chapter 3: transmission basics and networking media network+ guide to networks third edition

Chapter 3: Transmission Basics and Networking

Media

Network+ Guide to Networks

Third Edition

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Objectives

After reading this chapter and completing the exercises, you will be able to:

Identify organizations that set standards for networking

Describe the purpose of the OSI Model and each of its layers

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Objectives (continued)

Explain specific functions belonging to each OSI Model layer

Understand how two network nodes communicate through the OSI Model

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Objectives (continued)

Discuss the structure and purpose of data packets and frames

Describe the two types of addressing covered by the OSI Model

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Transmission Basics

• Transmit means to issue signals to the network medium

• Transmission refers to either the process of transmitting or the progress of signals after they have been transmitted

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Transmission Basics

• Analog and Digital Signaling

• On a data network, information can be transmitted via one of two signaling methods: analog or digital

• Both types of signals are generated by electrical current, the pressure of which is measured in volts

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• An analog signal, like other waveforms, is characterized by four fundamental properties: amplitude, frequency,wavelength, and phase

• A wave’s amplitude

• Frequency

• Phase

Transmission Basics (continued)

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• Digital signals composed of • pulses

• precise

• positive voltages and zero voltages

• Data Modulation• used to modify analog signals in order to make them

suitable for carrying data over a communication path


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• Modem reflects this device’s function as a modulator/demodulator

• Modulates digital signals into analog signals

• Modulation

• Frequency modulation (FM)

• Amplitude modulation (AM)


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• Transmission Direction

• Simplex

• Half-duplex

• Full-duplex

• Channel


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• Multiplexing

• Allows multiple signals to travel simultaneously over one medium

• In order to carry multiple signals, the medium’s channel is logically separated into multiple smaller channels, or sub channels

• A device that can combine many signals on a channel, a multiplexer (mux), is required at the sending end of the channel

• At the receiving end, a demultiplexer (demux) separates the combined signals and regenerates them in their original form


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• Time division multiplexing (TDM)

• Wavelength division multiplexing (WDM)

• WDM enables one fiber-optic connection to carry multiple light signals simultaneously

• Using WDM, a single fiber can transmit as many as 20 million telephone conversations at one time

• Statistical multiplexing


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• Throughput and Bandwidth

• Throughput is the measure of how much data is transmitted during a given period of time

• Bandwidth is a measure of the difference between the highest and lowest frequencies that a medium can transmit

• The higher the bandwidth, the higher the throughput


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• Baseband and Broadband

• Baseband is a transmission form in which (typically) digital signals are sent through direct current (DC) pulses applied to the wire

• Supports half-duplexing

• Ethernet is an example of a baseband system found on many LANs


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• Broadband is a form of transmission in which signals are modulated as radio frequency (RF) analog waves that use different frequency ranges

• Does not encode information as digital pulses

• Is used to bring cable TV to your home

• Is generally more expensive than baseband

• Can span longer distances than baseband


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• Transmission Flaws

• Noise is any undesirable influence that may degrade or distort a signal

• Crosstalk occurs when a signal traveling on one wire or cable infringes on the signal traveling over an adjacent wire or cable

• Attenuation is the loss of a signal’s strength as it travels away from its source


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• Latency is a delay between the transmission of a signal and its eventual receipt

• The most common way to measure latency on data networks is by calculating a packet’s round trip time (RTT), or the length of time it takes for a packet to go from sender to receiver, then back from receiver to sender

• RTT is usually measured in milliseconds


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Media Characteristics

• Five characteristics are considered when choosing a data transfer media:

• Throughput

• Costs

• Size and Scalability

• Connectors

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• Noise Immunity

• The type of media least susceptible to noise is fiber-optic cable

Media Characteristics (continued)

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• Because of its shielding, most coaxial cable has a high resistance to noise

• Coaxial cable is more expensive than twisted-pair cable because it requires significantly more raw materials to manufacture

• The significant differences between the cable types lie in the materials used for their center cores, which in turn influence their impedance

Coaxial Cable

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• Thicknet (10Base5) Ethernet

• Also called thick wire Ethernet, is a rigid coaxial cable approximately 1-cm thick that contains a solid copper core

• Thicknet is sometimes called “yellow Ethernet” or “yellow garden hose”

Coaxial Cable (continued)

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• IEEE designates Thicknet as 10Base5 Ethernet

• Thicknet uses a vampire tap and must abide by the 5-4-3 rule of networking.


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• Thinnet (10Base2) Ethernet

• Also known as thin Ethernet

• Because of its black sheath, Thinnet may also be called “black Ethernet”


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• Its core is typically made of several thin strands of copper

• Thinnet is less expensive than Thicknet and fiber-optic cable, but more expensive than twisted-pair wiring


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• Both Thicknet and Thinnet coaxial cable rely on the bus topology, in which nodes share one uninterrupted channel

• Networks using the bus topology must be terminated at both ends

• Without terminators, signals on a bus network would travel endlessly between the two ends of the network, a phenomenon known as signal bounce


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Twisted-Pair Cable

• Twisted-pair cable consists of color-coded pairs of insulated copper wires

• Every two wires are twisted around each other to form pairs and all the pairs are encased in a plastic sheath

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Twisted-Pair Cable (continued)

• The number of pairs in a cable varies, depending on the cable type

• The more twists per inch in a pair of wires, the more resistant the pair will be to all forms of noise

• The number of twists per meter or foot is known as the twist ratio

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• Twisted-pair cable is the most common form of cabling found on LANs today

• It is relatively inexpensive, flexible, and easy to install, and it can span a significant distance before requiring a repeater (though not as far as coax)


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• All twisted-pair cable falls into one of two categories: shielded twisted-pair (STP) or unshielded twisted-pair (UTP)

• Unshielded twisted-pair (UTP) • Consists of one or more insulated wire pairs

encased in a plastic sheath


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• 10BaseT

• A popular Ethernet networking standard that replaced the older 10Base2 and 10Base5 technologies

• The “10” represents its maximum throughput of 10 Mbps, the “Base” indicates that it uses baseband transmission, and the “T” stands for twisted pair, the medium it uses


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• 10BaseT

• On a 10BaseT network, one pair of wires in the UTP cable is used for transmission, while a second pair of wires is used for reception allowing full-duplex transmission


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• 100BaseT (Fast Ethernet)

• Also known as Fast Ethernet

• Uses base band transmission

• Configured in a star topology

• 100BaseT networks do not follow the 5-4-3 rule


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• 100BaseTX

• Requires CAT 5 or higher unshielded twisted-pair cabling

• Within the cable, it uses the same two pairs of wire for transmitting and receiving data

• Capable of full duplex transmission


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Fiber-Optic Cable

• Contains one or several glass or plastic fibers at its center, or core

• Data is transmitted via pulsing light sent from a laser or light-emitting diode (LED) through the central fibers

• Surrounding the fibers is a layer of glass or plastic called cladding

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• Fiber cable variations fall into two categories:

• Single-mode

• Multimode

Fiber-Optic Cable (continued)

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• Single-mode fiber

• Uses a narrow core (less than 10 microns in diameter) through which light generated by a laser travels over one path, reflecting very little

• Allows high bandwidths and long distances (without requiring repeaters)

• Costs too much to be considered for use on typical data networks


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• Multimode fiber

• Contains a core with a diameter between 50 and 115 microns in diameter; the most common size is 62.5 microns over which many pulses of light generated by a laser or LED travel at different angles

• It is commonly found on cables that connect a router to a switch or a server on the backbone of a network


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• 100BaseFX standard

• The 100BaseFX standard specifies a network capable of 100-Mbps throughput that uses baseband transmission and fiber-optic cabling

• 100BaseFX requires multimode fiber containing at least two strands of fiber


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• 1000BaseLX standard

• The most common 1-Gigabit Physical layer standard in use today, can reach 5000 meters and use one repeater between segments


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Cable Design and Management

• Cable plant

• Demarcation point (or demarc)

• Backbone wiring

• Punch-down block

• Patch panel

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Installing Cable

• Straight-through cable is so named because it allows signals to pass “straight through” between terminations

• Crossover cable is a patch cable in which the termination locations of the transmit and receive wires on one end of the cable are reversed

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Installing Cable (continued)

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Wireless Transmission

• Wireless LANs typically use infrared or radiofrequency (RF) signaling

• Characteristics of Wireless Transmission

• Antennas are used for both the transmission and reception of wireless signals

• To exchange information, two antennas must be tuned to the same frequency

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Wireless Spectrum

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Wireless Transmission (continued)

• Signal Propagation

• Line-of-sight (LOS)

• Signal Degradation

• Wireless signals also experience attenuation

• Wireless signals are also susceptible to noise (often called “interference”)

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Choosing The Right Transmission Medium

• Most environments will contain a combination of these factors; you must therefore weigh the significance of each

• Areas of high EMI

• Distance

• Security

• Existing infrastructure

• Growth

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Summary

• Identify organizations that set standards for networking

• Purpose of the OSI Model and each of its layers

• Specific functions belonging to each OSI Model layer

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Summary (continued)

• Networking nodes to communicate through the OSI Model

• Structure and purpose of data packets and frames

• Two types of addressing covered by the OSI Model

chapter 3: transmission basics and networking media network+ guide to networks third edition

Documents

network medium transmission

data network

transmission basics

network nodes

digital signals

throughput transmission

multiple signals

transmission form