Cable TestingCable Testing

IntroductionIntroduction

Networking media is the backbone of network. Networking media is the backbone of network. Inferior quality of network cabling may cause Inferior quality of network cabling may cause

network failures and unreliable performance.network failures and unreliable performance. Copper, optical fiber, and wireless networking Copper, optical fiber, and wireless networking

media all require testing to determine the quality. media all require testing to determine the quality. These tests involve certain electrical and These tests involve certain electrical and

mathematical concepts and terms, such as signal, mathematical concepts and terms, such as signal, wave, frequency, and noise. wave, frequency, and noise.

Student Should understand the concepts of: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 crosstalk, near-end crosstalk, far-end crosstalk, and power

sum near-end crosstalk.sum near-end crosstalk. Grounding and wire twistingGrounding 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.

Waves……..Waves…….. A wave is energy traveling from one place A wave is energy traveling from one place

to another.to another. It may be defined as any disturbance It may be defined as any disturbance

generated in any material, such as:generated in any material, such as:– Throwing a stone in waterThrowing a stone in water– Sound (created by disturbance in air)Sound (created by disturbance in air)– Electric supply at your house (electric impulses Electric supply at your house (electric impulses

generated in conductor wire by providing a generated in conductor wire by providing a pressure/ force or voltage level.pressure/ force or voltage level.

WavesWaves

Sine WavesSine 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.

Square WavesSquare 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.

SignalsSignals

Signals in a network can be represented in Signals in a network can be represented in two different ways.two different ways.

Analog SignalsAnalog Signals Digital SignalsDigital Signals

Time

Length

Analog SignalsAnalog Signals

Is wavy Is wavy

Has a continuously varying voltage versus Has a continuously varying voltage versus time graph time graph

Is typical of things in nature Is typical of things in nature

Has been widely used in Telecommunications Has been widely used in Telecommunications for over 100 yearsfor over 100 years

Digital SignalDigital Signal

Digital signals have a square wave with Digital signals have a square wave with instant transitions from low to high voltage instant transitions from low to high voltage states (0 to 1).states (0 to 1).

If voltage present then 1.If voltage present then 1. If no voltage then 0If no voltage then 0

Networks Use Digital SignalingNetworks Use Digital Signaling

Bits are represented by either no voltage (0) or Bits are represented by either no voltage (0) or +3 to +6 Volts (1).+3 to +6 Volts (1).

A Signal Reference Ground attached close to a A Signal Reference Ground attached close to a computer’s digital circuits establishes the computer’s digital circuits establishes the baseline for no voltage.baseline for no voltage.

Bits must arrive at the destination undistorted in Bits must arrive at the destination undistorted in order to be properly interpreted.order to be properly interpreted.

What six things can distort a bit?What six things can distort a bit?

DecibelsDecibels

The decibel (dB) is a measurement unit important in describing networking signals. The decibel is related to the exponents and logarithms.

•Pfinal is the delivered power measured in Watts

•Pfinal is the delivered power measured in Watts

•Vfinal is the delivered voltage measured in Volts

•Vreference is the original voltage measured in Volts

Viewing Signals in Time and Viewing Signals in Time and FrequencyFrequency

Viewing Signals in Time and Viewing Signals in Time and FrequencyFrequency

Analog and Digital Signals Analog and Digital Signals in Time and Frequencyin Time and Frequency

BandwidthBandwidth

Noise in Time and FrequencyNoise in Time and Frequency

Noise is unwanted additions to the signalNoise is unavoidableToo 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

Signaling over Copper and FiberSignaling over Copper and Fiber

Signaling over Copper and FiberSignaling over Copper and Fiber

Signaling over Copper and FiberSignaling over Copper and Fiber

Signaling over Copper and FiberSignaling over Copper and Fiber

Attenuation and Insertion Loss on Attenuation and Insertion Loss on Copper MediaCopper 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 medium’s distance requirement (100 meters for Cat 5 cable) By using repeaters that “amplify” the signal

EMI/RFI NoiseEMI/RFI Noise

EMI (Electromagnetic Interference) and EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) attack RFI (Radio Frequency Interference) attack the quality of electrical signals on the cable.the quality of electrical signals on the cable.

Sources of EMI/RFI include:Sources of EMI/RFI include:– Fluorescent lighting (EMI)Fluorescent lighting (EMI)– Electrical motors (EMI)Electrical motors (EMI)– Radio systems (RFI)Radio systems (RFI)

EMI/RFI Noise ExampleEMI/RFI Noise Example

Source computer sends out Source computer sends out a digital signal.a digital signal.

Along the path, the signal Along the path, the signal encounters EMI noise.encounters EMI noise.

The digital signal and EMI The digital signal and EMI combine to distort the signal.combine to distort the signal.

Digital Signal

EMI

Distorted Signal

EMI/RFI NoiseEMI/RFI Noise

Two ways to prevent EMI/RFI Noise:Two ways to prevent EMI/RFI Noise:– Through Through shieldingshielding the wires in the cable with a the wires in the cable with a

metal braid or foil. (Increases cost and diameter metal braid or foil. (Increases cost and diameter of the cable)of the cable)

– Through Through cancellationcancellation the wires are the wires are twistedtwisted together in pairs to provide self-shielding together in pairs to provide self-shielding within the network media.within the network media.

Canceling EMI/RFI NoiseCanceling EMI/RFI Noise

UTP Cat 5 has eight UTP Cat 5 has eight wires twisted into four wires twisted into four pairs.pairs.

In each pair, one wire is In each pair, one wire is sending data and the sending data and the other is receiving.other is receiving.

As the electrons flow As the electrons flow down the wire, they down the wire, they create a small, circular create a small, circular magnetic field around the magnetic field around the wire.wire.

Since the two wires are Since the two wires are close together, their close together, their opposing magnetic fields opposing magnetic fields cancel each other.cancel each other.

They also cancel out They also cancel out outside magnetic fields outside magnetic fields (EMI/RFI).(EMI/RFI).

Twisting of the wires Twisting of the wires enhances cancellationenhances cancellation

Canceling EMI/RFI NoiseCanceling EMI/RFI Noise

Sources of Noise on Copper Sources of Noise on Copper MediaMedia

Types of CrosstalkTypes of CrosstalkNear-end crosstalk (NEXT)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 avoidedby using proper installation including:

Strict adherence to RJ-45 termination proceduresUsing high quality twisted pair cabling

Types of CrosstalkTypes of CrosstalkFar-end crosstalk (FEXT)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.

Types of CrosstalkTypes of CrosstalkPower sum near-end crosstalk (PSNEXT)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.

Timing ProblemsTiming Problems DispersionDispersion—similar to attenuation; is the —similar to attenuation; is the

broadening of a signal as it travels down the broadening of a signal as it travels down the media.media.

JitterJitter—caused by unsynchronized clocking —caused by unsynchronized clocking signals between source and destination. signals between source and destination. This means bits will arrive later or earlier This means bits will arrive later or earlier than expected.than expected.

LatencyLatency—is the —is the delaydelay of a network signal of a network signal caused by:caused by:– Time it takes a bit to travel to its destinationTime it takes a bit to travel to its destination– Devices the bit travels throughDevices the bit travels through

CollisionsCollisions

Collisions occur in broadcast topologies Collisions occur in broadcast topologies where devices share access to the network where devices share access to the network media.media.

A collision happens when two devices A collision happens when two devices attempt to communicate on the shared-attempt to communicate on the shared-medium at the same time.medium at the same time.

Collisions destroy data requiring the source Collisions destroy data requiring the source to retransmit.to retransmit.

The prevention of collisions will be The prevention of collisions will be discussed in more detail later in the discussed in more detail later in the semester.semester.

Cable Testing StandardsCable Testing Standards

Cable Testing StandardsCable Testing Standards

Cable Testing StandardsCable Testing Standards

CrosstalkCrosstalk

Time-based ParametersTime-based Parameters

Testing Optical FiberTesting Optical Fiber

Testing Optical FiberTesting Optical Fiber

New StandardNew Standard

On June 20, 2002, the Category 6 (or Cat 6) On June 20, 2002, the Category 6 (or Cat 6) addition to the TIA-568 standard was published.addition to the TIA-568 standard was published.

This new standard specifies the original set of This new standard specifies the original set of performance parameters that need to be tested for performance parameters that need to be tested for Ethernet cabling as well as the passing scores for Ethernet cabling as well as the passing scores for each of these tests.each of these tests.

A quality cable tester is the Fluke A quality cable tester is the Fluke DSP-LIA013 Channel/Traffic Adapter DSP-LIA013 Channel/Traffic Adapter for Cat5e. for Cat5e.