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networkingchpt 8
terms
Question | Answer |
---|---|
wireless spectrum | continum of the electromagnetic waves used for data and voice communication |
wireless spectrum | spans frequencies between 9khz and 300ghz |
wireless spectrum | arranges by lowest to highest frequencies |
itu | sets standards for international wireless service,including frequency allocations,signaling,and protocols used by wireless devices;wireless equipment,satellite orbits |
radiation pattern | describes the relative strength over a three dimensional area of all the electromagnetic energy the antenna sends or receives |
frequency | how many times it repeats in a given interval |
frequency | measured in hertz |
most wireless networks use frequencies between | 2.4ghz or 5ghz |
gigahertz | one billion |
megahertz | one million |
hertz | 1 to 100 |
fcc | determines our frequencies and what ranges can be used for what purposes |
airwaves | collectionof frequencies available for communications |
similiarities with wired transmission | layer 3 and higher protocols |
similiarities with wired transmission | signal originationi,from electrical current,travel along conductor |
wired signals originate | from electrical current traveling along a conductor |
lack of a fixed path | requires wireless signals to be transmitted,received,controlled |
wireless transmission | tuned to the same frequency |
wired transmission | across cables |
tuned to the same frequency | tuned to the same channel |
directional antenna | issues wireless signals along a single direction |
omnidirectional antenna | issues and receives wireless signals with equal strength and clarity in all directions |
range | reachable geographical area |
reflection | the wave encounters an obstacle and bounces it back toward its source |
diffraction | signal splits into secondary waves when it encounters an o |
scattering | reflection or multiple different directions of signal |
reflection | bounce |
radiation | strength in the three dimensions |
three dimension | horizontal vertical backwards and forwards,depth |
directional antenna | point to point link |
omnidirectional | many different receivers must pick up the signal,tv and radio stations |
range | geographical area that an antenna or wireless sytem can reach |
line of sight | uses the least amount of energy and results in the reception of the clearest amount of energy |
line of sight | signals travel in a straight line,directly from transmitter to the receiver |
three phenomenas of signal propagation | reflection diffraction scattering |
multipath signals | wireless signals follow a number of different paths to their destination |
scattering | occurs when a wireless signal encounters an object that has small dimensions compared with a signals wavelength |
downside to multipath signaling | travel different distances between their transmitter and receiver |
significant cause of fading | multipath signaling |
fading | variation in signal strength as a result of electromagnetic energy |
multipath signal advantage | better chance of reaching destination |
multipath signal disadvantage | signal delay |
wireless signals | susceptible to noise,no wireless shielding |
noise | emi |
the extent of interference that a wireless signal experiences | depends partly on the density of signals in a geographical area |
signal degradation | fading attenuation noise |
attenuation | farther signal moves from the transmission antenna the weaker it gets |
narrowband | a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies |
amplifier | boots or strengthens an analog signal,wave signal |
amplify a signal with noise on it | makes the signal stronger and the noise stronger amplified |
2.4 ghz band older | frequency range of 2.4 - 2.4835 ghz |
2.4 ghz band older | 11 communication channels that anyone can use |
unlicensed frequency | one for which the fcc does not require users to register their service |
width of a band | how wide that specific frequency is,range, |
5ghz band ,newer | 5 billion |
5ghz band | 24 unlicensed bands each 20 mhz wide |
5ghz | used by weather,military radar communications |
four frequency bands | 5.1 5.3 5.4 5.8 |
broadband | relatively wide wireless spectrum band |
narrowband | transmitter concentrates signal energy at a single frequency |
spread spectrum | the use of multiple frequencies to transmit a signal |
spread spectrum | a signal never stays continuously within one frequency range during its transmission |
fhss | frequency hopping spread spectrum |
fhss transmission | a signal jumps between several different frequencies within a band in a synchronization pattern known only to the channels receiver and transmitter |
broadband | higher throughputs than narrowband |
spread spectrum | multiple frequencies used to transmit signal,offers security |
fhss | synchronization pattern known only to channels receiver,transmitter |
fhss | signal jumps between several different frequencies within a band |
dsss | direct sequence spread spectrum |
dsss | a signals bits are distributed over an entire frequency band at once |
dsss | each bit is coded so that the receiver can reassemble the original signal upon receiving the bits |
fhss devices in the is split the 2.4-2.4835 band | into 79 distinct frequencies |
wireless communication categories | fixed mobile |
fixed wireless systems | the location of the transmitter and receiver do not move |
advantage of fixed | receivers location is predicatable so no wasted energy |
fixed | transmitter,receiver locations do not move |
fixed | transmitting antenna focuses energy directly toward receiving antenna |
fixed | point to point link results |
mobile | receiver can be located anywhere within the transmitters range |
ad hoc wlan | trnsmit directly to each other via wireless nics without an intervening connectivity device |
wireless nodes | stations |
wlan architecture | adhoc wap |
ad hoc wlan | wireless nodes transmit directly to each other |
adhoc wlan | use wireless nics,no intervenig connectivity device |
adhoc wlan | poor performance |
wireless access points | wap |
wap | accepts wireless signals from multiple nodes |
wap | retransmits signals to network |
access points | base stations |