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WiFi Speed Degradation in Detail

Submitted by James Laughlin on Friday, September 21, 2012

On Tuesday of this week, we published a picture to our Facebook wall about Wi-Fi performance. We got the image from the Wall Street Journal and it contained good information we thought would be relevant to our customers.

WiFi-Speed-DegradationBut it sparked some internal debate.  As you might guess, we here at CMIT tend to be the technical and nerdy type, so any numbers get scrutinized and challenged.  We agreed that the graphic could be misleading, so we asked a member of our support team to write a clarification.  This is what he came up with.

The first frame is a bit misleading because really, who offers 300 Megabits-per-second (Mbps) wireless internet service? In a typical home environment, you have some form of internet service being delivered to your property.  It may be dial-up, cable, DSL, or in some areas Fiber Optics.

The internet signal is delivered to your property from one of these providers in wired (not wireless) form.  Some of these services can reach speeds up to 300 Mbps, but the only service we are aware of for residential at that speed is Verizon’s FiOS fiber optic service.  There is also Google Fiber which is 1 Gbps(1,000 Mbps) but you can only get that in Kansas City for now. Average residential internet speeds in the United States are currently about 15 Mbps.

The second frame of this image is talking about the router. 54 Mbps-90 Mbps Wi-Fi signal is the range for older wireless routers that follow the 802.11G standard.  Modern household grade routers support the 802.11N standard which has a range of 150 to 900 Mbps. Routers that support the 802.11ac standard are on their way.  When they get here, they will support speeds up to 1.75 Gbps (1,750 Mbps).

The third frame is accurate.  There are many things that can cause wireless interference.  Any device that broadcasts electromagnetic radio-waves on the 2.4ghz or 5.8ghz range can cause interference. All kinds of household appliances can cause this.  Some examples are: wireless phones, microwaves and other Wi-Fi devices in your neighborhood.

Line-of-sight is also a serious concern when dealing with wireless internet speed. Wireless Radio waves don’t ‘bend around walls’ to find your device.
Walls, insulation, metal, or concrete between your router and your computer can seriously degrade your Wi-Fi speed.

The fourth frame is not completely accurate either. Strictly speaking, devices do not ‘compete’ or ‘fight’ for Wi-Fi signal like living creatures.  Routers will offer devices with already established connections higher priority. For example, if Joe is already streaming a movie from the internet, and you’re trying to surf the web, the movie stream gets the higher priority.

The note about ‘50% goes to internal networking tasks’ is a little misleading also. There is not a whole lot of ‘behind the scenes’ action going on with your wireless devices, except for the occasional ‘are you still alive?’ signal.

Wireless devices can send, or receive, but not do both at the same time.  This does effectively cut the bandwidth in half because 50% is reserved for sending and 50% is reserved for receiving. So don’t rush out and purchase that fancy 900 Mbps Wireless N router, as it’s true speed is 450Mbps send + 450Mbps receive.  So a total max throughput on any transmission of 450Mbps (not that 900Mbps they advertise).


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