Understanding OSI and TCP/IP Models

Oct 10, 2024

Lecture Notes: OSI and TCP/IP Models

Overview

  • OSI Model: Stands for Open Systems Interconnection Model.
    • Has seven layers.
  • TCP/IP Model: Mainly used in this class.
    • Has five layers.
    • Derived from the OSI model.

Layering Concept

  • Provides abstraction.
  • Each layer performs a specific job:
    • Physical Layer: Bottom layer.
    • Data Link Layer: Delivers messages across a single hop.
    • Network Layer: Provides end-to-end delivery by stringing together many single hops.
    • Transport Layer: Ensures delivery to the correct program once data reaches the correct machine.
    • Session, Presentation, Application Layers: Combined in TCP/IP model.

Protocols

  • Key Protocols Studied:
    • Ethernet (Data Link Layer)
    • 802.11 (Wi-Fi, Data Link Layer)
    • Internet Protocol (Network Layer)
    • TCP and UDP (Transport Layer)
    • HTTP (Application Layer)
    • ARP: Bridges between network and data link layers.

Protocol Functionality

  • Communications Protocols: Rules for data communication.
    • Determines syntax, semantics, synchronization, and error recovery.
  • Historical Protocols:
    • Homing pigeons as unidirectional transmission.
    • Greek hydraulic semaphore distinguished protocol from transmission medium.
    • Optical telegraph had end-to-end encryption properties.

Physical Layer

  • Transmission Mediums:
    • Copper Cables: Use voltage modulation; challenges include crosstalk.
    • Fiber Cables: Use light modulation; issues include attenuation loss.

Channel Types

  • Simplex Communication: One-way delivery (e.g., TVs).
  • Duplex Communication:
    • Half-duplex (e.g., walkie-talkies): One party sends at a time.
    • Full-duplex (cables): Both parties can send simultaneously.

Network Devices

  • Hubs: Physical layer devices that duplicate received signals to all other ports.
    • Create collision domains, leading to half-duplex degradation.

Collision Management

  • Carrier Sense Multiple Access (CSMA): Verifies no signal before sending.
    • CSMA/CD (Collision Detection): Stops transmitting if another signal is detected.
    • CSMA/CA (Collision Avoidance): Prevents livelock using randomized timers.

Key Takeaways

  • Layering: Each layer abstracts specific functions, enabling flexibility and modularity.
  • Protocols: Critical for establishing clear communication paths and rules.
  • Physical Media: Different mediums have unique properties and limitations that impact network performance.
  • Network Components: Devices like hubs and switches play roles in managing data flow and preventing collisions.