1131AG Trying to get 108Mbps to work

Unanswered Question
May 19th, 2008

I have a Cisco 2100 series WLC and 3 Cisco 1131AG AP's. I'm trying to get 108Mbps by enabling both 802.11a & 802.11g networks on the controller. My laptop is set for 802.11a&g but I'm still only getting 54Mbps. What am I missing?

I have this problem too.
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rob.huffman Mon, 05/19/2008 - 14:02

Hi Todd,

As you have discovered the number 108 is the combinaton of 802.11g and 802.11a data rates, and you can only connect to one or the other, not both simultaineously. Have a look;

Approximate Throughput Comparison for 802.11a, 802.11b, and 802.11g

802.11b Data Rate (Mbps)=11 Approximate Throughput (Mbps)=6

802.11g (no 802.11b clients in cell) Data Rate (Mbps)=54 Approximate Throughput (Mbps)=22

802.11a Data Rate (Mbps)=54 Approximate Throughput (Mbps)=25

From this great doc;

http://www.cisco.com/en/US/products/hw/wireless/ps430/products_white_paper09186a00801d61a3.shtml

Hope this helps!

Rob

hollywoodmi Tue, 05/20/2008 - 08:27

Thanks for the feedback. After reading the replies and that white paper I now understand how it works.

Sushil Kumar Katre Tue, 05/20/2008 - 00:50

Hey Todd,

Just to add.

108Mbps is the term which is always misleading. Its basically 108 Mbps bandwidth which wouldbe shared by the users and not he speed at which the users would be connected to the AP. The fact is that the speed at which the client can get connected to the AP would remain 54 Mbps, either 802.11a or g as stated by Rob.

These are two terminologies - Speed - The rate which a client is connected. Bandwidth - at what rate you can push actual traffic excluding the overheads, which is typically 50 - 55 % of the speed in wireless communication.

However the benifit of having dual radio AP is that you can enable both the radios to provide coverage in the same area and get more clients served by the same AP. Its equivalent to installing two APs in the same region.

So for example earlier there were 20 clients associated to 802.11G, theoritically 54Mbps *BANDWIDTH* was shared between 20 users. Now when you have dual radio AP and enable both the radios, 108 [54 from 802.11a + 54 from 802.11g] would be shared among 20 users. 10 users connected using 802.11a [*SPEED* 54 Mbps] and remaining 10 connected using 802.11g [*SPEED* 54 Mbps].

Hope this clarifies.

-> Sushil

hollywoodmi Tue, 05/20/2008 - 08:15

Thank you for the info. I now have a better understanding of how that works. I was under the impression that the network card used both radios simultaneously to get the 108Mbps throughput. I understand now how that works. Thank You!

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