Linux Journal October 2015 by Linux Journal

Author:Linux Journal
Language: eng
Format: mobi, epub
Tags: Ubiquiti, Web, Varnish, Networking, NoSQL, Privacy, Cache, Apps, Virtual, Google Contacts, Android, HTTP Server, PIA, AWS, Wireless, Amazon, Raspberry Pi, UniFi, UltraHD, VPC, Drupe, VPN, CodeCombat, CLI, Database, PPTP, Science, Linux, EC2, OpenVPN, Wi-Fi, Maxima, Code, PostgreSQL, Secure, L2TP/IPSec, Coding, Bottleneck, Private, ORM, SQL, Large Screen, Tools, Networks, Cloud
Publisher: Belltown Media
Published: 2015-09-29T07:00:00+00:00

Figure 2. The 5GHz Channel Allocation (image from http://securityuncorked.com)

For most people, that means using the nine available non-overlapping channels that are outside the DFS range. You can see that channels 36, 40, 44, 48, 149, 153, 157, 161 and 165 are available to use without concern of getting bumped by weather or military. Things do become a little more complicated if you want to use more bandwidth per channel, however. Remember that 802.11n can use 40MHz per channel, which you see in Figure 2 will limit your available channels to four non-DFS, or 12 if you include DFS. Still, four completely open 40MHz channels is far, far better than the single 40MHz channel available in the 2.4GHz spectrum!

The new kid on the block is, of course, 802.11ac. This new standard uses only the 5GHz spectrum, and it allows a wide variety of channel widths. The old standard of 20MHz is allowed, but also widths of 40, 80 and even 160MHz are allowed for some serious throughput! As channel width increases, the number of non-overlapping channels decreases, of course, so Figure 2 shows how many options you have in each scenario. I don’t think there are any devices currently on the market that support 160MHz channels, but I could be wrong.

Why Is 802.11ac So Much Faster? (MIMO)

You might be wondering why 802.11ac is touted as so much faster than even 40MHz-wide 802.11n access points. The answer is similar to why 802.11n is so much faster than 802.11g. You probably noticed that 802.11n and 802.11g both use the 2.4GHz spectrum (Table 1), and yet although 802.11g is limited to 54Mbps, the “n” standard can achieve speeds up to 300Mbps. That’s because with 802.11n, Multiple Input Multiple Output (MIMO) technology allows multiple antennas to transmit and receive at the same time.

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