Understanding the Physical Layer in Networking

Oct 2, 2024

Cisco Introduction to Networks - Module 4: The Physical Layer

Objectives

  • Understand the purpose and functions of the Physical Layer in the OSI model.
  • Explore physical layer characteristics including copper cabling, UTP cabling, fiber optic cabling, and wireless media.

Introduction to the Physical Layer

  • A physical connection is required before any network communication can occur.
  • Network Interface Cards (NICs) connect devices to the network.
  • The Physical Layer is responsible for transmitting bits across network media.
  • This layer encodes frames from the Data Link Layer for transmission.

Physical Layer Characteristics

  • OSI Model layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical.
  • TCP/IP Model covers more functions in fewer layers compared to OSI.
  • Physical Layer standards are governed by organizations like ISO, IEEE, etc.

Components of the Physical Layer

  • Physical Components: Cabling, NICs, hardware devices.
  • Encoding: Conversion of data into a predefined code (e.g., voltage levels for copper cables).
  • Signaling: How bit values are represented on the physical medium.

Bandwidth

  • Refers to the capacity of a medium to carry data.
  • Measured in bits per second (bps), kilobits (kbps), megabits (Mbps), etc.
  • Influenced by physical media properties, technologies, and physics.

Key Concepts

  • Latency: Time taken for data to travel from source to destination.
  • Throughput: Measure of data transfer across media over a time period.
  • Goodput: Usable data transfer rate (Throughput - Overhead).

Copper Cabling

  • Common Types: UTP (Unshielded Twisted Pair), STP (Shielded Twisted Pair), Coaxial.
  • Limitations: Signal attenuation, interference from EMI/RFI, and crosstalk.
  • Mitigations: Adherence to length limits, shielding, and twisted pair designs.

UTP Cabling

  • Most common networking media.
  • Characteristics include color-coded plastic insulation and twisted pairs.

UTP Cabling Standards and Connectors

  • Standards by TIA/EIA and IEEE.
  • Ethernet Straight-Through and Crossover cables.
  • Connectors like RJ45.

Fiber Optic Cabling

  • More expensive and fragile than copper; ideal for high bandwidth and long distances.
  • Types: Single-mode (long distances, expensive lasers) and Multi-mode (shorter distances, LEDs).
  • Immune to electrical interference and has low signal loss.

Fiber Optic Usage

  • Used in enterprise networks, fiber to the home, long-haul networks, and submarine cables.
  • Connectors include ST, LC, SC, and duplex multi-mode LC.

Wireless Media

  • Carries signals via radio or microwave frequencies.
  • Limitations include coverage, interference, security, and shared medium.

Wireless Standards

  • IEEE 802.11 (Wi-Fi), 802.15 (Bluetooth), 802.16 (WiMAX), 802.154 (ZigBee).
  • Requires wireless access points and network interface cards.

Conclusion

  • The physical layer serves as the foundation for network communication, influencing how data is transmitted through hardware and media.
  • Understanding cabling, bandwidth, and wireless standards are crucial for network design and troubleshooting.

These notes summarize the fundamental concepts covered in Cisco's introduction to networks, focusing on the physical layer's role in supporting communication across data networks.