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NOISE IN SIGNALS - Network reflection not clearly explained in ccna sem1

CCNA Sem1 v2.1.2 Chapter 4.3.6 states that - Reflection occurs in electrical signals. When voltage pulses, or bits, hit a discontinuity some energy can be reflected. If not carefully controlled, this energy can interfere with later bits. -- what could be an example? How is it controlled?

If enough energy is reflected, the binary, two-state system can become confused by all the extra energy bouncing around. You can resolve this by ensuring that all networking components are carefully impedance matched. How can we measure impedance and if it does not match how is it solved? --can someone give specifics?

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New Member

Re: NOISE IN SIGNALS - Network reflection not clearly explained

Reflection is not a big deal, usually, in most network environments that you'll run into in the real world. Impedance is how much a device resists the flow of an AC signal, such as audio or RF. Impedance is similar to resistance which is how much a device resists the flow of a DC signal. Both impedance and resistance are measured in ohms. One could use an Ohm/Multimeter, or a specialized cable tester. An example of being concerned about reflections/impedance would be say, to make sure that you use a 50ohm cable, and not a 75 ohm cable when connecting a Cable Modem Headend amp, or a 75 ohm cable for a DS-3 mux, etc. Manufacturers, Cisco included, are usually pretty specific about what impedance (ohms) cables to use on any given piece of equipment. Just make sure you order the correct one. Or to use a cable tester on long runs of Cat. 5 wiring to make sure that all the punchdown blocks, patch cords, etc. aren't interfering with the signals.

Of more concern might be crosstalk between say Ethernet cables and an AC power line , where the cable pick up the 60Hz. hum.

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