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Network Interfaces and Cabling

Aug 2, 2025

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Overview

This lecture covers the essential concepts of network interfaces and cables, focusing on copper Ethernet (UTP) and fiber optic cabling, their standards, connectors, and when each type is used.

Interfaces and Connectors

  • Switches have multiple interfaces (ports) typically using RJ-45 connectors for copper Ethernet cables.
  • RJ-45 is a standard connector for copper Ethernet; "RJ" stands for Registered Jack.
  • Ethernet is a collection of network protocols and standards for local area networks (LANs).

Ethernet Cable Standards and Speeds

  • Common Ethernet types: 10BASE-T (10 Mbps), 100BASE-T (100 Mbps), 1000BASE-T (1 Gbps), 10GBASE-T (10 Gbps).
  • All use unshielded twisted pair (UTP) cables up to a maximum length of 100 meters.
  • "BASE" refers to baseband signaling; "T" means twisted pair.

Bits, Bytes, and Network Speed

  • A bit is 0 or 1; 8 bits = 1 byte.
  • Network speeds are measured in bits per second (bps), not bytes per second.
  • Prefixes: 1 kilobit = 1,000 bits; 1 megabit = 1,000,000 bits; 1 gigabit = 1,000,000,000 bits.

UTP Cable Structure and Pin Usage

  • UTP cables have 4 twisted pairs (8 wires) and use RJ-45 connectors (8 pins).
  • 10BASE-T/100BASE-T use 2 pairs (4 wires); 1000BASE-T/10GBASE-T use all 4 pairs (8 wires).
  • PCs, routers, and firewalls transmit on pins 1 & 2, receive on pins 3 & 6.
  • Switches transmit on pins 3 & 6, receive on pins 1 & 2.

Straight-Through vs. Crossover Cables

  • Straight-through cables connect devices with opposite transmit/receive pins (e.g., PC to switch).
  • Crossover cables connect similar devices (e.g., switch to switch, router to router).
  • Modern devices use Auto MDI-X, which detects and adjusts pin usage automatically.

Fiber Optic Cables and Standards

  • SFP (Small Form-Factor Pluggable) ports are used for fiber optic connections.
  • Fiber transmits data using light through glass fibers, with separate cables for transmit and receive.
  • Fiber types: multimode (shorter distances, cheaper, LED-based) and single-mode (longer distances, expensive, laser-based).
  • Common standards: 1000BASE-LX (multi/single-mode, up to 5 km), 10GBASE-SR (multimode, 400 m), 10GBASE-LR (single-mode, 10 km), 10GBASE-ER (single-mode, 30 km).

UTP vs. Fiber Optic Cables

  • UTP: Cheaper, limited to 100 m, susceptible to EMI, less secure, connects via RJ-45.
  • Fiber: More expensive, longer distances, not susceptible to EMI, more secure, connects via SFP.

Key Terms & Definitions

  • Ethernet — A family of network standards for local area networking.
  • RJ-45 — Standard 8-pin connector for Ethernet cables.
  • UTP (Unshielded Twisted Pair) — Copper cabling with twisted pairs, used for Ethernet.
  • Straight-through cable — Connects different device types; matching pins on both ends.
  • Crossover cable — Connects similar device types; transmit and receive pins crossed.
  • Auto MDI-X — Automatic pin-sensing feature on modern network devices.
  • SFP (Small Form-Factor Pluggable) — Transceiver module for fiber optic connections.
  • Multimode Fiber — Fiber with a wider core for short distances, cheaper.
  • Single-mode Fiber — Fiber with a narrow core for long distances, more expensive.

Action Items / Next Steps

  • Download and review Anki flashcards to memorize cable standards and pin configurations.
  • Complete the end-of-video quiz to test your understanding.
  • Watch the upcoming Packet Tracer lab video for hands-on practice.

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