Posted 20 September 2004 - 03:59 AM
A The two most important factors are transmit power of the and receive sensitivity of the devices. A client with a higher transmit power will be able to talk to an access point at greater distance and at a higher transmit speed. A better receive sensitivity allows the client to hear the access point from farther away. The same goes for access points the more power they have the greater the coverage area they will support. For comparison Engenius access points and clients have 200mW of transmit power while most Linksys products have less then 50mW.
Q What is the difference between the current Wi-Fi standards 802.11b, 802.11g and 802.11a? Which one is right for me?
A The main differences are in distance compatibility and speed.
The bottom line 802.11b will give you the best connection most of the time and the longest distance. if your application is internet access it will provide many time the throughput of the fastest internet connections. Although 802.11g products provide more bandwidth they are much more susceptible to noise. 802.11a products have the same speed as g but have shorter range while they provide a more reliable connection.
Speed wise 802.11b provides up to 11mpbs raw throughput or about 5.5mbps after protocol overhead. if your application is Internet access then 802.11b standard has many times the bandwidth of your internet connection be it Cable, DSL or a full T1. 802.11b also has enough bandwidth to stream high quality divx video to a set top box this requires about 1.5mbps sustained throughput. For distance 802.11b is the clear winner because of a couple of factors one being transmit power of up to 200mW the other is low protocol overhead of CCK. You can expect up to 800 feet or 1200 meters from a 200mW 802.11b card. For compatibility 802.11b compatible products with work with the greatest number of installed networks including all public Hot Spots. 802.11b is also backward compatible with 802.11g products because they both use the 2.5ghz ISM frequency band.
802.11g has 54mbps raw throughput or about 20mbps throughput after protocol overhead or 45mbps actual in turbo mode. If you application involves high speed bridging or copying large files over 100mb then 802.11g is worth looking at. Distance wise 802.11g will only provide the maximum 54mbps connection at close range usually less than 100 feet. After that the connection falls back to 802.11b speeds. 802.11g client devices are limited to 125mW output by the FCC at this time so their maximum range is less than the best 802.11b devices. 802.11g devices are more susceptible to noise than 802.11b devices because they use OFDM protocol. For compatibility 802.11g access points can be set in dual mode b and g supported. There is one issue with this as soon as a 802.11b client associates all clients on the network are kicked down to 802.11b speeds. This can be solved by putting the access point in g only mode. But then the vast majority of existing b clients will not be able to connect.
802.11a provides the same speed 54mbps connection speed as 802.11g using the 5 ghz UNIII band. Currently 802.11a allows for the most actual bandwidth and up to 45mbps of actual throughput in 2x mode vs around 20 for standard 802.11a and 802.11g. This band is less crowded then 2.4ghz allowing for a connection in business or special situations. the 5ghz band also passes through certain types objects better the the 2.4ghz band one of them being crowds of people. 802.11a would be good in a trading floor application or maybe hospital. For distance 802.11a does not have the range of b or g. Compatibility wise 802.11a will not talk with b or g products. However many access points and clients offer dual mode or 802.11b g and a.
Q What is 108Mbps 802.11a 2x mode? How fast is it really?
A The 802.11a 2x mode uses more than one 5Ghz channel to increase the overall bandwidth this is possible because there are more channels available and the band is less crowded than the 2.5Ghz band that 802.11b and 802.11g operate at. In our testing we saw overall throughput of up to 45mbps at close range.
Q What is 108Mbps 802.11g turbo mode? How fast is it really?
A The 802.11g turbo mode uses more than one 2.4Ghz channel to increase the overall bandwidth. Because there are only 3 non overlapping channels at 2.4Ghz channel 6 must be used. Even when the center channel is used there is still some overlap if you are running access points on channels 1 and 11. For this reason 802.11g turbo is better used in a situation where just one access point is required per location. In our testing we saw overall throughput of up to 45 mbps at close range.
Q What is the difference between and access point and a wireless router?
A Wireless Access Points add wireless to an existing network. An access point will not share your internet connection, you will still need a router for that. Wireless routers will share your internet connection for you as well as add wireless to your network.
We recommend a access point over a router for a several reasons.
It is better to locate the access point in a high location away from cables and computers. This will increase your range of the wireless network.
With a separate router you can locate it near your wired network (computers and cable modem).
When new technology comes out you just have to replace the access point or better yet add an additional access point. So if you have a 802.11b access point you can continue to use it for your b clients and then add a g access point (on a non overlapping channel) for your g clients.
For a SOHO we recommend the Linksys router products including the befsr41 they work well with our long range 200mW Engenius access points.
Q How does an antenna affect the range of a Wi-Fi network?
A Antenna design can also greatly affect the range. The antenna simply defines the network coverage area with its beam pattern. An omni directional antenna will cover the space around it more or less evenly spreading in all directions (light a open lightbulb). A highly directional antenna covers a narrow area but can travel very long distance (think of a focused flashlight). A semi directional antenna or yagi has a broader coverage at at medium distance (think of a wide beam flashlight).
Q What is 802.11b or Wi-Fi?
A The IEEE 802.11 specification is a wireless LAN standard developed by the IEEE committee in order to specify an "over the air" interface between a wireless client and a base station or Access Point, as well as among wireless clients. The IEEE created the specification but they do not certify equipment, WECA certifies wireless LAN products.
Q What is the connector on the ORiNOCO and the Senao PC Cards used for?
A This connector is for connecting an external antenna. By connecting an external antenna, the ORiNOCO PC Card on board antennae are disabled. By connecting a external antenna you range is increased on both cards. For every 3 dbi of antenna gain your transmit power doubles.
Q How many computers can I connect wirelessly to the wireless access points or routers?
A In theory can connect up to 253 clients to most wireless routers. In actuality most access points will run best with 25 or less associated clients. Once you have more than 25 clients associated most access points start to break down a better solution is to co located multiple access points and let them load ballance.
Q How many access points can I co locate in the same area.
A For 802.11b and g there are 3 non overlapping channels 1, 6 and 11. You can place 3 access points at the same location if you set the SSID to be the same or any clients will load balance to the best access point. For the best coverage you can use 3 120 degree sector antennas pointed in different directions.
Q What is Infrastructure Mode?
A A wireless network that consists of at least one Access Point connected to the wired network infrastructure and a set of wireless end stations
Q What is Ad-Hoc Mode?
A Set of 802.11b wireless stations that communicate directly with one another without using an access point or any connection to a wired network.
Q What is the maximum distance from a wireless router or access point?
A It depends on power output and chipset design and the type of wireless standard used. 802.11b is currently the longest range wireless standard because the FCC allows for more transmit power (up to 200mW) than 802.11g or 802.11a.
Access point made by manufacturers like Linksys, Dlink and Netgear because they use low quality chipsets with only 40mW to 80mW of transmit power they can generally reach up to 1500 feet outdoors.
Enterprise grade equipment from Cisco and Proxim has up to 100mW of transmit power and can reach up to 2000 feet outdoors.
Long range wireless access points with 200mW of transmit power can have a range of up to 1200 meters or almost 4000 feet outdoors! The only manufacturer with long range cards is Engenius Technologies click here to see the equipment.
The transmit power of your access point and client card have can greatly effect the range. Generally though it depends on your situation. Metal and Concrete can cause degradation in the signal, as well as microwave ovens and 2.4 GHz phones. If setup properly, a wireless access point or router will give you up to 150 feet indoors and up to 4000 feet outdoors with stock antennas.
Q What is WEP?
A WEP stands for "Wired Equivalent Privacy". It is based on the IEEE 802.11 standard and uses the RC4 encryption algorithm. Enabling WEP allows you to increase security by encrypting data being transferred over your wireless network. When WEP encryption is enabled, there are two options: 64-bit and 128-bit. 64-bit is the same as 40-bit WEP. The lower level of WEP encryption uses a 40-bit (10 character) "secret key" (set by the user), and a 24-bit "initialization vector" (not under user control). So lower level 40 and 64 bit WEP cards are equivalent in encryption strength and compatibility.
Early versions of WEP were implemented improperly allowing weak a IV key to be generated. It was later exploited by several WEP cracking programs like AirSnort. Most manufactures have since upgraded their device firmware to a WEP plus standard that can no longer be cracked.
Q What is WPA?
A WPA stands for "Wired Protected Access". It is based on the IEEE 802.11 standard and uses the pre 802.11I standard / encryption algorithm. Enabling WPA allows you to increase security by encrypting data being transferred over your wireless network. Designed to run on existing hardware as a
software upgrade, Wi-Fi Protected Access is derived from and will be forward compatible
with the upcoming IEEE 802.11i standard. When properly installed, it will
provide wireless LAN users with a high level of assurance that their data will remain
protected and that only authorized network users can access the network.
WPA is a very good security protocol and should be implemented if available. Many vendors have failed to release working WPA firmware upgrades for existing wireless lan hardware preferring that you purchase new hardware. Most new products released in 2003-2004 support WPA and include AES support for the upcoming 802.11i standard.
Q What is 802.1x?
A 802.1x is a port based authentication protocol it can be used on wireless or wired networks. 802.1x allows you to authenticate clients via username and password and can can be used as a mechanism to rotate WEP or WPA keys. There are 2 implementations of 802.1x EAP TTLS designed by Funk software requires a server certificate only. EAP TTLS requires a certificate on each client and on the server.
Q How can I protect our network from Driving or Stumbling?
A The best tool you can use is AirMagnet Click here for complete specs.
Q What is War Driving or Stumbling?
A War Driving, also called Stumbling, is the act of driving around searching for wireless networks. War Driving is done by people for research purposes like plotting an area of wireless networks, or informing a company of a security risk in their wireless network, as well as by hackers who want to take advantage of those security risks. War Driving has taken its name from the popular movie "War Games" in which hackers would do something called War Dialing. Read more about it at WarDriving.com and Netstumbler.com.
Q What are DSSS and FHSS?
A Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern that is known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise. Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted.
This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered. Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low power wideband noise and is rejected (ignored) by most narrowband receivers. Most wireless LAN vendors have been adopting DSSS technology after considering the trade off between cost and performance.
Would the information be intercepted while transmitting on air? WLAN features two-fold protection in security. On the hardware side, to an unintended receiver, DSSS appears as low power wideband noise and is rejected (ignored) by most narrowband receivers. On the software side, WLAN series offer the encryption function (WEP) to enhance security and Access Control. Users can set it up depending on their needs.
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Posted 19 February 2005 - 02:36 AM
A You may ask yourself this question when deciding to either upgrade your current card, or purchase a new PCI / PCMCIA / etc etc card for use with Linux and Windows 802.11 wireless discovery applications. As far as i know, and im not exactly qualified in wifi, but only prism chipsets (perhaps Atheros/Orinico) allow your wireless card to accept Raw Packets, im talking about chipsets, not models, as often some models may or maynot use the prism2/3 chipset even if the manufactorer is the same. The most comprehensive guide to what devices use what chipset can be found here: http://www.linux-wla...dapters.html.gz
Hopefully that post will help out some of the orinoco people.
Posted 28 January 2006 - 12:53 PM
Posted 01 March 2007 - 09:47 AM
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