Your Wireless Network is Slower Than You think

By Ronald Pacchiano

July 20, 2006

Hardware manufacturers employ numerous techniques to achieve advertised performance numbers. As a result, competing products might be capable of 108Mbps, but they're not completely compatible with one another.

After several years of hard work, my brother has finally managed to open his own Physical Therapy practice. To help make his life easier, I offered to setup a wireless network for him. So we took a trip to our local Best Buy to pickup the equipment we needed. This included a wireless router; a PC Card wireless adapter for his laptop and two USB wireless adapters, one for each desktop computer.

Whenever I go to Best Buy, they never seem to have everything I need from a single manufacturer. In this case, I was looking at the D-Link AirPlus Xtreme G Wireless 108G family of products. They had the wireless router and the PC Card adapter, but, unfortunately, not the two USB wireless adapters we needed for the desktops.

While I was digging through boxes hoping to find the USB adapters buried in the wrong location, my brother stumbled upon a Netgear version of the USB adapter. I told him that wouldn't work for us, and that we'll have to go looking elsewhere. He couldn't understand why especially since the packaging clearly said it was compatible with 802.11g and performed at 108Mbps. What my brother didn't realize, nor do many other people for that matter, is that even though both of these products indicate that they are capable of data transmission rates of 108Mbps and use the same 802.11g communication standard, the fact is they are not the same.

In order to achieve these very impressive performance numbers, hardware manufacturers employ numerous tricks and techniques that enable their products to reach faster speeds than the IEEE 802.11g standard defines. As a result, even thought both products might be capable of archiving 108Mbps, they do so in different ways and as such, are not completely compatible with one another.

For example, in a pure D-Link 108G environment, the DWL-2100AP router that I wanted would be able to take advantage of new wireless technologies such as Packet Bursting, Fast Frame, Compression & Encryption and Turbo mode to reach its claimed speed 108Mbps.

One of the key technologies that makes this possible is D-Link's Turbo mode. For those not familiar with it, this mode allows data transmissions to occur on two channels, which will improve the data rate (up to 72 Mbps). This technology is proprietary to D-Link products and in order for it to work; it must be enabled on all of the wireless hardware. If not, these devices can't communicate with each other.

Since Turbo mode is only available with D-Link's 802.11a and 802.11gwireless products, it wouldn't be compatible with NETGEAR's line of wireless 108Mbps products. Yet because both products adhere to the IEEE 802.11g standard, they would still be able to operate together in the slower, non-turbo 54Mbps mode.

The other interesting thing about this is that 108Mbps is a theoretical maximum speed that can be achieved only under ideal conditions. So the odds of you ever reaching these speeds, even when using wireless products from the same vendor, are highly unlikely. In fact you might be surprised to learn that your actual transmission speed is much lower. If you've ever noticed, all wireless products have a disclaimer on the box in regards to the performance of their wireless products. D-Link's reads as follows:

"Maximum wireless signal rate derived from IEEE Standard 802.11g specifications. Actual data throughput will vary. Network conditions and environmental factors, including volume of network traffic, building materials and construction, and network overhead, lower actual data throughput rate. Environmental factors will adversely affect wireless signal range."

So this begs the question, "How fast can you actually download data over a wireless network?" Well, it depends on a number of factors. When communicating from a wired device to a wireless device, a good rule of thumb is that you can expect to average roughly a third of the data rate advertised. That may surprise, disappoint or possibly even anger you, but it is true of most two-way wireless networks. This is just the nature of the technology, network protocols and radio transmissions. For example, suppose you have a desktop computer that is connected by Ethernet cable to an 802.11g "54 Mbps" wireless router. When sending a large file to a wireless laptop, you can expect roughly 18-22 Mbps of actual throughput.

I emphasize roughly because this rate can be considerably higher or lower depending upon a number of factors. These factors include:

  • The strength and clarity of the wireless signals
  • The interference caused by non-Wi-Fi devices that share the same radio frequencies as the wireless network; like cordless phones and microwaves.
  • The activity of neighboring Wi-Fi devices that are sharing the same radio frequency
  • The number and activity of clients on your own network
  • Any proprietary enhancements you might be using in your network (such as those that purport to go up to 108 Mbps or 125 Mbps on an 802.11g device)
  • The output speed of the device from which you are downloading the file
  • Other activity on your local computer or the sending computer

At this point you might be feeling a bit ripped off, but this isn't some evil conspiracy conceived by the networking manufacturers to dupe you of your cash — although a fair amount of creative marketing is certainly involved. Network devices are always described by their maximum data rate or signaling rate — the speed at which a network device can send or detect the electrical pulses (1's and 0's) being transmitted over the network. But because of all the factors above, the maximum throughput of any network device is always going to be less then the theoretical maximum advertised.

If you'd like to check your own network data transfer rates I suggest you take a look at a product called Qcheck. Ixia's free Qcheck utility is the easiest way to go if you want to dig in and do your own testing on networking equipment. It's basically a subset of Ixia's more powerful IxChariot network performance testing program with an easy-to-use interface, and best of all — it's free.

You do have to fill out a form to request the download because Ixia hopes that you'll like what you see and want to buy the full-featured Chariot, but that's a small price to pay for such a handy tool. I've used Qcheck for all my network product testing since I discovered it a few years back, and it's pretty simple to use. I highly recommend it.

When testing network performance there are a few common terms you should be familiar with. These are port speed, data rate and throughput.

The port speed is what the hardware and driver reports to the operating system (OS). Think of this as the maximum data rate. The port speed is also the speed that the OS will talk to the driver.

While it usually stays at the maximum, the driver may adjust the port speed lower if it detects errors when communicating to the OS. An example of this is when a USB 2.0 network device is inserted into a USB 1.1 connection. In most versions of Windows, when you hover over the network icon in the system tray a small pop-up window will appear showing you your current port rate.

The data rate is the current signaling rate of the wireless transmitters and receivers. In 802.11, and other protocols, this rate often varies up and down along a set of agreed-upon supported rates. This increase and decrease is based on the error rate of the wireless link. If the errors are increasing, then the link is slowed down (because slower packets are easier to decipher). Many of the Wi-Fi utilities provided by the manufacturers will report both the Transmission (TX) and Receiving (RX) rate in their monitoring utilities, You often see that they are somewhere below the port speed.

Finally, the throughput is the rate of the delivery of the actual cargo of the network — your desired data. This is what really matters to you. As a rule, the faster the data rate, the faster the throughput unless there are too many errors. Errors cause retransmissions, which takes bandwidth. It is more efficient to slow the data rate to the point where fewer errors occur.

To try Qcheck for yourself, visit the Ixia Web site. It's quick, easy and you might be surprised at the results.

Adapted from PracticallyNetworked.com, part of the EarthWeb.com Network.

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