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Chapter 4: Electronic and Signals

Chapter 4: Electronic and Signals. Aleksandar Radovanovic University of the Western Cape. Parts of an Atom. nucleus - the center part of the atom, formed by protons and neutrons protons - particles have a positive charge , and along with neutrons, form the nucleus

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Chapter 4: Electronic and Signals

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  1. Chapter 4: Electronic and Signals Aleksandar Radovanovic University of the Western Cape

  2. Parts of an Atom • nucleus - the center part of the atom, formed by protons and neutrons • protons - particles have a positive charge , and along with neutrons, form the nucleus • neutrons - particles have no charge (neutral), and along with protons, form the nucleus • electrons - particles have a negative charge, and orbit the nucleus

  3. Basics of Electricity • Voltage (V): Electrical pressure due to separation of electrical charge.Unit of measurement: Volt • Current (I): Flow of electrons Unit of measurement: Ampere • Resistance (R): Property of material that opposes electrical flow. Unit of measurement: OhmElectrons flow only incircuits that are closed, or complete, loops.

  4. Measuring electricity • A millimeter is a electrical testing tool that can perform measurement of: • voltage • resistance, • continuity (the level of resistance of a path) • Some of the networking related measurements: • CAT 5 cable • terminated coaxial cable • telephone wire • CAT 5 jacks • wall outlets

  5. Analog and Digital • Analog signals: • Continuous, “wave” voltage-versus-time graphs • used in telecommunications for over 100 years • Digital signals: • has discrete, or jumpy, voltage-versus-time graphs • Usually has two voltage levels

  6. Bits on Media • One bit, on an electrical medium, is the electrical signal corresponding to binary 0 or binary 1. • The bit takes a small amount of time to travel (propagate) along the medium. • The time it takes the bit to travel from one end of the medium and back again is referred to as the round trip time, (RTT).

  7. Attenuation • A 1 bit voltage signal loses amplitude as energy passes from the signal to the cable. • Attenuation is the loss of signal strength • Attenuation also happens to optical signals; the optical fiber absorbs and scatters some of the light energy. • One way to fix the problem is to change the medium. A second way is to use a repeater after a certain distance.

  8. Reflection • When voltage pulses, or bits, hit a discontinuity some energy can be reflected. If not carefully controlled, this energy can interfere with later bits. • Can be resolved by ensuring that all networking components are impedance matched. • Reflection occurs with optical signals. Optical signals reflect whenever they hit a discontinuity in the glass fiber, such as when a connector is plugged into a device.

  9. Dispersion, jitter, and latency • Dispersion is when the signal broadens in time. • Timing jitter happens when source and destination clock loose synchronization. • Latency, is a signal delay. To travel a distance, a bit takes at least a small amount of time to get to where it's going. If the bit goes through any devices, the transistors and electronics introduce more latency.

  10. Noise • Noise is unwanted additions to voltage, optical, or electromagnetic signals. • 1. NEXT-A and NEXT-B (near-end crosstalk): when electrical noise on the cable originates from signals on other wires in the cable, this is known as crosstalk.Solution: quality cables and termination. • 2. Thermal noise, due to the random motion of electrons, is unavoidable but usually relatively small compared to our signals. • 3. AC Power/Reference Ground Noise: bad grounding, long wires, faulty electrical devices.Solution: separate LAN power supply. • 4. Electromagnetic interference (EMI), and radio frequency interference (RFI).Solution: shielding and cancellation

  11. Collision • A collision occurs when two bits from two different communicating computers are on a shared-medium at the same time. • In the case of copper media, the voltages of the two binary signals are added, and cause a third voltage level. This voltage variation is not allowed in a binary system, which only understands two voltage levels. The bits are corrupted "destroyed".

  12. Summary • Electricity is based on the ability of electrons of certain types of atoms to separate, or flow. Electricity flows from negative to positive within electrical circuits • The concepts of voltage, current, and resistance, provide a means of measuring electricity which is required to be able to design and manufacture electronic devices. • One bit, on an electrical medium, is the electrical signal corresponding to binary 0 or binary 1. • Six things that can happen to 1 bit: • propagation • attenuation • reflection • noise • timing problems (dispersion, jitter, and latency) • collisions

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