Running wireless with just channels 1 and 6

Hi All, looking for some advice on a potential configuration change in our wireless setup. We are currently running a Cisco 4404 wireless LAN controller with over 70 APs spread over 3 campuses (a mix of 1131 and 1231 APs). Channels are automatically assigned by the WLC and this system has been in place for around 7 years and worked well up to press.

Due to some recent building renovations a door control system has been introduced that uses wireless technology for the access control readers. The manufacturers guidelines state that channel 11 should be reserved for their door control APs. We have implemented this system in one building so far and I have manually fixed the 4 Cisco APs on either channels 1 or 6. If the system is rolled out further I can make a global change on the WLC to only use channels 1 and 6 for dynamic allocation. However, I am uneasy about doing this as I believe it will significantly impact the existing wifi network. As we do not have Cisco Wireless Control System I am unable to produce any reports to verify my concerns, and I am trying to make a sound case to management why this might not be a good idea.

Can anyone throw in their technical expertise and share their thoughts on running a 2.4GHz wifi solution with just channels 1 and 6?

You can, but with 70 WAPs it's going to be tricky. Can't they change it to channel 13?

Alternatively move up to 5GHz, but please bear in mind most wireless NICs at the moment do not support 5GHz.

Caveat: I've managed four wireless networks from different vendors. I am researching high density deployments. I have not had training on wireless technology, nor have I any experience of Cisco Wireless networks. I have not had to lose a channel from any networks I have looked after.

By taking out a channel for general use you are creating a higher density wlan. Cisco has good documentation on the challenges of high density deployments. Co-Channel Interference being the most significant.

By making this change you are dramatically increasing Co-Channel interference on your sites. WCS has technology for mitigating this, however I have only seen that mitigation technology described in a 3 channel solution design to overcome the inevitable interference in high density deployments. That said two radios on the same channel can co-exisit and demodulate each others' transmissions and share the bandwidth amicably. (Cisco High Density Wireless LAN Design Guide - Cisco Systems)

That said, at the edges (-80dB or less) of the overlapping broadcast domains the APs may detect each other as noise. In effect raising the noise floor in your environment You need 20dB difference between the 'Noise' and signal to have an effective connection.

I'd be very uncomfortable in a situation where I had to lose an entire channel from a micro-cell architected network. However, finding that a channel is unusable across a particular site is not uncommon, and depending on the Wireless Controller software available and how good the APs are at analysing their RF environment, is something that some deployments can 'just deal with'.

Some questions to consider:
Are the doors actually wifi? If so are they using your infrastructure? Might you be able to reduce the power of radios serving them and restrict the SSID's presented by these AP's to isolate the channel in that broadcast domain around the door, while allowing for channel re-use at distance from them? Or perhaps apply some QoS to the door SSID to prioritise the door traffic in the event of contention, leving the channel available for all?

Final thought: Your infrastructure is seven years old. It might be time to start looking at a complete replacement for it, with the solution to the challenge these doors present as a requirement for your new implementation.

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Originally Posted by Michael

You can, but with 70 WAPs it's going to be tricky. Can't they change it to channel 13?

Alternatively move up to 5GHz, but please bear in mind most wireless NICs at the moment do not support 5GHz.

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I've had a look at the options for changing channel on the Access Control system and the channel range is a little unusual - it allows you to select channels 1 - 25 (currently set at 25). Suspect this could be Zigbee (or some other proprietary wifi system) using the 2.4GHz range?

I'm not entirely sure to be honest. Channel 13 is used mostly in the USA, but because a lot of products are manufactured for global use that's why we have it in Europe too, although technically it's not 'ratified' in Europe as such.

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Originally Posted by Michael

I'm not entirely sure to be honest. Channel 13 is used mostly in the USA, but because a lot of products are manufactured for global use that's why we have it in Europe too, although technically it's not 'ratified' in Europe as such.

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It's the other way around, USA channels are 1-11, Europe is 1-13

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Originally Posted by paulfinlay

It's the other way around, USA channels are 1-11, Europe is 1-13

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:doh: You're absolutely right, sorry about that!