By Art Reisman
I just came back from one of our user group seminars held at a very prestigious University. Their core networks are all running smoothly, but they still have some hard to find, sporadic dead spots on their wireless network. It seems no matter how many site surveys they do, and how many times they try to optimize their placement of their access points, they always end up with sporadic transient dark spots.
Why does this happen?
The issue with 802.11 class wireless service is that most access points lack intelligence.
With low traffic volumes, wireless networks can work flawlessly, but add a few extra users, and you can get a perfect storm. Combine some noise, and a loud talker close to the access point (hidden node), and the weaker signaled users will just get crowded out until the loud talker with a stronger signal is done. These outages are generally regional, localized to a single AP, and may have nothing to do with the overall usage on the network. Often, troubleshooting is almost impossible. By the time the investigation starts, the crowd has dispersed and all an admin has to go on is complaints that cannot be reproduced.
Access points also have a mind of their own. They will often back down from the best case throughput speed to a slower speed in a noisy environment. I don’t mean audible noise, but just crowded airwaves, lots of talkers and possible interference from other electronic devices.
For a quick stop gap solution, you can take a bandwidth controller and…
Put tight rate caps on all wireless users, we suggest 500kbs or slower. Although this might seem counter-intuitive and wasteful, it will eliminate the loud talkers with strong signals from dominating an entire access point. Many operators cringe at this sort of idea, and we admit it might seem a bit crude. However, in the face of random users getting locked out completely, and the high cost of retrofitting your network with a smarter mesh, it can be very effective.
Along the same lines as using fixed rate caps, a bit more elegant solution is to measure the peak draw on your mesh and implement equalizing on the largest streams at peak times. Even with a smart mesh network of integrated AP’s, (described in our next bullet point) you can get a great deal of relief by implementing dynamic throttling of the largest streams on your network during peak times. This method will allow users to pull bigger streams during off peak hours.
Another solution would be to deploy smarter mesh access points…
I have to back track a bit on my stupid AP comments above. The modern mesh offerings from companies such as:
Aruba Networks (www.arubanetworks.com)
Meru ( www.merunetworks.com)
Meraki ( www.meraki.com)
All have intelligence designed to reduce the hidden node, and other congestion problems using techniques such as:
- Switch off users with weaker signals so they are forced to a nearby access point. They do this basically by ignoring the weaker users’ signals altogether, so they are forced to seek a connection with another AP in the mesh, and thus better service.
- Prevent low quality users from connecting at slow speeds, thus the access point does not need to back off for all users.
- Smarter logging, so an admin can go in after the fact and at least get a history of what the AP was doing at the time.
Related article explaining optimizing wireless transmission.