Twisted Pair Network Cable

Before you start

Objectives: learn what are the specifics of twisted pair cable, types of UTP cables and different connectors which can be used.

Prerequisites: no prerequisites.

Key terms: twisted, category, pair, wire, cabling, utp, copper, interference, connector, ethernet, network, signal, types


Cable Components

Twisted pair wiring is composed of pairs of copper wiring twisted around each other. Two wires carry data signals (one conductor carries a positive signal, one carries a negative signal). Plastic insulation or PVC surrounds each wire. Multiple wire pairs are bundled together in an outer sheath. Most twisted pair networking cabling has four pairs of wires within it’s PVC sheath. Twisted pair cables can be classified according to the makeup of the outer sheath. Shielded Twisted Pair (STP) has a grounded outer copper shield around the bundle of twisted pairs or around each pair. This provides added protection against EMI. Unshielded Twisted Pair (UTP) does not have a grounded outer copper shield. UTP cables are easier to work with and are less expensive than shielded cables.

Twisted Pair Cable

197.1 – Unshielded Twisted Pair Cable

The Twisting

The unique thing about twisted pair network cabling is the fact that the wires are twisted. This is done because when we run an electrical current through a piece of copper wiring, Electromagnetic Interference (EMI) and crosstalk appear around the wires. That can be a problem when we have a second wire in close proximity because it can absorb the signal from the first wire. In that case the data on wires can get corrupted. The twisting of wires causes EMI and crosstalk signal to cancel itself out. There’s constructive interference and there’s destructive interference. In the case of two twisted wires, we have destructive interference. That means that the interference on one wire will cancel out the interference on other wire, and vice versa. That way the data on both wires can arrive intact.

Advantages

There are several advantages of twisted pair in contrast to, for example, coaxial cable. Twisted pair cable is very flexible so it is really easy to work with. It is also less expensive than coaxial cabling. The reason why twisted pair became so popular and widely implemented is because networking protocols and standards were designed to support twisted pair wiring.

Disadvantages

There are some disadvantages like the casing, the sheath around the twisted pair networking cabling which is relatively thin. It doesn’t have second insulator like coaxial cabling has. It is also a bit more susceptible to electromagnetic interference.

There are also some security concerns. If we have the right equipment we could actually pick up signals on the wire, capture it and see what data is being transferred on that twisted pair wiring. Coaxial is a bit more resistant to eavesdropping.

Types of UTP Cables

There are many different types of unshielded twisted pair (UTP) wiring. The main difference between the different categories of UTP is the quality of the copper that’s used to make the conductors and how tightly twisted the wires are together. The tighter the twist, the higher the bandwidth that the wire can support.

CAT3

The first type of UTP is called category three, more often denoted as just CAT3. It was designed to be used with 10 megabit Ethernet, or 16 megabit token ring. CAT3 was replaced in the later 1990’s with Category 5.

CAT5

Category 5 supports 100 megabit Ethernet or 1 gigabit Ethernet, and it’s also used with certain types of ATM networking.

CAT5e

Variation on Category 5 is called CAT5E. It’s similar to CAT5, but it offers better protection from the electromagnetic interference and it can be used with one gigabit Ethernet and 10 gigabit Ethernet (gigabit connections require the use of all four twisted pairs).

CAT6

Category 6 is designed to support very fast, high bandwidth, broadband communications.

If we have a specification that requires for example, Category 3 wiring, we can use Category 5, Category 5E or Category 6. It’s backwards compatible. If you have a specification, however, that requires Category 5, we can not use Category 3. While Category 3 and Category 5 cabling may appear similar physically, they are electrically different. Category 5 cabling is twisted much tighter than Category 3 cabling. This reduces cross talk and enables Category 5 wiring to support much faster data transmission rates

Connectors

There are two different types of connectors that are used with UTP cabling. The first one is called the RJ11 jack.

RJ11

RJ 11 Connector

Image 197.2 – RJ 11 Connector

The RJ11 jack has four connectors and supports up to two pairs. It has a locking tab to keep the connector from coming unplugged in the back. It is used to connect a modem to a phone jack in a wall outlet to establish a dial-up Internet connection. They’re not widely used with network cabling anymore.

RJ45

The one that is used for network cabling is the RJ45.

RJ45 Cable

Image 197.3 – RJ45 Cable

RJ45 is used for Ethernet and some token ring connections. It has eight connectors, so it supports up to four pairs of copper wires. It also has a locking tab to keep the connector from coming unplugged. We can use a crimping tool to attach connectors to UTP cable.

Remember

Unshielded Twisted Pair (UTP) does not have a grounded outer copper shield, and can have up to 4 pairs of wires. The twisting of wires causes EMI and crosstalk signal to cancel itself out. The main difference between the different categories of UTP is the quality of the copper that’s used to make the conductors and how tightly twisted the wires are together. There are two different types of connectors that are used with UTP cabling, RJ11 and RJ45.

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