• Ethernet is a collection of network protocols/standards
  • Ethernet == IEEE 802.3 → transmission over cables (copper or fibre-optic)
  • Wi-Fi == IEEE 802.11 → wireless transmission

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Connections and Speed

• Bit: 0 or 1; 1 kilobit (kb) = 1000 bits (not bytes!)
• Speed is measured in bits per second (Kbps, Mbps, Gbps)
• Data size is measured in bytes

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Ethernet Standards (Copper)

IEEE 802.3i, 802.3u, 802.3ab, 802.3an – standards with different data transmission speeds and names

Speed	Name (common)	IEEE (standard)	Name (informal)
10 Mbps	Ethernet	802.3i	10BASE-T
100 Mbps	Fast Ethernet	802.3u	100BASE-T
1 Gbps	Gigabit Ethernet	802.3ab	1000BASE-T
10 Gbps	10 Gig Ethernet	802.3an	10GBASE-T

• Maximum length of twisted-pair cables: 100 m
• RJ-45 (Registered Jack) is used at the end of copper Ethernet cables

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UTP (Unshielded Twisted Pair)

• 10BASE-T and 100BASE-T use 2 pairs (4 wires)
• 1000BASE-T and 10GBASE-T use 4 pairs (8 wires), each pair is bidirectional

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Full-Duplex Transmission

• Both devices can send and receive data at the same time (on separate wires → no collisions)
• Example: pins 1 & 2 Tx and pins 3 & 6 Rx

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Pin Usage

• Router, Firewall, PC → transmit on pins 1 & 2, receive on pins 3 & 6 (straight-through cable)
• Switch → transmit on pins 3 & 6, receive on pins 1 & 2 (crossover cable)

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Auto MDI-X

• Allows automatic detection of which pins are used for transmitting and which for receiving

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Ethernet Standards (Fibre-Optic)

IEEE 802.3z, 802.3ae – standards with different data transmission speeds and names

Name (informal)	IEEE (standard)	Speed	Cable type	Max Length
1000BASE-LX	802.3z	1 Gbps	Multi/Single	550m / 5km
10GBASE-SR	802.3ae	10 Gbps	Multimode	400m
10GBASE-LR	802.3ae	10 Gbps	Single-Mode	10 km
10GBASE-ER	802.3ae	10 Gbps	Single-Mode	30 km

• Maximum fibre-optic length: ~30 km (single-mode), ~550 m (multimode)

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SFP Transceiver (Small Form-Factor Pluggable)

• An SFP slot allows connection of fibre-optic cables (like RJ-45, but for fibre-optic)
• Fibre-optic cables always use 2 separate cables: one for transmitting, one for receiving data
• Copper cables use separate wires within the same cable for transmitting and receiving

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Fibre-Optic Cable Structure (4 layers)

1. Fibre glass core
2. Cladding (reflects light)
3. Protective buffer
4. Outer jacket

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Types of Fibre-Optic Cables

• Single-mode – narrower, single angle of light waves, more expensive (laser-based transmitter), longer distance
• Multimode – wider, multiple angles of light waves, cheaper (LED-based transmitter), shorter distance

📌 These are personal study notes. Please read the full disclaimer for more information.