An Overview of 802.11a and 802.11b Products

by Wei-Meng Lee
02/06/2003

By now, we're all familiar with 802.11b wireless networking. But there's also been lots of discussion recently about two other wireless standards, both of which are in the 802.11 family: 802.11a and 802.11g.

802.11g is still in the process of being finalized and is currently in draft specification. However, a few vendors are already marketing new 802.11g devices. In terms of availability, however, 802.11a products are more plentiful than 802.11g. In this article, I'll provide an overview of 802.11a and 802.11b devices that are currently available, and I'll share some of my compatibility tests on these devices to help you make informed decisions when adding to your WiFi network.

Comparing 802.11a and 802.11b

Before we take a look at the various WiFi products, let's compare some basic characteristics of 802.11a and 802.11b by looking at a few parameters:

• Technology - 802.11b uses the Direct Sequence Spread Spectrum (DSSS) modulation scheme, while 802.11a uses Orthogonal Frequency Division Multiplexing (OFDM). In terms of power efficiency, DSSS is more efficient than OFDM. Thus 802.11a devices consume more power compared to 802.11b devices.
• Frequency - 802.11b uses the 2.4 Ghz spectrum, which is overcrowded with devices like cordless phones and microwave ovens. Even Bluetooth devices use the 2.4Ghz spectrum. 802.11a, on the other hand, uses the less crowded 5Ghz spectrum. Though the 5Ghz spectrum is less crowded, the signals have higher absorption rate and this causes it to be easily blocked by walls and objects.
• Range - Due to the higher absorption rate at the 5Ghz spectrum, 802.11a devices have shorter operating range of about 150 feet, compared to the 300 feet achievable by 802.11b (optimally under ideal conditions). As a result, more transmitters are required for 802.11a networks.
• Data rate - 802.11a supports speeds up to 54Mbps, while 802.11b supports speeds of up to 11Mbps.
• Cost - Components for 802.11a devices are more expensive to produce and hence their price tags are higher than 802.11b devices. Also, the increased number of transmitters required for 802.11a network will drive up the cost of implementing an 802.11a network.
• Compatibility - 802.11a is not compatible with the 802.11b protocol. Hence 802.11a devices cannot work with existing 802.11b wireless access points. Note that if you plan on migrating to the newer 802.11g standard, your 802.11b cards can access the "g" network. This will not be the case for 802.11a radio cards.
• Users - 802.11a network can accommodate more users due to the increase in radio frequency channels and increased operating bandwidth.

The main draw of migrating to an 802.11a network is no doubt increased bandwidth. With the near five-fold increase in data rate (54Mbps), applications like audio and video streaming and networking games would be possible (or at least more responsive).

However, the drawback in adopting 802.11a is compatibility. Businesses and institutions that have invested in 802.11b networks are reluctant to migrate to a faster, but incompatible 802.11a network. For these reasons, vendors are coming out with dual-band wireless points. These dual-band access points support both 802.11a and 802.11b devices. You can deploy both 802.11a and 802.11b devices all in the same environment. Best of all, since these two protocols are operating in different frequencies, interference is minimized.

The following table shows some of the 802.11a and 802.11b devices available in the market:

 

Product Name	Type	Features
D-Link DWL-650+AirPlus	PCMCIA Wireless Adapter	802.11b, 22Mbps with AirPlus products
D-Link DWL-6000AP AirPro	Multimode Wireless Access Point	802.11a, 802.11b, 22Mbps with AirPlus products and 72Mbps with AirPro products
D-Link DI-714P+ AirPlus	Wireless Router and Print Server	802.11b, 22Mbps with AirPlus products
D-Link DWL-AB520 AirPro	Wireless PCI Adapter	802.11a, 802.11b
Linksys BEFW11S4	Wireless Access Point with 4-port switch	802.11b only
Linksys WAP51AB	Dual Band Wireless Access Point	802.11a, 802.11b, 72 Mbps with other Linksys 802.11a products
Linksys WPC51AB	PCMCIA Wireless Adapter	802.11a only
Linksys WPC11	PCMCIA Wireless Adapter	802.11b only

Testing the Products

I've managed to obtain evaluation units from two major vendors: Linksys and D-Link. For my test I'm primarily interested in comparing the data rates of the two 802.11 standards. I am also interested to know how compatible these devices are when I mix and match access points and adapters.

To test the raw speed of the devices, I setup a web server to serve a 624MB movie file. The wireless device will download the file and I want to see the effective download speed. I did not test the Internet access speed as too many factors can skew the results (such as network delays and server overloading). I placed the wireless client and the access point within the same room.

Presented below are the various configurations and their acquired data rates:

Wireless Access Point(s)	Wireless Clients	Data Rate
Linksys BEFW11S4	Linksys WPC11	528KB/s
This is a pure 802.11b network since both access point and client using 802.11b.
Linksys BEFW11S4	D-Link DWL-650+ AirPlus	546KB/s
I am using a normal Linksys access point with the D-Link Airplus 802.11b card. The data rate is comparable to the previous one.
D-Link DI-714P+ AirPlus	D-Link DWL-650+ AirPlus	723KB/s
I am using D-Link AirPlus products - access point and network card. The data rate is significantly higher since both are AirPlus products, which supports a faster data rate. Still, this is an 802.11b network.
Linksys BEFW11S4 connects to D-Link DWL-6000AP AirPro	D-Link DWL-650+ AirPlus	729KB/s
I connect my Linksys wireless access point (with router) to the D-Link multimode access point, which supports 802.11a and 802.11b. However my network card is still 802.11b. The improved performance (over standard 802.11b) is due to the AirPlus feature.
Linksys BEFW11S4 connects to Linksys WAP51AB	D-Link DWL-AB520 AirPro	1.11MB/s to 2.89 MB/s
I connect my Linksys wireless access point (with router) to the Linksys WAP51AB, which supports both 802.11a and 802.11b. On the client side, I use the D-Link PCI wireless point, which also supports both 802.11a and 802.11b. I obtained a data rate ranging from 1.11MBps to 2.80MBps.
Figure 1. Stacking up the two Linksys wireless access points
Linksys BEFW11S4 connects to Linksys WAP51AB	Linksys WPC51AB	1.11MB/s to 2.89 MB/s
I connect my Linksys wireless access point (with router) to the Linksys WAP51AB, which supports both 802.11a and 802.11b. On the client side, I use the Linksys wireless card, which supports only 802.11a. I obtained a data rate ranging from 1.11MBps to 2.80MBps.

Let's take a look at the numbers. For an 802.11b network, I have consistently achieved a data rate of 528KBps. This translates to 528*8 (bits) Kbps=4224 Kbps=4.125Mbps. Compare this to the advertised rate of 11Mbps; you can see that the effective data rate is actually much lower.

Even for products that use proprietary techniques to boost speed (such as the D-Link's 802.11b AirPlus), the figures are just slightly better. 729KBps=5.7Mbps. And this is the effective data rate for AirPlus's 22Mbps products.

For 802.11a products, the data rate is significantly better. Translating from my test result, the effective data rate of 802.11a products ranges from 8.88Mbps (1.11*8) to 23.12Mbps (2.89*8).

The chart in Figure 2 summarizes the comparative performance of 802.11a and 802.11b devices.

Figure 2. Comparing performances of 802.11

Summary

Is this the time for you to jump onto the 802.11a bandwagon? From the perspective of pure data rate, the answer is a definite yes. But if you have an existing wireless network utilizing 802.11b devices and access points, you have to consider the cost of upgrading all devices to 802.11a. However, an easy way out would be to consider a dual mode access point, which can support both 802.11a and 802.11b devices.

If time is on your side, I suggest you wait for the newer 802.11g standard to stabilize. 802.11g delivers the same performance as 802.11a but is compatible with 802.11b devices and thus preserves your investment on current technology. Vendors are already beginning to sell 802.11g devices based on the draft specification. I will talk more about 802.11g devices as they become more widely available in the market.

Wei-Meng Lee (Microsoft MVP) http://weimenglee.blogspot.com is a technologist and founder of Developer Learning Solutions http://www.developerlearningsolutions.com, a technology company specializing in hands-on training on the latest Microsoft technologies.

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