Unshielded twisted pair (UTP) cables are; widely used in the computer network as well as 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 cable around each other’s cancels electromagnetic interference (EMI) from external sources. Unshielded means no additional shielding like meshes or aluminium foil, which add bulk, are used. It is a small size which 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 by the following ways:-
When two wires in an electrical circuit 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 permitted per meter of cable. 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:-
5.Methods of testing cable
Electrical and Electronics Engineers (IEEE) define the electrical characteristics of copper cabling. IEEE placed cables into Categories based on their ability to carry higher bandwidth rates. For example, Category 5 (CAT5) cable 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 developed and adopted, CAT5e is now the minimally acceptable cable type.
CAT1 cable is usually used for telephone wire. It is not supporting computer networking. The cable is not twisted and also it a single pair cable, so it has zero capability to cancel the EMI and RFI. Support maximum of up to 1 Mbps data.
It is two pair twisted; pair network cable supported up to 4 Mbps data rate. Maximum working length of CAT2 cable is 100 meters. It is also used in telephone networks.
CAT3 is twisted four-pair network supported cable up to 10 Mbps data rate. The maximum data rate of CAT3 cable is 10 Mbps. Public telephone network also uses the CAT3 cable. Maximum working length of CAT3 cable is 100 meters.
CAT4 cable has four twisted pair cable supported up to 16 Mbps data rate and mostly used in token ring networks. Telephone network also uses CAT4 cable for their services. Maximum working length of the cable is 100 meters.
CAT5 cables are actually 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 ensure any interference one cable, cancelled with the twist of the partner cable. This type of wire can support computer network and also telephone traffic for higher speeds up to 100 Mbps. It was a popular cable in networking.
The more popular CAT5 wire was later on replaced by the CAT5e which provides improved crosstalk specification, allowing it to support speeds of up to 1Gbps.
CAT6 wire was designed; to support Gigabit Ethernet, although there are standards that will allow gigabit transmission over CAT5e wire. It is similar to CAT5e wire but contains a physical separator between the four pairs to further reduce electromagnetic interference. The maximum working length to support speeds of 1Gbps is 100 meters. The cable also supports 10Gbps speed for the lengths of up to 55 meters.
CAT6A supported 10G speed as well as with its higher specification of presenting better immunization to crosstalk and electromagnetic interference.
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, patch cords, jacks, and RJ-45 connectors must be CAT7 cable certified. CAT7 cable 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 cables 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 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 used to connect a workstation to a router or switch console port.
The figure 3-7 shows the UTP cable type, related standards, and typical application of these cables. It also identifies 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 the devices, but connectivity and communication between the devices will not take place. This is a common error in the lab and checking the device connections.
|Ethernet Straight-through||Both ends T568A or Both end T568B|
|Crossover||One end T568A, another end T568B|
|Rollover||Rollover Cisco proprietary|