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Guide to Network Cabling Fundamentals

Chapter 3

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Chapter 3 - Cables and the Cabling Infrastructure

Identify the various types of cable and their characteristics

Compare cable types and characteristics Identify and differentiate between the various

network topologies Create an effective network design Identify which network elements you must include in

your documentation

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When selecting telecommunications system cable, the system needs must be matched with the characteristics of the cable The three basic cable types are coaxial, twisted-pair,

and fiber-optic An alternative to cable is wireless technologies, which

transmit signals through the atmosphere The five basic cable characteristics are: throughput and

bandwidth; cost; size and scalability; connectors; and noise immunity

Cable Types and Characteristics

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Cable characteristics: Throughput is the amount of data that a cable can

transmit during a given period and is measured in megabits per second, or Mbps

Throughput potential is determined by the physical nature of the cable

Bandwidth is the measure of the difference between the highest and lowest frequencies that the media can transmit, it is measured in hertz (Hz)

Bandwidth is directly related to throughput, and the higher the bandwidth, the higher the throughput

Cable Types and Characteristics

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Cable characteristics (cont.): Cost for different types of cable varies depending on

available hardware, installation, transmission rate, and the obsolescence potential of the medium

Size and scalability is determined by the maximum nodes per segment, the maximum length per segment, and the maximum network length

Connectors are specific based on the type of cable used and can affect the cost of installation

Noise immunity is the cable’s ability to deter noise (EMI and RFI) that can distort data signals

Cable Types and Characteristics

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Cable types: Coaxial cable, also called coax, consists of a central

copper core surrounded by an insulator, braiding, and a plastic jacket

Coax has a high resistance to interference from noise due to its insulation and protective braiding

Coax carries signals farther than twisted-pair, but is more expensive and supports a lower throughput

A key specification for coax is impedance, or its measure of resistance to alternating current flow; each unit of resistance is expressed as an ohm

Cable Types and Characteristics

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Cable types (cont.): Twisted-pair is the most common form of cabling used

on LANs today; it is relatively inexpensive, flexible, and easy to install; but it does not span as great a distance as coax

Twisted-pair can easily accommodate a variety of network topologies, and can handle faster transmission rates than coax

Twisted-pair, because of its flexibility, is more prone to physical damage than coax

Cable Types and Characteristics

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Cable types (cont.): Twisted-pair consists of insulated copper wires, with 0.4

to 0.8 mm diameter, twisted in pairs around each other and encased in a plastic coating

The twists in a twisted-pair cable reduce the effect of crosstalk, the infringement of the signal from one wire pair on another wire pair’s signal; crosstalk is measured in decibels (dB), a measurement unit of signal strength of a sound’s intensity

The number of twists per inch determines how resistant the pair will be to noise

Cable Types and Characteristics

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Cable types (cont.): Shielded twisted-pair (STP) consists of individually

insulated twisted pairs surrounded by a metallic shielding that must be grounded

Unshielded twisted-pair (UTP) consists of insulated pairs of wires encased in a plastic sheath; it is less expensive and less resistant to noise than STP

Screened twisted-pair (ScTP) consists of insulated pairs of wires contained in a full foil laminate shield; it offers superior immunity to radio frequency fields and reduced crosstalk

Cable Types and Characteristics

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Cable types (cont.): Fiber-optic cable, also called fiber, contains one or more

glass fibers in its core; around the fibers is a layer of glass, called the cladding; over the cladding is layer of plastic and a braiding of kevlar

Data is transmitted by converting electrical signals at the sending end into optical signals, which are then transmitted through the fibers by light pulses

Fiber comes in single-mode, which carries a single mode of light to transmit data; and multimode, which can carry hundreds of thousands of modes of light simultaneously

Cable Types and Characteristics

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Cable comparisons: ThickNet (10Base5) is called ThickWire Ethernet ThickNet’s maximum transmission rate of 100 Mbps and

transmits using baseband, a method that allows only one signal to be transmitted at a time

ThickNet is less expensive than fiber, but much more expensive than ThinNet or twisted pair

ThickNet requires a vampire tap to connect to a transceiver, and a drop cable to connect devices

ThickNet has the highest resistance to noise and allows data to travel for greater distances

Comparing Cables and Their Characteristics

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Cable comparisons (cont.): ThinNet (10Base2) is called thin Ethernet ThinNet has a maximum transmission rate of 10 Mbps

and transmits using baseband ThinNet is less expensive than ThickNet or fiber, but

more expensive than twisted pair ThinNet uses BNC and BNC/T connectors to connect

wires to devices ThinNet is more resistant to noise than twisted-pair and

its maximum segment length is 185 m

Comparing Cables and Their Characteristics

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Cable comparisons (cont.): STP and UTP can transmit data at 10 Mbps; CAT5 UTP

at 100 Mbps; enhanced CAT5 and CAT6 can transmit data at 1000 Mbps

Costs of STP, ScTP, and UTP vary; STP and ScTP are usually more expensive than UTP

All twisted-pair cables use 8-pin RJ-45 connectors STP and ScTP are more resistant to noise than UTP and

the maximum segment length for STP and UTP is 100 m; for ScTP it is 98 m

Comparing Cables and Their Characteristics

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Cable comparisons (cont.): Fiber was used primarily as a backbone cable until

recently and can transmit data at 1 Gbps Fiber is one of the most expensive cables; network

communication devices, such as NICs and hubs, can cost more than those for other networks

Fiber cabling uses many types of connectors; the industry standards are the ST and SC; and MT-RJ small form factor connectors

Fiber is immune to both EMI and RFI and the maximum segment length is 100 m

Comparing Cables and Their Characteristics

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Cable comparisons (cont.): Wireless networking refers to computers that

communicate using standard networking protocols, but without the use of cabling to connect devices

The computers transmit data by means of wireless signals produced by infrared (requiring equipment to be in a direct line of sight) or radio waves

Wireless networks require installation of NICs with built-in antennas and uses access points as hubs

Wireless networks currently transmit data at approximately 11 Mbps

Comparing Cables and Their Characteristics

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There are two types of network topologies: Physical topology is the physical layout of the network,

including cable and device configuration Logical topology refers to the method used to

communicate between the devices It is important to understand the physical topology before

designing networks, because they can affect the logical topology chosen, how the building is cabled, and what kind of media is used

Physical topologies are classified according to three geometric shapes: bus, ring and star

Network Topologies

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Physical topologies: Bus consists of a single cable that connects all the

nodes of a network without intervening connectivity devices, and requires a terminator at each end

The single cable is called the bus and supports one channel, where each node shares total capacity

Bus advantages: easy to install and add devices; requires less cable; less expensive

Bus disadvantages: requires terminators; entire network shuts down if the cable breaks; difficult to troubleshoot; limit is about 10 connections

Network Topologies

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Physical topologies (cont.): Ring is where each node is connected to the two nearest

nodes, effectively forming a circle Data is transmitted in one direction around the ring, and

is typically done so using token passing The ring is used by Token Ring and FDDI networks Ring advantages: no network collisions; each node

functions as a repeater; less cable required Ring disadvantages: Single malfunctioning node can

disable entire network; not flexible or scalable; modifications requires network shutdown

Network Topologies

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Physical topologies (cont.): Star is where each node is connected through a central

device, such as a hub All nodes transmit data to the hub, which then

retransmits the data to the destination node Star advantages: a break in the cable does not shut

down the network; higher reliability; easier troubleshooting; no terminators required

Star disadvantages: uses more cable; hubs are more expensive than terminators; hub failures take down entire LAN segments

Network Topologies

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Physical topologies (cont.): Mesh is where all devices share many redundant

interconnections with each node; full-mesh means every node is interconnected, partial-mesh is where some nodes are connected to one or two others

Mesh advantages: if one connections fails, data can be redirected; higher level of security; easy troubleshooting; greater stability and reliability

Mesh disadvantages: uses much more cable; more expensive to install; difficult to install and configure on very large networks

Network Topologies

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Steps for ensuring flexible and solid network design that meets customer expectations: Assessing functional requirements includes listing tasks

to be automated and updated; determining which business applications will be used and how; identify needs such as e-mail, Internet access, etc.

Sizing the network includes establishing the number of users and their intended use; calculate user community growth and network capacity growth

Connectivity involves defining external connections; Internet requirements; assessing bandwidth

Creating an EffectiveNetwork Design

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After prerequisites, decisions are required for the following network design issues: Network type, including Ethernet, ATM, Token Ring Physical network, including cabling, faceplates, and other

components of the basic infrastructure Network communications equipment, such as hubs Network operating system, such as Windows/Novell Workstations, considering the hardware/software Network server hardware and data backup hardware and

software

Creating an EffectiveNetwork Design

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Network documentation needs: The first section describes the network: topology, network

architectures, operating systems, device and user counts, and contact information

The next section is used most frequently and it defines the physical layout of the network cabling; every time the network requires modification, this section will be consulted and modified

Also include in the documentation: equipment room items; the internetworking devices; device specifications, such as port usage, physical and logical addresses, model and serial numbers

Network Elements You Need to Document

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Chapter Summary

Cabling is the basic framework of a solid network foundation. To successfully design a network cable layout, you need a thorough knowledge of cable types, their specifications, and network topologies. This information helps you assess the organization’s current needs and plan for future growth

All cabling media have five basic characteristics you must consider when selecting cable for your telecommunications systems: throughput and bandwidth, cost, size and scalability, connectors, and noise immunity

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Chapter Summary

The three basic types of cable are coaxial, twisted-pair, and fiber-optic. Coax has a high resistance to interference, can carry signals farther than twisted-pair cable before requiring repeaters, and must be terminated with 50-ohm resistors. Twisted-pair cable is the same as the cable used to wire telephones, and is the most common LAN cabling used today. Twisted-pair is inexpensive, flexible and easy to install. It is shielded, unshielded, or screened. Fiber is a more expensive media, but has the highest throughput and bandwidth, transmits optical signals in the form of light over glass fibers

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Chapter Summary

There are two categories of fiber: multi-mode and single-mode. Single-mode fiber transmits in a single mode of light, which allows data to travel more rapidly and for greater distances. Multimode fiber transmits up to hundreds of thousands of modes of light simultaneously, which allows more data to be transmitted at one time. However, data cannot travel as fast or as far on multimode fiber

The coaxial cables used for networks are ThickNet (10Base5) and ThinNet (10Base2). Both were used extensively in the early years of Ethernet

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Chapter Summary

Wireless networking refers to computers that communicate using standard network rules or protocols, but without the use of cabling to connect the computers. A wireless network can be installed as the sole network in an organization, or it can extend a wired network to areas where wiring would be too difficult or expensive to implement. Wireless networks can be configured to provide the same network functionality as any wired network

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Chapter Summary

Network topologies come in three basic geometric shapes: bus, ring, and star. A fourth type of topology, referred to as fault-tolerant mesh, is often required for high-availability networks. The bus topology is the least expensive and the most difficult to troubleshoot. The ring topology is difficult to troubleshoot for the same reasons, but it is not subject to network collisions because of its communication method. The star topology is the most commonly used, and it offers the most advantages. It is more expensive because it uses more cabling than other topologies, but it is more reliable because of its wiring. If one station goes down in a star topology, the rest of the network is not affected

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Chapter Summary

Before you begin designing a network, you must know its relative scale and what your customer expects the network to accomplish. The prerequisites of a network design include assessing functional requirements, sizing the network, and defining connectivity needs. Once you complete the preliminary assessment, you can begin design work

Before you begin your documentation project or define your documentation policies, you must first decide what you need to document. Every network has its own documentation needs