PCLinuxOS New User Guide: advancedrf

Most recent edit on 2007-05-21 20:05:52 by SySy [moved]

Additions:
moved to http://docs.mypclinuxos.com/Advancedrf∞

Deletions:

Advanced WiFi Radio Frequency Topics and PCLinuxOS

Back to Advanced Topics
THIS PAGE BEING MOVED TO http://docs.mypclinuxos.com/Advancedrf∞
Once you have your WiFi card working with PCLinuxOS, you have some decisions to make as to the radio frequency levels and channels you use.
The simplest way to determine rf information about your wireless card is to use the wavemon package which you can install via synaptic.
Wavemon can be run by issuing the command "wavemon" (no quotes) as root. The below is a screenshot of wavemon showing statistics of an Orinico 802.11b PCMCIA adapter. 802.11a cards will be discussed later.
The important parts of the wavemon output are:
1. Link Quality
2. Signal Level
3. Noise Level
4. Signal-to-Noise Level
5. Frequency
6. Bitrate

Link Quality
The Link Quality is a general description of your signal quality. It should be above 25.
Signal Level
The strength of your signal. The greater the number, the stronger your signal is.
Noise Level
The strength of the "noise" or other radio activity on the same frequency as your wireless network (as seen by your PCMCIA adapter).
Signal-to-Noise Level
The difference between your signal and noise level. Bigger numbers here are better.
Frequency
This is the frequency, or channel your wireless card/AP are set to. There are only three channels of the available 11 that you should usually use - 1 (2.412 Ghz) 5 (2.432 Ghz) an 11 (2.452 Ghz).
Bitrate
This is the "speed", before overhead, of the link. It can be dynamically or statically set. The better your Link Quality and Signal to Noise Ratio, the higher your speed can be. Refer to #3 in Tips for Enhancing Wi-Fi Security∞.

802.11b Radio Network Planning

Having the above information can help you make RF choices. Take your laptop anywhere you will use it, and have wavemon running - make sure to record the results.
With the results in hand, you can make the following decisions:
1. How many access points do I need to get acceptable coverage?
Don't live with bad signal! Multiple access points, positioned and powered correctly, can make your signal great all over your house/apartment/business.
2. Is my signal too strong?
If you get great signal, and little noise (good signal-to-noise ratio) its time to turn down the power of your access point and move it to a place where you get worse signal - a signal too strong is begging for problems (your network is spilling into the neighbor's place).
3. Am I conflicting with nearby access points?
If you are seeing a lot of noise, you will need to try other channels. Its likely you have a neighbor on the same channel as you.
4. What bitrate should I use?
Set to 11 Mbps or 5.5 Mbps in your access point. This is the security feature talked about in #3 here Tips for Enhancing Wi-Fi Security∞.
The RF goals in setting up an 802.11b wi-fi network is to provide solid signals, 11 Mbps data rates, and avoid noise sources. The catch is that you don't want your 802.11b network serving your entire apartment building! Using the output of wavemon, you should have a network that is fast, and doesn't extend far beyond your own property.

Hidden Nodes and 802.11b

802.11b uses CSMA/CA - a protocol which allows data to operate in an envirnonment where only one device may talk to one access point at one time. When two try to talk at the same time a collision occurs and both devices have their packets dropped. If they immediately resend, they will collide, and the packets will get dropped again. This will continue until one of the two parties gives up.
The 802.11b standard considers solving of this problem of collisions with media reservation mechanism using special short packets (CTS/RTS) that are sent from every station before main packet transmission. They announce when they are sending, and if they see someone else is currently active, they back off for a random period of time and retry.
Unfortunately, the CTS/RTS packets are broadcasted by your wireless NIC card - what happens when your laptop can not "see" your other laptop, even though your access point can see both your laptops? A collision!
This process is very similar to the way in which Ethernet hubs∞ work - however, there is no chance that all the NIC cards in an Ethernet network will not be able to see each other.
Also, it is very important to note that 802.11b is half-duplex: an access point can only send or receive to one client at a time. Any collision as descrived above will affect all clients connected to the AP.
To avoid hidden node problems, you can do the below:
1. Get better antennas∞ for your wireless cards (this is usually only reasonable for desktops you have wirelessly connected).
2. Try a wireless repeater∞, although be aware that this will more than halve your bandiwdth.
3. Use a wireless bridge∞ instead of a wireless PCMCIA card - your PCLInuxOS laptop will need a standard Ethernet card to work with a wireless bridge.
4. Use more than one access point (turning down their power) to get more coverage.
5. In the PCLinuxOS control center, set the RTS value to be 250. By default, it is off.

CategoryWireless

Edited on 2007-05-18 14:42:09 by IanDawson [Porting to new wiki]

Additions:
THIS PAGE BEING MOVED TO http://docs.mypclinuxos.com/Advancedrf∞

Edited on 2006-07-27 13:37:09 by DevNet [added category wireless]

Additions:

CategoryWireless

Edited on 2005-12-05 14:31:52 by LexNL [Minor edits]

Additions:

Advanced WiFi Radio Frequency Topics and PCLinuxOS

Once you have your WiFi card working with PCLinuxOS, you have some decisions to make as to the radio frequency levels and channels you use.

Deletions:

Advanced WiFi Radio Frequency Topics and PCLinuxOS

Once you have your WiFi card working with PCLinuxOS, you have some decisions to make as to the radio frequency levels and channels you use.

Edited on 2005-09-24 02:20:29 by LexNL [Added back link]

Additions:
Back to Advanced Topics

Edited on 2005-07-31 14:47:59 by WifiGuy

Additions:
5. In the PCLinuxOS control center, set the RTS value to be 250. By default, it is off.

Edited on 2005-07-31 14:44:00 by WifiGuy

Additions:
The strength of your signal. The greater the number, the stronger your signal is.

Deletions:
The strength of your signal. THe greater the number, the stronger your signal is.

Edited on 2005-07-31 14:42:12 by WifiGuy

Additions:
802.11b uses CSMA/CA - a protocol which allows data to operate in an envirnonment where only one device may talk to one access point at one time. When two try to talk at the same time a collision occurs and both devices have their packets dropped. If they immediately resend, they will collide, and the packets will get dropped again. This will continue until one of the two parties gives up.
2. Try a wireless repeater∞, although be aware that this will more than halve your bandiwdth.

Deletions:
802.11b uses CSMA/CA a protocol which allows data to operate in an envirnonment where only one device may talk to one access point at one time. When two try to talk at the same time a collision occurs and both devices have their packets dropped. If they immediately resend, they will collide, and the packets will get dropped again. This will continue until one of the two parties gives up.
2. Try a wireless repeater∞, although be aware that this will halve your bandiwdth.

Edited on 2005-07-31 14:34:43 by WifiGuy

Additions:
3. Use a wireless bridge∞ instead of a wireless PCMCIA card - your PCLInuxOS laptop will need a standard Ethernet card to work with a wireless bridge.
4. Use more than one access point (turning down their power) to get more coverage.

Deletions:
3. Use a wireless bridge instead of a wireless PCMCIA card - your PCLInuxOS laptop will need a standard Ethernet card to work with a wireless bridge.
4. Use more than one access point to get coverage.

Edited on 2005-07-31 14:11:58 by WifiGuy

Additions:

802.11b Radio Network Planning

Deletions:

802.11b Radio Network Planning

Edited on 2005-07-31 14:11:27 by WifiGuy

Additions:

802.11b Radio Network Planning

Hidden Nodes and 802.11b

802.11b uses CSMA/CA a protocol which allows data to operate in an envirnonment where only one device may talk to one access point at one time. When two try to talk at the same time a collision occurs and both devices have their packets dropped. If they immediately resend, they will collide, and the packets will get dropped again. This will continue until one of the two parties gives up.
The 802.11b standard considers solving of this problem of collisions with media reservation mechanism using special short packets (CTS/RTS) that are sent from every station before main packet transmission. They announce when they are sending, and if they see someone else is currently active, they back off for a random period of time and retry.
Unfortunately, the CTS/RTS packets are broadcasted by your wireless NIC card - what happens when your laptop can not "see" your other laptop, even though your access point can see both your laptops? A collision!
This process is very similar to the way in which Ethernet hubs∞ work - however, there is no chance that all the NIC cards in an Ethernet network will not be able to see each other.
Also, it is very important to note that 802.11b is half-duplex: an access point can only send or receive to one client at a time. Any collision as descrived above will affect all clients connected to the AP.
To avoid hidden node problems, you can do the below:
1. Get better antennas∞ for your wireless cards (this is usually only reasonable for desktops you have wirelessly connected).
2. Try a wireless repeater∞, although be aware that this will halve your bandiwdth.
3. Use a wireless bridge instead of a wireless PCMCIA card - your PCLInuxOS laptop will need a standard Ethernet card to work with a wireless bridge.
4. Use more than one access point to get coverage.

Deletions:

802.11b Network Planning

Edited on 2005-07-31 12:36:02 by WifiGuy

Additions:
This is the "speed", before overhead, of the link. It can be dynamically or statically set. The better your Link Quality and Signal to Noise Ratio, the higher your speed can be. Refer to #3 in Tips for Enhancing Wi-Fi Security∞.

802.11b Network Planning

Edited on 2005-07-31 12:23:36 by WifiGuy

Additions:

Advanced WiFi Radio Frequency Topics and PCLinuxOS

Wavemon can be run by issuing the command "wavemon" (no quotes) as root. The below is a screenshot of wavemon showing statistics of an Orinico 802.11b PCMCIA adapter. 802.11a cards will be discussed later.
The important parts of the wavemon output are:
1. Link Quality
2. Signal Level
3. Noise Level
4. Signal-to-Noise Level
5. Frequency
6. Bitrate
Link Quality
The Link Quality is a general description of your signal quality. It should be above 25.
Signal Level
The strength of your signal. THe greater the number, the stronger your signal is.
Noise Level
The strength of the "noise" or other radio activity on the same frequency as your wireless network (as seen by your PCMCIA adapter).
Signal-to-Noise Level
The difference between your signal and noise level. Bigger numbers here are better.
Frequency
This is the frequency, or channel your wireless card/AP are set to. There are only three channels of the available 11 that you should usually use - 1 (2.412 Ghz) 5 (2.432 Ghz) an 11 (2.452 Ghz).
Bitrate
This is the "speed", before overhead, of the link. It can be dynamically or statically set. The better your Link Quality and Signal to Noise Ratio, the higher your speed can be. Refer to #3 in http://www.pclinuxonline.com/wiki/WireLess∞

Deletions:

Advanced WiFi Topics and PCLinuxOS

Wavemon can be run by issuing the command "wavemon" (no quotes) as root. The below is a screenshot of wavemon showing statistics of an Orinico 802.11b PCMCIA adapter.

Edited on 2005-07-31 11:49:49 by WifiGuy

Additions:

Deletions:

Oldest known version of this page was edited on 2005-07-31 11:49:29 by WifiGuy []

Page view:

Advanced WiFi Topics and PCLinuxOS

Once you have your WiFi card working with PCLinuxOS, you have some decisions to make as to the radio frequency levels and channels you use.

The simplest way to determine rf information about your wireless card is to use the wavemon package which you can install via synaptic.

Wavemon can be run by issuing the command "wavemon" (no quotes) as root. The below is a screenshot of wavemon showing statistics of an Orinico 802.11b PCMCIA adapter.