Introduction

Although modern wireless cards can advertise a maximum speed of 54 Mbps (megabits per second), or 450 Mbps for the new 802.11n adapters, you won't actually see that type of speed when you're using a wireless network. This page explains the various factors that can affect the speeds you experience over IllinoisNet Wireless and other wireless networks.

Like radio, wireless networks operate on certain specified frequencies. Your wireless card is like a pre-tuned radio that can detect one or two specific frequencies -- 5.5 Ghz (gigahertz) for the 802.11a wireless networking standard, and 2.4 Ghz for the 802.11b and 802.11g wireless networking standards. The 802.11n standard can operate using either 2.4 or 5Ghz frequencies, however, the wireless system at Illinois only supports 802.11n using the 5 GHz band.

On the other hand, wireless network cards aren't the only devices that can communicate on these two frequencies. These frequencies are part of what's called the "ISM band" -- a group of frequencies reserved for "industrial, school, and medical" use. Many consumer devices such as microwave ovens, cordless phones, X10 cameras, and research and medical equipment also use these frequencies, which means that they can interfere with your wireless networking signal. Currently, there are more devices using the 2.4 Ghz frequency than the 5 Ghz frequency. Part of the reason is that the 2.4 Ghz signals travel a greater distance than the 5 Ghz signals when all other factors (like power supplied and interference levels) are equal. So the choice of which frequency is best is a complicated one to answer; the answer may often be "both."

About the three wireless networking standards

The 802.11b wireless networking standard was the first widely available wireless networking solution that users could buy; the vast majority of public wireless spaces, including coffeehouses and restaurants and the like, use the 802.11b standard. It uses the 2.4 Ghz frequency for communication, and the fastest speed an 802.11b user can theoretically have is 11 Mbps. (More about why you won't actually see this speed in real life is explained below.) The 802.11b standard will be retired from IllinoisNet in the Fall of 2012.

The 802.11a and 802.11g standards both offer a higher theoretical maximum speed of 54 Mbps. However, nearly half of that is used for routine communication between your computer and the wireless access point it's communicating with, not for transfer of your data requests.

The 802.11a standard uses the 5 Ghz frequency, a signal which is less used by other devices (a bonus for wireless network users) but the signal strength drops off more quickly as you go farther from the access point.

The 802.11g standard shares the 2.4 Ghz frequency with the 802.11b standard, but 802.11g provides the higher theoretical maximum speed of 54 Mbps. Since they share the same frequency, many networking cards that support 802.11g also support 802.11b.

The 802.11n standard can use both the 2.4 and 5 GHz frequencies.  The wireless system at Illinois only supports 802.11n using the 5 GHz band. The current 802.11n deployment at Illinois is 802.11a backwards compatible.  802.11n adds several methods for increasing the speed of the connection. One is to allow for bonded channels – this allows a single connection to use twice as much radio spectrum as a 802.11a connection. This effectively doubles the connection speed.  The second speed enhancing technology is known as MIMO (multiple input multiple output).  MIMO uses multiple antennas on both the wireless access point and the client device to take advantage of a property of radio wave propagation called multi-pathing.  MIMO is unpredictable and therefore it is the policy of CITES to not count any of the speed advantages attributed to it. 

The difference between theory and experience

In addition to the specific limitations mentioned above, some factors will slow your connection speed no matter what type of wireless networking you're using.

Interference

Other devices ranging from your neighbor's handheld phone to a nearby gas station's wireless credit card checking system could interfere with your wireless network card's speed. When two devices use the same frequency in the same area, it can become more difficult for one or both of them to communicate successfully. When a wireless card can't communicate at top speed, it slows down until it can communicate with the access point at a slower speed.

Signal propagation

In addition, electronic devices aren't the only potential problem. A building's architecture has a great effect on the ability to support a robust wireless network. If the walls are too thick, constructed of signal-blocking material, or constructed of a material especially reflective of the frequencies used by WiFi, then the wireless signals can be adversely effected and reduce client connection speeds.

Shared bandwidth

Another factor is the number of users sharing the same access point. If you're in an area with no other wireless users, you'll see much faster network traffic than if you're one of several dozen wireless users in the area. An access point's bandwidth is divided among the number of users who are connecting to it; and as the number of users increases, the access point also needs to reserve more of its bandwidth for coordinating what information goes to what computer.

Distance

Distance from the access point is another major factor in how fast your connection speed can be. If you're sitting right under an access point that no one else is using, your speed is as fast as you can get. The further you move from the access point, the slower your connection will be, no matter which type of wireless networking you use.

Conclusion

On the IllinoisNet Wireless network, 802.11g wireless connections are available in any area marked as wireless-enabled on the list of wireless locations.

802.11a is also provided from all IllinoisNet Access Points; however, since the 5 GHz frequency used by 802.11a does not travel as far as the 2.4 GHz used by 802.11g, not all covered spaces will have 802.11a available.

802.11n is not yet available in all areas of the IllinoisNet Wireless network; but where it is available, it's the best option for high-speed networking.

If you're shopping for a wireless network card, your best option is to look for one that is compatible with all four standards (often called an a/b/g/n card). You'll be able to take advantage of both the highest available speed in a given area (802.11a/n) and the broadest range of wireless-accessible locations (802.11g). Look for the official logo on the wireless card's packaging:

Note that some wireless cards are b/g/n.  These cards most likely do not support 802.11n in the 5GHz band and cannot connect to IllinoisNet using 802.11n.

If you stay within about 30-40 feet of an 802.11a access point, or within about 100-150 feet of an 802.11b/g access point, you'll improve your chances of getting a high speed connection. You can't control the number of users connecting to the same access point, but if you're in a building like a library and looking around for a place to sit and study, a room with 2 or 3 laptop users will offer you better connection speeds than a room with 20 or 30 of them.

In summary, due to the factors listed above, you won't be able to get the theoretical maximum speeds of 11 Mbps, 54 Mbps or even 300Mbps when you connect to a wireless network. If you get half the theoretical maximum speed, you're doing pretty well.