Wireless Networking Speed: Ideals and Experiences

Introduction

Although modern wireless cards can advertise a maximum speed of 54 Mbps (megabits per second), 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 UIUCnet 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.

However, 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 5.5 Ghz frequency. Part of the reason is that the 2.4 Ghz signals travel a greater distance than the 5.5 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 802.11a 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. 24 Mbps is the highest speed that wireless cards are required to support, and you won't see those speeds in practice either (also explained below).

The 802.11a standard uses the 5.5 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. However, because there's less interference, it may be easier to design good 802.11a coverage than 802.11b or 802.11g coverage in a given area. All in all, though, 802.11a is currently the least common type of wireless network installation.

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. This is good for users who travel from network to network, since 802.11b is still the most commonly available type of wireless networking. However, having a user with an 802.11b card in an 802.11g network slows the maximum speed of all the wireless network's users to the 11 Mbps 802.11b standard.

The difference between theory and experience

In addition to the specific limitations mentioned above (the speed cap on 802.11b, the distance drop-off of 802.11a, and the backwards compatibility of 802.11g), 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.

In addition, electronic devices aren't the only potential problem. A building's architecture has a great effect on its ability to support a wireless network. If the walls are too thick or insulated with signal-blocking material, or if there's no way to get both electricity and a network cable to an access point, or if the best position for one access point makes it interfere with another, it can create problems in designing uniform high-speed coverage. Again, the wireless card will slow down its communications in these situations.

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.

Also, 802.11g is unique among the wireless standards in that its backwards compatibility is both a blessing and a curse. If you're in a wireless network where 802.11b is the only offering, it's a blessing. But if you're in a wireless network where 802.11g's 54 Mbps standard is available, and then an 802.11b user walks into the room, your network connection speed may be slowed by half or more when the 802.11b user connects.

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 UIUCnet Wireless network, 802.11b wireless connections are available in any area marked as wireless-enabled on the list of wireless locations. Many of these locations are also 802.11g compatible, meaning that if you have an 802.11g wireless card and no 802.11b users are in your area, you can have high-speed networking.

802.11a is not yet available in all areas of the UIUCnet Wireless network, but where it is available, it's the best option for high-speed networking because it can't be automatically halved by the presence of a user with a different network standard.

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

If you stay within about 30-40 feet of an 802.11a access point, or within about 100-150 feet of an 802.11b or 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 or 54 Mbps when you connect to a wireless network. If you get half the theoretical maximum speed, you're doing pretty well.