| A | B |
|---|
| Function of Physical Layer | to transmit data by defining the electrical specifications between the source and destination |
| Parts of an atom | nucleus - the center part of the atom, formed by protons and neutrons |
| The Periodic Table of Elements | lists all known types of atoms and their properties. All matter is composed of atoms |
| Opposite charges | react to each other with a force that causes them to be attracted to each other. |
| Like charges | react to each other with a force that causes them to repel each other |
| Static Electricity | Loosened electrons that stay in one place, without moving and with a negative charge, are called static electricity |
| ESD | If these static electrons have an opportunity to jump to a conductor, this can lead to electrostatic discharge (ESD). |
| Electrical insulators | are materials that allow electrons to flow through them with great difficulty, or not at all. |
| Example of Electrical Insulators | plastic, glass, air, dry wood, paper, rubber, and helium gas |
| Electrical conductors | materials that allow electrons to flow through them with great ease |
| Examples of Electrical Conductors | copper (Cu), silver (Ag), and gold (Au). |
| Ion | an atom that has more electrons, or fewer electrons, than a neutral atom |
| Semiconductors | materials where the amount of electricity they conduct can be precisely controlled |
| Voltage | an electrical force, or pressure, that occurs when electrons and protons are separated. The force that is created pushes toward the opposite charge and away from the like charge |
| Electrical current | the flow of charges that is created when electrons move |
| Ampere (Amp) | the number of charges per second that pass by a point along a path. |
| resistance | Materials through which current flows, offer varying amounts of opposition |
| ohm | The unit of measurement for resistance |
| Alternating current (AC) | voltages vary with time, by changing their polarity, or direction. AC flows in one direction, then reverses its direction, and repeats the process |
| Direct current (DC) | always flows in the same direction, and DC voltages always have the same polarity |
| Impedance | the total opposition to current flow (due to AC and DC voltages). |
| oscilloscope | an important, and sophisticated electronic device used to study electrical signals |
| circuit | closed, or complete, loops |
| multimeter | performs voltage, resistance, and continuity measurements, which are important in networking |
| Continuity | the level of resistance of a path |
| short circuit | If a path is unintentionally made into a low-resistance path |
| analog | is wavy |
| Attenuation | the loss of signal strength, for example, when cables exceed a maximum length. |
| reflection | Reflection occurs in electrical signals. small wave (pulse) returns (reflects) |
| discontinuity | When voltage pulses, or bits, hit a discontinuity some energy can be reflected. |
| Electrical Noise | unwanted additions to voltage, optical, or electromagnetic signals |
| crosstalk | When electrical noise on the cable originates from signals on other wires in the cable |
| NEXT | near-end crosstalk. When two wires are near each other and untwisted, energy from one wire can wind up in an adjacent wire and vice versa. This can cause noise at both ends of a terminated cable |
| AC Power and reference ground noises | Electricity is carried to appliances and machines by wires concealed in walls, floors, and ceilings. Consequently, inside these buildings AC power line noise is all around us |
| electromagnetic interference (EMI), | External sources of electrical impulses that can attack the quality of electrical signals on the cable include lighting, electrical motors |
| radio frequency interference (RFI). | frequencies in the 1-100 megahertz (MHz) frequency region, which happens to be where FM Radio signals are |
| shielding | In cable that employs shielding, a metal braid or foil surrounds each wire pair or group of wire pairs. This shielding acts as a barrier to any interfering signals |
| Dispersion | when the signal broadens in time |
| jitter | Clock pulses cause a CPU to calculate, data to store in memory, and the NIC to send bits. If the clock on the source host is not synchronized with the destination, which is quite likely, you will get timing jitter |
| Latency | also known as delay; a bit takes at least a small amount of time to get to where it's going |
| Latency solutions | the careful use of internetworking devices, different encoding strategies, and various layer protocols |
| collision | when two bits from two different communicating computers are on a shared-medium at the same time |
| (STP) | Shielded Twisted Pair; 10BaseT; Max. segment length 100 meters; 150 ohm cable; typically mylar sheathing |
| (UTP) | Unshielded Twisted Pair; 10BaseT; Max. segment length 100 meters; 100 ohm cable |
| Coaxial cable | of a hollow outer cylindrical conductor that surrounds a single inner wire made of two conducting elements. One of these elements - located in the center of the cable - is a copper conductor. Surrounding it is a layer of flexible insulation. Over this insulating material is a woven copper braid or metallic foil that acts as the second wire in the circuit, and as a shield for the inner conductor |
| thinnet | 10base 2; max segment length 185 meters; use BNC connectors |
| Fiber-optic cable | a networking medium capable of conducting modulated light transmissions |
| the core and the cladding | The light-guiding parts of an optical fiber |
| total internal reflection | allows the optical fiber to act like a light pipe, guiding light for tremendous distances, even around bends |
| 802.11 standards | application of wireless data communication is wireless LANs (WLANs), which are built in accordance with this IEEE standard |
| TIA/EIA-568-A | the most widely used standards for technical performance of networking media |
| The TIA/EIA standards address six elements of the LAN cabling process. These are: | horizontal cabling |
| common networking media | shielded twisted-pair |
| horizontal cabling | the maximum distance for cable runs in horizontal cabling is 90 meters (m). This is true for all types of CAT 5 UTP recognized networking media |
| T568A Crossover wire scheme | Transmit Green/White |
| T568A Straight through wire scheme | Transmit White/Orange |
