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802.11 protocols are what come to mind for many people when asked about wireless networking -- and with each channel working in a specific way, it can be critical to understand the ins and outs of these protocols and how they can affect your wireless network. This section of the Wireless Protocols Learning Guide is designed to provide an overview of the main 802.11 protocols in use by enterprises, wireless deployments and preparing for 802.11n.
If you ask most people familiar with wireless networking what are the differences between 802.11a, 802.11b and 802.11g, they'll tell you about the data rates and, certainly, that the jump from a max of 11 Mbps (with b) to 54 Mbps (with a or g) is a big deal.
But the different 802.11 specifications work in various channels in specific ways and it's important to understand the ways in which these differences can affect the network.
802.11a is one of several specifications in the 802.11 family applicable to WLANs. 802.11a provides specifications for wireless ATM systems and is used in access hubs.
802.11b is also a standard for WLANs -- often called Wi-Fi - and is part of the 802.11 series of WLAN standards from the IEEE. 802.11b is backward compatible with 802.11. It also defines channels that are spaced 5 MHz apart, and its frequency is the centre of a 22-MHz-wide channel.
802.11g is a standard for WLANs that offers transmission over relatively short distances at up to 54 Mbps, compared with the 11 Mbps theoretical maximum with the earlier 802.11b standard. And like 802.11b, the 802.11g specification also defines channels that are spaced 5 MHz apart. In fact, each defined frequency is the centre of a 22-MHz-wide channel.
The draft 802.11n standard defines 20-MHz-wide channels in both the 2.4 and 5 GHz bands, with an option to combine two 20 MHz channels into a single 40-MHz-wide (control + extension) channel to increase throughput.
For network designers, there is another important aspect -- the non-overlapping channels. 802.11b and g have only three, which means you can put three WAPs in the same area without interference from one another, while 802.11a has 12 non-overlapping channels. (Note that these numbers are for the U.S. and may vary in other countries.)
802.11 wireless deployments
In considering your existing wireless deployment -- which is almost invariably just an addition to the existing LAN switch deployment -- it can be necessary to consider what protocol you're currently running. Many organisations have deployed 802.11b hardware and now want to move to 802.11g. As you know, many hardware models are field upgradeable to 802.11a or g, so you may be tempted to simply upgrade to g since it's the most recent spec and leave the WAP in place. The tip here is to avoid this temptation, since it's not necessarily the best move for all environments. Instead, you should do a new site survey and consider using 802.11a for areas with higher user density.
With more non-overlapping channels you will probably find that you can manage your frequencies and floor space much more efficiently, particularly by adding WAPs where you couldn't previously do so because of overlap. And I suspect that much of the improvement noticed by the users will be due to decreased contention (fewer users on a given WAP) as opposed to just a simple increase in data rates.
As the 802.11n approval approaches, more enterprises are also considering what the new protocol will mean for their Ethernet and WLANs. Vendors, anxious to launch their new products designed for 802.11n, have already experimented with launching hardware that they say is draft 802.11n compliant. As the day draws closer were 802.11n is a certainty, enterprises should consider carefully what wireless solutions will continue to work best for them.
The upcoming IEEE 802.11n wireless standard will enable high-bandwidth applications such as streaming video to coexist with wireless VoIP. While final completion and acceptance of the standard is not expected until early in 2008, IT managers can begin now to consider the impact on existing networks and the environments in which the new standard will provide the greatest benefit.
The current version of the standard promises a data rate as high as 540 Mbits/second. Typical throughput should be in the 100 to 200 Mbits/second range, with potential for higher levels as the technology matures. IEEE 802.11n's throughput increase will affect your entire network, not just the wireless portion. A 100 MB Ethernet was sufficient to carry traffic from 802.11g access points (APs), but 802.11n will require a gigabit connection. The need to upgrade to handle the higher data rate will ripple throughout your entire network, even though most 802.11n products will provide compatibility with 802.11g equipment operating on the same channel by reducing speed to the level of 802.11g. The speed reduction will affect the entire wireless network, not just the 802.11g equipment.
The speed increase of 802.11n will be achieved through the use of MIMO technology, a wider radio frequency channel, and a method to decrease the time between transmissions. Signals from individual antennas will take different paths from the sender to the receiver. They will bounce off obstacles along the way and arrive at slightly different times, allowing the receiver to use the multiple signals to reconstruct the original data stream. The fact that obstacles in the path actually contribute to the ability of the receiver to reconstruct the signal means that 802.11n equipment can operate over much greater distances and with fewer dead spots than current technology.
IEEE 802.11n will also support frame aggregation. Once a station gains the authority to transmit a signal, it can transmit a series of frames without the requirement to release and regain authority for each frame. 802.11n will also enable high-bandwidth applications currently limited to wired networks to migrate to wireless. It will improve wireless VoIP reception. The benefits of higher speed and longer range will guarantee that IEEE 802.11n will be widely adopted, but it is important to prepare for IEEE 802.11n before deploying.
Wireless network and laptop vendors have been looking ahead to 802.11n for a while and have announced -- and have begun shipping -- equipment based on the draft specification. Further, the Wi-Fi Alliance plans to certify interoperability among products based on the draft. In preparing the corporate network for 802.11n, it is necessary to research the options carefully.
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