Tài liệu học CCNA kỳ 1 mod4 cabletesting

1 Module 4 – Cable Testing NIIT-ICT Hanoi info@niithanoi.vn 2 Overview Students completing this module should be able to: • Differentiate between sine waves and square waves. • Define and calculate exponents and logarithms. • Define and calculate decibels. • Define basic terminology related to time, frequency, and noise. • Differentiate between digital bandwidth and analog bandwidth. • Compare and contrast noise levels on various types of cabling. • Define and describe the affects of attenuation and impedance mismatch. • Define crosstalk, near-end crosstalk, far-end crosstalk, and power sum near-end crosstalk. • Describe how crosstalk and twisted pairs help reduce noise. • Describe the ten copper cable tests defined in TIA/EIA-568-B. • Describe the difference between Category 5 and Category 6 cable. 2 NIIT-ICT Hanoi info@niithanoi.vn 3 Background for Studying Frequency • Differentiate between sine waves and square waves. • Define and calculate exponents and logarithms. • Define and calculate decibels. • Define basic terminology related to time, frequency, and noise. • Differentiate between digital bandwidth and analog bandwidth. NIIT-ICT Hanoi info@niithanoi.vn 4 Amplitude and Frequency • A wave is type of energy traveling from one place to another. • Example: voltage waves in copper wires, light waves in fiber optic cables electromagnetic waves in wireless communication. 3 NIIT-ICT Hanoi info@niithanoi.vn 5 Analog Signal NIIT-ICT Hanoi info@niithanoi.vn 6 Digital Signals • Square waves, 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. • This value is held for some time, and then quickly changes back to the original value. • Square waves represent digital signals, or pulses. Like all waves, square waves can be described in terms of amplitude, period, and frequency. 4 NIIT-ICT Hanoi info@niithanoi.vn 7 Numbering Systems = + = 17 (decimal) 1 ×10 + 7×10 1 0 1×2 + 1×2 4 0 += = 10001 (binary) 1×16 + 1×16 1 0 += = 11 (hexadecimal) • Three important number systems: – Binary (base 2), – Decimal (base 10), – Hexadecimal (base 16). • Binary system uses 2 symbols: 0,1. • Decimal system uses 10 symbols: 0,1,2,3,4,5,6,7,8,9. • Hexadecimal system uses 16 symbols: 0,1, ,9,A,B,C,D,E,F • Example: using the Windows program CALC to perform conversion among number systems NIIT-ICT Hanoi info@niithanoi.vn 8 Exponents and Logarithms x y y = x 0 1 1 y = 10 x y = log x 10 5 NIIT-ICT Hanoi info@niithanoi.vn 9 Decibels • The decibel (dB) is a measurement unit important in describing networking signals. • The decibel is related to the exponents and logarithms described in prior sections. • There are two formulas for calculating decibels: dB = 10 log 10 (P final / P ref ) dB = 20 log 10 (V final / V reference ) NIIT-ICT Hanoi info@niithanoi.vn 10 Decibels There are two formulas for calculating decibels: dB = 10 log 10 (P final / P ref ) dB = 20 log 10 (V final / V reference ) 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 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 6 NIIT-ICT Hanoi info@niithanoi.vn 11 Code and Encode • Information (text, voice, picture, video, ) can be represented electrically by voltage patterns. • The data represented by these voltage patterns can be converted to light waves or radio waves, etc. (signals) to be transmitted over a media, and then back to voltage waves at the receiver. • Carrier refers to the signal/waves that carries the information. • Example: phone system transmitting voice, wireless communication, Ethernet. Infomation is travelling in digital signals Infomation is travelling in analog signals NIIT-ICT Hanoi info@niithanoi.vn 12 Viewing signals in time and frequency • An oscilloscope is an important electronic device used to view electrical signals such as voltage waves and pulses. • The x-axis on the display represents time, and the y-axis represents voltage or current. • There are usually two y-axis inputs, so two waves can be observed and measured at the same time. • Analyzing signals using an oscilloscope is called time-domain analysis, because the x-axis or domain of the mathematical function represents time. • Frequency-domain analysis has the x-axis representing frequency. Spectrum analyzer is the device that produde such the graph. 7 NIIT-ICT Hanoi info@niithanoi.vn 13 Analog and digital signals in time and frequency • To understand the complexities of networking signals and cable testing, examine how analog signals vary with time and with frequency. • Imagine the combination of several sine waves. a 2 f(x) ∼ F(x) = + [ a . sin (nx) + b . cos (nx) ] Σ n = 1 ∞ 0 nn NIIT-ICT Hanoi info@niithanoi.vn 14 Example 8 NIIT-ICT Hanoi info@niithanoi.vn 15 Noise in time and frequency • Noise is an important concept in communications systems, including LANS. • While noise usually refers to undesirable sounds, 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. • Even though noise cannot be eliminated, its effects can be minimized if the sources of the noise are understood. NIIT-ICT Hanoi info@niithanoi.vn 16 Noise in time and frequency There are many possible sources of noise: • Nearby cables which carry data signals • Radio frequency interference (RFI), which is noise from other signals being transmitted nearby • Electromagnetic interference (EMI), which is noise from nearby sources such as motors and lights 9 NIIT-ICT Hanoi info@niithanoi.vn 17 Narrowband Interference and White Noice Narrowband Interference White Noice • White noice affects all transmission frequencies. • Narowband interference only affects small ranges of frequencies. NIIT-ICT Hanoi info@niithanoi.vn 18 Signals and Noise • Compare and contrast noise levels on various types of cabling. • Define and describe the affects of attenuation and impedance mismatch. • Define crosstalk, near-end crosstalk, far-end crosstalk, and power sum near-end crosstalk. • Describe how crosstalk and twisted pairs help reduce noise. • Describe the ten copper cable tests defined in TIA/EIA-568-B. • Describe the difference between Category 5 and Category 6 cable. 10 NIIT-ICT Hanoi info@niithanoi.vn 19 Signaling over coper and fiber optic cabling • On copper cable, data signals are represented by voltage levels that represent binary ones and zeros. • The zero-voltage reference is called the signal ground. • If the transmitter and the receiver volt reference point are equal, they are said to be properly grounded. • Fiber optic cable is used to transmit data signals by increasing and decreasing the intensity of light to represent binary ones and zeros. • Optical signals are NOT affected by electrical noise, and optical fiber does NOT need to be grounded. • As price decrease and speed increase, optical fiber is more and more popular. NIIT-ICT Hanoi info@niithanoi.vn 20 Coaxial • Coaxial cable consists of a solid copper conductor surrounded by insulating material, and then braided conductive shielding. • 10Base-2: (thinnet) Ethernet 10 Mpbs, 185 m, BNC connector, 50 Ω. • 10Base-5: (thicknet) Ethernet 10 Mbps, 500 m, 50 Ω. [...]... shielded RJ45, 10 0m, 15 0 Ω ScTP (Screened TwistedPair) or FTP (Foiled TwistedPair) is similar with STP, with exeption that there is no inner foil shields Connector: shielded RJ45, 10 0m, 10 0 Ω 21 UTP • • • • • NIIT-ICT Hanoi info@niithanoi.vn UTP (Unshielded TwistedPair) has no shield This is the most popular cable used in LAN Connector: RJ45 10 0 m 10 0 Ω There are several categories: Cat -1, Cat-2, Cat-3,... NIIT-ICT Hanoi info@niithanoi.vn 31 Cable testing standards • • • The 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 The wires in UTP cable must be connected to the proper pins at each end of a cable NIIT-ICT Hanoi info@niithanoi.vn 32 16 Cable testing standards • The wire... (Unshielded TwistedPair) has no shield This is the most popular cable used in LAN Connector: RJ45 10 0 m 10 0 Ω There are several categories: Cat -1, Cat-2, Cat-3, Cat-4, Cat-5, Cat-5e, Cat-6, Cat-7, 22 11 Attenuation and insertion loss on copper media “good” original signal • • attenuation Attenuation is the decrease in signal amplitude over the length of a link Long cable lengths and high signal frequencies... title of the standard is ANSI/TIA/EIA-568-B.2 -1 Although the 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 NIIT-ICT Hanoi info@niithanoi.vn 38 19 Summary NIIT-ICT Hanoi info@niithanoi.vn... 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 NIIT-ICT Hanoi info@niithanoi.vn 28 14 Far-end Crosstalk (FEXT) • • • • Due to attenuation, crosstalk occurring further away from the transmitter creates less noise on a cable than NEXT This is called far-end crosstalk, or FEXT The noise... 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 NIIT-ICT Hanoi info@niithanoi.vn 30 15 Cable testing standards The ten primary test parameters that must be verified for a cable link to meet TIA/EIA standards are: • Wire map • Insertion loss • Near-end crosstalk (NEXT) • Power sum near-end... discontinuity or impedance mismatch, which causes reflection The combination of the effects of signal attenuation and impedance discontinuities on a communications link is called insertion loss jitter 24 12 Twisted-pair Cable • • • GOOD connector BAD connector: wires are untwisted too long NIIT-ICT Hanoi info@niithanoi.vn TIA/EIA-568-B certification of a cable requires testing for a variety of types of... verifies that all eight wires are connected to the correct pins on both ends of the cable • There are several different wiring faults that the wire map test can detect NIIT-ICT Hanoi info@niithanoi.vn 34 17 Time-based parameters • • Testers measure the length of the wire based on the electrical delay as measured by a Time Domain Reflectometry (TDR) test, not by the physical length of the cable jacket Since... signal recognition difficult Just as with UTP cable, improperly installed connectors are the main cause of light reflection and signal strength loss in optical fiber NIIT-ICT Hanoi info@niithanoi.vn 36 18 Testing optical fiber • Absence of electrical signals • There are no crosstalk problems on fiber optic cable • External electromagnetic interference or noise has no affect on fiber cabling • Attenuation... instruments measure crosstalk by applying a test signal to one wire pair The cable tester then measures the amplitude of the unwanted crosstalk signals induced on the other wire pairs in the cable 26 13 Types of crosstalk There are three distinct types of crosstalk: • Near-end Crosstalk (NEXT) • Far-end Crosstalk (FEXT) • Power Sum Near-end Crosstalk (PSNEXT) NIIT-ICT Hanoi info@niithanoi.vn 27 Near-end