The functions of each wire in a network cable

The functions of each wire in a network cable
A standard network cable (twisted pair) actually contains 8 thin copper wires, which are divided into 4 pairs, with each pair intertwined. These 8 wires do not all perform the same task simultaneously. Their specific division of labor depends on the network speed you are using (100 Mbps or 1 Gbps).
In simple terms, the division of labor for these 8 wires is as follows:

1. 100 Mbps network: Use only 4 wires
If your home network is 100 Mbps, or if the network cable only has 4 cores, the wires that actually function are these 4:
The 1st (orange white): Sends data +
The 2nd (orange): Sends data -
The 3rd (green white): Receives data +
The 6th (green): Receives data -
Note: The 1st and 2nd wires are specifically responsible for sending data, while the 3rd and 6th wires are specifically responsible for receiving data. That's why in older computers connected directly to each other, a "crossed wire" (switching the sending and receiving wire sequence) was needed for communication.
2. 1000 Mbps network (1 Gbps): All 8 wires are used
Nowadays, routers and computers are basically starting with 1 Gbps. To achieve faster speeds, 1 Gbps networks must use all 8 wires.
The 1st, 2nd, 3rd, and 6th wires: Continue to be responsible for sending and receiving data.
The 4th and 5th wires (blue): Bidirectional data transmission.
The 7th and 8th wires (brown): Bidirectional data transmission.
In 1 Gbps networks, these 4 pairs of wires (8 wires) are all transmitting data simultaneously and bidirectionally, so the speed is directly ten times faster.
3. What else can the remaining wires do? (PoE power supply)
As mentioned earlier, 1 Gbps networks use all 8 wires to transmit data. However, in 100 Mbps networks, the 4th, 5th, 7th, and 8th wires are actually "idle".
In many scenarios (such as connecting surveillance cameras or wireless APs), these 4 idle wires will be used for power supply (which is the PoE technology mentioned earlier). This eliminates the need for an additional power cord, as one network cable handles both "data transmission" and "power supply".
4. Why are they twisted in pairs? (Anti-interference)
You might be curious why these 8 wires are not arranged in parallel but are twisted in pairs (twisted pair)?
This is because when transmitting electrical signals through the network cable, it is very susceptible to external electromagnetic waves (such as when tied to the wire). Twisting two wires together can ingeniously cancel out the external electromagnetic interference, ensuring stable and uninterrupted network

signals. To sum up:
1, 2, 3, and 6 lines are the absolute core, responsible for transmitting data. Not a single one can be connected wrongly.
4, 5, 7, and 8 lines are responsible for speed improvement in gigabit networks and can be used for power supply in hundred-megabit networks.
If you are wiring the network cables yourself, you must strictly follow the T568B wiring sequence (orange white, orange, green white, blue, blue white, green, brown white, brown) to arrange the wires. Only in this way can the 8 wires perform their respective functions and achieve the full network speed.