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Community Manager
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Incorrect Supported Rates IE in beacons when using Wireless Hosted Network with Centrino adapters

Hello,

I'm seeing an odd issue when using Wireless Hosted Network on Windows 7 with a Centrino adapter. Essentially, the supported rates advertised in the beacon frames contain only the 802.11g OFDM rates and none of the 802.11b rates, even when the adapter is in a/b/g or b/g mode. I've used Wireshark to sniff the management frames over the air and see the following:

Centrino adapter configured to 802.11 a/b/g or b/g mode (via Device Manager):

Beacons and Probe Responses: sent at 6.0 Mbps, short preamble

Supported Rates IE contains: 6, 9, 12, 18, 24, 36, 48, 54

No Extended Supported Rates IE

Centrino adapter configured to 802.11 b mode (via Device Manager):

Beacons and Probe Responses: sent at 6.0 Mbps, short preamble (odd, since we should be configured in 11b mode)

Supported Rates IE contains: 1, 2, 5.5, 11

No Extended Supported Rates IE

We prefer using a/b/g mode and have done empirical testing of association/authentication reliability of other wireless devices connecting to Centrino versus other adapters. On the Centrino, due to the supported rates IE, 802.11 association and authentication take place using 6.0Mbps instead of the typical 1.0Mbps rate. All of the other Broadcom/Ralink/Atheros chipsets that we've tested advertise both 11b and 11g OFDM rates and thus all 802.11 association and authentication takes place at 1.0 Mbps.

We've run tens of thousands of test iterations in a semi-noisy environment and found that using the 6.0 Mbps OFDM rate for association/authentication causes an order of magnitude greater connect failure rate than on other adapters. This Supported Rates IE behavior was observed with the two Centrino chipsets that we tested - a Centrino Advanced-N 6235 (a/b/g/n) and a Centrino Wireless-N 100 (b/g/n). It has also been observed with two of the newest driver versions - 15.0.0.75 and 15.1.1.1.

Is there a driver fix that can be made so that both 802.11b and g rates can be advertised? Or is there possibly some way to use NDIS or other methods/utilities to control the supported rates IE?

Thanks in advance for any insights/pointers!

Jared

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2 Replies
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Employee
248 Views

Thank you for your post Jg,

 

As per the description of your issue it seems that you have your network set up with a short preamble and that you are trying to use a legacy standard such as 802.11b.

 

In case you want to use a legacy standard then you must use the long preamble set on the router configurations.

 

Here is the link for the preamble explanation:

 

http://www.intel.com/support/wireless/wlan/sb/CS-025317.htm http://www.intel.com/support/wireless/wlan/sb/CS-025317.htm

 

I hope this helps.

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Community Manager
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Thanks for the quick response, Victor! I think there's a slight misunderstanding though - I'm using Wireless Hosted Network so the Centrino laptop itself is the access point.

When I look at the options on the adapter in Device Manager, it seems like there's no way to control or set preamble. Here's an example screenshot from a Centrino Wireless-N 100:

I'm basically trying to find a way to have the Centrino (when acting as an AP via Microsoft's Wireless Hosted Network API) advertise 1, 2, 5.5, and 11 Mbps rates in addition to the OFDM rates (6, 9, 12, 18, 24, 36, 48, 54) when in b/g or a/b/g mode.

Thanks again for your reply!

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