SmallNetBuilder Forums
Go Back   SmallNetBuilder Forums > Wireless Networking > Wireless Article Discussions

Reply
 
Thread Tools Search this Thread Display Modes
  #11  
Old 05-03-2012, 02:05 PM
thiggins's Avatar
thiggins thiggins is offline
Mr. Easy
 
Join Date: May 2008
Posts: 8,974
Thanks: 149
Thanked 582 Times in 496 Posts
thiggins is just starting out
Default

I would not assume anything. The fallback mechanisms are part of the 802.11n spec and are supposed to be implemented, whether the product is Wi-Fi Certified or not.
__________________
Tim Higgins
Managing Editor,SmallNetBuilder.com
Reply With Quote
  #12  
Old 05-03-2012, 03:30 PM
somms's Avatar
somms somms is offline
Senior Member
 
Join Date: May 2008
Posts: 115
Thanks: 0
Thanked 15 Times in 9 Posts
somms is just starting out
Default

Quote:
Originally Posted by thiggins View Post
I would not assume anything. The fallback mechanisms are part of the 802.11n spec and are supposed to be implemented, whether the product is Wi-Fi Certified or not.

http://i181.photobucket.com/albums/x...oto/tomato.jpg

Just confirmed that neither tomato or dd-wrt will fallback to slower 20MHz bandwidth in the presence of 2.4GHz interference at least in my environment! Tested on ASUS RT-N66U w/tomato, WRT-600N w/dd-wrt and E2000 w/tomato...
Reply With Quote
  #13  
Old 05-03-2012, 03:48 PM
thiggins's Avatar
thiggins thiggins is offline
Mr. Easy
 
Join Date: May 2008
Posts: 8,974
Thanks: 149
Thanked 582 Times in 496 Posts
thiggins is just starting out
Default

Thanks for the info. Unfortunately, that is what I am finding with many of the products I tested for Part 2 with stock firmware.
__________________
Tim Higgins
Managing Editor,SmallNetBuilder.com
Reply With Quote
  #14  
Old 05-03-2012, 09:30 PM
somms's Avatar
somms somms is offline
Senior Member
 
Join Date: May 2008
Posts: 115
Thanks: 0
Thanked 15 Times in 9 Posts
somms is just starting out
Default

Quote:
Originally Posted by thiggins View Post
Thanks for the info. Unfortunately, that is what I am finding with many of the products I tested for Part 2 with stock firmware.
Well, I would prefer not to be forced to drop to the slower 20MHz due to circumstances beyond my control like my neighbors AP...
Reply With Quote
  #15  
Old 05-03-2012, 10:10 PM
stevech stevech is online now
Very Senior Member
 
Join Date: Mar 2010
Location: San Diego
Posts: 4,582
Thanks: 1
Thanked 323 Times in 311 Posts
stevech is just starting out
Default

there was, some time back, an agreement but not an IEEE requirement, but maybe a WiFi alliance recommendation, that automatic use of 40MHz would be disabled if any 20MHz networks were in range. I suppose a manual choice of 40MHz would override this "courtesy" mode.
Reply With Quote
  #16  
Old 05-04-2012, 11:40 AM
thiggins's Avatar
thiggins thiggins is offline
Mr. Easy
 
Join Date: May 2008
Posts: 8,974
Thanks: 149
Thanked 582 Times in 496 Posts
thiggins is just starting out
Default

Quote:
Originally Posted by stevech View Post
there was, some time back, an agreement but not an IEEE requirement, but maybe a WiFi alliance recommendation, that automatic use of 40MHz would be disabled if any 20MHz networks were in range. I suppose a manual choice of 40MHz would override this "courtesy" mode.
I downloaded a copy of 802.11-2012 (only $5). Section 10.15 and 10.17 are very helpful in understanding what is really supposed to happen.

Section 10.15.3.2 is quite clear:

Quote:
An FC HT AP 2G4 shall maintain a local boolean variable 20/40 Operation Permitted that can have either the value true or false. The initial value of 20/40 Operation Permitted shall be false.
This means that a 2.4 GHz AP must start in 20 MHz mode and can only switch to 40 MHz if numerous conditions are met. Conditions include no reception of the 40 MHz Intolerant bit and a channel scan that finds no interfering networks.

I cannot find anything in 802.11n-2012 that allows a "40 MHz only" mode in the 2.4 GHz band.
__________________
Tim Higgins
Managing Editor,SmallNetBuilder.com
Reply With Quote
The Following User Says Thank You to thiggins For This Useful Post:
  #17  
Old 05-04-2012, 06:27 PM
stevech stevech is online now
Very Senior Member
 
Join Date: Mar 2010
Location: San Diego
Posts: 4,582
Thanks: 1
Thanked 323 Times in 311 Posts
stevech is just starting out
Default

Perhaps the 20MHz by default or as a courtesy to nearby 20MHz networks is a recommendation or requirement of the WiFi alliance rather than IEEE. The FCC regulations don't dictate this - just power limits and out-of-band emissions.

WiFi supposedly has criteria to be met, such as transmitted waveform quality (Rho) and packet error rate vs. SNR and so on, else you don't get certified and cannot use the WiFi logo. I have my doubts as to how stringent the alliance is in such verifications - the alliance is funded by meager dues from member manufacturers and has few resources.

Last edited by stevech; 05-04-2012 at 06:29 PM.
Reply With Quote
  #18  
Old 05-05-2012, 05:20 AM
beisser beisser is offline
Senior Member
 
Join Date: Oct 2008
Posts: 106
Thanks: 0
Thanked 0 Times in 0 Posts
beisser is just starting out
Default

tim said "I downloaded a copy of 802.11-2012 (only $5)." this is ieee, not wifi alliance. wifi alliance only tests interoperability, not defines standards. ieee is for the standards and 802.11-2012 is a standard.

so any device not falling back is indeed no longer 802.11 compliant.
Reply With Quote
  #19  
Old 05-05-2012, 05:22 AM
beisser beisser is offline
Senior Member
 
Join Date: Oct 2008
Posts: 106
Thanks: 0
Thanked 0 Times in 0 Posts
beisser is just starting out
Default

Quote:
Originally Posted by somms View Post
Well, I would prefer not to be forced to drop to the slower 20MHz due to circumstances beyond my control like my neighbors AP...
well if there is a neighbors ap, your 40mhz mode wont work very well anyway as that ap WILL cause interference and framedrops and whatnot. what you will see is a rapid decline in performance and increasing packetloss. so sticking to 40 mhz mode wont do you any good in that scenario.

Last edited by beisser; 05-05-2012 at 06:30 AM.
Reply With Quote
  #20  
Old 05-05-2012, 07:51 AM
thiggins's Avatar
thiggins thiggins is offline
Mr. Easy
 
Join Date: May 2008
Posts: 8,974
Thanks: 149
Thanked 582 Times in 496 Posts
thiggins is just starting out
Default

As beisser reaffirmed, 20MHz in 2.4 GHz is in the 802.11-2012 spec. "40 MHz only" mode in 2.4 GHz is also against spec.
__________________
Tim Higgins
Managing Editor,SmallNetBuilder.com
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off


All times are GMT -4. The time now is 10:22 PM.


Top 10 Stats
Top Posters* Top Thanked
RMerlin  489
azazel1024  164
KGB7  139
stevech  137
sinshiva  112
hggomes  92
microchip  86
sm00thpapa  85
philmiami  82
Kel-L  81
RMerlin  5505
stevech  322
ryzhov_al  262
TeHashX  214
L&LD  188
RogerSC  187
sinshiva  139
joegreat  123
jlake  122
sfx2000  118
Most Viewed Threads* Hottest Threads*
Old Asuswrt-Merli...  73088
Old Asuswrt-Merli...  58316
Old Asuswrt-Merli...  15872
Old Asus locking...  8724
Old ASUS...  6485
Old Incoming...  5861
Old [Fork]...  5631
Old Asus...  4961
Old NETGEAR...  4551
Old How many of...  4449
Old Asuswrt-Merli...  392
Old Asuswrt-Merli...  389
Old Asus locking...  125
Old Asuswrt-Merli...  113
Old [Fork]...  59
Old Asus...  51
Old ASUS...  48
Old NETGEAR...  48
Old How many of...  47
Old Inherited PC...  45


Powered by vBulletin® Version 3.7.3
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
© 2006-2014 Pudai LLC All Rights Reserved.