Cisco CCNA Semester 1 Chapter 4 V3.0 By: Terren L. Bichard

Overview Networking media is literally and physically the backbone of the network.Networking media is literally and physically the backbone of the network. –Poor quality results in network failures and unreliability. All media requires testing to determine quality.All media requires testing to determine quality.

Goals Part OnePart One –Provide basic definitions Part TwoPart Two –Describes issues relating to the testing of media used for connectivity.

Definitions Wave = energy traveling from one place to anotherWave = energy traveling from one place to another –Caused by disturbances. AmplitudeAmplitude –Height measured in meters PeriodPeriod –Length of time between cycles FrequencyFrequency –number of cycles per second measured in Hertz

Types of Waves Copper wireCopper wire –Voltage waves Optical fiberOptical fiber –Light waves PulsePulse –A disturbance which is deliberately caused, and involves a fixed, predictable duration

Sine Waves Sine waves have certain characteristics.Sine waves have certain characteristics. Sine waves are periodicSine waves are periodic –They repeat the same pattern at regular intervals. Sine waves are continuously varyingSine waves are continuously varying –No two adjacent points on the graph have the same value.

Square Waves Like sine waves are periodic.Like sine waves are periodic. –However, square wave graphs do not continuously vary with time. The wave holds one value for some time, and then suddenly changes to a different value.The wave holds one value for some time, and then suddenly changes to a different value. This value is held for some time, and then quickly changes back to the original value.This value is held for some time, and then quickly changes back to the original value. Square waves represent digital signals, or pulses.Square waves represent digital signals, or pulses. –Like all waves, square waves can be described in terms of amplitude, period, and frequency.

Exponents and Logarithms In networking, there are three important number systems:In networking, there are three important number systems: –Base 2 – binary –Base 10 – decimal –Base 16 – hexadecimal The base of a number system refers to the number of different symbols that can occupy one positionThe base of a number system refers to the number of different symbols that can occupy one position

Example Binary numbersBinary numbers –2 positions 0 & 10 & 1 Decimal numbersDecimal numbers –10 positions Hexadecimal numbersHexadecimal numbers –16 positions 0-9 and A-F0-9 and A-F

Decibels A measurement unit important in describing networking signals. (dB)A measurement unit important in describing networking signals. (dB) There are two formulas for calculating decibels:There are two formulas for calculating decibels: dB = 10 log 10 (P final / P ref )dB = 10 log 10 (P final / P ref ) dB = 20 log 10 (V final / V reference )dB = 20 log 10 (V final / V reference )

The variables represent the following values.The variables represent the following values. –dB measures the loss or gain of the power of a wave. Decibels are usually negative numbers representing a loss in power as the wave travels, but can also be positive values representing a gain in power if the signal is amplifiedDecibels are usually negative numbers representing a loss in power as the wave travels, but can also be positive values representing a gain in power if the signal is amplified –log 10 implies that the number in parenthesis will be transformed using the base 10 logarithm rule –P final is the delivered power measured in Watts –P ref is the original power measured in Watts –V final is the delivered voltage measured in Volts –V reference is the original voltage measured in Volts

Formulas Db = 10 log 10 (P final / P ref )Db = 10 log 10 (P final / P ref ) –Describes decibels in terms of power (P) Db = 20 log 10 (V final / V reference )Db = 20 log 10 (V final / V reference ) –Describes decibels in terms of voltage (V) Typically, light waves on optical fiber and radio waves in the air are measured using the power formula.Typically, light waves on optical fiber and radio waves in the air are measured using the power formula. Electromagnetic waves on copper cables are measured using the voltage formula.Electromagnetic waves on copper cables are measured using the voltage formula.

Signals and Frequency One of the most important facts of the information age is that data symbolizing characters, words, pictures, video, or music can be represented electrically by voltage patterns on wires and in electronic devices.One of the most important facts of the information age is that data symbolizing characters, words, pictures, video, or music can be represented electrically by voltage patterns on wires and in electronic devices. Data represented by these voltage patterns can be converted to light waves or radio waves, and then back to voltage waves.Data represented by these voltage patterns can be converted to light waves or radio waves, and then back to voltage waves. –The sound waves of the caller’s voice, on a telephone, enter a microphone in the telephone. –The microphone converts the patterns of sound energy into voltage patterns of electrical energy that represent the voice.

Viewing Signals An oscilloscope is an important electronic device used to view electrical signals such as voltage waves and pulses.An oscilloscope is an important electronic device used to view electrical signals such as voltage waves and pulses.

Spectrum Analyzer List Price: $24,000.00

Noise in Time and Frequency Noise is an important concept in communications systems, including LANS.Noise is an important concept in communications systems, including LANS. Noise related to communications refers to undesirable signals.Noise related to communications refers to undesirable signals. Noise can originate from natural and technological sources, and is added to the data signals in communications systems.Noise can originate from natural and technological sources, and is added to the data signals in communications systems.

Noise All communications systems have some amount of noise.All communications systems have some amount of noise. Noise cannot be eliminatedNoise cannot be eliminated –Effects can be minimized if the sources of the noise are understood. Many possible sources of noise:Many possible sources of noise: –Nearby cables which carry data signals –Radio frequency interference (RFI) Noise from other signals being transmitted nearbyNoise from other signals being transmitted nearby –Electromagnetic interference (EMI) Noise from nearby sources such as motors and lightsNoise from nearby sources such as motors and lights Laser noise at the transmitter or receiver of an optical signalLaser noise at the transmitter or receiver of an optical signal

Different Types of Noise White noiseWhite noise –Noise that affects all transmission frequencies When detected on a radio receiver, white noise would interfere with all radio stations.When detected on a radio receiver, white noise would interfere with all radio stations. When detected on a LAN, white noise would affect all data transmissionsWhen detected on a LAN, white noise would affect all data transmissions Narrowband interferenceNarrowband interference –Noise that only affects small ranges of frequencies Narrowband interference would affect only a few stations whose frequencies are close together.Narrowband interference would affect only a few stations whose frequencies are close together. Narrowband interference might disrupt only certain signals. If the band of frequencies affected by the narrowband interference included all frequencies transmitted on the LAN, then the performance of the entire LAN would be compromised.Narrowband interference might disrupt only certain signals. If the band of frequencies affected by the narrowband interference included all frequencies transmitted on the LAN, then the performance of the entire LAN would be compromised.

Bandwidth Two types of bandwidth on LANs are analog bandwidth and digital bandwidth.Two types of bandwidth on LANs are analog bandwidth and digital bandwidth. Analog bandwidthAnalog bandwidth –radio station frequencies –an electronic amplifier –The units of measurement for analog bandwidth is Hertz analog bandwidth values are 3 kHz for telephonyanalog bandwidth values are 3 kHz for telephony 20 kHz for audible signals20 kHz for audible signals 5 kHz for AM radio stations5 kHz for AM radio stations 200 MHz for FM radio stations.200 MHz for FM radio stations.

Bandwidth (cont.) Digital bandwidth measures how much information can flow from one place to another in a given amount of time.Digital bandwidth measures how much information can flow from one place to another in a given amount of time. –The unit of measurement for digital bandwidth is bits per second (bps). –Since LANs are capable of speeds of millions of bits per second, measurement is expressed in kilobits per second (Kbps) or megabits per second (Mbps). –Physical media, current technologies, and the laws of physics limit bandwidth.

Bandwidth (cont.) During cable testing, analog bandwidth is used to determine the digital bandwidth of a copper cable.During cable testing, analog bandwidth is used to determine the digital bandwidth of a copper cable. Analog frequencies are transmitted from one end and received on the opposite end.Analog frequencies are transmitted from one end and received on the opposite end. The two signals are then compared, and the amount of attenuation of the signal is calculated.The two signals are then compared, and the amount of attenuation of the signal is calculated. In general, media that will support higher analog bandwidths without high degrees of attenuation will also support higher digital bandwidths.In general, media that will support higher analog bandwidths without high degrees of attenuation will also support higher digital bandwidths.

Signaling Over Copper and Fiber Cable On copper cable, data signals are represented by voltage levels that represent binary ones and zeros.On copper cable, data signals are represented by voltage levels that represent binary ones and zeros. Voltage levels are measured with respect to a reference level of zero volts at both the transmitter and the receiver.Voltage levels are measured with respect to a reference level of zero volts at both the transmitter and the receiver. This reference level is called the signal ground.This reference level is called the signal ground. It is important that both transmitting and receiving devices refer to the same zero volt reference point.It is important that both transmitting and receiving devices refer to the same zero volt reference point. –When they do, they are said to be properly grounded. –When they do, they are said to be properly grounded.

Signaling Over Copper and Fiber Cables In order for the LAN to operate properly, the receiving device must be able to accurately interpret the binary ones and zeros transmitted as voltage levels.In order for the LAN to operate properly, the receiving device must be able to accurately interpret the binary ones and zeros transmitted as voltage levels. As technology progresses it is critical that all devices and media meet highest standards of excellence.As technology progresses it is critical that all devices and media meet highest standards of excellence.

Copper Cable Two basic typesTwo basic types –Unshielded UTPUTP –Shielded STPSTP CoaxCoax

Fiber Optic Cable Transmits data signals by increasing and decreasing the intensity of light to represent binary ones and zeros.Transmits data signals by increasing and decreasing the intensity of light to represent binary ones and zeros. Not affected by electrical noiseNot affected by electrical noise Does not need to be groundedDoes not need to be grounded Used between buildings and between floors within the buildingUsed between buildings and between floors within the building

Attenuation on Copper Media AttenuationAttenuation –The decrease in signal amplitude over the length of a link –Expressed in decibels (db) using negative numbers –The larger the number the better the link.

Sources of Noise on Copper Noise is any electrical energy on the transmission cable that makes it difficult for a receiver to interpret the data sent from the transmitter.Noise is any electrical energy on the transmission cable that makes it difficult for a receiver to interpret the data sent from the transmitter. –Crosstalk The transmission of signals from one wire to a nearby wire.The transmission of signals from one wire to a nearby wire. Twisting one pair of wires in a cable also helps to reduce crosstalk of data or noise signals from an adjacent wire pair.Twisting one pair of wires in a cable also helps to reduce crosstalk of data or noise signals from an adjacent wire pair.

Three Types of Crosstalk Near-end Crosstalk (NEXT)Near-end Crosstalk (NEXT) Far-end Crosstalk (FEXT)Far-end Crosstalk (FEXT) Power Sum Near-end Crosstalk (PSNEXT)Power Sum Near-end Crosstalk (PSNEXT)

NEXT Near-end crosstalk (NEXT) is computed as the ratio of voltage amplitude between the test signal and the crosstalk signal when measured from the same end of the link.Near-end crosstalk (NEXT) is computed as the ratio of voltage amplitude between the test signal and the crosstalk signal when measured from the same end of the link. This difference is expressed in a negative value of decibels (dB).This difference is expressed in a negative value of decibels (dB). –Low negative numbers indicate more noise, just as low negative temperatures indicate more heat.

FEXT Far-End crosstalk, or FEXT.Far-End crosstalk, or FEXT. Crosstalk occurring further away from the transmitter creates less noise on a cable than NEXT.Crosstalk occurring further away from the transmitter creates less noise on a cable than NEXT. Noise caused by FEXT still travels back to the source, but it is attenuated as it returns.Noise caused by FEXT still travels back to the source, but it is attenuated as it returns. FEXT is not as significant a problem as NEXT.FEXT is not as significant a problem as NEXT.

PSNEXT Power Sum NEXT (PSNEXT) measures the cumulative effect of NEXT from all wire pairs in the cable.Power Sum NEXT (PSNEXT) measures the cumulative effect of NEXT from all wire pairs in the cable. PSNEXT is computed for each wire pair based on the NEXT effects of the other three pairs.PSNEXT is computed for each wire pair based on the NEXT effects of the other three pairs. The combined effect of crosstalk from multiple simultaneous transmission sources can be very detrimental to the signal.The combined effect of crosstalk from multiple simultaneous transmission sources can be very detrimental to the signal. TIA/EIA-568-B certification now requires this PSNEXT test.TIA/EIA-568-B certification now requires this PSNEXT test.

Cable Testing Standards The TIA/EIA-568-B standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs.The TIA/EIA-568-B standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs. The ten primary test parameters that must be verified for a cable link to meet TIA/EIA standards are:The ten primary test parameters that must be verified for a cable link to meet TIA/EIA standards are:

Cable Testing Standards Wire mapWire map Insertion lossInsertion loss Near-end crosstalk (NEXT)Near-end crosstalk (NEXT) Power sum near-end crosstalk (PSNEXT)Power sum near-end crosstalk (PSNEXT) Equal-level far-end crosstalk (ELFEXT)Equal-level far-end crosstalk (ELFEXT) Power sum equal-level far-end crosstalk (PSELFEXT)Power sum equal-level far-end crosstalk (PSELFEXT) Return lossReturn loss Propagation delayPropagation delay Cable lengthCable length Delay skewDelay skew

Cable Testing Standards Ethernet standard specifies that each of the pins on an RJ-45 connector have a particular purpose.Ethernet standard specifies that each of the pins on an RJ-45 connector have a particular purpose. A NIC transmits signals on pins 1 and 2, and it receives signals on pins 3 and 6.A NIC transmits signals on pins 1 and 2, and it receives signals on pins 3 and 6.

Wiring Tests Wire map test insures that no open or short circuits existWire map test insures that no open or short circuits exist Reversed-pair fault occurs when a wire pair is correctly installed on one connector, but reversed on the other connector.Reversed-pair fault occurs when a wire pair is correctly installed on one connector, but reversed on the other connector. Split-pair wiring fault occurs when two wires from different wire pairs are connected to the wrong pins on both ends of the cable.Split-pair wiring fault occurs when two wires from different wire pairs are connected to the wrong pins on both ends of the cable. Transposed-pair wiring faults occur when a wire pair is connected to completely different pins at both ends.Transposed-pair wiring faults occur when a wire pair is connected to completely different pins at both ends.

Other Test Parameters Insertion loss = the combination of the effects of signal attenuation and impedance discontinuities on a communications link.Insertion loss = the combination of the effects of signal attenuation and impedance discontinuities on a communications link. –Insertion loss is measured in decibels at the far end of the cable. –The TIA/EIA standard requires that a cable and its connectors pass an insertion loss test before the cable can be used as a communications link in a LAN. –The TIA/EIA standard requires that a cable and its connectors pass an insertion loss test before the cable can be used as a communications link in a LAN.

Other Test Parameters Crosstalk is measured in four separate tests.Crosstalk is measured in four separate tests. –PSNEXT Power Sum equal-level Far-End CrosstalkPower Sum equal-level Far-End Crosstalk –FEXT Far-End crosstalkFar-End crosstalk –ELFEXT Equal-Level Far-End CrosstalkEqual-Level Far-End Crosstalk –PSELFEXT is the combined effect of ELFEXT from all wire pairs.is the combined effect of ELFEXT from all wire pairs.

Other Test Parameters Return lossReturn loss –measure in decibels of reflections that are caused by the impedance discontinuities at all locations along the link.

Time-Based Parameters Propagation delayPropagation delay –How long it takes for a signal to travel (propagate) along the cable being tested. delay in a wire pair depends on its length, twist rate, and electrical properties.delay in a wire pair depends on its length, twist rate, and electrical properties. Cable LengthCable Length –TDR test is used not only to determine length, but also to identify the distance to wiring faults such as shorts and opens. Delay SkewDelay Skew –The delay difference between pairs is called.

Testing Optical Fiber A fiber link consists of two separate glass fibers functioning as independent data pathways.A fiber link consists of two separate glass fibers functioning as independent data pathways. Testing fiber optic cable primarily involves shining a light down the fiber and measuring whether a sufficient amount of light reaches the receiver.Testing fiber optic cable primarily involves shining a light down the fiber and measuring whether a sufficient amount of light reaches the receiver.

Testing Optical Fiber Optical link loss budget.Optical link loss budget. –The acceptable amount of signal power loss that can occur without dropping below the requirements of the receiver.

New Cat 6 Standard On June 20, 2002, the Category 6 (or Cat 6) addition to the TIA-568 standard was published.On June 20, 2002, the Category 6 (or Cat 6) addition to the TIA-568 standard was published. –The official title of the standard is ANSI/TIA/EIA- 568-B.2-1 Cat 6 tests are essentially the same as those specified by the Cat 5 standard.Cat 6 tests are essentially the same as those specified by the Cat 5 standard. –Cat 6 cable must pass the tests with higher scores to be certified. –Cat6 cable must be capable of carrying frequencies up to 250 MHz and must have lower levels of crosstalk and return loss.

Summary Waves are energy traveling from one place to another, and are created by disturbances.Waves are energy traveling from one place to another, and are created by disturbances. –All waves have similar attributes such as amplitude, period, and frequency. Sine waves are periodic, continuously varying functions.Sine waves are periodic, continuously varying functions. –Analog signals look like sine waves. Square waves are periodic functions whose values remain constant for a period of time and then change abruptly.Square waves are periodic functions whose values remain constant for a period of time and then change abruptly. –Digital signals look like square waves.

Summary (cont) Exponents are used to represent very large or very small numbers.Exponents are used to represent very large or very small numbers. –The base of a number raised to a positive exponent is equal to the base multiplied by itself exponent times. For example, 10 3 = 10x10x10 = 1000.For example, 10 3 = 10x10x10 = Logarithms are similar to exponents.Logarithms are similar to exponents. –A logarithm to the base of 10 of a number equals the exponent to which 10 would have to be raised in order to equal the number. For example, log = 3 because 10 3 = 1000.For example, log = 3 because 10 3 = 1000.

Summary (cont) Decibels are measurements of a gain or loss in the power of a signal.Decibels are measurements of a gain or loss in the power of a signal. –Negative values represent losses and positive values represent gains. Time-domain analysis is the graphing of voltage or current with respect to time using an oscilloscope.Time-domain analysis is the graphing of voltage or current with respect to time using an oscilloscope. Frequency-domain analysis is the graphing of voltage or power with respect to frequency using a spectrum analyzer.Frequency-domain analysis is the graphing of voltage or power with respect to frequency using a spectrum analyzer.

Summary (Cont) Undesirable signals in a communications system are called noise.Undesirable signals in a communications system are called noise. –Noise originates from other cables, RFI, and EMI. White noise affects all frequencies, while narrowband interference affects only a certain subset of frequencies.White noise affects all frequencies, while narrowband interference affects only a certain subset of frequencies. Analog bandwidth is the frequency range that is associated with certain analog transmission, such as television or FM radio.Analog bandwidth is the frequency range that is associated with certain analog transmission, such as television or FM radio. Digital bandwidth measures how much information can flow from one place to another in a given amount of time.Digital bandwidth measures how much information can flow from one place to another in a given amount of time. –Its units are in various multiples of bits per second.

Summary (Cont) Most LAN problems occur at the physical layer.Most LAN problems occur at the physical layer. –The only way to prevent or troubleshoot many of these problems is through the use of cable testers. Proper cable installation according to standards increases LAN reliability and performance.Proper cable installation according to standards increases LAN reliability and performance. Copper media is available in shielded and unshielded forms.Copper media is available in shielded and unshielded forms. –Unshielded cable is more susceptible to noise.

Summary (Cont) Signal degradation is due to various factors such as noise, attenuation, impedance mismatch, and several types of crosstalk.Signal degradation is due to various factors such as noise, attenuation, impedance mismatch, and several types of crosstalk. –These factors cause decreased network performance. The TIA/EIA-568-B standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs.The TIA/EIA-568-B standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs. Optical fiber must also be tested according to networking standards.Optical fiber must also be tested according to networking standards. Category 6 cable must meet more rigorous frequency testing standards than Category 5 cable.Category 6 cable must meet more rigorous frequency testing standards than Category 5 cable.