Introduction to computer networks and physical layer
Introduction
Computer Networks
group of interconnected computers and devices that can communicate and exchange data with each other.
Protocols
Set of rules and standards that governs the communication between devices in a network. It defines format, timing, sequencing, error control of message exchanged.
Domain Name System (DNS) is used for translating domain names into IP Addresses.
OSI Model (Open System Interconnection)
Concept model that defines the communication between different devices in a network. It consists of 7 layers, each with specific function and set of protocols. This model provides framework and facilitates the interoperability of different network devices and technology.
Application Layer
Provides network services to applications and end-users, such as file transfer and emails.
Presentation Layer
Translates data into a format that the application layer can understand, provides encryption and decryption services.
Session Layer
Manages and maintains connections between devices and applications and establishes, manages and terminates communication services.
Transport Layer
Provides reliable data transport services between devices, and manage flow control and error detection and correction.
Network Layer
Controls the operation of subnet and provides routing services to move data across multiple networks.
Data Link Layer
Transmits data over the physical network and provides error detection and correction services.
Physical Layer
Transmits and receives raw bit streams over the physical network.
TCP/IP Layer
It is a network communication model that is widely used in the internet and other IP-based networks. It consists of 4 layers, each with specific rules and set of protocols.
Application Layer
contains protocols that supports end-user applications such as email, file-transfer and web browsing. Example of protocols are HTTP, FTP and SMTP.
Transport Layer
provides end-to-end communication services between applications on different devices and ensures reliable data transfer. The two main protocol in this layer are:
- TCP (Transmission Control Protocol)
- UDP (User Datagram Protocol)
Internet Layer
provides routing services to move data between different networks and handles the fragmentation and reassembly of data packets. The Internet Protocol (IP) is the main protocol used in this layer.
Link Layer/Network Access
responsible for transmitting data over the physical network, and includes protocols for accessing and controlling the network medium. Example of link layers are Ethernet, Wi-Fi, Bluetooth etc.
Difference between OSI Model & TCP/IP Model
| TCP/IP Model | OSI Model |
|---|---|
| It refers to Transmission Control Protocol | It refers to Open System Interconnections. |
| has 4 layers | has 7 layers. |
| more reliable. | less reliable. |
| doesn’t have strict boundaries. | have strict boundaries. |
| follows horizontal approach. | follows vertical approach. |
| used both session and presentation layer in the application layer itself. | different session and presentation layer. |
| developed protocols then models | developed models then protocols. |
| transport layer doesn’t provide assurance delivery of packets | transport layer provides assurance delivery of packets |
| network layer only provides connection less services | connection less and connection oriented services are provided in network layer |
| protocols cannot be easily replaced | protocols are better covered and easy to replace |
Networking Devices
- Switches: device that connects devices in a network and forwards data between them.
- Routers: forwards data packets between different computer networks and uses IP Address to determine the best path for data to reach destination.
- Hubs: device that connects devices in a network and sends incoming data packets to all connected devices.
- Modems: modulates digital signal into analog for transmission and demodulates back into digital signals.
- Network Interface Cards (NICs): hardware devices that connects a device to a network. it enables communication between devices.
- Repeaters: device that amplifies and regenerates signals in a network to extend over which data is transmitted.
- Bridges: device that connects two or more network segments and forwards traffic between them.
Transmission Media
Guided Media
those transmission media that provides a physical path along which the data is transmitted.
- Twisted Pair Cables: Used for communicating devices in a LAN. consists of twisted copper wires.
- Coaxial Cables: used for cable TV and high speed internet connection, copper core surrounded by insulator and a metallic shield.
- Fiber Optics Cable: used for high speed data transfer, uses light to transmit data
- Leased lines: point to point connection between devices, used for high speed data transfer over long distances.
Unguided Media
- Radio Waves: wireless communication such as radio, television broadcasting, Wi-Fi, etc.
- Microwaves: higher frequency electromagnetic waves than radio waves, used for point to point communications.
- Infrared Radiations: wavelength longer than light but shorter than radio waves, used for short range communication like remote control.
- Light Waves: used in fiber optics and Li-Fi.