Computer networks trace back to 19th-century transatlantic telegraph cables. World War II led to the advancements of submarine communication, laying the groundwork for underwater acoustic systems. Modern developments involve sensor networks, fiber optic cables, and underwater drones, enhancing oceanic research, data transmission, and global connectivity prospects.

Client - Server Architecture :

In this Architecture, the client interacts with the server using a request and the server interacts with the user using a Response.

PROTOCOLS: International standards that are set for the proper transfer of data.

TCP : (Transmission Control Protocol)
UDP : (User datagram protocol)
HTTP : (Hypertext Transfer Protocol)

How is data transferred?

Data gets transferred in packets(all in 0 and 1).

The interesting fact here is each Application is differentiated by port numbers (16-bit numbers). These numbers help us in sending information to the right application.

How cables are connected?

1. Physical (Wired) Connections: Physical connections involve the use of cables or wires to establish a direct, tangible link between devices. There are several types of physical cable connections :

Ethernet Cables
USB Cables: USB (Universal Serial Bus)
HDMI and DisplayPort Cables
Audio Cables
Power Cables

2. Wireless Connections: Wireless connections, as the name suggests, do not involve physical cables and instead rely on electromagnetic signals to transmit data and information between devices. Wireless connections are often achieved through various wireless communication technologies:

Wi-Fi(Wireless Fidelity)
Bluetooth
NFC (Near Field Communication)
Infrared
Cellular Networks
Satellite Communication

Topologies

Network topologies refer to the arrangement of devices and their interconnections in a communication network. Each topology has unique strengths and weaknesses, impacting data flow, fault tolerance, scalability, and management complexity. The choice depends on specific network requirements.

Structure of the Network :

1. OSI - Open System Interconnection

Application Layer: Implemented in Software, Provides a platform for users to interact via an application.
1. Client-Server Architecture :
  - Servers control the websites that we are hosting.
  - collection of all these servers is called Data-centre.
  - Data Centres are just the connection of many computers with high upload speed.
  - Command to get upload speed ping google.com .
2. Peer-Peer Architecture :
  - No dedicated server is allowed.
  - The interesting thing about this is that every client is itself a server.
  - It can easily be scaled.
Presentation Layer: It converts those messages, and data into machine-understandable binary language. (Encoding, Encryption happens here)It also provides Abstraction, Compression, and Translation.
Session Layer: Helps in setting and managing connections. ( i.e. Authentication and Authorization takes place here).
Transport Layer: Here data is divided into small packets called Segments. Each segment is given its own Port.No, Sequence-number, flow control, and Error control.
1. Basics :
  - It provides abstraction.
  - Data travels in packets.
  - The transport layer will attach these sockets to the packets.
  - The transport layer also looks into congestion.(congestion control algorithm was built in TCP).
2. Checksums: This helps us to know whether the data is properly transferred or not.
3. Timers
Network Layer: Here logical addressing takes place. (i.e. transmission of segments to different IP addresses takes place.
1. Basics:
  - Here work with routers.
  - Every Router is assigned a logical address and the packets are sent to the receiver using a routing table.

Network layer protocols:
- IP(internet protocol) :
  - IPv4 --> 32-bit , 4-words(2^32)
  - IPv6 --> 128-bits, 8-words(2^128)
- Sub-netting: Blocks of IP addresses are assigned to the ISP.
- Sub-net masking: It masks the network part and leaves us the host part.
- Packets: header contains 20 bytes. [ IPv, length, identification No. , flags, protocols, checksums, addresses, TTL].

Data-layer: Physical addressing takes place here. (This helps the data to know which application was requested)

Frame--> Data unit of Data-link layer.
Physical Layer: Here we get to see physical linking layers. (E.g. hardware like cables, and wires

2. TCP/IP Model

Electronic devices used in Computer Networking

Repeater: A two-port device, which regenerates the signal when it becomes too weak (or) corrupted. It works at the physical layer.
Hub: A multiport-repeater, which doesn't have any intelligence in selecting the best path for data transfer.
Bridge: A two port[single I & O] device same as a repeater but has an add-on functionality that it can filter out the data by reading mac-addresses.It works at the Data-Link layer.
Switch: It is a Multiport-Bridge that works to increase the performance by correcting the errors before the head. It works at the Data-Link layer.
Router: A device-like switch that routes data based on IP addresses. It works at the network layer.
Gateway: Passage to connect two networks working on different protocols.

Protocols

Web-protocols:

- TCP/IP :
  - HTTP (hypertext transfer protocol)
    - Application layer protocol.
    - It is a client-server protocol.
    - It uses TCP.
    - It is a stateless protocol(i.e. server will not store any data about the user)
    - Methods:
      1. GET (requesting data)
      2. POST (client submits the data to the server)
      3. PUT (puts the data at the spec location)
      4. DELETE (deletes the data)
  - DHCP (dynamic host control protocol)
  - FTP (file transfer protocol)
  - SMTP (simple mail transfer protocol)
  - POP3 & IMAC [recieves E-mals]
  - SSH (secure shell)
  - VNC (virtual network computing)
  - TELNET (tele-type network)
  - UDP (user datagram protocol)
  - Sockets: The interface between processes & network
  - Ephemeral ports:
    - Ports that define which application we are working with.
    - Ephemeral ports deep-dive into these applications and help us find which application (or) tab we are working on.

Cookies

The unique string is stored in the client's browser.
Every time we visit a website a cookie is sent to the network(server).

UDP (User Datagram protocol)

Data may not be delivered completely.
High chances of Data Corruption.
Connectionless protocol.
UDP uses Checksums.

TCP (Transmission Control protocol)

Transport layer protocol.
The app layer sends raw data and TCP segments this layer then divides it into chunks, and adds headers.
It also collects data from the network layer.
It also looks into congestion control.

How does E-mail work?

Domain-Name system(DNS)

DNS is like the dictionary of the internet. It's a system that translates human-readable domain names (like "example.com") into IP addresses (like "192.0.2.1"). This translation is essential because computers communicate using IP addresses, but humans find it easier to remember and use domain names.

Domain names are mapped to IP addresses.
The top-level Domain stores all the data we browsed.

Dream.Achieve.Repeat

Computer Networking Course

The Underwater Magic

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