problem with configuring 40mhz width channel on Aironet 1141

[Temur Kalandia]

hello,

      recently we purchased cisco aironet AIR-AP1141N-E-K9 standalone model.  after configuring it , client has no problem with connection and coverage, but there is problem with thoughput.  clients are not able to connect at higher rates, even if i set channel width at 40 mhz, max rate for N capable client device is 54mb.

      can someone give me a little hints  how to solve this problem?

this is my configuration , or see attached file

http://pastebin.com/1WHeSvmq

many thanks

[Temur Kalandia]

hello leo

  Can you please tell me where is written in the data sheet that there is 802.11 b radio?   i cant find any information about this.  this  is exact data sheet of my AP :

http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps10092/datasheet_c78-502793.pdf

[Scott Fella]

The 1141 you have has only a 2.4ghz radio. This means it support both 802.11b and 802.11g. Does the code on your 1141 have support for 40mhz on the 2.4ghz? I never knew they had that available on any APs except for the 1252's, but then that was short lived.

Sent from Cisco Technical Support iPhone App

[Roger Alderman]

Lets get things into perspective on this discussion.

The AP is an 802.11g/n device so yes it does only have a 2.4GHz radio. However, providing the AP supports it there is absolutely nothing to say you can't bond channels in 2.4GHz. We all know that's not a good move and its not good practise but if you only have a single AP and you're not going to cause problems for anyone else then what's to stop you?

If the AP has been configured for the higher data rates using channel bonding (which it has and it's a stand-alone AP so no controller settings are relevant here) then the issue isn't likely to lie with the AP.

To achieve the higher data rates the client adaptor also needs to support channel bonding, 2 spatial streams and it must be configured accordingly. Does the adaptor even support 11n? Is it configured for 11n?

You can muck about with the AP all day but if the client isn't correct then you're wasting your time.

Give us some details of the client please?

[daviwatk · Accepted solution]

You cannot configure channel bond on 2.4GHz; this is explained in the document linked via the answer marked "correct" and is in quotations below.  I suppose it's feasible his AP is running a much older IOS release, but it looks like a 12.4 release

Temur:  Can you provide the exact IOS version you are running?

Roger Alderman wrote:
Lets get things into perspective on this discussion.
The AP is an 802.11g/n device so yes it does only have a 2.4GHz radio. However, providing the AP supports it there is absolutely nothing to say you can't bond channels in 2.4GHz. 

"Cisco does not support channel bonding in 2.4 GHz frequency (802.11 b/g), because only three non-overlapping channels 1, 6 and 11 are available."

How Does 802.11n Provide Greater Throughput

Various techniques are employed in 802.11n to provide higher data rates and better coverage. This section details the techniques used.

MIMO: In the existing 802.11 a or 802.11 b/g technologies, transmission and reception of data streams usually happen using only one of the antennas. However, in 802.11n data streams can be transmitted and received over both the antennas. This results in a greater number of bits transmitted and received at a given point of time, effective usage of multipath signals which is usually a problem in indoor coverage. This leads to increased throughput and wider coverage. Table 1 shows the data rates of 802.11n currently supported by Cisco¹. MCS 0-7 are the data rates achieved using single spatial stream (data bits). MCS 8-15 are the data rates achieved using 2 spatial streams, one over each antenna. Note that the data rates are doubled from 8-15. These data rates (0-15) are described as MCS rates throughout this document.

Note: ¹Further higher data rates are planned for future deployments.

Channel Bonding: The amount of data that can be transmitted also depends on the width of the channel used in data transmission. By bonding or combining two or more channels together, more bandwidth is available for data transmission. In 2.4 and 5 GHz frequency band, each channel is approximately 20 MHz wide. In 802.11n, two adjacent channels, each of 20 MHz are bonded to get a total bandwidth of 40 MHz. This provides increased channel width to transmit more data. Cisco does not support channel bonding in 2.4 GHz frequency (802.11 b/g), because only three non-overlapping channels 1, 6 and 11 are available. However, the channel bonding has more relevance in 5 GHz frequency range where you have as many as 23 adjacent non-overlapping channels currently available. Channel bonding is supported only in 5 GHz, for example 802.11a. Table 2 shows the data rates achieved through channel bonding.

[daviwatk]

Also the same data sheet referenced by original poster reflects the channel widths/etc showing 2.4GHz doesn't include 40MHz.  While it does show that there is a 300Mbps maximum PHY rate (which is true); it's under particular configurations/circumstances. ie. 40MhHz 802.11n on 5GHz with client adapters that have minimum of 2 spatial streams, given all other necessary 802.11n requirements: WPA2/AES or Open, WMM enabled.

Notice in the same data sheet 40MHz is not referenced in 2.4GHz whether b/g or n, however in the 5GHz, we see 40MHz listed in 802.11n.

Maximum Number of NonOverlapping Channels

2.4 GHz

● 802.11b/g:

◦ 20 MHz: 3

● 802.11n:

◦ 20 MHz: 3

5 GHz

● 802.11a:

◦ 20 MHz: 21

● 802.11n:

◦ 20 MHz: 21

◦ 40 MHz: 9

Given you're achieving 144Mbps (MCS 15); you're getting the max data rate achievable on an 1141 AP; ie these clients "do" have two spatial streams, however your AP doesn't support channel bonding to double that throughput sinc you don't have a 5GHz radio.

[Leo Laohoo]

Hi David,

You're on!

*Endorsed*