Ask the Wi-Fi Guru About 5GHz 802.11n

By Aaron Weiss

May 25, 2010

Our monthly Q&A series offers advice to those seeking help with home or small business WLANs. This month our guru helps settle the 5GHz/2.4GHz 802.11n question, offers hope to owners of aging laptops and drops tips on sharing an Internet connection.

Our monthly Q&A series offers advice to those seeking help with home or small business WLANs. This month our guru helps settle the 5GHz/2.4GHz 802.11n question, offers hope to owners of aging laptops and drop tips on sharing an Internet connection.

Would you like to ask the guru a question? Write the editor.

With the recent launch of the Apple iPad, enthusiasts have been snapping up the wireless tablets by the millions and discovering all kinds of fun new features. For example, its inability to properly release DHCP IP addresses. The problem, first discovered by network administrators on the campus of Princeton University, seems to be related to the iPad's sleep mode. When the device sleeps, its wireless network connection remains active. Normally, when a wireless router assigns an IP address to a client via DHCP, it is leased for a specified period of time. When this time expires, the device can renew the lease, or else that IP address becomes available for another client. But when the iPad goes to sleep, it holds onto its IP address regardless of the lease time, including when it is awoken. As a result, the wireless router could assign this same address to another client, thinking it had expired, when in fact there is an iPad still using it. Network sadness ensues.

As far as bugs go, this one should be relatively easy for Apple to fix with a software update, although it hasn't yet. More interesting is that the bug made it into production in the first place. After all, wireless networking protocols are nothing new. There are thousands of devices on the market which handle this exact situation properly, including Apple's other products. The point here isn't simple Apple-bashing -- every vendor struggles with bugs. But it is an instructive lesson about taking things for granted and maybe a little bit humbling that even a bug related to a well-established technology could survive to production in a major product release.

Which Provides Better 802.11N? 5GHz or 2.4GHz?

Q: I have a Cisco E3000 High Performance router connected to a 30Mbps Comcast Wan Link. I have two computers that are attached via wifi both are 802.11N but one is going at 130mbps on the 2.4GHz frequency and the other is going at 300mbps on the 5GHz frequency. Seems the 5GHz connection is faster. Is it true that the 5GHz Wireless N connection would see significant performance and/or quality gains even though both are connected to the same router at 30Mbps? -- Eric

A: Great question, and one that many newcomers to 802.11n networking may encounter. Not to blow the punchline, but the short answer is yes.

But first, a clarification: Your broadband connection to the Internet is 30mbps, but the connection speed between your router and your wireless clients is totally independent of this. In other words, a 130mbps link between your PC and your router is not going to make your Internet experience any faster because your outbound connection is limited to 30mbps. (Although "limited" is a funny word here because 30mbps is a very fast Internet connection many would envy!)

Except for rare cases, usually due to configuration problems, your wireless router link will be far faster than your Internet connection. The most useful benefit for your fast wireless link is internal networking: sharing files or streaming media within your own network from one computer to another, for instance. Here, maximizing your wireless link speeds can make a noticeable difference in performance.

The reason behind your observation is precisely what you think it is. 802.11N is a dual-band protocol that can operate on either the 2.4GHz frequency (used for 802.11B/G networks and many other wireless devices) or the 5GHz frequency. The 5GHz frequency offers several advantages. The spectrum itself is less crowded with interference compared to 2.4GHz. When using 5GHz, your 802.11N devices can use a double-width channel—40MHz rather than 20MHz. This is likely why you are seeing a doubling of link speed using your 5GHz clients.

Why not use 5GHz all the time? For one, it could be costly to upgrade all of your wireless clients to 802.11N versions. If you don't need maximum LAN speed (because you're not file sharing or streaming media), the benefit may not be worth the cost. Also, 5GHz range is shorter than 2.4GHz. This is simple physics—lower frequency wavelengths travel further. If you were trying to cover a larger area with 802.11N, you would need more access points to provide the same coverage at 5GHz. For the typical residential home, this may not be an issue, but in an office or larger environment it could be.

Is My Compaq Presario 2100 Too Old for Wi-Fi?

Q:I have an old notebook from 2004 - it is a Compaq Presario 2100. I am trying to get a connection to Wi-Fi but the computer maybe too old? Do you have any suggestions? – Kim

A: Ah, 2004…I remember it like it was six years ago. Actually, your computer is not at all too old to enjoy a Wi-Fi connection. We tend to assume that any computer older than, say, yesterday, is already obsolete but often this is not really the case.

The old Presario 2100 was sold with an optional built-in wireless adapter, but presumably your model did not include this option. Not to fear. You have two more options to bring wireless connectivity to this old beast.

You have one slot for a Type II PC Card. This is your best option because there are many Type II wireless cards available which support 802.11G, the reasonably fast version of wireless you find in most modern routers. You can find these cards, often for under $30, from all major Wi-Fi vendors including Linksys, D-Link, and Netgear.

If your card slot is already occupied with another kind of adapter, your alternative choice is a USB wireless adapter. The Presario 2100 has two USB ports but unfortunately, they are the slow USB 1.1 speed. This means you can, at best, achieve 802.11B Wi-Fi which is relatively slow by today's wireless standards but is good enough for basic e-mail and web surfing. Many inexpensive models are available, although remember that even though they often advertise USB 2.0/wireless-G support, they will be backwards compatible (at the slower speed) with your USB 1.1 port at wireless-B speed.

How Do I Share the Internet Connection Provided by My Verizon Modem?

Q:I'm trying to share an Internet connection provided by the Verizon USB720 modem that receives the Internet from a cell tower. I know that some modems (normally more expensive ones) seem to be almost plug and play. Simply plus the USB Modem into the router and set up like normal. I assume. I was wondering if the WRTSL54GS was one such case. Its USB port is marketed as "network storage". But I'm not sure if it matters. Can the WRTSL54GS work with a Wireless USB modem? If not. Then why? Is it a hardware thing or is it because the WRTSL54GS lacks the right software? And if it's the latter could DD-WRT fix this problem? – John

A: Good and bad news. The good: you can share your 3G Internet connection using Wi-Fi. The bad: you can't do it using only a WRTSL54GS router, with or without DD-WRT firmware. It is true that the WRTSL54GS has a USB port, but this port can be used only for attached storage in the form of an external hard drive or thumb drive. You cannot plug in and share a USB 3G modem.

There are so-called 3G routers designed specifically for the purpose you describe, such as the Netgear MBR624GU and Cradlepoint MBR900. With either of these, you plug in your subscribed USB720 modem and its Internet connection will be shared via Wi-Fi to nearby clients. Easy, but you'll have to pay around $100 for the privilege.

If you'd prefer to keep using your WRTSL54GS router, you could set up Internet sharing through one of your computers. In other words, you plug the USB720 into a PC which is also connected (either by Ethernet or wireless) to the router, and configure that PC to share the 3G connection. If you're using a recent version of Windows, Internet Connection Sharing is built-in. Of course, this means your Internet-connected PC will need to be powered up any time you want to access the Internet from any other machine in your house.

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