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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
Chapter 4: Electronic and Signals

Aleksandar Radovanovic

University of the Western Cape

parts of an atom
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
basics of electricity
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.
measuring electricity
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
analog and digital
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
bits on media
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).
attenuation
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.
reflection
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.
dispersion jitter and latency
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.
noise
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
collision
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".
summary
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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