to a public DNS server like Google’s 8.8.8.8).

• Step 4: The DNS server looks up the IP address for www.google.com and returns it to your computer.

2. TCP Connection

• Step 1: The browser initiates a TCP connection to the IP address retrieved in the DNS resolution step, typically to port 443 (for HTTPS).

• Step 2: This involves a three-way handshake:

  • SYN: The client sends a SYN (synchronize) packet to the server.

  • SYN-ACK: The server responds with a SYN-ACK (synchronize-acknowledge) packet.

  • ACK: The client sends an ACK (acknowledge) packet back to the server.

3. SSL/TLS Handshake (if HTTPS)

• Step 1: The client and server exchange encryption keys to establish a secure connection.

• Step 2: This involves the server sending its SSL/TLS certificate, which the client verifies against trusted certificate authorities.

• Step 3: Once verified, both the client and server generate session keys to encrypt the data.

4. HTTP Request

• Step 1: The browser sends an HTTP GET request to the server hosting www.google.com. This request includes headers with information such as the browser type and cookies.

• Step 2: The server processes the request and prepares the response.

5. Server Response

• Step 1: The server sends back an HTTP response, which includes the status code (e.g., 200 OK) and the requested HTML document along with other resources like images, CSS, and JavaScript files.

• Step 2: If the content is compressed (e.g., using gzip), the browser decompresses it.

6. Rendering the Page

• Step 1: The browser parses the HTML document and builds the DOM (Document Object Model).

• Step 2: It sends requests for additional resources (images, CSS, JavaScript) referenced in the HTML.

• Step 3: The browser constructs the CSSOM (CSS Object Model) from the CSS files.

• Step 4: It then combines the DOM and CSSOM to form the Render Tree.

• Step 5: The browser calculates the layout and paints the content to the screen.

7. Executing JavaScript

• Step 1: The browser downloads and executes any JavaScript files referenced in the HTML.

• Step 2: JavaScript can manipulate the DOM and CSSOM, causing reflows and repaints as needed.

8. Displaying the Content

• Step 1: The browser continues to render and display the content, making additional network requests as necessary for any dynamic content loaded via JavaScript (e.g., AJAX requests).

What is DNS ?

According to cloudflare

Types of Network?

What are CDNs?

Types of Topology?

Important Devices

Physical Layer (Layer 1)

• Network Interface Cards (NICs): Convert data to electrical signals and vice versa.

• Cables (Twisted Pair, Coaxial, Fiber Optic): Transmit data as electrical or optical signals.

• Hubs: Connect multiple computers and broadcast data to all devices.

• Repeaters: Regenerate signals to extend the distance they can travel.

Data Link Layer (Layer 2)

• Switches: Filter and forward data to specific devices on the network.

• Bridges: Connect and filter traffic between different network segments.

Network Layer (Layer 3)

• Routers: Determine the optimal path for data to travel between networks.

• Layer 3 Switches: Perform routing functions within a local network.

Unicast, Multicast, Broadcast

Unicast

• Function: One-to-one communication where data is sent from one sender to one receiver.

• Layer: Typically operates at the Network Layer (Layer 3) and sometimes at the Transport Layer (Layer 4).

• Example: Sending an email from one computer to another.

Multicast

• Function: One-to-many communication where data is sent from one sender to multiple specific recipients who have expressed interest in receiving the data.

• Layer: Operates at the Network Layer (Layer 3).

• Example: Streaming video or audio to multiple users who have subscribed to a multicast group.

Broadcast

• Function: One-to-all communication where data is sent from one sender to all devices on the network.

• Layer: Operates at the Data Link Layer (Layer 2) and sometimes at the Network Layer (Layer 3).

• Example: ARP (Address Resolution Protocol) broadcasts used to resolve IP addresses to MAC addresses in a local network.