Wireless Networking, where more is not always better

I was sent out to help a new client with a wireless networking problem that had been progressively getting worse, and which their efforts to resolve where failing short.

The problem network was covering a large warehouse in which Symbol scanners were used by the employees to process their product and shipments. This company had recently been purchased/merged with another company, and as part of the merger, the wireless network was completely changed over from about 12 Cisco Autonomous Access Points to a similar number of Cisco APs connected to a Wireless LAN Controller.

Shortly after making the change in gear, the workers began experiencing a much higher number of scanner disconnects and delays. The internal networking team attacked the problem in a typical way by doubling the number of access points, and raising the power level of all APs to maximum. After making these changes, the problems didn’t improve, and may have actually gotten worse. They then reached out for some external assistance.

My first visit to the site was a quick one to gather some information and do a quick walk through of the space to familiarize myself with the network. Upon deeper inspection, I began to notice that the access points reported significant channel interference measurements, and that the suggested power levels were much lower than the hard set maximum configured. I scheduled another site visit to perform some more in-depth RF analysis of the areas.

What I found during the next visit was in any one area in the warehouse, my scanner picked up very solid signal strength from anywhere between 4 and 8 access points. Being that this network was supporting older 802.11b scanners, this meant that there was significant co-channel interference almost everywhere, as well as the potential for client confusion with so many “good” choices for access points to connect to.

With this information, I suggested re-enabling the automatic power level control (RRM and TPC) available on Cisco’s Wireless LAN Controller. Shortly after making this change, as well as some other best practice adjustments, wireless scans in the area looked much better, and instances of client disconnects dropped to nearly none.

What did I learn…

This is a great example of how in wireless networking, more and stronger can actually have a significant negative impact on network performance. Though intuitively adding access points and raising the power levels would seem to be a good idea, either of these choice can actually cause significant adverse affects to the network.

Key to a healthy wireless network is a good site survey and RF analysis. Today, this is most easily accomplished by using the intelligence built into the wireless control systems. Both Cisco’s RRM and Aruba’s ARM features can make both channel and power level assignments and adjustments very simple.

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About hfpreston
Hank has spent time in most areas of IT services, but is glad to have his feet firmly planted in sane and predictable world of pushing packets these days. Having the rapid fire attention span common to IT, he dabbles in many network technologies, bouncing from Data Center, to wireless, then security, and ending on core route/switch around dinner time. You can find Hank on Twitter (@hfpreston) and Google Plus (http://gplus.to/hfpreston).

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