Greg Wolf
Greg Wolf is a principal with NetForecast, helping to develop and implement performance engineering practices for enterprises. Greg has more...
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Greg Wolf | May 22, 2012 |


RF Interference: When Things Go Bump in the Air

RF Interference: When Things Go Bump in the Air RF interference acts like a light switch. Absent interference, things work fine. However, as soon as interference is present performance comes almost to a grinding halt.

RF interference acts like a light switch. Absent interference, things work fine. However, as soon as interference is present performance comes almost to a grinding halt.

Over the past two months I have attended Enterprise Connect in Orlando and Interop in Las Vegas. Although these conferences typically draw different types of audiences, both conferences had a strong focus on the incredibly fast growth of BYOD in the enterprise. One key to BYOD's success in the enterprise is that it needs access to a well performing Wi-Fi network in order to provide the user access to the enterprise's wired network, so that the user can limit the time connected to (and therefore the charges from) the public cellular network.

The convenient thing about Wi-Fi networks is that they are generally easy to implement. And Wi-Fi networks have a tendency to grow quickly and organically as they are needed. However, like many things, this convenience comes at a price, two to be exact. The first is that Wi-Fi networks operate using a limited amount of spectrum (2.4 GHz and 5 GHz), which tends to grow more crowded and congested as more users take advantage of the BYOD model. The second thing about Wi-Fi networks is that they do not like RF interference--which is the focus of this article.

Simply stated, RF interference is a Wi-Fi network killer! The adverse effect of RF interference is that it causes Wi-Fi performance to suffer, potentially to the point that an application can be rendered unusable.

Network engineers have not had to concern themselves with Layer 1 (physical medium) issues in a very long time but that will need to change. Although RF interference is difficult to eliminate totally, if you can identify the sources of RF interference, many times those sources can be moved or even removed.

RF (radio frequency) interference is generated by any device that operates on the same frequency as the Wi-Fi network. Some common sources of RF interference include Bluetooth, cordless phones, wireless headsets, video cameras, wireless audio devices, and my favorite, the microwave oven. I think it is a safe to say that one or more of these devices exist in most enterprises. Keep in mind that the devices mentioned above typically operate in the 2.4 GHz spectrum, but there are an increasing number of devices that are starting to operate in the 5 GHz spectrum as well.

Another point to mention is that RF interference is not unique to the enterprise. Just take a look around you the next time you are sitting in a Starbucks surfing the web or checking your e-mail using the local Wi-Fi network; I think you would be amazed at how many sources of RF interference are lurking about.

The following diagram shows what happens to Wi-Fi performance when a strong source of RF interference is present. The test consisted of using a laptop on a 2.4 GHz network to download a file from an FTP server. A microwave was turned on twice during the transfer, which resulted in the throughput of the file download almost stopping.

Unlike traditional network performance issues (i.e., latency, jitter, and congestion) that adversely affect application performance, RF interference acts more like a light switch. In the absence of RF interference (light switch off) things work fine. However, as soon as RF interference is present (light switch on) performance comes almost to a grinding halt.

As stated earlier, RF interference is unavoidable. However, network engineers will need to start using tools to help them determine sources of RF interference in their environments and do their best to mitigate the effects of RF interference whenever possible. At a minimum, identifying the presence and sources of RF interference will go a long way when troubleshooting Wi-Fi performance issues.

One of the most valuable tools for detecting RF interference is an RF spectrum analyzer. The one used to conduct the testing for this article is called Chanalyzer Pro (software component) and Wi-Spy DBx (hardware component), which was developed by a company called Metageek. Another excellent set of tools is Wireshark and AirPcap wireless adapters, both owned by Riverbed.

Regardless of what you chose the use, the key is to embrace a set of tools that will give you complete Wi-Fi visibility. Knowing what is floating in the airwaves will pay big dividends as the use of BYOD over Wi-Fi in the enterprise becomes more pervasive.


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