No line by the correct knowledge of the channel

Channels can be compared to RJ45 network cables, a total of 11 available channels. Considering that there are overlapping regions between the adjacent two wireless APs, in order to ensure that the signal channel used in this part of the region can not be covered by each other, the wireless AP with the specific signal covering each other must use different channels, otherwise it is easy to cause the signal of each wireless AP to interfere with each other, thus causing the overall performance of the wireless network to drop.





However, each channel will interfere with the channel on both sides of the calculation, there are three effective channels, please have a lot of wireless equipment, you must pay attention to frequency band segmentation.





with the price of wireless products continue to reduce the popularity of WLAN (Wireless LAN) is changing the trend, more and more offices, families began to use wireless LAN. As a result, some users have begun to appear in the WLAN channel congestion problem, resulting in a drop in network speed, off the line, Internet work is not normal and so on, what is going on?





What is a wireless channel





Wireless channel is often said wireless "band (Channel)", which is the wireless signal as the transmission media data signal transmission channel.





you know, in the wireless network installation, the general use of wireless network equipment with the management tools, set the connection parameters, regardless of which wireless network of the most major settings items include network mode (centralized or peer-to-peer wireless network), SSID, channel, transmission rate of four, Just a few wireless devices drive or setup software that simplifies these steps, and generally uses the default settings (that is, without any settings) to make it easy to use a wireless network.





but a lot of problems, but also because of the pursuit of convenience, you know, commonly used IEEE 802.11b/g work in the 2.4~2.4835ghz band, these bands are divided into 11 or 13 channels. When there are more than two APS in the wireless AP wireless signal coverage range, it is necessary to set different frequency bands for each AP to avoid the common channel conflict. And many users use the wireless device default settings are Channel 1, when more than two of such wireless AP devices "Encounter" when the conflict is inevitable.





Why is the current wireless channel conflict so interesting, in addition to home or office wireless equipment because the price of the constant decline in the geometric growth, wireless standards of the innate lack of shake is also a major cause of this dilemma:





As we all know, the current mainstream wireless protocols are developed by the IEEE (American Electrical and Electrotechnical Association), in the IEEE three wireless Standard ieee802.11b, ieee802.11g, ieee802.11a, the number of channels is different.





ieee802.11b




The
adopts the 2.4GHz frequency band, the modulation method adopts the compensation code keying (CKK), and a total of "3" non overlapping transmission channels. Transmission rate can be automatically reduced from 11Mbps to 5.5Mbps, or according to the direct sequence spread spectrum technology to the 2Mbps and 1Mbps, to ensure the normal operation and stability of the equipment.





ieee802.11a




The
expands the standard physical layer, requiring the layer to use a 5GHz band. The standard adopts OFDM modulation technology, there are "12" non-overlapping transmission channels, the transmission rate range is 6mbps-54mbps. However, this standard is incompatible with the IEEE802.11B standard. Wireless APs and wireless cards that support the protocol are less common in the marketplace.





ieee802.11g





This standard altogether has "3" a not overlapping transmission channel. Although the same operation in the 2.4GHz, but backward-compatible ieee802.11b, and because of the use of the same modulation mode with the ieee802.11a OFDM (orthogonal frequency), so that the wireless LAN to achieve 54Mbps data transmission rate.





from the above we can see that either the IEEE802.11B or the IEEE802.11G standard supports only 3 non-overlapping channel channels, only channels 1, 6, 11, or 13 are not conflicting, but devices using channel 3 interfere with 1 and 6, and devices using Channel 9 interfere with 6 and 13 ......。





In the case of 802.11b/g, the available channels overlap each other in frequency, resulting in only three non-overlapping channels for network-covered service areas, resulting in users sharing only the three channel data bandwidth. These three channels are also subject to interference from other radio sources, as the 802.11b/g WLAN standard uses the most commonly used 2.4 GHz radio band. This frequency band is also used in a variety of applications, such as Bluetooth wireless connection, mobile phone and even microwave ovens, these applications in this frequency of interference may further limit the available bandwidth of WLAN users.





in the 802.11g and 802.11a standards of the same 54Mbps transmission rate, 802.11A has a greater advantage in channel availability. This is because 802.11a works in a more relaxed 5GHz band with 12 non-overlapping channels, while 802.11b/g only 11, and only 3 are non-overlapping channels (Channel 1, Channel 6, Channel 11, or Channel 13). So 802.11g is not as good as 802.11a in coordinating adjacent access points. Since the 802.11a 12 non-overlapping channels can provide more choices to the access point, it can effectively reduce the conflict between the channels.





but the two sides of things in the ieee802.11a performance, 802.11a is also due to high frequency band, so that 802.11a transmission distance greatly reduced, the wireless AP coverage of only about half of the 802.11b/g or lower, in practical terms, If a 802.11B wireless AP indoor coverage of up to 80 meters, then 802.11a can only reach about 30 meters. In addition, the cost of wireless products based on 802.11a standards is much higher than 802.11b due to the complexity of the design. Channel number of superior backward-compatible 802.11a it is not difficult to understand the eventual failure of the market.





Of course, 802.11G has defeated 802.11a with 54Mbps of high-speed and backward-compatible 802.11b, but 802.11b/g is also facing embarrassment as the popularity of wireless devices. 802.11A supports 12 non-overlapping channels, so its total bandwidth is 54mbps*12=648mbps. The 802.11g only supports 3 non-overlapping channels with a total bandwidth of only 54mbps*3=162mbps. In other words, when the number of clients is small, you may not be able to distinguish between 802.11a and 802.11g speed difference, but as the number of clients increased, the data flow increased, 802.11g will be more and more slow, until the bandwidth is depleted, let alone 802.11b.





Many people think that Intel's new Centrino 2 generation is used in the intel® Pro/wireless 2195a/b/ G Three-frequency wireless network card new support 802.11A standard, as a kind of market regression or standstill, but we through the above analysis, you will find that Intel may also be facing the 802.11b/g of the channel and bandwidth confusion, at least for the time being from foreign wireless access to the earlier foreign users of the feedback look , and that's exactly the case.





In addition, while some vendors are currently developing a dual-frequency compatible 802.11a (5GHz) and 802.11g (2.4GHz) WLAN solution, a dual-frequency access point typically requires two independent RF modules and corresponding independent data processing capabilities, This will lead to the high cost of stand-alone equipment. But the frequency band interleaving technology such as the Italian-French semiconductor (STMicroelectronics) uses the frequency band interleaving technology The access point to work alternately between two frequency bands, but does not work simultaneously in two frequency bands, although can reduce the cost, but it still is higher than the ordinary single frequency access node's cost. Therefore, Intel in the next generation Centrino compatible 802.11A standards, can be seen as a new wireless standard before the introduction of a helpless for this strong demand for the user short-term solution.





In addition, why do the commonly used IEEE 802.11b/g work in the 2.4~2.4835ghz band, which are divided into 11 or 13 channels--Why are there 11 channels and 13 channels? This is the standard of different countries in various regions, the North American/FCC Standard, It adopts 2.412~2.462ghz, a total of 11 channels, of which 1, 6, 11 channel is not overlapping transmission channel channel; European/ETSI Standard, it adopts 2.412~2.472ghz, there are 13 channels, of which 1, 6, 13 channel is not overlapping transmission channel channel; little Japan, It uses 2.412~2.484ghz,14 channel, in addition, France 4 channel, Spain 2 channel and other Non-mainstream standards. If the wireless network card is supported, it is generally recommended that the FCC (North America) or ETSI (Europe) standard be selected when installing the driver for a regional channel standard selection.