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Cable Testing. Introduction Networking media is the backbone of network. Networking media is the backbone of network. Inferior quality of network cabling.

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Presentation on theme: "Cable Testing. Introduction Networking media is the backbone of network. Networking media is the backbone of network. Inferior quality of network cabling."— Presentation transcript:

1 Cable Testing

2 Introduction Networking media is the backbone of network. Networking media is the backbone of network. Inferior quality of network cabling may cause network failures and unreliable performance. Inferior quality of network cabling may cause network failures and unreliable performance. Copper, optical fiber, and wireless networking media all require testing to determine the quality. Copper, optical fiber, and wireless networking media all require testing to determine the quality. These tests involve certain electrical and mathematical concepts and terms, such as signal, wave, frequency, and noise. These tests involve certain electrical and mathematical concepts and terms, such as signal, wave, frequency, and noise.

3 Student Should understand the concepts of: Sine waves and square waves. Sine waves and square waves. Calculate exponents and logarithms. Calculate exponents and logarithms. Calculate decibels. Calculate decibels. Time, frequency, and noise. Time, frequency, and noise. Digital and analog bandwidth. Digital and analog bandwidth. Noise levels Noise levels Attenuation and impedance mismatch. Attenuation and impedance mismatch. crosstalk, near-end crosstalk, far-end crosstalk, and power sum near-end crosstalk. crosstalk, near-end crosstalk, far-end crosstalk, and power sum near-end crosstalk. Grounding and wire twisting Grounding and wire twisting copper cable tests defined in TIA/EIA-568-B. copper cable tests defined in TIA/EIA-568-B. Category 5 and Category 6 cable. Category 5 and Category 6 cable.

4 Waves…….. A wave is energy traveling from one place to another. A wave is energy traveling from one place to another. It may be defined as any disturbance generated in any material, such as: It may be defined as any disturbance generated in any material, such as: –Throwing a stone in water –Sound (created by disturbance in air) –Electric supply at your house (electric impulses generated in conductor wire by providing a pressure/ force or voltage level.

5 Waves

6 Sine Waves They repeat the same pattern at regular intervals. They occur naturally and change regularly over time. No two adjacent points on a graph have the same value.

7 Square Waves They repeat the same pattern at regular intervals. They repeat the flat pattern on both the top and bottom of the wave. They do not continuously vary with time.

8 Signals Signals in a network can be represented in two different ways. Signals in a network can be represented in two different ways. Analog Signals Analog Signals Digital Signals Digital Signals

9 Time Length Analog Signals Is wavy Has a continuously varying voltage versus time graph Is typical of things in nature Has been widely used in Telecommunications for over 100 years

10 Digital Signal Digital signals have a square wave with instant transitions from low to high voltage states (0 to 1). Digital signals have a square wave with instant transitions from low to high voltage states (0 to 1). If voltage present then 1. If voltage present then 1. If no voltage then 0 If no voltage then 0

11 Networks Use Digital Signaling Bits are represented by either no voltage (0) or +3 to +6 Volts (1). Bits are represented by either no voltage (0) or +3 to +6 Volts (1). A Signal Reference Ground attached close to a computers digital circuits establishes the baseline for no voltage. A Signal Reference Ground attached close to a computers digital circuits establishes the baseline for no voltage. Bits must arrive at the destination undistorted in order to be properly interpreted. Bits must arrive at the destination undistorted in order to be properly interpreted. What six things can distort a bit? What six things can distort a bit?

12 Decibels The decibel (dB) is a measurement unit important in describing networking signals. The decibel is related to the exponents and logarithms. P final is the delivered power measured in Watts V final is the delivered voltage measured in Volts V reference is the original voltage measured in Volts

13 Viewing Signals in Time and Frequency

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15 Analog and Digital Signals in Time and Frequency

16 Bandwidth

17 Noise in Time and Frequency Noise is unwanted additions to the signal Noise is unavoidable Too much noise can corrupt a bit turning a binary 1 into a binary 0, or a 0 into a 1, thus destroying the message. There are five kinds of noise: NEXT A; Thermal Noise; Impulse/Reference Ground Noise; EMI/RFI; & NEXT B

18 Signaling over Copper and Fiber

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22 Attenuation and Insertion Loss on Copper Media Attenuation is the loss of signal strength. The signal degrades or losses amplitude as it travels (propagates) along the medium Loss of amplitude means that the receiving device can no longer distinguish a 1 bit from a 0 bit. Attenuation is prevented by: Not exceeding a mediums distance requirement (100 meters for Cat 5 cable) By using repeaters that amplify the signal

23 EMI/RFI Noise EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) attack the quality of electrical signals on the cable. EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) attack the quality of electrical signals on the cable. Sources of EMI/RFI include: Sources of EMI/RFI include: –Fluorescent lighting (EMI) –Electrical motors (EMI) –Radio systems (RFI)

24 EMI/RFI Noise Example Source computer sends out a digital signal. Along the path, the signal encounters EMI noise. Along the path, the signal encounters EMI noise. The digital signal and EMI combine to distort the signal. The digital signal and EMI combine to distort the signal. Digital Signal EMI Distorted Signal

25 EMI/RFI Noise Two ways to prevent EMI/RFI Noise: Two ways to prevent EMI/RFI Noise: –Through shielding the wires in the cable with a metal braid or foil. (Increases cost and diameter of the cable) –Through cancellation the wires are twisted together in pairs to provide self-shielding within the network media.

26 Canceling EMI/RFI Noise UTP Cat 5 has eight wires twisted into four pairs. In each pair, one wire is sending data and the other is receiving. As the electrons flow down the wire, they create a small, circular magnetic field around the wire.

27 Since the two wires are close together, their opposing magnetic fields cancel each other. They also cancel out outside magnetic fields (EMI/RFI). Twisting of the wires enhances cancellation Canceling EMI/RFI Noise

28 Sources of Noise on Copper Media

29 Types of Crosstalk Near-end crosstalk (NEXT) NEXT computed as the ratio of voltage amplitude between the test signal and the crosstalk signal when measured from the same end of the link. Crosstalk is avoided by using proper installation including: Strict adherence to RJ-45 termination procedures Using high quality twisted pair cabling

30 Types of Crosstalk 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 caused by FEXT still travels back to the source, but it is attenuated as it returns.

31 Types of Crosstalk Power sum near-end crosstalk (PSNEXT) 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. The combined effect of crosstalk from multiple simultaneous transmission sources can be very detrimental to the signal.

32 Timing Problems Dispersionsimilar to attenuation; is the broadening of a signal as it travels down the media. Dispersionsimilar to attenuation; is the broadening of a signal as it travels down the media. Jittercaused by unsynchronized clocking signals between source and destination. This means bits will arrive later or earlier than expected. Jittercaused by unsynchronized clocking signals between source and destination. This means bits will arrive later or earlier than expected. Latencyis the delay of a network signal caused by: Latencyis the delay of a network signal caused by: –Time it takes a bit to travel to its destination –Devices the bit travels through

33 Collisions Collisions occur in broadcast topologies where devices share access to the network media. Collisions occur in broadcast topologies where devices share access to the network media. A collision happens when two devices attempt to communicate on the shared- medium at the same time. A collision happens when two devices attempt to communicate on the shared- medium at the same time. Collisions destroy data requiring the source to retransmit. Collisions destroy data requiring the source to retransmit. The prevention of collisions will be discussed in more detail later in the semester. The prevention of collisions will be discussed in more detail later in the semester.

34 Cable Testing Standards

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37 Crosstalk

38 Time-based Parameters

39 Testing Optical Fiber

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41 New 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. This new standard specifies the original set of performance parameters that need to be tested for Ethernet cabling as well as the passing scores for each of these tests. This new standard specifies the original set of performance parameters that need to be tested for Ethernet cabling as well as the passing scores for each of these tests. A quality cable tester is the Fluke DSP-LIA013 Channel/Traffic Adapter for Cat5e. A quality cable tester is the Fluke DSP-LIA013 Channel/Traffic Adapter for Cat5e.


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