802.11n introduces efficiencies, which allow for the reduction of the guard interval, cutting the time in half, hence a "short" guard interval. Though necessary, a guard interval is essentially wasted time, which means wasted bandwidth. Aggregation has been available in shipping 11n hardware for a while, but support for both aggregation techniques has been inconsistent from manufacturer to manufacturer, though this is changing and most new hardware is now supporting both types of aggregation.Ī guard interval is a period of time that is inserted between data transmissions to prevent overlap between the transmissions. The use of aggregation, and the specific type required, is determined by the hardware itself and is transparent to the end user. Though these approaches are quite different, the end result is the same - reduced protocol overhead, which effectively increases data throughput.Īggregation is a sophisticated 11n technique, but the user need not worry about it. For large data sets that can't fit into even the maximum allowed data packet, 11n decomposes the data into multiple packets, but treats the packet stream as if it was a single packet, and then uses the block acknowledgement feature. For very small amounts of data, 11n combines data that would originally have been sent using multiple data packets into a single data packet. Block acknowledgements are also already widely used in shipping 802.11n-capable hardware.Īggregation assembles data into more efficient packages for transmission across the network. Though the throughput gains are not nearly as large as those achieved with MIMO or channel bonding, the efficiencies achieved with block acknowledgements are certainly worth mentioning. This reduces protocol overhead and effectively increases data throughput. Block acknowledgements allow more data to be sent before the receiving party must acknowledge receipt of the data. To be safe, reserve the use of channel bonding to the 5GHz channels.īlock acknowledgements are a tried and true method of wired networking. Though effective in both frequency ranges, its use is sometimes not recommended in the 2.4GHz band because it uses so much of the existing spectrum and can cause interference with neighboring 802.11b/g infrastructures. In the 2.4GHz range, where the channels are closer together, the bonded channels are spaced several channels apart, so when channel bonding is used in the 2.4GHz band, a significant portion of the available 2.4GHz spectrum is used to service the one bonded channel.Ĭhannel bonding is already widely used. In the 5GHz band, the channels that are bonded together are adjacent channels, for example channels 36 and 40 in the U.S. Two times the bandwidth is essentially equal to two times the throughput, so this is another significant feature in 11n. To take full advantage of the increased throughput the wireless clients must also be capable of operating at the same number of data streams as the APs, and wireless client adapters are a bit further behind the APs, making three-stream capable wireless adapters still somewhat hard to come by from commercial channels.Ĭhannel bonding does exactly that, it takes two existing 802.11 channels and groups them together to form a single channel, with twice the bandwidth. Most currently available equipment takes advantage of only two data streams, but equipment is finally coming to market that uses up to three data streams. The 802.11n specification allows for up to four data streams. This is one area where technology is just catching up with theory. At least one antenna is required per data stream, but keep in mind that not every antenna must be used for data, so the maximum number of data streams is limited by, but not necessarily equal to, the number of antennas on the AP. This is also why 11n access points (APs) have more antennas than the older a/b/g models. Three streams deliver three times the data.
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