Twisted pair

lastmod 2024-09-03created 2015-04-2217 edits

Twisted pair cabling (Korean yeonseon, 撚線 → "twisted wire"; twisted pair → "a twisted pair (雙) of") refers to twisting two copper wires together and covering them as a single conductor, and its purpose is to suppress electromagnetic interference (EMI) from external sources. For example, it is used to block electromagnetic waves in unshielded twisted pair (UTP) and crosstalk between neighboring wires.

Unlike foiled twisted pair (FTP) and shielded twisted pair (STP), unshielded twisted pair (UTP) cable is not surrounded by any shield. Twisted pair is the main wire for telephones and is very common in computer networks. (Especially for patch cables or temporary network connections)

Pinouts (802.3af)

802.3af standard A and B on the power sourcing equipment side (MDI-X)
Switch pin	T568A color	T568B color	10/100 mode B, DC on spares		10/100 mode A, mixed DC and data		1000 (1 gigabit) mode B, DC and bi-directional data		1000 (1 gigabit) mode A, DC and bi-directional data
Pin 1	Wire_white_green_stripe.svg.png White/green stripe	Wire_white_orange_stripe.svg.png White/orange stripe	Rx +		Rx +	DC +	TxRx A +		TxRx A +	DC +
Pin 2	Wire_green_stripe.svg.png Green solid	Wire_orange_stripe.svg.png Orange solid	Rx −		Rx −	DC +	TxRx A −		TxRx A −	DC +
Pin 3	Wire_white_orange_stripe.svg.png White/orange stripe	Wire_white_green_stripe.svg.png White/green stripe	Tx +		Tx +	DC −	TxRx B +		TxRx B +	DC −
Pin 4	Wire_blue_stripe.svg.png Blue solid	Wire_blue_stripe.svg.png Blue solid		DC +	Unused		TxRx C +	DC +	TxRx C +
Pin 5	Wire_white_blue_stripe.svg.png White/blue stripe	Wire_white_blue_stripe.svg.png White/blue stripe		DC +	Unused		TxRx C −	DC +	TxRx C −
Pin 6	Wire_orange_stripe.svg.png Orange solid	Wire_green_stripe.svg.png Green solid	Tx −		Tx −	DC −	TxRx B −		TxRx B −	DC −
Pin 7	Wire_white_brown_stripe.svg.png White/brown stripe	Wire_white_brown_stripe.svg.png White/brown stripe		DC −	Unused		TxRx D +	DC −	TxRx D +
Pin 8	Wire_brown_stripe.svg.png Brown solid	Wire_brown_stripe.svg.png Brown solid		DC −	Unused		TxRx D −	DC −	TxRx D −

Effective range of LAN cables

UTP cable is rated 120m–150m, but in practice it is about 100m. Coaxial cable, a line like the cable TV line, is about 500m, and I understand that some wireless LANs have a longer effective range depending on the type.

Shielded twisted pair (STP)

Shielded twisted pair is described as twisted pair with the shield layer unwrapped, and is also called STP (Shielded Twisted Pair). It is used in factories or outdoors where there is a lot of signal interference, and in places that need fast communication speeds. In Europe, STP is mainly used and UTP is barely in use.

Unshielded twisted pair (UTP)

Unshielded twisted pair is described as twisted pair with the shield layer not unwrapped, and is also called UTP (Unshielded Twisted Pair). It is used for telephone lines, Ethernet, etc. Because it is simple to handle and cheap, it is the standard for Ethernet LAN use where fast transmission is not required. It is usually used with an RJ-45 jack attached.

How a crossover cable works

Normally, to build a network, the LAN card installed in each computer must be connected to a hub. But a hub is also a piece of hardware, so buying one costs money. The hub's role is to connect the Transmit signal used by wires 1 and 2 to the Recevie signal on wires 3 and 6. When connecting several computers, the Transmit signal must go into the Recevie signal wire of a specific computer, so a hub is essential, but when connecting two computers, connecting the cable directly also works. So when connecting two computers over LAN, a cable made with the wire order swapped at one end's port is used. Because the positions of wires 1 and 3, and 2 and 6, are crossed, the cable is called a crossover cable.

Difference between 568A and 568B

Reportedly 568A is mainly used in the United States, while 568B is widely used in Korea. However, networks that share network and telephone systems use 568A. This is because 568B may not be compatible with the standard used in telephone networks (USOC:/Universal Standard Order Code). The end of a UTP cable has a connector called RF(Registered Jack)-45 attached, which makes it easy to connect to other devices.

Utp_568a_vs_568b.jpg

Direct

Direct (direct, PC to Hub) cable: both ends are wired in the order 12345678. Mainly used to connect a hub and a PC, or a router and a hub. On both ends of the cable, pins 1 and 2 are TX (transmit side: output terminals) and pins 3 and 6 are RX (receive side: input terminals). That is, communication uses only 4 of the 8 wires, and the remaining 4 wires are spares.

Utp_direct.png

Crossover

Crossover (crossover, PC to PC) cable: one end is wired 12345678 and the other end 36145278. Pins 1, 2 and 3, 6 are swapped. Used to connect device to device. Mainly used to connect PCs to each other or hubs to each other. The cable's internal wiring is changed so that the signal from the output terminal of one network card is delivered to the input terminal of the other network card.

Utp_cross.png

CAT.6 Cable

What_is_cat6_cable.png

The theoretical transmission distance is about 100m.

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