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Ch. 14 Wireless LANs With Correct Answers
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Ch. 14 Wireless LANs With Correct AnswersHow WANs work - ANSWER are either point-to-point, involving a direct connection
between two sites, or operate across packet-switched networks, in which data are
transmitted in packets over shared circuits. Depending on the service, WANs can be
used for almost any data-sharing purpose for which LANs can be used. Slower
transmission speeds, however, may make some applications less practical for WANs.
The most basic uses of WANs are for electronic mail and file transfer, but WANs can
also permit users at remote sites to access and enter data on a central site's database,
such as instantaneously updating accounting records.
In this, point-to-point WAN service may either involve analog dial-up lines, where a
modem is used to connect the computer with the telephone line, or dedicated leased
digital telephone lines, also called "private lines." Analog lines, which are part of the
public-switched telephone network or leased lines, are appropriate for batch data
transmissions like nonurgent order entry and point-of-sale transactions. Dedicated
digital phone lines are able to permit continuous, secure transmission of data at fixed
costs.
Wireless LANs ANSWER provide connectivity within a limited geographic area. It is a
LAN that does not depend on wired Ethernet connections. A WLAN might be an
extension to an existing wired network or a replacement.
Data transfer rates of WLAN range between 1 and 54 Mbps with proprietary solutions of
a few manufacturers supporting 108 Mbps data rates. The 802.11n standard supports
data transfer rates of 300-600 Mbps
Some key advantages of WLANs - ANSWER are that is eliminates the wiring cost, that
usually is the most expensive part of a LAN, and that it accommodates mobile
workstations. The three transmission techniques are used in WLANs: spread spectrum,
narrowband microwave, and infrared. The most significant set of standards defining
WLANs are those defined by the IEEE 802.11 committee.
Wireless LAN Applications - ANSWER LAN extension -- Originally targeted to reduce
cost of wiring, but new buildings now have sufficient wiring in place
Still useful in buildings where wiring is problematic: buildings with large open areas,
historical buildings with insufficient twisted pair, small offices wired LANs are not
,economical
Typically, a wireless LAN will be linked into a wired LAN on the same premises
Cross-building interconnect --
Nomadic access --
Ad hoc networks --
what you need to even have a wireless LAN: - ANSWER A WLAN must meet the same
sort of requirements typical of any LAN, including high capacity, ability to cover short
distances, full connectivity among attached stations, and broadcast capability. a, there
are a number of requirements specific to WLAN environments:
(Throughput to dynamic)
Efficient Throughput - ANSWER the MAC protocol should make as effective use as
possible of the wireless medium to maximize capacity
Number of Nodes - ANSWER WLANs may need to support hundreds of nodes across
multiple cells
Multiplexing Techniques - ANSWER multiplexing def= a fxn that permits two or more
data sources to share a common transmission medium such that each data source has
its own channel.
1. Time division multiplexing (TDM) permits the use of multiple channels by allowing the
channels to send data by turns - time on the circuit shared equally - each channel gets a
specified time slot, whether needed or not. (ex: packet switching)
2. FDM-Frequency division multiplexing: It divides the total bandwidth available to the
system into frequency non-overlapping sub-bands for transmission over a single digital
communication channel. For FM broadcasting over a cable system.
3. Frequency modulation: Encoding technique that changes the time between wave
peaks in an analog signal to convey data.
Connection to backbone LAN - ANSWER In most instances there is a need to
interconnect with stations on a wired backbone LAN. In the case of an infrastructure
WLAN this can easily be provided by the use of control modules which connect to both
, types of LAN. There may also need to be accomidation for mobile users and ad hoc
wireless networks.
Service Area - ANSWER A typical coverage area for a WLAN has a diameter of
100-300m.
Battery Powered Consumption - ANSWER mobile workers use battery-powered
workstations that must have extended battery life when using wireless. Typical WLAN
deployments have features to reduce power consumption while not being used over the
network, such as a sleep mode.
Transmission Robustness and Security - ANSWER Unless properly designed, a WLAN
may be easily interference prone and eavesdropped upon. The design of a WLAN must
permit reliable transmission even in noisy environment and should provide some level of
security against eavesdropping
Collocated network operation - ANSWER as WLANs become more popular, it is quite
likely for two or more WLANs to operate in the same area or in some area where
interference between the LANs is possible. Such interference may thwart the normal
operation of a MAC algorithm and may allow unauthorized access in particular LAN.
License-free operation - ANSWER Users would prefer to operate WLAN products
without having to secure a license for the frequency band used by the LAN.
Handoff/roaming - ANSWER The MAC protocol in use in the WLAN should enable mobile
stations to move from one cell into another
Dynamic configuration - ANS the MAC addressing and network management aspects of
the LAN shall enable dynamic and automated addition, deletion and relocation of
end-systems without disruption to other users.
Nomadic Access - ANS Provides a wireless link between a LAN hub and a mobile data
terminal (e.g laptop computer)
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