Unshielded twisted-pair (UTP) cabling consists of four pairs of color-coded copper wires that have been twisted together and then enclosed in a flexible plastic sheath. Its small size can be helpful during installation. 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 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 also cancel out any outside EMI and RFI signals.
• Varying the number of twists per wire pair: To improve the cancellation effect of paired circuit wires, designers vary the number of twists of each wire pair in a cable. UTP cable must follow precise specifications governing how many twists or braids are permitted per meter of cable. Notice in the figure 3-3 that the orange/orange white pair is twisted more than the green/green-white pair. Each colored pair is twisted a different number of times.
Standards of UTP Cabling
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:-
• Cable types
• Cable lengths
• Cable termination
• 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 is used commonly in 100BASE-TX Fast Ethernet installations. Other categories include Enhanced Category 5 (Cat5e) cable, Category 6 (Cat6), and Category 6a.
Cables in higher categories are supported higher data rates. As new gigabit speed Ethernet technologies are being developed and adopted, Cat5e is now the minimally acceptable cable type.
• Used for voice communication
• Most often used for phone lines
CAT-5 and CAT-5e UTP
• Used for data transmission
• Cat5 supports 100 Mb/s and can support 1000 Mb/s, but it is not recommended
• Cat5e supports 1000 Mb/s
• Used for data transmission
• An added separator is between each pair of wires allowing it to function at higher speeds
• Supports 1000 Mb/s – 10 Gb/s, though 10 Gb/s is not recommended
• UTP Connectors
UTP cable is generally terminated with an RJ-45 connector. This connector is used for a range of physical layer specifications, one of which is Ethernet. The TIA/EIA-568 standard describes the wire color codes to pin assignments for Ethernet cables.
RJ-45 is a male connector, crimped at the end of the cable. The socket is the female component of a network device, wall, cubicle partition outlet, or patch panel.
Figure 3-5 displays an example of RJ-45 Plug and figure 3-6 display the example of RJ-45 Sockets.
Types of UTP cable by use
Different situations may require UTP cables to be wired according to different wiring conventions. This means that the individual wires in the cable have to be connected in different orders to different sets of pins in the RJ-45 connectors. Following are the main cable types that are obtained by using specific wiring conventions:
• Ethernet Straight-through: The most common type of networking cable. It is generally used to connect a 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 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 that the device connections are correct should be the first troubleshooting action if connectivity is not achieved.
|Ethernet Straight-through||Both ends T568A or Both end T568B|
|Crossover||One end T568A, another end T568B|
|Rollover||Rollover Cisco proprietary|