Categories of twisted-pair cable

Category 5e is usually rated at 350 MHz, but the actual speed varies depending on several different networking factors. Category 6 already has different versions that run at 250 MHz and 500 MHz. Due to the different types of category 5e and category 6, it is better to simply say that these are rated for 100 Mbps networks and gigabit networks. Take a look at one of your network cables now. Quite often, the category type is printed directly on the plastic jacket of the cable. For today’s networks, category 3 (and even category 5) is not adequate; category 5e or higher is necessary for current high-bandwidth applications. Interference can be a real problem with twisted-pair networks, or any networks for that mat- ter. Interference is anything that disrupts or modifies a signal that is traveling along a wire. There are many types of interference, but there are only a few you should know for the exam, including the following:
Electromagnetic interference (EMI): This is a disturbance that can affect electrical circuits, devices, and cables due to electromagnetic conduction and possibly radiation. Just about any type of electrical device causes EMI: TVs, air conditioning units, motors, unshielded electrical cables (Romex), and so on. Copper-based cables and network devices should be kept away from these electrical devices and cables if at all possible. If this is not possible, shielded cables can be used, for example shielded twisted-pair (STP) cables. STP cables have an aluminum shield inside the plastic jacket that surrounds the pairs of wires. Alternatively, the device that is emanating EMI can be shielded. For example, an air conditioning unit could be boxed in with aluminum shielding in an attempt to keep the EMI generated by the AC unit’s motor to a minimum. In addition, electrical cables should be BX (encased in metal) and not Romex (not encased in metal); in fact, most states require this to meet indu
Radio frequency interference (RFI): This is interference that can come from AM/FM transmissions and cell phone towers. It is often considered part of the EMI family and is sometimes even referred to as EMI. The closer a business is to one of these towers, the greater the chance of interference. The methods mentioned in the EMI bullet can be employed to help defend against RFI. In addition, filters can be installed on the network to eliminate the signal frequency being broadcast by a radio tower, although this will usu- ally not affect standard wired Ethernet networks.
One serious issue with data networks, especially networks with copper-based cabling is data emanation (also known as signal emanation). This is the electromagnetic (EM) field that is generated by a network cable or network device, which can be manipulated to eavesdrop on conversations or to steal data. Data emanation is sometimes also referred to as eavesdropping in itself, although this is not accurate. Data emanation is the most commonly seen security risk when using coaxial cable, but it can also be a security risk for other copper-based cables such as twisted pair. There are various ways to tap into these (EM) fields in order to get unau- thorized access to confidential data. To alleviate the situation, you could use shielded cabling or run the cabling through metal conduits. You could also use electromagnetic shielding on devices that might be emanating an electromagnetic field. This could be done on a small scale by shielding the single device, or on a larger scale by shielding a
Another common type of interference is crosstalk. Crosstalk is when the signal that is trans- mitted on one copper wire or pair of wires creates an undesired effect on another wire or pair of wires. Crosstalk first occurred when telephone lines were placed in close proximity to each other. Due to the fact that the lines were so close, the signal could jump from one line to the next intermittently. If you have ever heard another conversation while talking on your home phone (and not a cell phone), then you have been the victim of crosstalk. If the signals are digital (e.g., Ethernet data transfers or voice over IP), you already have an environment that is less susceptible to crosstalk. Data can still bleed over to other wires, but it is less common. Sometimes this occurs because cables are bundled too tightly, which could also cause crimping or other damage to the cable. If this is the case, a continuity tester will let you know which cable has failed so that it can be replaced.
When it comes to twisted-pair cabling, crosstalk is broken down into two categories: near end crosstalk (NEXT) and far end crosstalk (FEXT). NEXT occurs when there is measured interference between two pairs in a single cable, measured on the cable end nearest the trans- mitter. FEXT occurs when there is similar interference, measured at the cable end farthest from the transmitter. If crosstalk is still a problem, even though twisted-pair cable has been employed and digital data transmissions have been implemented, shielded twisted pair (STP) could be used. Normally, companies opt for regular twisted-pair cabling, which is unshielded twisted pair (also known as UTP), but sometimes, there is too much interference in the environment to send data effectively, and STP must be utilized.
Cables that are installed inside walls or above drop ceilings where they cannot be accessed by sprinkler systems in the case of a fire should be plenum-rated or low-smoke rated. Plenum- rated cables have a Teflon coating that makes them more impervious to fire. They are used in these situations because standard twisted-pair cables have a PVC jacket, which when burned can emit deadly gas into the air that ultimately gets breathed in as hydrochloric acid. Finally, the physical plant should be grounded. Quite often, server rooms or wiring closets are the central connecting point for all the cabling. All of the cables are punched down to patch panels, which are screwed into data racks. These racks should be bolted to the ground and connected with 10 gauge or thicker grounding wire (usually with a green jacket) to a proper earth bonding point, such as an I-beam in the ceiling. This protects all of the cabling (and the devices it connects to) from surges, spikes, lightning strikes, and so on
Fiber optic cable transmits light (photons) instead of electricity, and this light is transmitted over glass or plastic. Glass is known as the media for fiber optics, just like copper is known as the media for twisted-pair cabling. The glass or plastic strands in fiber optic cabling are extremely small; in fact, they are measured in microns.
If you happen to have fiber optic cables, connectors, and devices available, attempt to identify those after you have completed the following steps: 1. Execute a Bing search in the Images section for “optical fiber.” 2. Run Bing searches for the following connector images: • FC connector • LC connector • MT-RJ connector • SC connector • ST connector • TOSLINK 3. Execute a Bing image search for the following devices: • Fiber optic network adapter • Fiber optic switch • Fiber optic router 4. If you do have any fiber optic equipment handy, go ahead and identify it now, based on what you have seen on the Internet.
Fiber optic cable can be either single mode or multi-mode: • Single-mode (SM) optic is a cable with an optical fiber that is meant to carry a single ray of light—one ray of light, one mode. This type of cable is normally used for longer distance runs, generally 10 km and up to 80 km. • Multi-mode (MM) optic is a cable with a larger fiber core, capable of carrying multiple rays of light. This type of cable is used for shorter distance runs, up to 600 meters. Though much shorter than single mode fiber runs, this is still six times the distance of twisted-pair cable runs. Usually, fiber optic cable is used for high-speed connections, backbone connections, storage area networks (SANs), and direct connections between servers. 1 Gbps and 10 Gbps speeds are common, although you will still see 100 Mbps connections. Table 3-3 defines some of the 100 Mbps, 1 Gbps, and 10 Gbps versions of fiber optics, as well as their medium type and typical maximum distance.
When it comes to interference, a cable itself can be its worst enemy. Generally, fiber optic cables are not affected by EMI, because they are inherently light based, not electricity based. Although a fiber optic cable will still produce a type of electromagnetic radiation, the cable is not traditionally affected by EMI in the same way copper-based cables are. However, if a fiber run is installed improperly, it can give strange results when it comes to the data signal. Exact installation rules must be followed including proper termination, specific radii for turns, avoiding bunching, and so on. Improper installation results in the signal becoming “bent,” which causes data loss. Chromatic dispersion is also a factor, as opposed to attenuation on twisted-pair cables. If the light is refracted too often, again, the signal will degrade. Fiber optic cable in general is the most secure cable, allows for the longest runs, and offers data transfer rates that are equal to or greater than twisted
By far the most well-known wireless device is the wireless access point (WAP). This device quite often also acts as a router, firewall, and IP proxy. It allows for the connectivity of various wireless devices such as laptops, PDAs, handheld computers, and so on. It does so by making connections via radio waves on specific frequencies. Client computers and handheld devices must use the same frequency in order to connect to the WAP. In the following exercise, we will identify wireless access points, wireless network adapters, and wireless bridges and repeaters.

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	Created by Miguel Rios over 9 years ago