Unshielded Twisted Pair(UTP) Cabling

Unshielded twisted pair (UTP) cables are widely used in the computer network and in the telecommunications industry as Ethernet cables and telephone wires.  Unshielded twisted-pair (UTP) cabling consists of four pairs of colour-coded copper wires twisted together and then enclosed in a flexible plastic sheath. The twist of the copper cables around each other cancels electromagnetic interference (EMI) from external sources. Unshielded means no additional shielding like meshes or aluminium foil, which add bulk, are used. It is small, which is helpful during installation. Unshielded twisted-pair (UTP) cable does not use shielding to counter EMI and RFI effects. Cable designers discovered that they can limit the negative effect of crosstalk in the following ways:-

Cancellation

When two wires in an electrical circuit are placed close jointly, their magnetic fields are the exact opposite of each other. So, the two magnetic fields cancel each other and cancel out any outside EMI and RFI signals.

Varying the several twists per wire pair

To improve the cancellation effect of paired circuit wires, designers vary the several twists of each wire pair in a cable. UTP cable must follow precise specifications governing how many twists or braids are permitted per cable meter. Notice in the figure below that the orange/orange-white pair is twisted more than the green/green-white pair. Each coloured pair is twisted a different number of times.

Standards of Unshielded Twisted Pair (UTP) Cabling

Unshielded Twisted Pair (UTP) cabling conforms to the standards recognized by the TIA/EIA. Specifically, TIA/EIA-568 stipulates the commercial cabling standards for LAN installations and is the standard most commonly used in LAN cabling. Some of the elements defined are below:-
1. Cable types
2. Cable lengths
3. Connectors
4. Cable termination
5. Methods of testing cable

Electrical and Electronics Engineers (IEEE) define the electrical characteristics of copper cabling. IEEE categories cables based on their ability to carry higher bandwidth rates. For example, Category 5 (CAT5) cable is commonly used in 100BASE-TX Fast Ethernet installations. Other Categories include Enhanced Category 5 (CAT5e) cable, Category 6 (CAT6), and Category 6a.
Cables in higher Categories support higher data rates. As new gigabit-speed Ethernet technologies are developed and adopted, CAT5e is now the minimally acceptable cable type.

CAT1 Cable

CAT1 cable is usually used for telephone wire. It does not support computer networking. The cable is not twisted and is also a single-pair cable, so it has zero capability to cancel the EMI and RFI. It supports a maximum of up to 1 Mbps data.

CAT2 Cable

It is a two-pair twisted-pair network cable supported by up to 4 Mbps data rate. The maximum working length of CAT2 cable is 100 meters. It is also used in telephone networks.

CAT3 Cable

CAT3 is a twisted four-pair network-supported cable with up to 10 Mbps data rate. The maximum data rate of CAT3 cable is 10 Mbps. Public telephone networks also use CAT3 cable. The maximum working length of CAT3 cable is 100 meters.

CAT4 Cable

CAT4 cable has four twisted pair cables supported up to 16 Mbps data rate and is mostly used in token ring networks. Telephone networks also use CAT4 cable for their services. The maximum working length of the cable is 100 meters.

CAT5 Cable

CAT5 cables are 4 pairs of twisted copper wire and have more twists per inch than CAT4, and CAT3, therefore, can run at higher speeds. The “twist” effect of each pair in the cables ensures any interference in one cable is cancelled with the twist of the partner cable. This type of wire can support computer networks and also telephone traffic for higher speeds of up to 100 Mbps. It was a popular cable in networking.

CAT5e Cable

The more popular CAT5 wire was later on replaced by the CAT5e, which provides improved crosstalk specification and allows it to support speeds of up to 1Gbps.

CAT6 Cable

CAT6 wire was designed to support Gigabit Ethernet, although there are standards that allow gigabit transmission over CAT5e wire. It is similar to CAT5e wire but contains a physical separator between the four pairs to reduce electromagnetic interference further. The maximum working length to support speeds of 1Gbps is 100 meters. The cable also supports 10Gbps speed for lengths of up to 55 meters.

CAT6A Cable

CAT6A supported 10G speed and its higher specification of presenting better immunization to crosstalk and electromagnetic interference.

CAT7 Cable

CAT7 cable is a newer copper cable designed to support speeds of 10Gbps at lengths of up to 100 meters. To achieve this, the cable features four individually shielded pairs plus an additional cable shield to protect the signals from crosstalk and electromagnetic interference (EMI). Due to the extremely high data rates, all components like patch panels, cords, jacks, and RJ-45 connectors must be CAT7 cable certified. CAT7 cable is usually used in Data Centers for backbone connections between servers, network switches, and storage devices.

Types of UTP cable by use

Different situations required UTP cable wiring with different conventions. This means that the individual wires in the cable have to connect in different orders to different sets of pins in the RJ-45 connectors. Following are the main cable types using specific wiring conventions:

Ethernet Straight-through is the most common type of networking cable. A straight-through cable generally connects the host to a switch and a switch to a router.

Ethernet Crossover: A cable used to connect similar devices. For example, to connect a switch to a switch, a host to a host, or a router to a router.

Rollover: A Cisco proprietary cable connects a workstation to a router or switch console port.
Figures 3-7 show the UTP cable type, related standards, and typical applications of these cables. They also identify the individual wire pairs for the TIA-568A and TIA-568B standards.

Using a crossover or straight-through cable incorrectly between devices may not damage them, but connectivity and communication between them will not take place. This is a common error in the lab and when checking device connections.