cisco networking academy programcopyright 2003fundamentals of voice and data cabling 1.2 chapter 4...

Copyright 2003 Fundamentals of Voice and Data Cabling 1.2 Cisco Networking Academy Program

Chapter 4 Copper Media

• Twisted Pair Cables.

• Twisted Pair Fundamentals.

• Other Twisted Pair Configurations.

• Coaxial Cables.

• Outside Plant Cables (OSP).


Copper Properties

Copper has several important properties which make it well suited for electronic cabling:

• Conductivity — Copper is an excellent conductor of electric current and heat.

• Corrosion Resistance — Copper will not rust and is fairly resistant to corrosion.

• Ductility — Copper possesses the ability to be drawn into thin wires without breaking.

• Malleability — Pure copper is easy to shape.

• Strength — Copper keeps its strength and toughness up to about 400 °F.


Copper Properties

Types of Copper Cables used in Voice and Data Networks


Copper Cable Components

Regardless of the construction, most cables contain certain common elements. These are:

• A sheath or jacket for protection.

• Insulation to prevent short circuits between the individual conductors.

• Spacers to preserve the electrical properties of the cable.


Solid Versus Stranded

• Stranded wires are series of very fine copper strands that are twisted together like a rope. Since these strands are so fine, the resulting wire is very flexible.


Cable Insulation

Insulation is a high resistance material that is coated on the conductor to resist the flow of current between conductors in the cable. There are three primary categories of insulators:

• Thermoplastics - Polyvinylchloride (PVC), Polyethylene, Polypropylene. These are widely used and resist most sunlight, ozone, oil, and solvents.

• Flouropolymers - Halar and Teflon. These are used for high temperature applications.

• Elastomers - These are rubber like and return to shape after tension is released.


Insulation Displacement Connectors (IDCs)

• Solid wires are more desirable when using IDCs.

• These connectors work by inserting the wire into grippers that have sharp internal edges.

• These grippers cut through the insulation and bite into the copper conductor.


NEC Cable Type Codes

• The National Electrical Code (NEC) describes various types of cables and materials used in the cables.

• The NEC contains the standards most widely supported by local licensing and inspection officials.

• In general terms, the NEC describes how a cable burns.

• The cable type codes determine what type of cables can be used for certain applications.


Plenum

• NEC cable type codes are important because cables often run in ventilation system return spaces above ceilings or below floors.

• Such spaces, called plenums, must not quickly fill with toxic gasses should a small fire break out because the air conditioning system will spread the poisonous fumes to other areas of the building.

• Plenum-rated cables have jackets made of materials that are slow burning and do not emit noxious fumes.


Cable Plant

• A cable plant, or structured cable system, is more than a collection of individual cables.

• Inside plant cable is run inside buildings. Outside plant cable (OSP) is usually thicker and comes equipped with a stronger, denser jacket material.

• OSP may be filled with water-resistant gel and covered with a layer of armoring.


Twisted Pair Copper Cable

• Twisted-pair cabling consists of pairs of insulated copper wires that are twisted together and then housed in a protective sheath.


Coaxial Copper Cable

• Coaxial cable consists of a copper center conductor, either stranded or solid, which is wrapped in insulation and covered with one or more layers of braid and foil.


Twisted-Pair Connectors

The most common connector system for terminating a twisted-pair cable is the 8-position, 8-contact (8P8C) modular connector, also known as the Registered Jack 45 (RJ-45) connector.


Benefits of Twisted-Pair Cables

• The twisting of each pair of wires provides a cancellation effect that helps neutralize noise and null out interference.

• Because the signals in each wire of the pair are going opposite directions, the interference adds to the signal in one wire as it resists the signal in the other wire.

• The result is that in twisted-pairs, interference such as EMI and RFI tends to be canceled out.


Cable Categories

Category is the term used to distinguish the grades of twisted-pair cables.

• Category 3 – Telephone services (16 MHz).

• Category 5 – Ethernet Networks (100 MHz).

• Category 5e – Ethernet Networks (100 MHz). This cable type further reduces crosstalk.

• Category 6 – Gigabit Ethernet Networks (250 MHz).


Cancellation Effect

• The interwoven nature of each pair of wires in twisted-pair cables provides a cancellation effect that helps neutralize noise and null out interference.

• The cancellation effect only works if the signals go down the correct wires.

• Different pairs in a piece of cable have different numbers of twists. This helps keep the alternating fields from coming into frequent alignment and increasing the possibility of crosstalk.


Unshielded Twisted-Pair (UTP) Cable

• UTP cable is used in a variety of networks. It can come with many different numbers of pairs inside the jacket.

• The most common number of pairs is four as is used for Category 3, 5e, and 6.

• This type of cable relies solely on the cancellation effect, produced by the twisted wire pairs, to limit signal degradation caused by EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference).


Shielded Twisted-Pair (STP) Cable

• STP cable has shielding around each pair to prevent EMI and crosstalk.


Screened Twisted-Pair (ScTP)

• ScTP has only a single shield, usually foil, that protects all the pairs of the cable.

• Each pair is not wrapped in a shield like STP.

• Since it does not have the extra shielding around the pairs, ScTP is less expensive, has a lighter weight, has a smaller diameter, and is easier to ground than STP.


Color code for 4-pair

• Each of the wires in a pair has a unique name, tip or ring.

• The "primary color" in a four-pair cable, such as Category 5e, is the tip, which is usually white with a tracer, or stripe, that is the same color as the pair's solid color wire, which is the ring.


ANSI/TIA/EIA T568A and T568B

• These particular standards depict the arrangement of each color conductor when terminating four-pair data cables. The two schemes are similar with two of the four pairs reversed in the termination order.


Multi-Pair Cables

• Telecommunications cable comes in many sizes, starting with a single pair of wires to 4200 pairs of wires.

• A standard color coding scheme is used for 25 pairs of wires.

• When a cable has more than 25 pair groups, each group is wrapped with colored tape to form binder groups.


Color Codes for 25-Pair Cables

• The standard four-pair cable colors are a subset of a large scheme of colors.

• Pairs 1-4 of a four-pair cable use the same color system that is used in a 25-pair cable.

• When indicating colors for a pair, the tip colors come first, because that is the order in which the cables are punched on a punch block. Ring colors are just the opposite.


The 25-Pair Color Code

• The tip wire has a stripe of the ring color in it and the ring wire has a stripe of the tip color in it.


High Pair Count Cables

• Cables that have more than 25 pairs group the wires in 25-pair units, each of which is wrapped with colored tape to form binder groups.

• The binder groups follow the same color code as the wires of each pair, that is, the first binder is blue/white, the second binder is orange/white, and so on.


Coaxial cable

• Coaxial cable has a central copper conductor encircled by a layer of insulation, then a layer of shielding, and finally an outer jacket layer.


Coaxial Cable Connectors

• The BNC connector is usually used for networking and video applications.

• The F-series connector is used for modulated radio frequency applications, such as cable-TV.


How Coaxial Cable Works

• Coaxial cable forms a transmission line, that is, a network with electrical effects caused by the physical shape of the wire.

• The fields that developed between the parallel conductors carried the information forward in the form of radio waves that followed the path of the wires.

• It is the spatial relationship between the center conductor and the shield that allows the coaxial cable to carry signals.


Exterior cables

Environmental factors that can damage a cable during its service life are:

• Sunlight

• Extremes of hot or cold

• The pressures of direct burial


OSP Protection

Several steps can help overcome environmental problems including the following:

• Use gel filled cables.

• Use cables with UV (ultraviolet) resistant jackets.

• Use cables that have high molecular weight jackets to cushion the pressure points caused by rocks, roots, and other obstacles.

• Use cables with armoring, or special protective coating, so that they are not easily sheared or damaged.


Filling Compounds

•Filling compounds are used to fill OSP because outside plant cables are susceptible to water from many sources.

cisco networking academy programcopyright 2003fundamentals of voice and data cabling 1.2 chapter 4...

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