Ethernet
Ethernet is a family of wired computer networking technologies commonly used in LANs, and WANs.
BASE (Baseband)
Baseband means the Ethernet signal uses the entire cable for one signal at a time (as opposed to broadband, which splits the cable into multiple channels).
Most Ethernet today is baseband.
| Standard | Speed | Cable / Media Type | Max Distance |
|---|---|---|---|
| 10BASE-T | 10 Mbps | Cat3 | 100 m |
| 100BASE-TX | 100 Mbps | Cat5 | 100 m |
| 1000BASE-T | 1 Gbps | Cat5e/Cat6 | 100 m |
| 10GBASE-T | 10 Gbps | Cat6a/Cat7 | 100 m |
| 25GBASE-T | 25 Gbps | Cat8 | 30 m |
| 40GBASE-T | 40 Gbps | Cat8 | 30 m |
| 10GBASE-SR | 10 Gbps | Fiber (multi-mode) | 300 m |
| 10GBASE-LR | 10 Gbps | Fiber (single-mode) | 10 km |
| 40GBASE-SR4 | 40 Gbps | Fiber (multi-mode, 4 lanes) | 100 m |
| 100GBASE-SR4 | 100 Gbps | Fiber (multi-mode, 4 lanes) | 100 m |
| 100GBASE-LR4 | 100 Gbps | Fiber (single-mode, 4 wavelengths) | 10 km |
| 400GBASE-SR16 | 400 Gbps | Fiber (multi-mode, 16 lanes) | 100 m |
- T = Twisted pair copper cable
- TX = Twisted pair variant
- SR = Short-range fiber (multi-mode)
- LR = Long-range fiber (single-mode)
- ER/ZR = Extended reach fiber
Cat (Category of Cable)
Higher category = higher frequency, more shielding, higher speed
| Category | Max Speed (Copper) | Max Frequency | Max Distance |
|---|---|---|---|
| Cat3 | 10 Mbps | 16 MHz | 100 m |
| Cat4 | 16 Mbps | 20 MHz | 100 m |
| Cat5 | 100 Mbps | 100 MHz | 100 m |
| Cat5e | 1 Gbps | 100 MHz | 100 m |
| Cat6 | 1 Gbps-10 Gbps | 250 MHz | 100 m / 55 m @ 10G |
| Cat6a | 10 Gbps | 500 MHz | 100 m |
| Cat7 | 10 Gbps | 600 MHz | 100 m |
| Cat7a | 10 Gbps-40 Gbps | 1000 MHz | 100 m |
| Cat8 | 25-40 Gbps | 2000 MHz | 30 m |
there were cables before Cat3, but they’re mostly historical telephone/voice cables, not really Ethernet-capable.
Above max distance, Ethernet may fail or drop speed. To go beyond max distance, networking uses intermediate devices or different mediums or like place a switch every 90-100m to regenerate the signal.
Modular Connector vs Registered Jack (RJ)
Modular connector referring to the physical, plastic plug/jack hardware and registered jack referring to the standardized wiring, pinout, and application. They are interchangeable terms in many contexts.
| RJ / Connector | Pins / Contacts | Cable Type |
|---|---|---|
| RJ‑11 | 4 or 6 (4P4C / 6P4C) | Cat1 / phone wire |
| RJ‑14 | 6 (6P6C) | Cat1 / phone wire |
| RJ‑25 | 6 (6P6C) | Cat1 / phone wire |
| RJ‑21 | 25 (50 wires) | Cat1 / multi-line cable |
| RJ‑45 | 8 (8P8C) | Cat3 - Cat8 twisted pair |
| RJ‑48 | 8 (8P8C) | Cat3-Cat6 |
| GG45 | 8-12 | Cat7 |
| TERA | 8-12 | Cat7 / Cat8 |
For almost all modern Ethernet, they use RJ‑45.
Twisted-Pair Cables
From outside to inside:
1. Outer Jacket / Sheath
LSZH (Low Smoke Zero Halogen): for indoor, public, or confined spaces requiring high safety, as it minimizes toxic fumes and smoke during fires.
PVC (Polyvinyl Chloride): for cost-effective, durable, and flexible applications in less restrictive, well-ventilated areas.
Other less common types:
-
Plenum-rated (CMP): Fire-resistant, used in air ducts
-
Riser-rated (CMR): For vertical runs in buildings
2. Rip Cord / Tensile Strength Member (TSM)
Rip Cord: Nylon string under the jacket, helps tear jacket when stripping
Tensile Strength Member: Strong fiber or aramid (Kevlar) cord inside the cable, carry pulling force during installation
Both are not part of electrical signaling.
3. Shielding
Shielding is used to protect the twisted pairs from electromagnetic interference (EMI) and crosstalk. Different shielding schemes exist:
| Abbreviation | Full Name | Description |
|---|---|---|
| STP | Shielded Twisted Pair | Entire cable wrapped in metallic shield (braid or foil) |
| FTP | Foiled Twisted Pair | Entire cable wrapped in foil only, sometimes called F/UTP |
| S/FTP | Shielded Foiled Twisted Pair | Each pair individually wrapped in foil + overall braid |
4. Twisted Pairs
Ethernet cables have 4 twisted pairs (8 wires):
- White/Green + Green
- White/Orange + Orange
- White/Blue + Blue
- White/Brown + Brown
Twisted pairs reduce electromagnetic interference (EMI).
UTP (Unshielded Twisted Pair) vs STP (Shielded Twisted Pair)
UTP is cheaper, flexible, and best for common office/home networks, while STP offers superior, shielded protection against electromagnetic interference (EMI) for industrial or high-bandwidth environments
T568A vs T568B
They are wiring standards for terminating an Ethernet cable using an 8P8C (commonly called RJ45) connector, define which wire goes in which RJ‑45 pin.
There is NO performance difference between T568A and T568B. The standard comes from TIA/EIA-568.
Contacts facing you, clip down:
| |
| |
[1] [2] [3] [4] [5] [6] [7] [8]
T568B (B)
| Pin | Color | Purpose (10/100 Mbps) |
|---|---|---|
| 1 | White-Orange | TX+ (Transmit +) |
| 2 | Orange | TX- (Transmit -) |
| 3 | White-Green | RX+ (Receive +) |
| 4 | Blue | Unused (Gigabit: pair 2) |
| 5 | White-Blue | Unused (Gigabit: pair 2) |
| 6 | Green | RX- (Receive -) |
| 7 | White-Brown | Unused (Gigabit: pair 4) |
| 8 | Brown | Unused (Gigabit: pair 4) |
10/100 Mbps uses only pins 1,2,3,6
1 Gbps and above uses all 4 pairs
T568A (A)
| Pin | Color | Purpose (10/100 Mbps) |
|---|---|---|
| 1 | White-Green | TX+ |
| 2 | Green | TX- |
| 3 | White-Orange | RX+ |
| 4 | Blue | Unused (Gigabit: pair 2) |
| 5 | White-Blue | Unused (Gigabit: pair 2) |
| 6 | Orange | RX- |
| 7 | White-Brown | Unused (Gigabit: pair 4) |
| 8 | Brown | Unused (Gigabit: pair 4) |
Only difference with T568B is green and orange pair swapped.
TX / RX
- TX Transmit (sending data out)
- RX Receive (receiving data)
Each pair of wires carries the same signal but inverted:
- One wire = original signal (+)
- Other wire = inverted signal (−)
The receiver subtracts the two signals, this is called differential signaling.
Now for communication:
- TX of one device is RX of the other
- RX of one device is TX of the other
Straight-Through
Pins connect same way on both ends so it’s used for different devices
Crossover
Swaps TX/RX pairs, used for same devices
A crossover cable means one end use T568A, other end use T568B
Both devices transmit on the same pins. So you must cross TX and RX manually.
MDI vs MDIX vs Auto-MDIX
MDI (Medium Dependent Interface)
Standard Ethernet port on a device. Defines which pins transmit (TX) and receive (RX)
Connecting two MDI ports directly with a straight-through cable will not work, because both devices transmit on the same pins
MDIX (MDI Crossover Interface)
A port wired as a crossover interface. Swaps TX and RX internally
Auto-MDIX (Automatic Medium-Dependent Interface Crossover)
Ethernet port automatically detects whether TX/RX need to be swapped. Automatically configures the connection for correct communication.
Works with any cable type (straight-through or crossover)
| Term | Key Idea |
|---|---|
| MDI | Normal TX/RX wiring |
| MDIX | Built-in crossover |
| Auto-MDIX | Detects and swaps automatically |
Coaxial (Legacy)
Used before twisted pair Ethernet like 10BASE2 (thin coax) and 10BASE5 (thick coax) are mostly historical. Rarely used today.