Challenges of Wireless LAN
spatial multiplexing power saving?
power saving technology that automatically reduces the power consumed by radios when data not being transferred, done by shutting down all but one radio when not in use
define effective area
the optimal physical area in range that the antenna can operate in
802.11B max transfer rates
up to 1,2 or 11Mbps
what standard defines how Ethernet works over wireless connections
IEEE 802.11
what does beamforming allow
allows the transmitter to focus its signal on a single receiver
WiMAX cell radius
between 3-10km
an ounce of protection
application layer encryption for all communication or TCP/IP layer => IPSEC; sectors and yagis will help from signal leaking into undesired areas; don't boost signals, prevent hot spots
wireless network devices are unlicensed devices, what is a precaution of this
because of low power, range of transmitted signal is limited; causing there to be a high potential of interference with nearby devices
what is MIMO
multiple input multiple output (MIMO) is key component of 802.11N devices
wireless works best when....
there is an unobstructed, clear line of sight between the two points of operation
outdoor point-to-point
used to connect wired LANs between buildings up to 20km apart
a wireless installation consists of what
very low power radio transmitters and radio receivers
certified interoperability supplied by who?
The WiFi alliance is the organization that has certified interoperability since June 2007
WiMAX speeds
1st gen = 40Mbps, 2nd gen = 300 Mbps, user can expect 1-5Mbps, currently found in notebooks and PDAs
wireless devices operate at what two frequencies
2.4Ghz and 5.2Ghz radio frequency band -- can operate at both
IEEE 802.11 Throughput "rated"?
The rated throughput in Mbps of a wireless device can be considerable more than actual throughout at any given time
WAP advantages
WAP does better job of "managing" a network for improved throughput, WAP has ability to adjust throughput for each station
two sources of wireless network threats
accidental access, deliberate access
802.11 allows devices to operate as what two things
ad hoc or client/server infrastructure devices
spread spectrum characteristics
allows radio transmission to a series of frequencies, features abilities to function at low power and to reject random interferences
parabolic antenna characteristics
antenna uses a dish to capture extra signals and focus them onto an antenna, increases the effective area which produces very high signal gain
WIMAX characteristics
based on 802.16 standard, designed to support wireless broadband services, uses similar cell structure to cell phone system
IEEE 802.11 uses what for collision management
collision avoidance technology
give examples of where wireless interference can come from
cordless phones, aircraft, digital equipment, microwaves ovens, other wireless networks
omni directional antenna characteristics
design transmits its signal equally in all directions, most perfected design of this antenna => "theoretical isotropic antenna"
two categories of antennas
directional or omni directional
what happens when frequency is avoided
flow of data drops down to a slower rate
what happens when frequency is clear
flow of data shifts up to higher rate
if frequency repeatedly unavailable then?
frequency is avoided
directional antenna characteristics
has gain in a single direction - example: parabolic dish used for satellite reception and the Yagi Design
infrastructure arrangement allows for what
higher power external antennas which can extend the range of a network
WiFi protected access (WPA)
improvement over WEP, uses improved protocol and algorithm to improve security of keys, changes key processing and rotates keys more often, also adds function to prevent packet forgeries
what is spatial multiplexing
improvement over beamforming, transmitter receiver each have multiple antennas, ea. antenna has own radio, benefit => improvement in throughputs and mobility of clients
in the case of tuned antenna what is effective area?
inversely proportional to the frequency of operation, meaning: 2.4Ghz unit will have 2x range of a 5.2Ghz unit of same power
accidental access
is gained by a user unknowingly accessing an unsecured wireless system
deliberate access
is willful accessing of either an unsecured or secured system by an unauthorized user; is ILLEGAL
what is major advantage of spread spectrum
multiple devices can use the same frequency at the same time without interference simply by varying the frequency shift times
gain antenna characteristics
omni directional antenna that has equal gain in all horizontal directions
ad hoc mode is?
one device acts as a temporary controller to control the sequence of transmissions as part of the collision avoidance design
infrastructure arrangement is?
one machines acts as a access point server and controls the Wireless Access Point(WAP)
indoor point-to-multipoint
one or more access points for indoor use -- (WirelessLANConfigs)
what is modulation
process of adding a data stream to an operating frequency
transmit beamforming requirements
receiver has a single antenna and there are few obstructions preventing line of sight transmission, minimum radio-reflective surfaces, both transmitter receiver have fixed positions
what does beamforming rely on and outcome
relies on feedback from the receiver regarding the quality of the received signal; allows transmitter to tune itself to the receiver (feedback not avail. non-802.11N devices)
Wireless is a very cost effective, portable method of installing a .... network
residential network
a wireless network uses what type of modulation
spread spectrum modulation
802.11 N characteristics
supports upto 300Mbps, 802.11N requires interoperability
what is spread spectrum modulation
the carrier frequency moves between specific frequencies within the band, data can be easily encoded
wireless attenuation is caused by?
the inability of radio signals used with wireless technology to penetrate materials; greater the difficulty in penetration, the greater the attenuation
what does it mean when wireless networks have no exclusive claim to their bandwidth
they are both low power and unlicensed
why does a spread spectrum receiver have to be synchronized with the transmitter?
to match the frequency changing pattern
802.11 G characteristics
upto 54Mbps, backward compatible with 802.11 B, B+G can work on the same network up to max speed of each device; proprietary protocols
outdoor point-to-multipoint
used to connect wired LANs in several buildings within a 8-10km radius
how does MIMO work
uses multiple antennas in an access point to transmit a signal, signal sent out by each antenna is vastly improved over other 802.11 versions
what is multipath interference
when wireless signals are reflected off a large metal surface causing related signals to be out of phase with each other
if there is noise on particular frequency what does spread spectrum do
will rely on encoding structure to recover the data
WEP & what is it
wired equivalency privacy (WEP) - the wireless router and authorized NICs shared a common encryption key when data is transmitted; minimum level of security
MAC address filtering?
wireless router is programmed to acknowledge contact only from NICs with specific MAC addresses
WiMAX stands for?
worldwide interoperability for microwave access