802.11n and Channel Bonding
An 802.11n Wi-Fi network connection supports up to 300 Mbps of rated theoretical bandwidth under best-case conditions. However, an 802.11n link sometimes operates at slower speeds like 150 Mbps and below. For an 802.11n connection to run at its maximum speed, Wireless-N broadband routers and network adapters must be linked and running in what’s called channel bonding mode. In 802.11n, bonding uses two adjacent Wi-Fi channels simultaneously to double the wireless link bandwidth compared to 802.11b/g. The 802.11n standard specifies 300 Mbps theoretical bandwidth is available when using channel bonding. Without it, about 50 percent of this bandwidth is lost (actually slightly more due to protocol overhead considerations), and in those cases, 802.11n equipment generally reports connections in the 130 to 150 Mbps rated range.
Set Up 802.11n Channel Bonding
802.11n products normally do not enable channel bonding by default. Instead, these products run in conventional single-channel mode to keep the risk of interference low. Both the router and Wireless-N clients must be configured to run in a channel bonding mode together to achieve any performance benefit. The steps to configure channel bonding vary depending on the product. The software sometimes refers to single-channel mode as 20 MHz operations (20 MHz being the width of a Wi-Fi channel) and channel bonding mode as 40 MHz operations.
Limitations of 802.11n Channel Bonding
802.11n equipment can ultimately fail to run in the maximum (300 Mbps) performance range for these reasons:
Some 802.11n gear cannot support channel bonding. For example, this mode of wireless signaling is government-regulated in certain countries like the UK. If the 802.11n network includes any 802.11b/g clients, network performance might be negatively affected, depending on the router’s capabilities. Because 802.11b/g clients do not support channel bonding, these must be set up properly with a mixed-mode Wireless-N router to minimize performance impact. Interference from other 802.11n networks nearby can prevent a Wireless-N router from sustaining channel bonded connections. Some Wireless-N routers automatically fall back to single-channel operation when they detect wireless interference on the channels. Even if a connection can run at 300 Mbps, it doesn’t mean that devices can download and upload data that fast. One major reason for this is that the ISP subscription doesn’t allow high speeds (like if you’re only paying for 100 Mbps).
As with other networking standards, applications running on an 802.11n network typically see less actual bandwidth than the rated maximums imply, even with channel bonding in place. A 300 Mbps rated 802.11n connection often yields 200 Mbps or less of user data throughput.
Single Band vs. Dual Band 802.11n
Some Wireless-N routers (so-called N600 products) advertise support for 600 Mbps speeds. These routers do not provide 600 Mbps of bandwidth on a single connection but 300 Mbps channel bonded connections on each of the 2.4 GHz and 5 GHz frequency bands.
