Computer Networks: Types, Models, and Devices

Posted on Jan 14, 2025 in Computer Engineering

Computer Networks

Computer networks enable the sharing of resources, facilitate communication, and support various applications such as:

  • Email: Instant messaging and communication.
  • Web Services: Access to websites and online services.
  • File Sharing: Collaborative work and data storage.
  • Streaming Services: Multimedia distribution.

  1. Based on Topologies:

    • Bus: Single central cable; simple and cost-effective.
    • Star: Central hub; easy to manage and expand.
    • Ring: Each device connected to two others; data travels in one direction.
    • Mesh: Each device connected to multiple others; highly resilient.

  2. Based on Geographical Distribution:

    • LAN (Local Area Network): Covers a small geographical area, like a home or office.
    • WAN (Wide Area Network): Spans large geographical areas, often using leased telecommunication lines.
    • MAN (Metropolitan Area Network): Covers a city or a large campus.

  3. Based on Communication Techniques:

    • Circuit Switching: Dedicated communication path (e.g., traditional telephone networks).
    • Packet Switching: Data is sent in packets over shared networks.

OSI Model

The OSI (Open Systems Interconnection) model consists of seven layers:

  1. Physical: Hardware transmission of raw bit streams.
  2. Data Link: Node-to-node data transfer and error detection.
  3. Network: Routing of data packets between devices.
  4. Transport: End-to-end communication and reliability.
  5. Session: Managing sessions and connections.
  6. Presentation: Data formatting and encryption.
  7. Application: User interface and application services.

TCP/IP Model

The TCP/IP model simplifies the OSI model into four layers:

  1. Link: Combines the OSI’s physical and data link layers.
  2. Internet: Corresponds to the OSI’s network layer.
  3. Transport: Similar to the OSI transport layer.
  4. Application: Combines the session, presentation, and application layers.

Connecting Devices

  • Hub: A basic device that connects multiple Ethernet devices; broadcasts data.
  • Repeater: Amplifies signals to extend transmission distance.
  • Switch: Directs data packets to specific devices on the network, improving efficiency.
  • Bridge: Connects two network segments, filtering traffic.
  • Router: Routes data between different networks, using IP addresses.
  • Gateway: Connects different networks and translates protocols.

Transmission Media

Wired Media

  • Twisted Pair: Common in LANs; susceptible to interference.
  • Coaxial Cable: Used for cable television; better shielding than twisted pair.
  • Fiber Optic: Uses light for transmission; high bandwidth and immunity to interference.

Wireless Media

  • Radio Waves: Common for Wi-Fi and mobile communications.
  • Microwaves: Used for satellite communications and point-to-point links.
  • Infrared: Short-range communication, e.g., remote controls.

Multiplexing Techniques

  • FDM (Frequency Division Multiplexing): Multiple signals transmitted over different frequency channels.
  • TDM (Time Division Multiplexing): Time slots are allocated to different signals over the same channel.

Unit 2: Data Link Layer

Functions

  • Framing: Encapsulating packets into frames for transmission.
  • Error Control: Detecting and correcting errors during data transmission.

Error Control Techniques

  • Error Detection Codes:
    • Parity Bit: Adds a bit to ensure an even or odd count of ones.
    • CRC (Cyclic Redundancy Check): Uses polynomial division for error checking.
  • Error Correction Codes:
    • Hamming Code: Adds redundancy bits to detect and correct single-bit errors.

Flow Control

  • Stop and Wait Protocol: Sender transmits a frame and waits for an acknowledgment.
  • Sliding Window Protocol: Allows multiple frames to be sent before needing an acknowledgment. Variants include:
    • Go-Back-N: Resends all frames from an error point.
    • Selective Repeat (ARQ): Resends only the erroneous frames.

MAC Sub-layer Protocols

  • ALOHA: Simple random access protocol; can cause collisions.
  • CSMA (Carrier Sense Multiple Access): Listens before transmitting to avoid collisions.
  • CSMA/CD (Collision Detection): Detects collisions and retries transmission.
  • IEEE Standards:
    • 802.3: Ethernet standard.
    • 802.4: Token Bus.
    • 802.5: Token Ring.