This weekend, I took a closer look at my Airport setup and found some interesting results.
My setup: Time Capsule (ac) as main router in the basement office, connected by Cat5e to cable modem with Comcast 50Mbps service. On the far end of the basement, AP Extreme (dual-band n) connected by GB Ethernet to the Time Capsule. AP Express (dual-band n) upstairs connected by TPLink 1200Mbps Power Line adapter to the Time Capsule.
All Airports were set to dual mode (2.4 + 5GHz), setup as Roaming (Create a Wireless Network), and all were set to automatic channel selection on both 2.4 and 5GHz bands. In reality, all three were using channel 6 for 2.4GHz. Two neighbors have Wi-Fi networks broadcasting 2.4GHz signals in the channel 1-9 range but were weaker signals than my own network. The neighbor's 5G signals were virtually non-existant. With this setup, I got internet speeds of 50-60Mbps on 5GHz everywhere, and 8-60Mbps on the 2.4GHz band.
Next, I staggered the 2.4GHz channels on the three Airport devices so one was set on Channel 1, another on Channel 6, and another on Channel 11. I then re-tested both bands, 5GHz remained unchanged and 2.4GHz ranged from 24-60Mbps where the lowest speeds were in locations where my neighbor's signal was the strongest.
My take, the overlapping channels on my own Airports were causing collisions\interference with each other and my neighbors signals weren't helping matters. As I understand, each channel range is a separate collision domain. Hosts in a given collision domain must wait in queue for access to use the channel. The more hosts in a given channel range, the contention for access to use the channels increases, thus speed slows. Since packets are sent to all radios in a given channel range, even foreign networks, the contention increases when neighboring networks and hosts operate in the same range of channels.
To analyze where your bottlenecks reside, start with the physical LAN by connecting a Mac\PC to an Ethernet port at each Access Point location and test the speeds using something like speedtest.net and\or LAN Speed Test (see below). The results should be similar in all locations, else you have a weak Ethernet link between that location and the router. Ideally, LAN speeds should be equal or greater than your ISP service.
Next, test 2.4 and 5GHz Wi-Fi speeds The easiest way to do this is to use a different SSID (network name) on the 2.4 and 5G bands (ex: NETWORK and NETWORK5G) on all of your Airport devices. Then, test and note results on each frequency while connected and close to each access point. Results should be relatively consistent on 5G given interference should be minimal. For the 2.4GHz band, expect varying results.
Then, using AP Utility, spread the channels on all of the Airports so they avoid overlapping. Repeat the Wi-Fi testing. Finally, if neighbor networks appear in your home, figure out which 2.4G channels they are using and set the Airport channels so that the overlap occurs on the Airport device where the neighbor's signals are weakest.
The tools I used were:
LAN Speed Test Lite - free tool for Mac or PC, for testing local network connection speeds available
here. Note that this tests file transfer speeds, disk read\write speeds impact the test results. To get network speeds accurately, there is a combo of server and client you can purchase for $11 which tests without reading\writing from disk.
Airport Utility - to verify my Mac or iPhone was on the list of connected devices on the Airport device I was testing.
Speedtest by Ookla - free in the ATV and iOS app stores, and
Speedtest.net on PC or Mac via browser to test speeds throughout the home to internet locations.
Wi-Fi Scanner ($19.99 in the MAS
here). This is a good tool for visual representation of the Channels used by all networks within range. If you have a portable Mac or PC, all the better as you can test in all locations. Any Mac or PC WiFi analysis tool will work, the key is being able to see which channels are in use at each location to find the overlap.
Final thoughts: avoid using 2.4 GHz if possible, it is most prone to contention. If you must use 2.4GHz, limit the number of Access Points and hosts you use on this frequency, and avoid channel overlapping. And, if your only option for connecting additional Access Points is wirelessly to the router, only use 1 device connecting this way or your entire 2.4GHz band will suffer. Some experts claim more than 1 wireless extender will absolutely clobber your entire Wi-Fi network.
