Overview
Networking media is the backbone of a network. Networking media is literally and physically the backbone of a network. Inferior quality of network cabling results in network failures and unreliable performance. Copper, optical fiber, and wireless networking media all require testing to ensure that they meet strict specification guidelines. These tests involve certain electrical and mathematical concepts and terms such as signal, wave, frequency, and noise. These terms will help students understand networks, cables, and cable testing.
The first lesson in this module will provide some basic definitions to help students understand the cable testing concepts presented in the second lesson.
The second lesson of this module describes issues related to cable testing for physical layer connectivity in LANs. In order for the LAN to function properly, the physical layer medium should meet the industry standard specifications.
Attenuation, which is signal deterioration, and noise, which is signal interference, can cause problems in networks because the data sent may be interpreted incorrectly or not recognized at all after it has been received. Proper termination of cable connectors and proper cable installation are important. If standards are followed during installations, repairs, and changes, attenuation and noise levels should be minimized.
After a cable has been installed, a cable certification meter can verify that the installation meets TIA/EIA specifications. This module also describes some important tests that are performed.
This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams.
Students who complete this module should be able to perform the following tasks:
• 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 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
Waves
4.1.1 This lesson provides definitions that relate to frequency-based cable testing. This page defines waves.
A wave is energy that travels from one place to another. There are many types of waves, but all can be described with similar vocabulary.
It is helpful to think of waves as disturbances. A bucket of water that is completely still does not have waves since there are no disturbances. Conversely, the ocean always has some sort of detectable waves due to disturbances such as wind and tide.
Ocean waves can be described in terms of their height, or amplitude, which could be measured in meters. They can also be described in terms of how frequently the waves reach the shore, which relates to period and frequency. The period of the waves is the amount of time between each wave, measured in seconds. The frequency is the number of waves that reach the shore each second, measured in hertz (Hz). 1 Hz is equal to 1 wave per second, or 1 cycle per second. To experiment with these concepts, adjust the amplitude and frequency in Figure .
Networking professionals are specifically interested in voltage waves on copper media, light waves in optical fiber, and alternating electric and magnetic fields called electromagnetic waves. The amplitude of an electrical signal still represents height, but it is measured in volts (V) instead of meters (m). The period is the amount of time that it takes to complete 1 cycle. This is measured in seconds. The frequency is the number of complete cycles per second. This is measured in Hz.
If a disturbance is deliberately caused, and involves a fixed, predictable duration, it is called a pulse. Pulses are an important part of electrical signals because they are the basis of digital transmission. The pattern of the pulses represents the value of the data being transmitted.
The next page will introduce sine waves and square waves.
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