The publication of the IEEE 802.11n speciﬁcations was a turning point in wireless networking. It allowed enterprise managers to deploy wireless networks at speeds far above the old 54Mbps limit. Anyone currently considering creation of an enterprise-class wireless infrastructure should focus on 802.11n and eliminate any pre-802.11n equipment from the network.
The following strategies can be used to optimize performance of networks based on 802.11n:
Legacy wireless equipment often uses the 802.11b/g band, but it can be diﬃcult to get good network performance in that band when 802.11n is deployed. The small number of channels available (three) in the 2.4GHz band means that the 802.11n high-performance 40MHz channels cannot be used.
For best performance, devices should employ the 5GHz band whenever possible. This assures that the higher capacity 40MHz channels can be used and that more devices can share the radio-frequency space in a smaller physical area. Those factors are critical for successful Wi-Fi deployments that involve crowded classrooms, conference rooms and the like.
Because 802.11n is a multiple-antenna, multiple-stream standard, user devices and APs can have from one to four streams.
Today, most devices supporting 802.11n have two streams and two antennas (2x2:2) or two streams and three antennas (2x3:2 or 3x2:2). These are limited to a top speed of about 13Mbps, or 270Mbps if double-wide channels are used in the 5GHz band. Newer devices coming on the market have three streams across three antennas (3x3:3). These have a top speed of 195Mbps, or 405 Mbps with double-wide channels.
The longevity required of APs makes it worthwhile to purchase devices that support three antennas and three data streams. This will extend an organization’s refresh cycle.
The most commonly ignored wireless advice is to keep power levels as low as possible. Wireless devices must share the same radio-frequency space. Therefore, additional power simply creates noise and performance slowdowns for adjacent devices and APs. Although wireless APs generally can support power of up to 100 megawatts, setting a maximum power level of 50MW or lower will yield better network performance.
If users report poor signal strength, the ﬁrst solution should be to add another access point. It’s rarely wise to turn up wireless power. A low power setting will increase the battery life of all wireless devices, especially smartphones and tablets.
When a device on the edge of the wireless network connects, the network will attempt to accommodate the user by reducing the device’s speed. This impacts performance in two ways: The user has a slow connection, and this slow user could block wireless access for all other users for an extended period.
Enterprise networks should block clients from connecting at low data rates by increasing the data rate use for beacon frames (the 10-times-a-second frame that every AP emits to announce its capabilities) as well as the minimum connection speed allowed. The default should be raised above not only the commonly used 1Mbps and 2Mbps, but also over the old 802.11b rate of 11Mbps. This adjustment will have the desired eﬀect of blocking old 802.11b devices from connecting to the network and causing performance problems.
Networks that have multicast applications, such as multicast video, should have their minimum data rates increased as well, although this requires more sensitive tuning that will depend on the capabilities of the wireless product selected.
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