Posted April 30, 2010 by Jon Caruana (SDE) – Jon
I'm a developer on the Xbox shell and platform team. My corner of the team tends towards the platform and is responsible for some of the lowest levels of the system including the kernel. (Shell is focused more around the user interface of the guide and dashboard.) That is what led us to working on the driver for the recently released Xbox 360 Wireless N Networking Adapter which added support for the new 802.11n standard. In this post I will try to clear up some of the confusion around wireless technologies and give some tips for improving your connection.
Tip 0: Everyone’s home is different so these tips are more like guidelines than actual rules. To best use these guidelines you’ll need to consult your router’s documentation to find out your router’s configuration.
CHANNELS AND FREQUENCIES
Wireless networking uses radio waves just like AM/FM radio or broadcast television, so I’ll use those as an analogy that hopefully everyone is familiar with. This may have worked better before the days of cars that play MP3s and cable televisions. (And I will use these analogies in a U.S. centric way. Sorry, but that is what I am familiar with.)
AM/FM radio stations are well known by their frequency such as “88 point 1” (88.1 MHz), but when you talk about a television station they are “channel 12.” In order for the radio inside the TV to tune to that station it converts the channel number to the frequency band (204-210 MHz for channel 12) by some high school algebra (or, a chart). Wireless networking is like broadcast television with a channel to frequency mapping.
802.11 is the IEEE standard for wireless networking. It has amendments denoted by letters from a to n. But there are only four you will really hear about:
- 802.11a is the earliest, but not widely adopted. It is notable and still interesting because it uses 5GHz frequencies. Depending on your country there are about 20 defined channels, none of which overlap.
- 802.11b and 802.11g came next. Both use 2.4GHz frequencies. There are 11 channels commonly defined, but most of them overlap.
- 802.11n is the newest standard. It gives the best of both worlds: the standard applies to both 2.4GHz and 5GHz frequencies.
Even though 802.11n can be used on both 2.4GHz and 5GHz frequency bands, not all 802.11n devices will necessarily support both bands. In fact, many of the cheaper devices will only support 2.4GHz since that is more commonly used and is the cheaper technology. But in many cases using 5GHz can give you a better experience, which I explain below. Both the Xbox 360 Wireless N Networking Adapter and the older original Xbox 360 Wireless Networking Adapter support connecting to either a 2.4GHz or 5GHz network.
Tip 1: When looking to buy a wireless router, beware of routers that say they are "dual band". That often means it can transmit on 2.4GHz or 5GHz, but you will have to select one and only one in the configuration. While you can select 5GHz, most laptops are unlikely to support it. To get the best use our of your Xbox wireless adapter on a 5GHz band, you will most likely want a “simultaneous dual band” router.
INTERFERENCE WHEN USING 2.4GHZ
Interference between two transmitters is something you’ve probably experienced in your car as you drive between two cities where each city has a different station on the same frequency. Somewhere between them, your rock music becomes mixed with a classical piano piece and the result is not enjoyable. To prevent that from happening everywhere, in the U.S. the FCC licenses AM/FM/TV transmitters and requires a minimum physical separation between them. You won’t end up with two stations on the same frequency (or even adjacent frequencies) transmitting right on top of each other.
Most wireless networking is not nearly so lucky. It usually operates in “unlicensed” bands so anyone can setup a “station” anywhere. That is why you didn’t need to apply to the FCC for a permit to purchase your Xbox 360 Wireless N Networking Adapter. This is convenient, but it leads to interference between “stations.” The 2.4GHz unlicensed band in particular is used by almost everything in your home already: cordless phones, Bluetooth devices, microwaves, and even the Xbox wireless controllers.
And it gets worse: There are only three non-overlapping 802.11 channels in 2.4GHz. Go look at the available wireless networks your laptop or Xbox can see; I bet it's more than three. From my couch there are eighteen. By the pigeon hole principle, there are at least two networks on one channel (and probably a whole lot more) who are experiencing “classical rock” interference with each other! 5GHz by contrast has tens of non-overlapping 802.11 channels and is used by very few other devices or wireless networks.
“So what,” you ask, “How does interference hurt?” It is true that your Xbox 360 Wireless N Networking Adapter can’t feel pain. But, it coldly ignores any packet (lyric) that it didn’t receive 100% correctly. Imagine the silence you would hear instead of “classical rock” if your car radio did that. In wireless networking, the transmitter has to retry sending the lost packet at a later time. A whole book, rather than a blog post, could be written on how retries work, but the bottom line is: a retry means it takes longer for your Xbox to talk your Halo game host which means you have more lag or a lower quality Netflix video stream.
One downside to 5GHz is that walls more effectively block the signal. If your router and Xbox have a few walls between them, you may find that 2.4GHz is better for you despite all of the above. (Even 2.4GHz can have trouble with walls though.)
Tip 2a: If you have a simultaneous dual band router, try connecting your Xbox to its 5GHz network. If the Xbox is connected via 5GHz, the channel number shown in the wireless network configuration on the Xbox will be greater than 30.
Tip 2b: Some routers use the same network name for both their 2.4GHz and 5GHz network. When you selected the network, if the Xbox warned you there were multiple networks with the same name, it randomly selected one and may not have made the optimal choice. Your router probably has an advanced setting to specify a different name for each frequency’s network.
Previous to 802.11n, all wireless networks selected a single center channel and transmitted within ~10MHz on each side of that channel's frequency. One of the new features of 802.11n is support for 40MHz wide "channels". This is accomplished by effectively taking two 20MHz channels and using them both. Remember what I said earlier about 2.4GHz having only three non-overlapping channels? Using wide channels, you would be using 66% of them and doubling your potential for interference.
Most 802.11n routers today have 40MHz channel width enabled by default. And most people do the minimum work to configure a new router. So it was realized this behavior did not lead to a “pit of success.” The 802.11n certification process was finalized just a few months ago and new requirements were added for using 40MHz in 2.4GHz. These requirements will effectively force devices to automatically disable 40MHz unless the device is in the middle of nowhere. Unfortunately, that change only happened this year so almost all devices and routers out there today (including your Xbox) will stay in 40MHz even when it would be more friendly to your neighbors and better for your own performance to switch down to a 20MHz channel width.
Since 5GHz has so many channels, 40MHz doesn’t cause the same problems on that frequency band.
Tip 3: If your router is set to "Auto", "20/40MHz", or "40MHz" and using 2.4GHz, try setting it to 20MHz only. You will probably have higher bandwidth, lower latency, and less disconnects due to interference.
Security of wireless networks has been an escalating arms race between standards and tools that attack your network to gain unauthorized access or the ability to eavesdrop on data you are sending over the air.
To try to protect your network, the Xbox won't use 802.11n in combination with WEP or WPA TKIP encryption. If your router requires those encryption settings the Xbox will attempt to connect to it at the slower 802.11b/g/a data rates.
Tip 4: The best wireless security that is Xbox compatible is WPA2 with AES encryption. Almost all modern 802.11/b/g/a wireless devices and all 802.11n devices support WPA2. You should probably setup your router to use it.
THE CD DOES NOTHING?
Included in the Xbox 360 Wireless N Networking Adapter package is a CD whose only purpose is to offer your console a system update that includes a driver. Many people’s consoles have already received that update from Xbox LIVE, from xbox.com, or from any number of recent game discs.
Tip 5 : If the CD doesn’t offer you a system update, try to configure your adapter anyway. Plug in the adapter, go to system settings, then network settings, then configure network. If you have a button saying wireless, you are already updated and ready to configure the Xbox for your wireless network.