Seamless roaming is specified in what IEEE standard?
Answer(s): E
Seamless roaming is specified in the 802.11F standard.In situations where seamless roaming is required, a technique called channel reuse is used inorderto alleviate adjacent and co-channel interference while allowing users to roam throughadjacent cells. Channel reuse is the side-by-side locating of non-overlapping cells to form a mesh of coverage where no cell on a given channel touches another cell on that channelAfter a wireless LAN is installed, it might not work exactly as planned, although it may be close. Spot-checking by a site surveyor after installation is complete is most helpful in avoiding troubleshooting situations during production use of the network. Items that should be checked are:? Coverage in perimeter areas? Overlapping coverage for seamless roaming? Co-channel and adjacent channel interference in all areas
Identify all true statements below.
Answer(s): C
A frequency hopping system will operate using a specified hop pattern called a channel. Frequency hopping systems typically use the FCC's 26 standard hop patterns or a subset thereof. Some frequency hopping systems will allow custom hop patterns to be created, and others even allow synchronization between systems to completely eliminate collisions in a co-located environment.Though it is possible to have as many as 79 synchronized, co-located access points, with this many systems, each frequency hopping radio would require precise synchronization with all of the others in order not to interfere with (transmit on the same frequency as) another frequency hopping radio in the area. The cost of such a set of systems is prohibitive and is generally not considered an option. If synchronized radios are used, the expense tends to dictate 12 co-located systems as the maximum. In frequency hopping systems, the carrier changes frequency, or hops, according to a pseudorandomsequence. The pseudorandom sequence is a list of several frequencies to whichthe carrier will hop at specified time intervals before repeating the pattern. The transmitteruses this hop sequence to select its transmission frequencies. The carrier will remainat a certain frequency for a specified time (known as the dwell time), and then use asmall amount of time to hop to the next frequency (hop time). When the list of frequencieshas been exhausted, the transmitter will repeat the sequence.In order for a frequency hopping system to be 802.11 orOpenAir compliant, it must operate in the 2.4 GHz ISM band (which is defined by the FCC as being from 2.4000 GHz to 2.5000 GHz). Both standards allow operation in the range of 2.4000 GHz to 2.4835 GHz.
What is a disadvantage of having a short dwell time when using a FHSS system?
Answer(s): B
When a frequency hopping radio jumps from frequency A to frequency B, it must change the transmit frequency in one of two ways. It either must switch to a different circuit tuned to the new frequency, or it must change some element of the current circuit in order to tune to the new frequency. In either case, the process of changing to the new frequency must be complete before transmission can resume, and this change takes time due to electrical latencies inherent in the circuitry. There is a small amount of time during this frequency change in which the radio is not transmitting called the hop time. The hop time is measured in microseconds (µs) and with relatively long dwell times of around 100-200 ms, the hop time is not significant. A typical 802.11 FHSS system hops between channels in 200-300 µs.With very short dwell times of 500 - 600µs, like those being used in some frequency hoppingsystems such as Bluetooth, hop time can become very significant. If we look at theeffect of hop time in terms of data throughput, we discover that the longer the hop timein relation to the dwell time, the slower the data rate of bits being transmitted. This translates roughly to longer dwell time = greater throughput.
What does the PRNG acronym stand for in regards to the WEP protocol?
The IEEE 802.11 standard specifies the use of WEP.WEP is a simple algorithm that utilizes a pseudo-random number generator (PRNG) and theRC4 stream ciphe r
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