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12: Cabling - UTP and STP cables part 2



Unshielded Twisted-Pair (UTP) cable

To begin with, Unshielded Twisted-Pair (UTP), the most common media.  In Ethernet, UTP comprises eight wires with each two wires twisted together and put inside a cable jacket. See the following figure.


The reason behind twisting each two pairs is to keep the cable away from the influence of outside interference. Because of the fact that each wire in the pair carries signals in the opposite direction, the task of twisting them leads the magnetic fields on the wire pair to cancel each other. The act of being interfered by the magnetic field on the wire pair is referred to as cross-talk.

UTP cable has several categories which have started evolving since the past few years. The differences between the categories vary in the level of bandwidth defined by IEEE and, the quality of cable, and the protection level against interference. The most renowned UTP cable categories start from Category 3 (Cat 3) to Category 5 (Cat 5) ; such categories support the speed rate of 100 megabit per second. In the next few years after Cat 5, specifically in 1999, another category, Category 5e (Cat 5e), emerged. Enhancing Cat 5 to Cat 5e has brought new  improvement in terms of the nature of data transmission, lying in enabling full-duplex Fast Ethernet gigabit transmission.

After Cat 5e, another UTP cabling catergory came into existence in 2002, which is Cat 6. This UTP category is so strong and advanced that works at high performance and reducing  the cross-talk that occurs between cables at the moment of the transmission of data signals. The coming of Cat 6 does not signify that the previous standard is outdated, but rather Cat 5e is still employed in many LANs. However, to have a network with a high-data transmission speed, Cat 6 is highly recommended. Furthermore, UTP category 6 is backward compatible, which means that even having old-fashioned devices or a network being installed using previous-generation cable categories, Cat 6 is still completely suitable.

Such cables are commonly connected to devices such as computers, switches, and  routers by means of RJ-45 connector at the end of each cable. The UTP wires is inserted into the connector in a specific order. The different colors of the eight wires are there to help putting each wire in its proper place. Such wires order within UTP is referred to as pinout. Importantly, the order of colors, or pinout, depends on which device is to be used. For example, connecting a computer to a router requires  a certain order, whereas linking a computer to a switch needs a different wires order. In case the wires are put into the pinouts in an incorrect way, no signals will be transmitted on the cable and thus no connection will be established between sender and receiver. The telecommunication industry that is responsible for putting such rules is TIA/EIA (Telecommunications Industries Association/Electronic Industries Association) , which defined the order of the wires in the pinouts as 568A and 568B as standards.

What follows is a set of instructions of how to do cabling in order to connect different devices. It is important to mention that there are three ways of ordering wires in the pinouts. Such ways of arranging the wires results in naming three types of cable, which are Straight-through cable, Crossover cable, and Rollover cable.

The aforementioned types of cable are used with specific devices, that is, to connect a given device to another, you should be able to identify which cabling type to use. To figure out all that, see the following figure.


The above figure clarifies the way devices should be connected, or rather the types of cable that should be used.  As you can see, to connect either a computer or a router to either a hub or a switch, we need to use straight-through. But if we want to connect either a computer or a router to another a computer or a router, we should use cross over.  In the same way, if we wish to link either a hub or a switch to another a hub or a switch, we are required to use crossover. Significantly, rollover cable is not included on the grounds that it is Cisco-proprietary, that is to say, it is used only to connect Cisco devices with each other. It is utilized in connecting a machine with a serial port to a device with console port. Take a look at the following figure to know how rollover cable looks like.


So far we covered what types of cable we need to use to connect different devices, but what is more important is to recognize how the wires in the pinouts of straight-through and crossover cables are placed. The tools that you need in order to get a cable done are Crimping tool, connectors, and a testing device so as to test whether the cable is well done or not. This figure shows the tools needed.


Once the tools are available, take the cable and the connector, and remove the end part of the outer jacket of the cable. (to get the right size removed, put the end of the cable onto the end pins of the connector to measure how much you you should remove, because removing larger size of the outer jacket than the size of the connector causes the connector to be inefficient in terms of cabling. See the following figure to know how a connector should be done).


Next, get the twisted wires away from each other and order them according the the cabling type you want. Taking straight-through as an example, the wires are ordered from right to left taking orange-white – orange – green-white – blue – blue-white – green – brown-white – brown. The following figure shows how wires in straight-through are ordered according to the colors.

After arranging the wires, bring the connector holding the insertion lock tabs on the bottom, and insert the wires in a steady way. Then, take the crimping tool and press on the pins until each pin touches its wire counterpart. Finally, in order to test whether the cable works or not, you need a testing machine wherein both ends of the cable are plugged and if a set of points of light flash, it means the cable is perfectly done. See the following figure to get an idea.

Concerning the cabling method of crossover, it follows exactly the same process with the exception of four wires which has to be placed on different pins. It differs from the previous method in what regards the the position of the colors. Thus to get a crossover type of cable done, arrange the wire colors of the cable in the order shown in the following figure.
Shielded twisted-pair (STP) cable

Shielded twisted-pair is another copper cable type that is rarely used in today’s networks. It was especially used in IBM Token Ring network technology. It becomes less common in recent years because it has died out as Token Ring has been substituted by Ethernet technology.

STP cable is more protective against outside interference than UTP thanks to the way the cable is made and the material used. It is designed to reduce noise caused by external devices that generate electromagnetic field. To fight against such interferece, the wires inside the cable are twisted together and shielded in a mesh. The following figure shows an example of STP cable.


STP cable is much more expensive than UTP cable on the grounds of its unique characteristics that make the cable safer and which shield it from outside noise. Notwithstanding the limited use of the cable at the present time, it is still used in areas where it is very difficult to avoid the interference. As such the cable is recommended in case there is no way but to use it for protection against external noise that causes unwanted signals.

See the next lesson from here
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12: Cabling - UTP and STP cables part 2 Reviewed by M. Bouftira on 6:14:00 AM Rating: 5

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