In the course of development of WLAN, once the emergence of many technologies and protocols, such as IrDA, Blue Tooth and HyperLAN2 and so on. But the development has been large-scale promotion and commercial areas are in the WLAN IEEE 802.11 series of standard protocols, WLAN is also defined as a standard protocol based on IEEE 802.11 wireless LAN. We have no stranger to 802.11 at the time of purchase to support WLAN-enabled products can see the shadow of 802.11. The main issue we are talking about at 802.11 standard protocol landmark: 802.11a, 802.11b, 802.11g, 802.11n and 802.11ac. Although the agreement relatively boring, but to understand these protocols will help us deploy WLAN, below follow the small series with a look at several major agreements it 
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WLAN and wired LAN biggest difference is the "wireless", by learning period we know that WLAN communication medium is radio frequency, RF and wired LAN medium (cable or fiber) has a completely different physical characteristics compared to, which leads to a WLAN The physical layer (PHY) and media access control layer (MAC) is different from the wired LAN. Therefore, the main 802.11 protocol is the definition of the physical layer and MAC layer of WLAN.
In the early 1990s, in order to meet the growing demand for WLAN, IEEE 802.11 set up a special working group, specializing in custom and standard WLAN protocols, and introduced the first generation WLAN protocol in June 1997 --IEEE 802.11-1997 protocol defines the physical layer is operated in 2.4G ISM band, the data transfer rate is designed to 2Mbps. Because of the design of the protocol on the transmission rate and distance can not meet people's needs, it has not been large-scale use.
Subsequently, IEEE 1999 launched the 802.11a and 802.11b. 802.11a working on the ISM band of 5GHz, and selects the orthogonal frequency-division multiplexing OFDM (Orthogonal Frequency Division Multiplexing) technology, can effectively reduce the influence of multipath fading and improve the spectrum utilization rate of the physical layer of 802.11a up to 54Mbps. 802.11b is still working at the 2.4GHz ISM band, but technical improvements on the basis of 802.11, based on the 802.11b communication speed up to 11Mbps.
OFMD is a multicarrier modulation technique is mainly divided into several subchannels designated channel using a subcarrier modulated on each sub-channel, and each of the subcarriers are transmitted in parallel, can effectively improve the spectrum utilization ratio of the channel.
While 802.11b access rate offered is lower than 802.11a, 5GHz chip development but it was too slow, 802.11b has been widely used during the chip to be launched. Because 802.11a is not compatible with 802.11b, coupled with the higher 5GHz chip prices and local regulations restrictions and other reasons, so that 802.11a is not widely used.
In early 2000, IEEE 802.11g working group began developing an only provide 54Mbps rate, but also backward compatible with the 802.11b protocol standard. And in November 2001 presented the first draft IEEE 802.11g, the draft in 2003, it became the standard. 802.11g is compatible with 802.11b, continue to use the 2.4GHz band. In order to achieve a rate of 54Mbps, 802.11g 802.11a borrowed results in the 2.4GHz band using orthogonal frequency-division multiplexing (OFDM) techniques. IEEE 802.11g launch was to meet the demand for bandwidth, the development of WLAN played a great role.
You may have a question: Why not in 1999 to develop standards 802.11b and 802.11a directly using the same OFDM technology, so that you can get an earlier rate of 54Mbps in the 2.4GHz band, and without waiting for the end of 2001 802.11g It appears. In fact 802.11b discussed in 1999, when, OFDM technology applications are being offered to the 802.11b standard, but when the US Federal Communications Commission (FCC) prohibit the use of OFDM in the 2.4GHz band, the ban was only until 2001 revocation, six months later, 802.11g draft uses OFDM technology was able to successfully introduced.
In the online world 54Mbps rate of rapid development will not always be full of user needs. A new IEEE working group --IEEE 802.11 Task Group N that is TGn (Task Group n) was established in 2002, began to study for a faster WLAN technology, the goal is to achieve a rate of 100Mbps. To achieve the goal of twists and turns, because the two camps debated within the group of protocol standards, the new agreement until September 2009 was only finalized and approved, this agreement is 802.11n. In the seven-year development process, 802.11n 100Mbps rate also from the original design, perfect to up to 600Mbps, 802.11n uses a dual-mode, supports 2.4GHz and 5GHz, and is compatible with 802.11a / b / g.
After just settled 802.11n standard, IEEE began work to develop the next generation of WLAN standard protocol --802.11ac. And in 2013 officially launched the 802.11ac standard protocols, working in the 5GHz band 802.11ac, 802.11n and backward compatible with 802.11a, 80.211ac follows the 802.11n technology and the many technical improvements made, the rate up to 1.3Gbps.
The following table will help us understand the main parameters 802.11 each protocol.
Huawei's products V200R003C00 and earlier support for 802.11n, 802.11g, 802.11b, and 802.11a, from V200R005C00 version began to support 802.11ac, and introduced support for 802.11ac AP: AP5030DN and AP5130DN.
Huawei's products V200R003C00 and earlier version, use the configuration command to configure the type of radio:
[6605_v2r3_111-wlan-radio-prof-test] radio-type ?
80211an 802.11an
80211bgn 802.11bgn
80211gn 802.11gn
80211n 802.11n
80211b 802.11b
80211a 802.11a
80211bg 802.11bg
80211g 802.11g
Wherein, 80211n means is configured to radio mode 802.11n, if the terminal does not only support 802.11b or 802.11g support 802.11n, you can not access the WLAN. And 80211bgn, said support and 802.11n radio supports both 802.11b and 802.11g, this time 802.11b, 802.11g and 802.11n terminal can access the WLAN. Similarly, if the parameter is configured to 80211an, 802.11n and 802.11a support the RF, 802.11n and 802.11a support terminal can access the WLAN ....... To V200R005C00 version, Radio-of the type command is deleted, users do not need to configure the type of radio frequency, radio frequency will automatically compatible protocol supported by the terminal, it simplifies user operation. In addition V200R005C00 and configure RF support the maximum rate of V200R003C00 versions are not the same, we can refer to the specific product manuals WLAN: WLAN product manuals
In the current agreement due to 802.11ac 802.11 each just launched, the public support 802.11ac end products are not many, 802.11n products is still the mainstream product. 802.11n mainly has the following advantages compared to the previous standard protocols: the polymerization packets more subcarriers, a higher coding rate, shorter GI (Guard Interval), wider channel, more spatial streams and MAC layers function, and get these advantages of 802.11ac technology is also in use. Here we look at how Huawei product configuration in order to better play the advantages of 802.11n.
More subcarriers: 802.11n ratio 802.11a / g more than four active subcarriers (802.11b technology do not use OFMD comparative), as long as the user does not need to use the configuration communications 802.11n 802.11n advantage of this can be obtained. The figure is the theoretical rate of 58.5Mbps 802.11n standard more than the previous sub-carriers can bring.
Higher coding rate: the WLAN data using radio frequency transmission, in addition to the efficient transmission of user data, the need to include more error codes FEC (Forward Error Correction), when factors valid data during the transfer due to fading, interference caused by when a data error, the more error correction code data may be, reduced to the correct data. 802.11n before the effective code rate of 3/4 up to 5/6, to improve this point that enhance the rate of 11% 802.11n. As long as users do not need to configure the use of 802.11n can also communicate directly 802.11n advantage of this.
Shorter the GI (Guard Short the Interval ): When using 802.11a / b / g transmission data, must ensure the presence of 800 ns time interval data to avoid interference between data frames, this interval is called Guard Interval ( GI). 802.11n default still use GI 800ns, but in the space environment is better, the interval can be configured to 400ns, this improvement can be increased by nearly 10% (about 72.2Mbps) throughput. The user can command in the RF template view 80211n-Guard-interval The MODE Short disposed 802.11n short GI function of:
<AC6605> system-view
[AC6605] wlan
[AC6605-wlan-view] radio-profile name 80211n
[AC6605-wlan-radio-prof-80211n] 80211n guard-interval-mode short
Run the 802.11ac can 80211ac guard-interval-mode short configuration 802.11ac short GI function, such as:
<AC6605> system-view
[AC6605] wlan
[AC6605-wlan-view] radio-profile name 80211ac
[AC6605-wlan-radio-prof-80211ac] 80211ac guard-interval-mode short
It should be noted that not all environments are suitable configuration short GI. Complex space environment, an obstacle may cause RF reflection phenomena can cause multi-path transmission between the AP and the STA (multipath effects). In a multipath environment, before sending a data block has not been completed, after a first data block may be arrived through different paths, the GI length can be reasonable to avoid mutual interference. Long unreasonable if GI, will reduce the efficiency of the link.
Therefore, the proposed short GI function off (corresponding to commands in a complex environment 80211n-Guard-interval The MODE Normal , 802.1 lac as 80211ac Guard-interval The MODE- Normal ) .
Wider channel: We already mentioned when talking radio, 802.1 In the adjacent channel support bound to two 20MHz 40MHz channel, the channel is wider transmission capacity is even greater, can bring more than 2 fold increase . In view Run RF channel command can 40MHz channels, a primary channel and specifies:
<AC6605> system-view
[AC6605] wlan
[AC6605-wlan-view] ap 0 radio 0
[AC6605-WLAN-Radio-0/0] Channel 40Mhz PLUS-1 // represents configured 40MHz wide channels, the main channel is 1.
In 802.11ac channel bandwidth can support 80Mhz, such as:
<AC6605> system-view
[AC6605] wlan
[AC6605-wlan-view] ap 0 radio 1
[AC6605-wlan-radio-0/1] channel 80Mhz 149
More spatial stream: 802.1 la / B / access point and the client is achieved g technical data transmission through a single antenna to single spatial Single Input Single Output SISO (Single Input Single Output) fashion stream. In 802.11n supports a maximum of four spatial streams multiple input multiple output MIMO (Multiple Input and Multiple Output) transmission of data (802.1 lac maximum support 8x8 MIMO). Huawei AP supports multi-antenna MIMO, such as AP5130, AP7110, AP5030 support 3 * 3 MIMO, AP3010, AP6510 , AP6610 support 2 * 2 MIMO.
MAC packets polymeric layer: in the 802.11 MAC layer protocol, there are many fixed overhead, especially acknowledgment information between two frames. In the highest data transfer rate, these excess costs even longer than the entire frame of data to be transferred. For example: 802.11g theoretical transfer rate of 54Mbps, but in fact only 22Mbps, nearly half the rate of more than wasted. 802.11n MAC protocol data unit MPDU (MAC Protocol Data Unit) frame aggregation, a plurality of MPDU may be aggregated into one physical layer packet, only once or channel contention backoff, the transmission can be completed while the MPDU of N, reducing the N-1 MPDU transmission packet brings channel resource consumption. Run 80211n a-mpdu enable may enable the 802.11n MPDU frame aggregation, and then perform 80211n A-MPDU max-length-exponent The command to configure the maximum length of the frame aggregation, 802.11n convergence maximum frame length is 65535 bytes. Such as:
<AC6605> system-view
[AC6605] wlan
[AC6605-wlan-view] radio-profile id 0 name rp01
[AC6605-wlan-view] 80211n a-mpdu enable
[AC6605-WLAN-Radio-Prof-RP01] 80211n-A-MPDU max length-exponent The //. 3. 3 represents the maximum length of a frame aggregation is 65535 bytes
802.11ac MPDU default support function, and supports a maximum length of 1,048,575 bytes of frame aggregation. So no need to use the command is enabled, you can directly configure the aggregation frame length:
[AC6605-WLAN-Radio-Prof-RP01] 80211ac-A-MPDU length exponent The max. 7- //. 7 represents the maximum length of a frame aggregation is 1,048,575 bytes
Further, 802.1 lac supports MAC service data unit MSDU (Mac Service Data Units) aggregation, greatly improving the efficiency of data transmission, such as specific configuration:
<AC6605> system-view
[AC6605] wlan
[AC6605-wlan-view] radio-profile name rp01
[AC6605-wlan-radio-prof-rp01] a-msdu send enable
[AC6605-WLAN-Radio-Prof-RP01] A-MSDU Subframes 2 // Send max-2 indicating the number of aggregation.
In addition to the 802.11 standard protocol in WLAN field there is a more common and more commonly used term --Wi-Fi. Our technology has been posted to the serial No. 3, there has been no mention of what is Wi-Fi. 802.11 in the understanding of each agreement, but also to explain what exactly is Wi-Fi-timing.
WiFi is a wireless fidelity (Wireless Fidelity) abbreviation. In the era of 802.11b, although all 802.11b products use the same 802.11b standard, but to ensure that products from different vendors can have good compatibility, 1999. Some WLAN equipment manufacturers formed an industry coalition together - wireless Ethernet network compatibility Alliance WECA (Wireless Ethernet compatibility Alliance), later renamed the Wi-Fi Alliance. Wi-Fi Alliance have set up a verification 802.11b product compatibility testing program, known as Wi-Fi certification, certified products through the program can use the Wi-Fi certification label. Later, the range of Wi-Fi certified and gradually extended to 802.11a, 802.11g, and 802.11n. In addition, because it can not stand the lengthy standardization process and promote market demand 802.11n, Wi-Fi Alliance to 802.11n 2.0 draft version as the basis for product certification, before the 802.11n standard has been around for hundreds of approved certification 802.11n products. This is why when the 802.11n standard has not been officially released, but we are already on the market can buy all kinds of good reasons for compatibility with 802.11n products.
The current issue:
If a wireless network card terminal supports only 2.4GHz, the terminal can not access the 802.11ac WLAN?
