Ethernet

What is Ethernet?

Ethernet is the most common wired networking technology used in homes, offices, and data centers. It allows computers and other devices to communicate over a local area network (LAN) using cables and standardized protocols.

Ethernet Cable Wiring Standards

Ethernet cables use twisted pairs of wires to carry data. They use an RJ-45 connectors and there are two main wiring schemes used to arrange the wires in those connectors:

T568A

T568B

T568B is more commonly used in commercial networks, while T568A is often used in residential installations.

Cable Types

UTP (Unshielded Twisted Pair)

UTP cables have no shielding around the pairs of wires. They are lightweight, affordable, and widely used — but more prone to electromagnetic interference.

STP (Shielded Twisted Pair)

STP cables have extra shielding to protect the signal from interference. These are used in environments with lots of electrical noise.

F/STP (Foiled Shielded Twisted Pair)

This type of cable includes foil around each twisted pair and braided shielding around the entire cable for maximum protection.

Cable Types by Purpose

Straight Through Cable

Used to connect different types of devices, like:

Computer → Switch
Router → Switch
Both ends follow the same wiring scheme (typically T568B - T568B).

Crossover Cable

Used to connect same-type devices, like:

Computer → Computer
Switch → Switch
One end uses T568A, and the other uses T568B.

Ethernet Cable Categories

Each cable category supports different speeds, frequencies, and maximum distances.

Category	Max Speed	Max Bandwidth	Max Distance @ Max Speed	Min Cable Type Needed	Shielding	Notes
Cat 1	N/A (voice only)	-	-	N/A	None	Used in old telephone lines
Cat 2	4 Mbps	~1 MHz	100 m	Token Ring networks	None	Obsolete
Cat 3	10 Mbps	16 MHz	100 m	10BASE-T	None	Also used in early telephone systems
Cat 4	16 Mbps	20 MHz	100 m	Token Ring LAN	None	Obsolete
Cat 5	100 Mbps	100 MHz	100 m	100BASE-TX	None	Now replaced by Cat 5e
Cat 5e	1 Gbps	100 MHz	100 m	Gigabit Ethernet	Optional	Enhanced Cat 5; very common
Cat 6	1 Gbps (10 Gbps up to 55 m)	250 MHz	100 m (1G), 55 m (10G)	10GBASE-T	Optional	Tighter specs than Cat 5e
Cat 6a	10 Gbps	500 MHz	100 m	10GBASE-T	Usually shielded	Suitable for data centers
Cat 7	10 Gbps	600 MHz	100 m	10GBASE-T	Always shielded	Not officially recognized by ANSI/TIA
Cat 8	25–40 Gbps	2000 MHz	30 m	25G/40GBASE-T	Fully shielded	Data center/high-performance use only

Ethernet Naming Conventions (BASE Standards)

In Ethernet, names like 10BASE-T or 1000BASE-SX follow this format:

[Speed][BASE][Signaling Type]

Speed: Data rate in megabits or gigabits per second
BASE: Short for "baseband" (Ethernet always uses baseband signaling)
T / F / SX / LX / LR / SR / ER / BX / CX / CR / SR4 / LR4: Indicates the physical medium and signaling type:
- T = Twisted pair (copper)
- F = Fiber (general)
- SX = Short wavelength over multimode fiber
- LX = Long wavelength over singlemode or multimode fiber
- LR = Long Reach over singlemode fiber (~10 km)
- SR = Short Reach over multimode fiber (~100–300 m)
- ER = Extended Reach over singlemode fiber (~40 km)
- BX = Bidirectional over a single strand of fiber (uses different wavelengths for TX/RX)
- CX = Copper (typically very short-range DAC)
- CR = Copper Twinax (used with SFP+/QSFP+ for short links)
- SR4 = 4-lane Short Reach (parallel fiber, e.g., 40G/100G)
- LR4 = 4-lane Long Reach (parallel fiber over long distances)

Ethernet BASE Standards (Grouped by Medium)

Copper-Based Ethernet Standards (Twisted Pair)

Standard	Speed	Cable Type	Max Distance	Connector	Description
10BASE-T	10 Mbps	Cat 3	100 m	RJ-45	Classic Ethernet over copper
100BASE-TX	100 Mbps	Cat 5	100 m	RJ-45	Fast Ethernet
1000BASE-T	1 Gbps	Cat 5e	100 m	RJ-45	Gigabit Ethernet
2.5GBASE-T	2.5 Gbps	Cat 5e	100 m	RJ-45	Intermediate speed, backward compatible
5GBASE-T	5 Gbps	Cat 6	100 m	RJ-45	Midway upgrade without needing Cat 6a
10GBASE-T	10 Gbps	Cat 6a	100 m	RJ-45	10G Ethernet over copper
25GBASE-T	25 Gbps	Cat 8	30 m	RJ-45	Data center optimized high-speed copper
40GBASE-T	40 Gbps	Cat 8	30 m	RJ-45	Maximum-speed Ethernet over twisted pair copper

Fiber Optic Ethernet Standards

Standard	Speed	Fiber Type	Max Distance	Connector	Description
100BASE-FX	100 Mbps	Multimode	2 km	SC/ST	Fast Ethernet over fiber
1000BASE-SX	1 Gbps	Multimode	220–550 m	LC/SC	Short wavelength, used in LANs
1000BASE-LX	1 Gbps	Singlemode/Multimode	5–10 km	LC/SC	Long wavelength laser, long distance support
10GBASE-SR	10 Gbps	Multimode	~300 m	LC	Short range 10G, typical for data centers
10GBASE-LR	10 Gbps	Singlemode	10 km	LC	Long range over singlemode fiber
40GBASE-SR4	40 Gbps	Multimode (parallel)	~100 m	MPO	Parallel fiber, short high-speed connections
100GBASE-SR4	100 Gbps	Multimode (parallel)	~100 m	MPO	Core switching, aggregation in modern networks

Coaxial Ethernet Standards (Legacy)

Standard	Speed	Cable Type	Max Distance	Connector	Description
10BASE-2	10 Mbps	Thin coaxial	185 m	BNC	"Cheapernet", used in small networks
10BASE-5	10 Mbps	Thick coaxial	500 m	AUI	First-generation Ethernet (obsolete)

Key Notes

T → Twisted pair copper (Cat 5, 6, 8, etc.)
SX/LX/LR/ER → Fiber optic (short, long, extended reach)
BASE → BASE stands for baseband transmission (vs broadband). Always means baseband signaling (one signal at a time)
Backward compatibility is common (e.g. 2.5GBASE-T works on Cat 5e)
RJ-45 connectors dominate copper standards. RJ-45 is the standard connector for most copper (twisted pair) Ethernet standards.
Fiber standards use SC, LC, or MPO connectors depending on mode and speed.
Fiber options are ideal for long distances, high EMI environments, or backbone connections.
Coaxial is obsolete but included for historical context.

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