Wire+Media

There are two types of communication media in networking: guided and unguided. This page discusses the concept of guided media which is communication through wires. With guided media communication, transmission flows along a physical guide. This physical guide includes wires such as twisted pair wiring, coaxial cable and fiber optic cable.

=Twisted Pair = Twisted pair cables were invented by Alexander Graham Bell in 1881. By 1900, the entire American telephone line network was either twisted pair or open wire with transposition to guard against interference. Today, most of the millions of kilometers of twisted pairs in the world are outdoor landlines, owned by telephone companies, used for voice service, and only handled or even seen by telephone workers. Twisted pair wiring is composed of pairs of copper wiring twisted around each other. Two wires carry the data signals (one conductor carries a positive signal; one carries a negative signal). PVC or plenum plastic insulation surrounds each wire. Multiple wire pairs are bundled together in an outer sheath. Most twisted pair networking cabling has four pairs of wires within it's PVC sheath. Twisted pair cables can be classified according to the makeup of the outer sheath. Shielded Twisted Pair (STP) has a grounded outer copper shield around the bundle of twisted pairs or around each pair. This provides added protection against EMI. Unshielded Twisted Pair (UTP) does not have a grounded outer copper shield. UTP cables are easier to work with and are less expensive than shielded cables. The unique thing about twisted pair network cabling is the fact that the wires are twisted. This is done because when we run an electrical current through a piece of copper wiring, Electromagnetic Interference //(//EMI//)// and crosstalk appear around the wires. That can be a problem when we have a second wire in close proximity because it can absorb the signal from the first wire. In that case the data on wires can get corrupted. //**Twisting**// The twisting of wires causes EMI and crosstalk signal to cancel itself out. There's constructive interference and there's destructive interference. In this case, we have destructive interference. That means the data on both wires can arrive intact. Because the wires are twisted, EMI should affect both wires equally and can be cancelled out. //**Unshielded Twisted Pair (UTP)**// There are many different types of unshielded twisted pair (UTP) wiring. The main difference between the different categories of UTP is the quality of the copper that's used to make the conductors and how tightly twisted the wires are together. The tighter the twist, the higher the bandwidth that the wire can support. CAT3-The first type of UTP is called category three, more often denoted as just CAT3. It was designed to be used with 10 megabit Ethernet, or 16 megabit token ring. CAT3 was replaced in the later 1990's with Category 5. CAT5-Category 5 supports 100 megabits Ethernet or 1 gigabit Ethernet, and it's also used with certain types of ATM networking. CAT5e-Variation on Category 5 is called CAT5E. It's similar to CAT5, but it offers better protection from the electromagnetic interference and it can be used with one gigabit Ethernet and 10 gigabit Ethernet (gigabit connections require the use of all four twisted pairs). CAT6-Category 6 is designed to support very fast, high bandwidth, broadband communications.
 * If we have a specification that requires for example, Category 3 wiring, we can use Category 5, Category 5E or Category 6. It's backwards compatible. If you have a specification, however, that requires Category 5, we can not use Category 3. While Category 3 and Category 5 cabling may appear similar physically, they are electrically different. Category 5 cabling is twisted much tighter than Category 3 cabling. This reduces cross talk and enables Category 5 wiring to support much faster data transmission rates

//**Shielded Twisted Pair (STP) Cable**// Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution. Shielded cables can also help to extend the maximum distance of the cables. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Shielded twisted pair cable is available in three different configurations:
 * 1) <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Each pair of wires is individually shielded with foil.
 * 2) <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">There is a foil or braid shield inside the jacket covering all wires (as a group).
 * 3) <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">**Coaxial Cable** <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Coaxial cable has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis. Coaxial cable was invented by English engineer and mathematician [|Oliver Heaviside] in 1880. Coaxial cable differs from other [|shielded cable] used for carrying lower-frequency signals, such as audio signals, in that the dimensions of the cable are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently a radio frequency transmission line. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers with their antennas, computer network Internet connections, and distributing cable television signals. One advantage of coax over other types of radio transmission line is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors. This allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Coaxial cable conducts electrical signal using an inner conductor (usually a flexible solid or stranded copper wire) surrounded by an insulating layer and all enclosed by a shield layer, typically a woven metallic braid; the cable is often protected by an outer insulating jacket. Normally, the shield is kept at ground potential and a voltage is applied to the center conductor to carry electrical signals. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, and cost. The inner conductor might be solid or stranded; stranded is more flexible. To get better high-frequency performance, the inner conductor may be silver-plated. Sometimes copper-plated iron or steel wire is used as an inner conductor. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">The insulator surrounding the inner conductor may be solid plastic, a foam plastic, or air with spacers supporting the inner wire. The properties of dielectric control some electrical properties of the cable. A common choice is a solid polyethylene (PE) insulator, used in lower-loss cables. Solid Teflon (PTFE) is also used as an insulator. Some coaxial lines use air (or some other gas) and have spacers to keep the inner conductor from touching the shield.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;"> <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Coaxial Cable is:
 * <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Less prone to interference than TP due to shield
 * <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">More expensive than TP
 * <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Used mostly for cable TV, but sometimes used for digital network transmission
 * <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Cable companies use this to offer cable modem service, though switching to fiber optics

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Fiber Optic Cable
<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;"> Fiber optic cable is a technology that uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves. The design of fiber optic cable consists of practical fibers, the cladding is usually coated with a layer of acrylate polymer or polyimide. This coating protects the fiber from damage but does not contribute to its optical waveguide properties. Individual coated fibers (or fibers formed into ribbons or bundles) then have a tough resin buffer layer and/or core tube(s) extruded around them to form the cable core. Several layers of protective sheathing, depending on the application, are added to form the cable. Rigid fiber assemblies sometimes put light-absorbing ("dark") glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces [|cross-talk] between the fibers, or reduces [|flare] in fiber bundle imaging applications. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Modern fiber cables can contain up to a thousand fibers in a single cable, with potential bandwidth in the terabytes per second. Companies can lease or sell the unused fiber to other providers who are looking for service in or through an area. Many companies are "overbuilding" their networks for the specific purpose of having a large network of [|dark fiber] for sale, reducing the overall need for trenching and municipal permitting. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Optical fibers are inherently very strong, but the strength is drastically reduced by unavoidable microscopic surface flaws inherent in the manufacturing process. The initial fiber strength, as well as its change with time, must be considered relative to the stress imposed on the fiber during handling, cabling, and installation for a given set of environmental conditions. There are three basic scenarios that can lead to strength degradation and failure by inducing flaw growth: dynamic fatigue, static fatigues, and zero-stress aging. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">

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