Cable Testing
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CCNA 1 – Module 4 Cable Testing
1
CCNA 1 – Module 4 Objectives At the end of this module you will be able to: • • • • • • • • •
Differentiate between sine and square waves Define basic terminology related to time, frequency, and noise Differentiate between digital 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 tests used for copper cable defined in TIA/EIA 568-B Describe the difference between CAT-5 and CAT-6 cable 2
Waves • A wave is energy traveling from point to point • Voltage waves on copper media (light waves in optical fiber) use alternating electric and magnetic fields called the electromagnetic spectrum • Wave, or signal amplitude, represents height and is measured in volts • Wave period is the amount of time to complete one cycle (past a given point) and measured in seconds • Wave frequency is the number of complete cycles per second, measured in Hertz • If a disturbance is caused, and involves a fixed, predictable duration, then it is called a pulse. Pulses determine the value of the data being transmitted 3
Sine and Square Waves • Sine waves are mathematical functions with certain characteristics • Sine waves are periodic, (repeat the same pattern at regular intervals) and continuously varying (no two adjacent points have the same value). They are graphical representations of natural occurrences changing over time
• Square waves are periodic, however do not vary with time. They hold a value for some time, then suddenly changes to a different value. They represent digital signals, or pulses 4
Viewing Signals in Time and Frequency • An oscilloscope is an electronic device used to view electrical signals, such as voltage waves and pulses • The horizontal (x-axis) shows time, and the vertical (y-axis) shows 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 the oscilloscope is called timedomain analysis because the x-axis represents time 5
Noise in Time and Frequency • Noise usually refers to undesirable sounds, however noise in communications is undesirable • Possible sources for noise: – Nearby cables which carry data signals – RFI, is noise from other signals transmitted nearby – EMI, is noise from nearby sources such as motors and lights – Laser noise at the transmitter or receiver end of an optical (photonic) signal • Noise affecting all transmission frequencies is called white noise • Noise affecting only a small range of narrowband frequencies is called narrowband interference 6
Bandwidth • Two ways of considering bandwidth important to LANs is analog and digital bandwidth • Analog bandwidth describes the frequencies transmitted by a radio station or electronic amplifier. The unit of measurement is Hertz • Digital bandwidth measures how much information can flow from one place to another in a given amount of time. The unit of measurement is bits per second
7
Attenuation & Insertion Loss on Copper • Attenuation is the decrease in signal amplitude over the length of a link. Long cable runs and high signal frequencies contribute to greater signal attenuation • Attenuation on a cable is measured in decibels (dB), using negative numbers. Smaller negative dB values are an indication of better link performance • Impedance is the measurement of resistance of the cable to alternating current (AC), and measured in ohms. If a connector is improperly installed on a cable, it has a different impedance value than the cable, which is called impedance mismatch • Impedance mismatch causes attenuation because a portion of the transmitted signal is reflected back to the transmitting device, rather than continuing to the receiver • The combination of the effects of signal attenuation and impedance mismatch on a communications link is called insertion loss 8
Sources of Noise on Copper Media • Noise is electrical energy on the cable making it difficult for a receiver to interpret the data from the transmitter • Crosstalk involves the transmission of signals from one wire to a nearby wire. Adjacent wires in the cable act like antennas, receiving the transmitted energy, interfering with data on those wires • Cable testers measure crosstalk by applying a test signal on one wire pair. The tester then measures the amplitude of the unwanted crosstalk signals induced on the other wire pairs in the cable
9
Types of Crosstalk Three distinct kinds of crosstalk: • NEXT (Near-end Crosstalk) – computed as the ratio of voltage amplitude between the test signal and the crosstalk signal when measured from the same end • FEXT (Far-end Crosstalk) – crosstalk occurring further away from the transmitter, creating less noise on the cable as NEXT • PSNEXT (Power Sum NEXT) – 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 wire pairs 10
Cable Testing Standards Ten primary test parameters to be verified for a cable link to meet TIA/EIA standards are:
• • • • • • • • • •
Wire map Insertion loss NEXT – Near-end crosstalk PSNEXT – Power sum near-end crosstalk ELFEXT – Equal-level far-end crosstalk PSELFEXT – Power sum equal-level far-end crosstalk Return loss Propagation delay Cable length Delay skew 11
Wire Map Test • Ethernet standards specify each of the pins on the RJ45 connector have a specific purpose • A NIC transmits on pins 1 and 2, and receives on pins 3 and 6 • Wire map tests ensure no open or short circuits exist on the cable • Wire map tests also ensure all 8 wires are connected to the correct pins on both ends of the cable 12
Other Test Parameters • • •
Insertion loss is measured in decibels at the far end of the cable Crosstalk is measured in four separate tests A cable tester measures NEXT by applying a test signal on one cable pair and measuring the amplitude of the crosstalk received by the other cable pairs • ELFEXT measures FEXT, and is expressed in decibels as the difference between the measured FEXT and the insertion loss of the wire pair whose signal is disturbed by the FEXT • Return loss is a measure, in decibels, of reflections that are caused by impedance mismatches at all locations along the link. The main problem is that the signal echoes caused by the reflections from the impedance mismatches will strike the receiver at different time intervals causing jitter
13
Testing Optical Fiber •
•
•
•
Because noise is not an issue with optical fiber, the main concern on the fiber link is the strength of the light signal that arrives at the receiver If attenuation weakens the light signal at the receiver, then data errors will result The acceptable amount of signal power loss that can occur without dropping below the requirements of the receiver is called the optical link loss budget If the fiber test fails, the cable test instrument indicates where the optical discontinuities occur along the length of the cable link 14
Category 6 Cable • On June 20, 2002, the CAT-6 addition to the TIA-568 standard was published • Cables certified as CAT-6 must pass all ten tests as those for CAT-5 • The CAT-6 tests are essentially the same as those specified by the CAT-5 standard, but CAT-6 must pass the tests with higher scores to be certified • A quality cable tester similar to the Fluke DSP 4000 series or Fluke OMNIScanner 2 can perform all the test measurements for CAT-5, CAT-5e, and CAT-6
15
See the Fluke website for more details @ www.flukenetworks.com
Summary You should now be able to: • • • • • • • • •
Differentiate between sine and square waves Define basic terminology related to time, frequency, and noise Differentiate between digital 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 tests used for copper cable defined in TIA/EIA 568-B Describe the difference between CAT-5 and CAT-6 cable 16
Questions???
17
1
CCNA 1 – Module 4 Objectives At the end of this module you will be able to: • • • • • • • • •
Differentiate between sine and square waves Define basic terminology related to time, frequency, and noise Differentiate between digital 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 tests used for copper cable defined in TIA/EIA 568-B Describe the difference between CAT-5 and CAT-6 cable 2
Waves • A wave is energy traveling from point to point • Voltage waves on copper media (light waves in optical fiber) use alternating electric and magnetic fields called the electromagnetic spectrum • Wave, or signal amplitude, represents height and is measured in volts • Wave period is the amount of time to complete one cycle (past a given point) and measured in seconds • Wave frequency is the number of complete cycles per second, measured in Hertz • If a disturbance is caused, and involves a fixed, predictable duration, then it is called a pulse. Pulses determine the value of the data being transmitted 3
Sine and Square Waves • Sine waves are mathematical functions with certain characteristics • Sine waves are periodic, (repeat the same pattern at regular intervals) and continuously varying (no two adjacent points have the same value). They are graphical representations of natural occurrences changing over time
• Square waves are periodic, however do not vary with time. They hold a value for some time, then suddenly changes to a different value. They represent digital signals, or pulses 4
Viewing Signals in Time and Frequency • An oscilloscope is an electronic device used to view electrical signals, such as voltage waves and pulses • The horizontal (x-axis) shows time, and the vertical (y-axis) shows 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 the oscilloscope is called timedomain analysis because the x-axis represents time 5
Noise in Time and Frequency • Noise usually refers to undesirable sounds, however noise in communications is undesirable • Possible sources for noise: – Nearby cables which carry data signals – RFI, is noise from other signals transmitted nearby – EMI, is noise from nearby sources such as motors and lights – Laser noise at the transmitter or receiver end of an optical (photonic) signal • Noise affecting all transmission frequencies is called white noise • Noise affecting only a small range of narrowband frequencies is called narrowband interference 6
Bandwidth • Two ways of considering bandwidth important to LANs is analog and digital bandwidth • Analog bandwidth describes the frequencies transmitted by a radio station or electronic amplifier. The unit of measurement is Hertz • Digital bandwidth measures how much information can flow from one place to another in a given amount of time. The unit of measurement is bits per second
7
Attenuation & Insertion Loss on Copper • Attenuation is the decrease in signal amplitude over the length of a link. Long cable runs and high signal frequencies contribute to greater signal attenuation • Attenuation on a cable is measured in decibels (dB), using negative numbers. Smaller negative dB values are an indication of better link performance • Impedance is the measurement of resistance of the cable to alternating current (AC), and measured in ohms. If a connector is improperly installed on a cable, it has a different impedance value than the cable, which is called impedance mismatch • Impedance mismatch causes attenuation because a portion of the transmitted signal is reflected back to the transmitting device, rather than continuing to the receiver • The combination of the effects of signal attenuation and impedance mismatch on a communications link is called insertion loss 8
Sources of Noise on Copper Media • Noise is electrical energy on the cable making it difficult for a receiver to interpret the data from the transmitter • Crosstalk involves the transmission of signals from one wire to a nearby wire. Adjacent wires in the cable act like antennas, receiving the transmitted energy, interfering with data on those wires • Cable testers measure crosstalk by applying a test signal on one wire pair. The tester then measures the amplitude of the unwanted crosstalk signals induced on the other wire pairs in the cable
9
Types of Crosstalk Three distinct kinds of crosstalk: • NEXT (Near-end Crosstalk) – computed as the ratio of voltage amplitude between the test signal and the crosstalk signal when measured from the same end • FEXT (Far-end Crosstalk) – crosstalk occurring further away from the transmitter, creating less noise on the cable as NEXT • PSNEXT (Power Sum NEXT) – 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 wire pairs 10
Cable Testing Standards Ten primary test parameters to be verified for a cable link to meet TIA/EIA standards are:
• • • • • • • • • •
Wire map Insertion loss NEXT – Near-end crosstalk PSNEXT – Power sum near-end crosstalk ELFEXT – Equal-level far-end crosstalk PSELFEXT – Power sum equal-level far-end crosstalk Return loss Propagation delay Cable length Delay skew 11
Wire Map Test • Ethernet standards specify each of the pins on the RJ45 connector have a specific purpose • A NIC transmits on pins 1 and 2, and receives on pins 3 and 6 • Wire map tests ensure no open or short circuits exist on the cable • Wire map tests also ensure all 8 wires are connected to the correct pins on both ends of the cable 12
Other Test Parameters • • •
Insertion loss is measured in decibels at the far end of the cable Crosstalk is measured in four separate tests A cable tester measures NEXT by applying a test signal on one cable pair and measuring the amplitude of the crosstalk received by the other cable pairs • ELFEXT measures FEXT, and is expressed in decibels as the difference between the measured FEXT and the insertion loss of the wire pair whose signal is disturbed by the FEXT • Return loss is a measure, in decibels, of reflections that are caused by impedance mismatches at all locations along the link. The main problem is that the signal echoes caused by the reflections from the impedance mismatches will strike the receiver at different time intervals causing jitter
13
Testing Optical Fiber •
•
•
•
Because noise is not an issue with optical fiber, the main concern on the fiber link is the strength of the light signal that arrives at the receiver If attenuation weakens the light signal at the receiver, then data errors will result The acceptable amount of signal power loss that can occur without dropping below the requirements of the receiver is called the optical link loss budget If the fiber test fails, the cable test instrument indicates where the optical discontinuities occur along the length of the cable link 14
Category 6 Cable • On June 20, 2002, the CAT-6 addition to the TIA-568 standard was published • Cables certified as CAT-6 must pass all ten tests as those for CAT-5 • The CAT-6 tests are essentially the same as those specified by the CAT-5 standard, but CAT-6 must pass the tests with higher scores to be certified • A quality cable tester similar to the Fluke DSP 4000 series or Fluke OMNIScanner 2 can perform all the test measurements for CAT-5, CAT-5e, and CAT-6
15
See the Fluke website for more details @ www.flukenetworks.com
Summary You should now be able to: • • • • • • • • •
Differentiate between sine and square waves Define basic terminology related to time, frequency, and noise Differentiate between digital 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 tests used for copper cable defined in TIA/EIA 568-B Describe the difference between CAT-5 and CAT-6 cable 16
Questions???
17
