In the late 1990s, devices supporting the 802.11b wireless networking standard first appeared in the mass consumer market.
802.11b claims to provide "11 Mbps" transmission rate, which is higher than the original wired Ethernet 10 Mbps transmission rate. Anyone who knows a little bit about mathematics should think that 802.11b is faster than 10 Mbps wired Ethernet.
However, at that time, because smartphones have not yet appeared, the price of the laptops is still extremely expensive, and they have poor performance and are heavy and heavy, so I do not have any devices that can use wireless networks. When I really came into contact with the wireless network, my office and my home were already equipped with a 100 Mbps wired network. At this time, the 802.11b with a transmission rate of only 1/10 was not attractive to me.
In the early 21st century, with the built-in Wi-Fi notebooks becoming smaller, lighter, and cheaper, some small companies are eyeing the "up to" 11Mbps transmission rate of 802.11b: Since the original office has 10 Mbps of cable Ethernet is enough, but when setting up a new office building, why don't you just use the "faster" 802.11b wireless network?
This is also the first time I really used Wi-Fi.
However, the first "close contact" with Wi-Fi did not leave any good impression on me. I knew at that time that the original 11 Mbps was just the maximum physical layer rate, not the actual rate at which your data was transferred from one device to another.
In actual use, the transmission rate and reliability of 802.11b are not much stronger than those of dial-up Internet. Even if you put two devices close enough and are all placed near the wireless router built-in AP, the maximum transmission rate is 1 Mbps (that is, 125 KB/s). To know that this is the best case, if you have 10 PCs trying to access a server at the same time, 125 KB/s becomes 12.5 KB/s per PC.
The D-Link DI-514 wireless router was a very good product at the time, but the days of using 802.11b were really bad...
When we gradually accepted the fact that 802.11b was "junk," 802.11g came.
802.11g claims to provide a staggering 54 Mbps, although this figure is only half the number of high-speed Ethernet (100 Mbps) at the time, but it is five times the original Ethernet (10 Mbps)!
However, just like 802.11b, the 802.11g's known 54 Mbps transmission rate is actually only the physical layer rate, and the actual transmission rate shown on the download progress bar is two different things. Like 802.11b, the fastest transmission rate of 802.11g in daily use is almost one-tenth of 54 Mbps, which is about 5 Mbps. If you assign 5 Mbps to multiple PCs on the same network, the speed of each PC is still very "moving."
Around 2000, 802.11n devices first appeared in the consumer market, claiming to provide a maximum transmission rate of 600 Mbps!
Although this transmission rate is somewhat different from the emerging Gigabit Ethernet at that time, it is 6 times that of 100 Mbps wired Ethernet, which is commonly used by users at that time!
Of course, not surprisingly, in actual use, the actual transmission rate of 802.11n may only reach 1/10 of the publicity even if the environment is ideal and only one device is connected.
When 802.11ac products hit the market at the end of 2013, almost every router product advertised its transmission rate "hysterically".
It started with 1.3 Gbps, then 2.7 Gbps, then 5.3 Gbps! This figure has surpassed most of the wired Ethernet. But after experiencing 802.11b/g/n, I already saw everything: dealers’ propaganda was a lie, and I was counting on Wi-Fi as fast as wired Ethernet.
So what is the maximum transmission rate of 5.3 Gbps?
Let's take D-Link DIR-895L/R as an example. In the product description of its official website, we can see the following description:
"The groundbreaking three-band Wi-Fi technology can deliver an amazing wireless transmission rate of up to 5332 Mbps while improving the reliability and coverage of wireless networks with 4x4 data transmission, beamforming and MU-MIMO technology."
In addition to D-Link, we can see similar descriptions on mainstream AC5300 routers such as Netgear, Linksys, ASUS, and TP-Link.
The D-Link DIR-895L/R is a three-band router that can support two 5 GHz frequency bands and one 2.4 GHz frequency band. The highest transmission rate is 2166 Mbps in the 5 GHz frequency band, and the maximum transmission rate in the 2.4 GHz frequency band is 1000 Mbps, and 2166 Mbps × 2 + 1000 Mbps = 5332 Mbps, the transmission rate of 5.3 Gbps is calculated as such.
Specifically for each frequency band, the highest rate of the radio frequency band at the physical layer is multiplied by the maximum number of MIMO streams supported by the frequency band (usually four high- and mid-range routers). But after careful calculation, there seems to be some problems here.
The 5 GHz band (80 MHz bandwidth) of the D-Link DIR-895L/R has a maximum transmission rate of 433 Mbps at the physical layer, which is multiplied by 4 after 1732 Mbps, compared to the D-Link official promotion rate of 2166 Mbps. Worth 108.5 Mbps, what's going on?
On this issue, the router vendor's explanation is usually a somewhat vague expression of "using dedicated data compression technology," so the 108.5 Mbps is more like a marketing tool. It should be noted that this "speed-up" approach has become a "new normal" in the router industry. Recently, many 3x3 dual-frequency routers suddenly changed from "AC1700" to "AC1900."
In addition, in the 2.4 GHz band, the situation is even more troublesome.
D-Link claims that the 2.4 GHz band can achieve a transmission rate of 1000 Mbps. However, the maximum transmission rate in the 801.11n 2.4 GHz band (40 MHz bandwidth) is 150 Mbps, which is also multiplied by 4 MIMO streams at 600 Mbps, which is a total of 400 MMbps away from 1000 Mbps...
In this regard, router manufacturers generally interpret this way: With the adoption of the 256-QAM modulation module, it is possible to increase the transmission rate of 50 Mbps for each stream, so that the original 600 Mbps becomes 800 Mbps (although 256-QAM Is a non-standard, non-IEEE-approved product with little terminal support). As for the remaining 200 Mbps, it is basically a meaning to use the “data compression†speed increase method in the 5 GHz band.
Seeing here, everyone should have already felt that the so-called 5332 Mbps is basically a lie. Let's take a look at how much the D-Link DIR-895L/R, a 5332 Mbps wireless router, can actually transmit in actual use.
Before this, we need to talk about 4×4 MIMO first.
The full name of MIMO is Multiple Input Multiple Output (MIMO). MIMO technology can be understood as multiple cutting of network resources and then synchronous transmission through multiple antennas to increase the data transmission speed of a single device. 4×4 MIMO stands for Has 4 transmitting antennas and 4 receiving antennas.
It is a good thing that the router supports 4×4 MIMO, but the problem is that almost all the terminal devices around us, including laptops, tablets, and smart phones, do not support 4×4 MIMO. According to my understanding, as of February 2017, the terminal equipment available on the market is either single-stream or 2x2. In the case that your terminal equipment does not support this, it means that the router's 4x4 MIMO does not have any "usefulness".
You may think so. There are not 4 MIMO streams. I can assign two of them to the laptop and the other two to the tablet. Unfortunately, this is also impossible. The technology that this kind of router sends data to multiple devices at the same time is called MU-MIMO. This technology may be supported by your home router, but your terminal device may not support it. (The flagship handsets such as the Samsung Galaxy S7 support MU-MIMO, but laptops that support this technology are almost none.)
In addition, even if both routers and terminal devices support MU-MIMO (Multi User for MUs), the actual increase in the actual transmission rate of this technology may not be as much as we think. I used a router that supports MU-MIMO and two MU-MIMO-enabled terminals to test. Compared to turning off MU-MIMO on the router, the throughput of the two terminals only increased by 20 after the MU-MIMO was turned on. %.
Re-emphasize that most of the terminals we use everyday can only support SU-MIMO (SU, Single User). At the same time, AP can only communicate with one terminal. In other words, if you are the fastest The terminal equipment supports 2x2, then this AP can only provide 2x2 speed at the fastest, nothing more.
Until now, we have learned that "up to 5.3 Gbps transmission rate" is actually obtained with three frequency bands plus one. When looking at only one frequency band, the maximum transmission rate is 2.166 Gbps. Then we knew that the practice of "data compression" to get a higher transmission rate was fundamentally flawed, with 2.166 Gbps becoming 1.732 Gbps. In addition, we also learned that, due to the limitation of terminal equipment, the 4 MIMO streams appearing in advertisements by router manufacturers can usually only use two, and 1.732 Gbps becomes 866 Mbps.
Unfortunately, this is not finished yet. Because in actual use, it is impossible to reach the maximum rate of the physical layer.
In an ideal use scenario (about 3 meters from the router, there are no interfering objects such as partitions, there is no extra interference), and an excellent terminal device's transmission rate can reach 1/3 to 2/3 of the physical layer rate. This number is multiplied by the number of MIMO transceiving streams supported by the terminal device, which is the actual network transmission rate.
The Acer C720 Chromebook that I use every day is a Qualcomm Atheros AR9462 802.11n adapter (supporting 2x2). The maximum transfer rate I tested was around 205 Mbps. I also tested two 802.11ac USB NICs, the TP-Link Archer T4U and the Linksys WUSB-6300 (both supporting 2x2), with a maximum transfer rate of 350 Mbps.
The best performer is the MacBook Pro with the Broadcom BCM94360CS wireless network card. The maximum data transfer rate can reach around 600 Mbps. This is because the Broadcom BCM94360CS supports 3x3 MIMO, which has not escaped the "physical layer" mentioned in the previous paragraph. Rate 1/3 to 2/3" range.
However, it should be noted that most of the time, we will be more than 3 meters away from the router, and often there will be a variety of interfering objects such as walls. When you are 30 meters from the router and two walls in between, even if your AP and terminal equipment are of high quality and there is no other person and equipment and you "grab the speed", the actual transmission rate is probably only 80 Mbps...
This is still not finished, because many devices have significantly different upload and download rates.
Among the devices I tested, the Linksys WUSB-6300 is quite "normal" and the upload and download rates are similar, but the Qualcomm AR9462 and Archer T4U both obviously tend to download. The upload rate is often only 1/2 or even less than the download speed... ... Even though the same chip is used internally, the performance of the terminal equipment is often very different due to different internal designs (the "normal" Linksys WUSB-6300 and the "unusual" Archer T4U are all Realtek RTL8812au wireless. Network card). .
Hey, test Wi-Fi.
Although Wi-Fi technology based on the 802.11 protocol standard has made great progress in the past two decades, if you want to get the fastest and most stable Internet experience, high-speed wired Ethernet has always been better. Choice, this has never changed.
But when our lives are surrounded by smart phones, tablets, and numerous IoT devices, simply relying on "old" wired Ethernet is obviously an unrealistic thing. If you have too many terminal equipment in your home, the existing multi-frequency AC router still can not meet the demand. In addition to using wired Ethernet, the new generation router based on mesh network represented by eero and Google Wifi is a It is a good choice, which is the direction of the next generation of router manufacturers after the dual-band and tri-band AC routers.
24v power supply, the current range is 2A-9.2A, the max power is 220w. We also can meet your specific requirement of the prodcuts.The material of this product is PC+ABS. All condition of our product is 100% brand new.
Our products built with input/output overvoltage protection, input/output overcurrent protection, over temperature protection, over power protection and short circuit protection. You can send more details of this product, so that we can offer best service to you!
24V Power Supply,24V Pc Power Supply,24V Dc Power Supply ,24V Power Supply For Pc
Shenzhen Waweis Technology Co., Ltd. , https://www.waweispowerasdapter.com