Wi-Fi protocol supports 13 communication channels; how do these channels relate to the volume of devices you can have on the network and the quality of the connection? Read on learn more about Wi-Fi channel usage.

今天的問答環節是由SuperUser提供的，SuperUser是Stack Exchange的一個分支，它是一個由Q&a網站組成的社群驅動分組。

問題

超級使用者讀者Diogo需要對Wi-Fi頻率通道的功能做一點說明：

As ********* reference, 802.11 standards (which defines Wi-fi networks) tell us that wireless networks works with 13 different channels on OFDM (depending on the release, a, b, g or n). From this I was wondering, if I have more than 13 machines on the same room (one room work for example with 50 notebooks), it would be impossible to connect all of them to internet at the same time? I mean, each device would use one specific channel to communicate with the acess point, limiting the acess point to 13 permanent connecti***.

How does all this stuff really work?

許多現代計算技術對終端使用者都是隱藏的，Wi-Fi也不例外。Wi-Fi頻道與網路流量和質量的關係究竟如何？

答案

幾個超級使用者貢獻者回答了Diogo的問題。喬爾·科霍恩回答說：

First of all, the U.S. only allows 11 of those 13 channels. Additionally, the original wifi developers made a mistake, of sorts, and signals within channels bleed over to their neighbors… there are really only 3 channels you should use: 1, 6 and 11.

That said, you can have far more than 3 devices on wifi at a time, because devices will share time on each channel. It’s just like having someone listen to several conversati*** taking place at once in a crowded room: not everyone is talking all the time. If two people talk at the same time, the listener may have to ask one or both to repeat themselves. The more people you add to the room, the less total information you can pass around, because people will c***tantly interrupt one another at an increasing rate. A good rule of thumb is around 25 devices per channel for casual browsing, but this can drop significantly for non-casual traffic like gaming, p2p file sharing, video streaming, and large file transfers.

In networking parlance, we say a wifi cell is unswitched and half-duplex, making it very sensitive to collisi***. Wired networks typcially don’t have these weaknesses (switched and full-duplex), and so while wifi is a “good enough” technology to use at home, serious networks always like to push as many people to a wired connection as possible.

I run the campus network at a **all college, and it’s sad to see how many new students arrive this year who have never used a wire for network access. They think the notion of needing a wire is quaint, and don’t understand the physical limitati*** involved, and why 80 devices (nearly 2 per student on average) in dorm space the size of their parents’ house doesn’t work so well. Re-educating them about this is hard.

Kurtnelle強調了一些頻率通道注意事項：

Just adding my 2 cents:

1. All Access points, and devices are sharing the channel. So if there are 10 access points and 200 devices on channel 6 (regardless of if they are yours or not) are sharing the capacity of the channel. For the G protocol that would be ~50 Mbps, for N ~150Mbps.
2. Devices and access points (or routers) time share sending and receiving data on the channel. Each device on the channel takes turns sending and receiving data.
3. Some advanced routers can communicate on 2 and 3 channels at once! This requires more compute power of course but it is possible. The really advanced devices are able to filter out devices that are not on its “network” and improve speed performance for it’s devices.
4. Wireless N uses the 5Ghz frequency spectrum which is newer, which relates to less devices being on those frequencies.

To answer your question in short: You could have thousands of devices on your network; theoretically. All of the 13 computers (devices) will be able to access the internet at the same time.

有關調整路由器和Wi-Fi頻道的實用方面的更多資訊，請檢視我們以前的How To Geek文章綜述，主題是：保護網路安全和最佳化路由器的最佳Wi-Fi文章。

有什麼要補充的解釋嗎？在評論中發出聲音。想從其他精通技術的超級使用者貢獻者那裡讀到更多答案嗎？點選這裡原來的超級使用者討論執行緒。