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Troubleshooting Q&A - March 25, 2004

Wireless Alphabet Soup

This week's Q&A looks at the pros and cons of the various flavors of 802.11 wireless technology. It also addresses potential problems that can prevent you from networking two machines via a crossover cable.

By Ron Pacchiano

Q. I just bought a new house and am in the process of moving. The other day I was breaking down the network in my home office and was just amazed at the collection of cables crammed behind my desk and wall unit. This got me thinking that it would be a shame to clutter up my new house with all these wires.

So for this reason, I’m considering switching to a wireless network. However, I’m not sure whether I should purchase products based on the 802.11a or 802.11g standard. Do you have any advice on which I should choose? Also it should be noted that I have a few other devices in my home that also operate in the 2.4 GHz range. Thank you.

A. Despite the fact that both 802.11a and 802.11g advertise speeds approaching 54MBps and appear to be similar, they are in fact quite different. Unlike 802.11b/g products that operate in the 2.4 GHz band, 802.11a products operate at much higher frequencies; typically between 5 and 6 GHz. They also use a modulation scheme known as Orthogonal Frequency-Division Multiplexing (OFDM) for achieving its speeds.

My experience with 802.11a products typically has not been good. They suffer from shorter range than “B and G” products and have always seemed more prone to interference by obstructions like walls and doors. Not to mention that they aren’t backwards compatible with 802.11b products. Since this will be your first wireless purchase, the compatibility issue won’t be a big deal; however, you should be aware of it.

802.11g on the other hand offers users the best of both worlds. It gives you the same high speed data transmission rates as “A” (54Mbps) products, yet is fully compatible with “B” products. G-based products are also usually a bit cheap than their “A” counterparts, and in my experience are more reliable, have greater range, and are less prone to interference (despite the fact that they operate in the same 2.4 GHz range as some of the other devices in your home).

For these reasons, my suggestion would be to invest in wireless equipment based on the 802.11g standard. If I had to recommend a piece of hardware to you I would probably suggest the D-Link XtremeG family of wireless routers and networking adapters. They’re inexpensive and quite secure thanks to enhanced 256-bit WEP encryption as well as support for the newer Wi-Fi Protected Access (WPA) specification. The products are also capable of supporting the government-grade AES encryption as well as the upcoming 802.11i standards.

D-Link XtremeG products have also managed to significantly boost performance within the 2.4GHz frequency range thanks to some advanced hardware-based compression technologies. This gives them a class-leading theoretical maximum data transfer rate of 108Mbps.

Now as impressive as that 108Mbps speed sounds, I should point out that even though both 802.11a and 802.11g products advertise 54Mbps, realistically you shouldn’t expect to see much more than 24 – 28 Mbps out of them. 54Mbps is a theoretical limit that can only be reached under ideal conditions — conditions that I have yet to experience in the real world.

This fact applies to the XtremeG products as well. There are a multitude of conditions that have to exist before they could approach anywhere near the speeds being advertised.

However, I can say that in testing I have seen the XtremeG products reach speeds in the low – mid 40Mbps range. So while this is slower than advertised, it is far faster then any of the other products I have used in recent memory. More information on the D-Link XtremeG products can be found at http://www.dlink.com/products/108mbps_xtremeg.asp. Hope this helps!

Q. For the last few days I have been trying to network the two PCs in my dorm together with a crossover cable. Unfortunately, I can’t seem to make it work. I’ve got a crossover cable and network adapters in both the laptop and PC, but still can’t seem to make a functional connection.

The computer keeps indicating that the network connection is unplugged, even though the cable is securely fastened to the RJ-45 slot. Can you please help me? I have tried every networking site I can think of looking for an explanation as to what the problem is, but I haven’t been able to come up with anything. Thanks!

A. Networking two PCs together with a crossover cable is pretty straightforward. If your network adapters are correctly configured in Windows and yet it still indicates that your network connection is unplugged, even though both PCs are connected to the crossover cable, then simply put, you are not using a crossover cable. If it is a crossover cable, then more than likely it’s a defective one. My advice is to just go out and purchase a new one.

When you connect a working crossover cable to the network adapter in each PC, the link light should illuminate. Once the cable situation has been resolved, getting computers properly configured is easy. Just follow these steps.

The first thing you need to do is configure each of the PCs with a static IP address and a common Subnet mask. For our example, we’ll assign the first PC an IP address of 192.168.0.1 and the second PC 192.168.0.2. Both machines should use the Subnet 255.255.255.0.

You should also verify that both machines have been configured as members of the same workgroup. Any name will work for the workgroup name as long as it doesn’t exceed 15 characters (ex.WORKGROUP). All that’s left to do now is reboot the systems.

After the systems reboot, go to the PC using IP address 192.168.0.1. Open a command prompt and try to Ping the other PC. To do this, just type PING and the IP address of the system you’re trying to reach. In this case that would be C:\>PING 192.168.0.2. You should get 5 successful replies.

If for some reason your Ping returns a timeout message, then you might have another problem. The most common is that Windows XP’s Internet Connection Firewall (ICF) is enabled on one of the machines. ICF is designed to protect your PC from threats outside of your network by blocking unauthorized traffic from reaching your PC. It is supposed to be used only on the interface that directly connects to your Internet connection.

However, if ICF is being used on an adapter that is being used to connect to another PC, it will block all the transmissions being sent to it. It will not even respond to pings. ICF must be disabled in order for this to work.

To disable ICF, simply right-click on “My Network Places” and select Properties. Right-click on your LAN connection and again select Properties. Go to the Advanced tab and uncheck the box that reads “Protect my computer and network by limiting or preventing access to this computer from the Internet”. Click OK. Now try to ping the other PC again. It should work fine. Good Luck!


Use our feedback form to submit your questions on home or SOHO networking issues. We cannot guarantee to answer every question we get, but we’ll consider them all.



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