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Belyivulk
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802.11n Extension Channel

Sun Oct 02, 2011 10:10 am

Hey Guys,

A quick question for anyone in the know; when selecting an extension channel; running in super channel mode will it work as expected? I.E

Control channel 5695mhz

40mhz above control; will this select 5715mhz as the centre of the upper channel?
40mhz below control; will this select 5675mhz as the centre for the lower channel?

Or will it resort to the nearest standard channel? I.E 5660 / 5745 Or will it not work at all?

Advice appreciated; we are struggling a bit with understanding how it will actually work vs how it does work. Our findings so far have not been fantastic.

Cheers!
 
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 12:32 am

Hey Guys,

A quick question for anyone in the know; when selecting an extension channel; running in super channel mode will it work as expected? I.E

Control channel 5695mhz

40mhz above control; will this select 5715mhz as the centre of the upper channel?
40mhz below control; will this select 5675mhz as the centre for the lower channel?

Or will it resort to the nearest standard channel? I.E 5660 / 5745 Or will it not work at all?

Advice appreciated; we are struggling a bit with understanding how it will actually work vs how it does work. Our findings so far have not been fantastic.

Cheers!
What is the problem in this?
If you take "above control" you add 20Mhz upwards. "below control" means downwards.
The new channel is 40Mhz wide. So for up 5695-10=5685Mhz is low end limit, + 40Mhz gives 5725 as upper limit.
Halve of that is 5705 which gives the new centre frequency.

Be aware1; at given frequency of 5695Mhz the upper channel is not accepted by the software if country is set. Because the upper limit to use for the 5Ghz band is 5705Mhz. So the ROS won't accept the setting and you have to opt for the ´below´ channel option.

Be aware 2; If setting such 40Mhz channel, be aware that other radio's working channels that had some marginal channel separation suddenly might fall in this radio's frequency. Interference on both might become a problem.
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 12:40 am

Wireless Rudy; Thats not what the specifications for 802.11n (that i can find online) state; thats why the question is on the forum and is directed at people who can do more than make further assumptions.

Everything i can find online is "Control +1 or -1". An example specifically given is if control is 5700mhz (140); the +1 will be 5745 (149) (because there is no valid "Standard" channel inbetween). This gives rise to the question IS it simply + or - 20mhz; or is the implentation + or - 1 CHANNEL.

Given that in this case our Control is not a valid "Standard" channel; i wonder if it breaks. We are having issues getting the extension channel to operate correctly.
 
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 3:08 am

Wireless Rudy; Thats not what the specifications for 802.11n (that i can find online) state; thats why the question is on the forum and is directed at people who can do more than make further assumptions.
Well, if you call some simple math facts "assumptions" I understand why you are full of them:
Everything i can find online is "Control +1 or -1". An example specifically given is if control is 5700mhz (140); the +1 will be 5745 (149) (because there is no valid "Standard" channel inbetween). This gives rise to the question IS it simply + or - 20mhz; or is the implementation + or - 1 CHANNEL.

Given that in this case our Control is not a valid "Standard" channel; i wonder if it breaks. We are having issues getting the extension channel to operate correctly.
I read here "Everything i can find", "This gives rise to the question", "or is the implen....", "i wonder if it breaks"....... Who is making assumptions here?



Now, lets not make assumptions, but look at the facts:MT manual reference manual clearly states:
ht above and ht below allows to use additional 20MHz extension channel and if it should be located below or above control (main) channel. Extension channel allows 11n device to use 40MHz of spectrum in total thus increasing max throughput.
The logic math will only give this explanation on how it works.
Combined with my own experience in using it I note that this is how it's done.

To blame me for making "assumptions"! You must think you are quit somebody isn't it? Lets make another one; 'I assume you are not from this planet.' :(


Ok, let me put you with your feet on the ground and give you a lesson in logic reasoning. Lets analyse what you leave open as a possibility:

If up or down extension would be in terms of an official channel number, while the centre of the base is set to an ´in-between channel´ frequency, you would either not get 40Mhz or have a ´gap´ in the range. It's just not possible. You would either create a 35Mhz channel or a 45Mhz channel with a 5Mhz exclusion part! (Which is physically impossible.)

The use of frequencies not equal to the 'channel's reference numbers' is also nothing strange. MT doesn't give it a name, it just gives you all the 5Mhz different channels where others call it "channel shift" or similar.

The second assumption I now make in this reply is that you probably would assume this is in conflict of the 802.11n specifications. Because that is what you find 'online'. I suggest you report MT and others to the IEEE 802.11n workgroup. That will shake the industry! brrrr.

Give me a break.......
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 3:38 am

Well so far; you haven’t actually given me any FACTS to work with, only your version of logical reasoning :) That was my understanding of channel bonding as well; but after some digging and because it is not working as expected for us i thought to ask on the forum to clarify its ACTUAL operation.

I have made no assumptions so far, only asked questions to confirm my thinking, or not. MT often implement features in their own way and without precise documentation; an example: The lack of short GI for N. RouterOS has in the past had many bugs as well which cause unexpected operation; without asking how would i know how it will work / how it is intended to work?
 
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 3:59 am

Wireless Rudy; Thats not what the specifications for 802.11n (that i can find online) state; thats why the question is on the forum and is directed at people who can do more than make further assumptions.
Well, if you call some simple math facts "assumptions" I understand why you are full of them:
Everything i can find online is "Control +1 or -1". An example specifically given is if control is 5700mhz (140); the +1 will be 5745 (149) (because there is no valid "Standard" channel inbetween). This gives rise to the question IS it simply + or - 20mhz; or is the implementation + or - 1 CHANNEL.

Given that in this case our Control is not a valid "Standard" channel; i wonder if it breaks. We are having issues getting the extension channel to operate correctly.
I read here "Everything i can find", "This gives rise to the question", "or is the implen....", "i wonder if it breaks"....... Who is making assumptions here?



Now, lets not make assumptions, but look at the facts:MT manual reference manual clearly states:
ht above and ht below allows to use additional 20MHz extension channel and if it should be located below or above control (main) channel. Extension channel allows 11n device to use 40MHz of spectrum in total thus increasing max throughput.
The logic math will only give this explanation on how it works.
Combined with my own experience in using it I note that this is how it's done.

To blame me for making "assumptions"! You must think you are quit somebody isn't it? Lets make another one; 'I assume you are not from this planet.' :(


Ok, let me put you with your feet on the ground and give you a lesson in logic reasoning. Lets analyse what you leave open as a possibility:

If up or down extension would be in terms of an official channel number, while the centre of the base is set to an ´in-between channel´ frequency, you would either not get 40Mhz or have a ´gap´ in the range. It's just not possible. You would either create a 35Mhz channel or a 45Mhz channel with a 5Mhz exclusion part! (Which is physically impossible.)

The use of frequencies not equal to the 'channel's reference numbers' is also nothing strange. MT doesn't give it a name, it just gives you all the 5Mhz different channels where others call it "channel shift" or similar.

The second assumption I now make in this reply is that you probably would assume this is in conflict of the 802.11n specifications. Because that is what you find 'online'. I suggest you report MT and others to the IEEE 802.11n workgroup. That will shake the industry! brrrr.

Give me a break.......
Considering the ITU bands and UNII bands dont cover 5.6ghz it's a valid question, Your statment about gap channels being physically impossible is flawed, Many licensed bands use a gap between the TX and RX. Given MT's history of doing things their way and that fact that IEEE didn't design for odd channels the question is valid. Nothing in the manual states how the spectrum is joined or if there is any space, There are references out there to the fact that under 802.11N in some modes the "extra" channel will be put to sleep unless the higher data rates are required by throughput. There are many changes that occur when going from 802.11a/b/g to 802.11n and many people get confused by the lack of clear explanation, For example if the extra 802.11n channel is just stuck right next to the operational channel then why the need for the change from "turbo" mode under 802.11a/g? There must have been a valid reason for giving the user the option to place the channel below or above the control channel

So how about you let MT respond to this one and go back to your "port flapping" thread?
 
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 5:52 am

So to figure this one out ourselves; we fired up airview, set up two new sxt's and tested. Centre frequency for the test is 5545mhz

You can see in the file 20mhz; centre frequency is clearly 5545mhz although there is a concerning amount of bleed either side of the centre frequency.

In the file 40mhz you can clearly see that an additional 20mhz channel has been tacked on as well as a considerable (10mhz) amount of bleed in the upper frequency. This doesn't not appear to have shifted the centre frequncy; and the additional channel appears to be detected at a slightly lower power level than the control channel.

So not only is the channel detected as being a lot wider than 40mhz; it does not appear to create a new centre frequency as you stated.

Of course; i would be happy to hear other interpretations of these attachments.
You do not have the required permissions to view the files attached to this post.
 
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 10:58 pm

Well so far; you haven’t actually given me any FACTS to work with, only your version of logical reasoning :) That was my understanding of channel bonding as well; but after some digging and because it is not working as expected for us i thought to ask on the forum to clarify its ACTUAL operation.

I have made no assumptions so far, only asked questions to confirm my thinking, or not. MT often implement features in their own way and without precise documentation; an example: The lack of short GI for N. RouterOS has in the past had many bugs as well which cause unexpected operation; without asking how would i know how it will work / how it is intended to work?
hmm, what is written in the MT manual is not taken as FACTS in your opinion. Well, maybe true. A bit bold to state so but ok, you might be right in a way that indeed they are not always very clear in their explanations.
(By the way, I don't understand what channel bonding has to do with this discussion. It is of a complete different nature.)

If your defence that your words are not to be explained as making assumptions, why then do you blame me for doing so where I only reproduce what is written in the manual and where I explain what simple math tells us?
Don't put fellow members of this forum in a corner if you yourself are coming from it. You might expect some ´nasty´ replies.

The reason your setup doesn't work with the extended channel can have several other reasons. I use them on several links and they works exactly like MT explains and what I would expect taken the plain math I'd learned at school.

Anyway, no hard feelings. Just watch a bit what you write if pointing fingers at someone. :)
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 11:07 pm

Well so far; you haven’t actually given me any FACTS to work with, only your version of logical reasoning :) That was my understanding of channel bonding as well; but after some digging and because it is not working as expected for us i thought to ask on the forum to clarify its ACTUAL operation.

I have made no assumptions so far, only asked questions to confirm my thinking, or not. MT often implement features in their own way and without precise documentation; an example: The lack of short GI for N. RouterOS has in the past had many bugs as well which cause unexpected operation; without asking how would i know how it will work / how it is intended to work?
hmm, what is written in the MT manual is not taken as FACTS in your opinion. Well, maybe true. A bit bold to state so but ok, you might be right in a way that indeed they are not always very clear in their explanations.
(By the way, I don't understand what channel bonding has to do with this discussion. It is of a complete different nature.)

If your defence that your words are not to be explained as making assumptions, why then do you blame me for doing so where I only reproduce what is written in the manual and where I explain what simple math tells us?
Don't put fellow members of this forum in a corner if you yourself are coming from it. You might expect some ´nasty´ replies.

The reason your setup doesn't work with the extended channel can have several other reasons. I use them on several links and they works exactly like MT explains and what I would expect taken the plain math I'd learned at school.

Anyway, no hard feelings. Just watch a bit what you write if pointing fingers at someone. :)
I think the pictures above paint a clear picture that extension channels dont work the way most people assume them to work, the channel chosen in ROS with an extension channel above ends up being -10mhz to +30mhz from the channel chosen and reverse for extension channel below, This is counter to what resources online point it to be. The manual doesn't explain this behavior and as such can't be incorrect but it's a failure of MT to explain this behavior when it's very different to the behavior that clients using turbo mode are used to and difficult to diagnose without a spectrum analyzer
 
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Re: 802.11n Extension Channel

Mon Oct 03, 2011 11:55 pm

So to figure this one out ourselves; we fired up airview, set up two new sxt's and tested. Centre frequency for the test is 5545mhz

You can see in the file 20mhz; centre frequency is clearly 5545mhz although there is a concerning amount of bleed either side of the centre frequency.

In the file 40mhz you can clearly see that an additional 20mhz channel has been tacked on as well as a considerable (10mhz) amount of bleed in the upper frequency. This doesn't not appear to have shifted the centre frequncy; and the additional channel appears to be detected at a slightly lower power level than the control channel.

So not only is the channel detected as being a lot wider than 40mhz; it does not appear to create a new centre frequency as you stated.

Of course; i would be happy to hear other interpretations of these attachments.
Well, I don't know what you call a "centre frequency". I would call it the middle of the frequency range of the bandwidth the radio transmits in. So if you widen the band upwards, the centre frequency travels with it upwards. (half as far). Your pictures are showing this perfectly. Take the upper limit and the down limit of the 40Mhz channel and you find the new ´centre frequency'.
That now this 20Mhz extension might have some slightly lower power as the original chosen 20Mhz band has nothing to do with it. (Although it is interesting to see!)

That MT in its ROS still uses the original centre frequency of the first chosen 20Mhz band is merely an approach of them.
You might find this confusing. Maybe pure mathematically it would be better to show the new 40Mhz centre frequency. I think it is also some resemblance of how they used same in older ROS versions.

´Bleeding´ of radio energy outside the set working frequency's limits is nothing abnormal. Plenty is written about that in this forum. EVERY radio bleeds outside its working band. It is merely how much the bleeding is that distinguish between poor radio's and good radio's. (Or capping filters in use.)

No hard feelings but I'm sorry to say that my interpretation of your pictures are more proof to exactly what MT means in their manual and I see happening in real live and what makes sense if taken it mathematically.
Your interpretation has some ground, but not as much as mine.

It is also not a big issue. You are the first I ever see mentioning this issue while there must be plenty of operators using the extension channel for years now and they exactly know what they are up to. If there were any ´real´ issues on the extension channel I'm sure it would make it to this forum many times before you did.
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:07 am

Fair enough.

With 802.11A when you used "Turbo Mode" for 40mhz; the frequency selected in ROS was the centre frequency and you could plan for interference around knowing 100% for sure that you would transmit 20mhz either side of this.

With 802.11N when you use the above or below extension channel it is initially confusing that the frequency selected is the centre frequency of the control; more confusing is that the extension channel is enabled and disabled as throughput increases / decreases; unlike turbo mode it does not appear to always be "ON".

The question i initially asked has largely been answered however by our own investigation and i hope other forum users find value from it.
 
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:11 am

I think the pictures above paint a clear picture that extension channels dont work the way most people assume them to work, the channel chosen in ROS with an extension channel above ends up being -10mhz to +30mhz from the channel chosen and reverse for extension channel below, This is counter to what resources online point it to be. The manual doesn't explain this behavior and as such can't be incorrect but it's a failure of MT to explain this behavior when it's very different to the behavior that clients using turbo mode are used to and difficult to diagnose without a spectrum analyzer
This post again makes me wonder what your your intake is in this
First you jump in this discussion with arguments missing the point showing you are not in any position to comment even simple discussions.
Then you send me a private message using offensive language and deprive me of karma points not even earned by me on this subject! You came close for reporting you for abuse to the moderator of this forum.
And now you make a conclusion that is obviously beside the truth. Writing "dont work the way most people assume them to work" is a bold statement questioning the intelligence of other users :( .

Since this issue never came up on this forum before and the extension channels are widely in use I don't think many of us users have problems with it and they clearly understand how MT is explaining how it works. But maybe your are disagreeing with us all?

To keep this discussion a bit more academic it would be better if you would refrain from further comments and proceed in what you are good in; reading my posts.... CU! :)
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:14 am

Well, I don't know what you call a "centre frequency". I would call it the middle of the frequency range of the bandwidth the radio transmits in. So if you widen the band upwards, the centre frequency travels with it upwards. (half as far). Your pictures are showing this perfectly. Take the upper limit and the down limit of the 40Mhz channel and you find the new ´centre frequency'.
That now this 20Mhz extension might have some slightly lower power as the original chosen 20Mhz band has nothing to do with it. (Although it is interesting to see!)

That MT in its ROS still uses the original centre frequency of the first chosen 20Mhz band is merely an approach of them.
You might find this confusing. Maybe pure mathematically it would be better to show the new 40Mhz centre frequency. I think it is also some resemblance of how they used same in older ROS versions.
The point is the center frequency is not being reported in MT, With a 20mhz channel the selected freq in Winbox is the center, You operate -10mhz and +10mhz from this point, Under turbo mode in 802.11a/g you would be operating -20mhz to +20mhz of this selection however under N you operate either -10mhz to +30mhz or -30mhz to +10mhz. I suspect most operators out there don't operate these kinds of link's on a noisy site but since we do because we have 90+ high sites.

Looking around at how OTHERS do it like UBNT and your normal 802.11n home AP the channel you select with 40mhz will operate -20mhz to +20mhz of the channel and as such MT's operation is counter to the norm, Please highlight the section of the manual where this is explained
 
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:18 am

Fair enough.

With 802.11A when you used "Turbo Mode" for 40mhz; the frequency selected in ROS was the centre frequency and you could plan for interference around knowing 100% for sure that you would transmit 20mhz either side of this.

With 802.11N when you use the above or below extension channel it is initially confusing that the frequency selected is the centre frequency of the control; more confusing is that the extension channel is enabled and disabled as throughput increases / decreases; unlike turbo mode it does not appear to always be "ON".

The question i initially asked has largely been answered however by our own investigation and i hope other forum users find value from it.
That's exactly the purpose of this forum! I'll bet some readers are following this one with interest!

I can see where you are coming from. And like I wrote, pure mathematically it would be better if MT would have chosen a different approach. On the other hand, I don't think many users are coming form the "Turbo Mode" era. Simply because that is in most countries not allowed. So these are a bit ´virgin´ when it came to the use of extension channels in ´n´ mode.

The bottom line is that for all readers it might be clear now how it works.
The way MT presents it is indeed questionable as you show but I presume (hé, here is one! :D ) most users don't have an issue with it.
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:22 am

I can see where you are coming from. And like I wrote, pure mathematically it would be better if MT would have chosen a different approach. On the other hand, I don't think many users are coming form the "Turbo Mode" era. Simply because that is in most countries not allowed. So these are a bit ´virgin´ when it came to the use of extension channels in ´n´ mode.

The bottom line is that for all readers it might be clear now how it works.
The way MT presents it is indeed questionable as you show but I presume (hé, here is one! :D ) most users don't have an issue with it.
Turbo mode is illegal? ISM bands never had channel width limits unless you wanted to us a 100mhz wide channel in a 2.4ghz band, 40mhz channels were never illegal. With 2.4ghz 40mhz you had only 1 channel you could us to be within the band. Just because "most users" dont have an issue with it is not an excuse for poor documentation, Remember the way it's been clarified here was with a UBNT unit!
 
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:25 am

The point is the center frequency is not being reported in MT, With a 20mhz channel the selected freq in Winbox is the center, You operate -10mhz and +10mhz from this point, Under turbo mode in 802.11a/g you would be operating -20mhz to +20mhz of this selection however under N you operate either -10mhz to +30mhz or -30mhz to +10mhz. I suspect most operators out there don't operate these kinds of link's on a noisy site but since we do because we have 90+ high sites.

Looking around at how OTHERS do it like UBNT and your normal 802.11n home AP the channel you select with 40mhz will operate -20mhz to +20mhz of the channel and as such MT's operation is counter to the norm, Please highlight the section of the manual where this is explained
http://wiki.mikrotik.com/wiki/Manual:Interface/Wireless
Go to "General Interface properties" and look for "channel-width"

Its sad now I even have to read the manual for you..... :( :(
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:28 am

The point is the center frequency is not being reported in MT, With a 20mhz channel the selected freq in Winbox is the center, You operate -10mhz and +10mhz from this point, Under turbo mode in 802.11a/g you would be operating -20mhz to +20mhz of this selection however under N you operate either -10mhz to +30mhz or -30mhz to +10mhz. I suspect most operators out there don't operate these kinds of link's on a noisy site but since we do because we have 90+ high sites.

Looking around at how OTHERS do it like UBNT and your normal 802.11n home AP the channel you select with 40mhz will operate -20mhz to +20mhz of the channel and as such MT's operation is counter to the norm, Please highlight the section of the manual where this is explained
http://wiki.mikrotik.com/wiki/Manual:Interface/Wireless
Go to "General Interface properties" and look for "channel-width"

Its sad now I even have to read the manual for you..... :( :(
It uses the same terms above and below control but doesn't actually explain what this does in the spectrum, It's normal on pretty much anything other than MT to use the set freq as the center freq no matter what width you select
 
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:30 am

Turbo mode is illegal?
Yes they are in many countries. Unless you are telling us now that MT is selling us illegal stuff!
If ROS is set to regulatory domain and your country is set you'll find for many countries the use of 40Mhz is excluded.
MT builds ROS to comply with the regulations....

regarding the other comments I'm not even bothering to reply on these. Good night.
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:39 am

Turbo mode is illegal?
Yes they are in many countries. Unless you are telling us now that MT is selling us illegal stuff!
If ROS is set to regulatory domain and your country is set you'll find for many countries the use of 40Mhz is excluded.
MT builds ROS to comply with the regulations....

regarding the other comments I'm not even bothering to reply on these. Good night.
Then 802.11n 40mhz is illegal too since regulatory domains aren't concerned with the tech just the raw mhz in use :) You've shown time and time again around here you dont have much clue about what you talk about and lack the experience to see the oddities in ROS that are different from industry norms, Do you operate a transmission site where you use 200+mhz of spectrum(non overlapping!), Because if you dont then you wont understand the impact of not running in a reported center channel can cause. Just because you've stumbled your way into operating a network doesn't mean that difference like this one wont have an impact on anyone and again it's a lack of explanation in MT's documentation that has brought us here
 
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 12:53 am

@Beccara: You are really full of the same "#%&*@!" as what you accused me off in your private message.

You show in this topic you really lack proper conduct and have not a clue what you speak about. You are becoming an nuisance to this forum this way. :?

Off course do I run in the full 200mhz of spectrum. I am one of the users that pointed MT on the interference issues in previous version of ROS5 and actually showed them the repercussion of the use of their NV2 in interference prone channels. I work with in total 14 radio's all in ´hearing distance´ from each other in this 200Mhz wide band and run a stable network with NV2. Something many of this forum show they still have problems with.
You are making over and over again statements that are not in anyway positive to this forum.

I'd actually replied to you in another topic and although here is the change for you to show you have at least somewhere some knowledge of running a network so far all that comes from your direction is a lot of useless comments.
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 1:02 am

14 Radios?
 
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 1:03 am

Do you actually mean 140 radios? OR 1400 radios?
 
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 4:02 am

Do you actually mean 140 radios? OR 1400 radios?
I mean that in an area of some 15km radius I have in total 14 AP's.
In between all these I have links running, so actually I have more radio's transmitting in my region.

Each AP has at least one radio for the AP function. And at least one radio for the Backhaul.
Some towers serve more than one other tower so on some towers I have in total 4 or 5 backhauls grouped.
some towers also have more than one AP-radio combination since some work with sectors.

Basically I have 14 AP's with as many backhaul links. All my AP's work in 10Mhz bandwidth and all my backhaul in either legacy 802.11a 20Mhz channel width or some links in 802.11a+n and 40Mhz bandwidth.

Consider that at least 3 other towers with several units of the competition also use several AP's, all working in the same 802.11a or 802.11a+n band as I do (Some use MT, some ubnt's Airmax) and we also have 2 Wimax providers in the same region (work in adjacent bands) than you can imagine the spectrum here is made good use of!

If I run wireless scans on each of my AP's I can almost everytime pickup at least 14 other radio's transmitting in the same 200Mhz band. Some with signal strenghts that are quit strong!

So you can imagine I have had my share in interferences. But together with others on the forum we nagged MT long enough about their NV2 protocol to have them fine tune it in such extend my network is now very stable on the moment with ros 5.6.
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 4:21 pm

While your fight is pretty funny, the argument is interesting..
I would like to know if really an extension channel "above control" is +30 and -10 from the frequency used or not..
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 6:10 pm

While your fight is pretty funny, the argument is interesting..
I would like to know if really an extension channel "above control" is +30 and -10 from the frequency used or not..
I'm going to just dodge this while flame war and try to answer the question as best I can:

Unless operating in regulatory domain, wireless radios to not inherently understand "channels". They are a product of local jurisdiction and designed to make things easier on users. Firmware can be told to limit certain ranges from use, but the underlying hardware doesn't really care. As long as the internal frequency generator/multiplier can hit a frequency, it can broadcast. This is why superchannel mode exists. Whether you can or can't operate legally at a frequency is a local legal matter and outside the scope of this discussion.

The Wikipedia chart for 2.4Ghz may or may not make this clearer for some:
http://en.wikipedia.org/wiki/IEEE_802.1 ... 4.C2.A0GHz

It works the same way with 5GHz, just without the overlap of channels.
In 20MHz mode, if 5695MHz is set, it will use 5685MHz-6005MHz (20MHz with a center at 5695MHz).

If 40MHz is selected, with a 5695MHz Control channel and extension channel above,
then the radio will use 5685MHz-5725MHz, but will have 2 "center" frequencies.
The "extended" center of 5705MHz will be used to talk to 40MHz clients.
The original center of 5695MHz will be used to talk to legacy 20MHz clients.

If 40MHz is selected, with a 5695MHz Control channel and extension channel below,
then the radio will use 5665MHz-5705MHz, but will have 2 "center" frequencies.
The "extended" center of 5685MHz will be used to talk to 40MHz clients.
The original center of 5695MHz will be used to talk to legacy 20MHz clients.

This assumes 2 things: The card is capable of transmitting on the frequencies specified and there is no weird block in the firmware preventing the use of certain channels. To my knowledge, Mikrotik does not block any channels when operating in superchannel mode, though the card may have different limitations.

The 20MHz legacy compatibility is why spectral scans don't show a flat 40MHz wide channel, and the cause for a lot of confusion in interpretations of the 802.11n spec.

I hope this helps clear up the confusion for some.
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 10:09 pm

While your fight is pretty funny, the argument is interesting..
I would like to know if really an extension channel "above control" is +30 and -10 from the frequency used or not..
I'm going to just dodge this while flame war and try to answer the question as best I can:

Unless operating in regulatory domain, wireless radios to not inherently understand "channels". They are a product of local jurisdiction and designed to make things easier on users. Firmware can be told to limit certain ranges from use, but the underlying hardware doesn't really care. As long as the internal frequency generator/multiplier can hit a frequency, it can broadcast. This is why superchannel mode exists. Whether you can or can't operate legally at a frequency is a local legal matter and outside the scope of this discussion.

The Wikipedia chart for 2.4Ghz may or may not make this clearer for some:
http://en.wikipedia.org/wiki/IEEE_802.1 ... 4.C2.A0GHz

It works the same way with 5GHz, just without the overlap of channels.
In 20MHz mode, if 5695MHz is set, it will use 5685MHz-6005MHz (20MHz with a center at 5695MHz).

If 40MHz is selected, with a 5695MHz Control channel and extension channel above,
then the radio will use 5685MHz-5725MHz, but will have 2 "center" frequencies.
The "extended" center of 5705MHz will be used to talk to 40MHz clients.
The original center of 5695MHz will be used to talk to legacy 20MHz clients.

If 40MHz is selected, with a 5695MHz Control channel and extension channel below,
then the radio will use 5665MHz-5705MHz, but will have 2 "center" frequencies.
The "extended" center of 5685MHz will be used to talk to 40MHz clients.
The original center of 5695MHz will be used to talk to legacy 20MHz clients.

This assumes 2 things: The card is capable of transmitting on the frequencies specified and there is no weird block in the firmware preventing the use of certain channels. To my knowledge, Mikrotik does not block any channels when operating in superchannel mode, though the card may have different limitations.

The 20MHz legacy compatibility is why spectral scans don't show a flat 40MHz wide channel, and the cause for a lot of confusion in interpretations of the 802.11n spec.

I hope this helps clear up the confusion for some.
Excellent post! Completely in line to what I was trying to explain. I was only carried away too much by some 'intruder' of this discussion that I lost the focus a bit. I am glad you found a way to put things on paper in an understandable way.
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Re: 802.11n Extension Channel

Tue Oct 04, 2011 11:22 pm

Excellent thanks CCDKP

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