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I run a small home network to cover house and garden with network access. I have written about it before [1][2]. However, upon revisiting the articles, I realized that a) I got some things wrong, and b) they will certainly get you started, but they are by no means a good guide. This, erm, guide is supposed to fix this.
To make use of this guide you will need to satisfy some requirements.
1) two or more devices capable of running OpenWrt [1].
2) a general purpose computer, eg. a laptop, with an RJ45 or "local area network" (LAN) port (or an adapter) [2].
3) Two LAN cables with RJ45 connectors [3].
[1] A list of devices supporting OpenWrt.
[2] Pictures of the connector.
[3] CAT-5 will do [4].
OpenWrt is running on many different devices, from single-board computers to enterprise-level rack boxes. For a small home network you should look for consumer Wi-Fi routers and access points (AP, see below ). They range from 20€ to over 400€, depending on manufacturer and features. After reading the basic Wi-Fi information below you will see that your home network will in general be fine with cheap routers, but you should sort out devices — routers and clients — that only support the IEEE standards 802.11b or 802.11g (or worse). Today most devices for home use, with the notable exception of some IoT-crap, support the 802.11n (aka Wi-Fi4) standard or better.
I recommend reading the section on Wi-Fi basics or even better, the links to Duckware and/or the Elektronik Kompendium (again, see below).
From our point of view routers and access points (AP) are basically the same. Once OpenWrt is installed on the device they have the same capabilities on the software side of things. The hardware side may be different. The job of a router is to route network traffic through different LAN, therefore it usually has many switched [1] LAN ports, AP usually have one port to connect to the LAN.
[1] Switching just means that each port creates its own collision domain. Don't bother about it, if you don't intend to dive into computer networking. Just know that switching is one of the things that makes your measly 100 MBit/s wired connection so much more performant than your 1200 MBit/s wireless connection.
[1] OpenWrt compatibility list. Filter for "WLAN Hardware".
Wireless Fidelity (Wi-Fi) is a marketing term. It encompasses all wireless ethernet networks. Wireless ethernet networks are networks that replace the connecting cable of the original Ethernet with defined channels on certain, standardized radio frequencies. They are usually layed out as wireless local area networks, or WLAN. Let's take a a quick rundown of some basics of wireless ethernets before we start. For a more indepth look, check out the Elektronik Kompendium (German only, sorry) [1] or Duckware [2]. Both are excellent resources.
[1] Das Elektronik Kompendium / WLAN-Grundlagen
You will encounter names like "Wi-Fi 5" or "802.11ac". The Wi-Fi-followed-by-a-number is the marketing name of a specific, technical IEEE standard. Wi-Fi 4 = 802.11n, Wi-Fi 5 = 802.11ac, Wi-Fi 6 = 802.11ax. They will be used interchangeably in this guide.
Avoid devices with the older standards, such as 802.11b and 802.11g. Devices conforming to these standards force your wireless local area network into compatibility modes or do strange things to the airwaves that have negative performance consequences for all other wireless devices around you. Make sure all your wireless network devices support at least 802.11n.
All 802.11 standards define channel width in Megahertz (MHz). Wi-Fi 4 allows 20 or 40 MHz. Wi-Fi 5 allows 80 and 160 MHz. Wi-Fi 6 allows 20, 40, 80, and 160 Mhz. The wider a channel, the more data it can transport at once. But also, the wider the channel the more noise is to be expected, which makes the connection unreliable and therefore slow. The channel width is something the user has to configure on his networking devices. Wi-Fi 6 is somewhat less susceptible to noise thanks to orthogonal frequency-division multiple access (OFDMA; splitting a channel into smaller sub-channels on a per client base), therefore you generally get away with wider channels, but keep in mind, the wider the channel, the shorter the range.
Wireless ethernet from Wi-Fi 4 up to Wi-Fi 6E uses quadratic amplitude modulation (QAM) of varying depth to modulate the data onto the frequency wave. Unlike digital modulation, which only knows 0 and 1, QAM can modulate many more states at once. The number of states is usually a number before the postfix QAM, eg. 64QAM. The higher the number of states, the more data can be modulated on a frequency wave, thus the more data can be transported at once. On the negative side dense date is more easily corrupted. Over distance noise also increases greatly, making data corruption more likely. Wi-Fi being an ethernet reacts with sending the corrupted data again (and again, and again) thus reducing the effective speed of the connection.
Your devices will drop to lower QAM levels, eg. 256QAM, to reduce the impact of noise! At distances approaching 10m it is not unreasonable to expect the weakest modulation, 64QAM, with all consequences for top speed. Thus, while Wi-Fi 6 uses 1024QAM under optimal conditions, you virtually never see it in use beyond a meter or so of distance between router and client. In practice the 1024QAM advantage is very small, some even claim there is no advantage [1].
Streams, or more precisely multi-input/multi-output streams, aka MIMO streams, depend on the number of sending and receiving units (ie. antennas) on a device. The more antennas, the more MIMO streams a device can handle. The number of streams between two devices depends on the device with the lowest number of antennas, usually the client. Typical Wi-Fi 5 routers have four antennas, allowing for a so called 4x4 setup, ie. 4 MIMO streams at once. Most client devices only have two antennas, allowing for a 2x2 setup. If a 2x2 client is connecting to a 4x4 router, the connection is limited to 2x2.
The actual bandwidth available is a function of channel width, modulation, number of streams, air-time, distance, noise, physical limitations, and protocol overhead [1][2]. You notice that this number includes some stark uncertainties. In general each and every wireless client on your wireless network will get far, far, far slower connections then what is advertised by the manufacturers of the router and the client [3].
[1] The Certified Wireless Network Professional's (CWNP) take on overhead
[2] Duckware on physical speed limitations.
[3] An example of actual bandwith in router/client interaction.
Your router and your client devices will always communicate on the lowest common denominator. That means, if you configure your 802.11ac router to use a 160 MHz channel but your 802.11ac client only supports 80 MHz your channel width will be 80 MHz, thus limiting your top speed. Your 802.11ax router supports 1024QAM, the 802.11ac client only supports 256QAM. The connections will at best use 256QAM, thus limiting your top speed. Your 802.11ac router supports 4x4 MIMO, but your client only has one antenna — no MIMO for you. And so on. The examples make it look as if the client is the limiting factor. And that's right. Even cheap Wi-Fi 5 routers support the full 802.11ac specification and usually sport 4x4 MIMO setups, while client support usually is limited.
This guide is showing you how to set up a network of routers and AP to provide coverage for a larger area. But you can get very far with only one powerful router.
Let's take a look at the advantages and disadvantages of a router/AP setup versus one beefy router. If you read the Wi-Fi basics it should be pretty obvious by now.
For the price of one high-performance, consumer-level Wi-Fi 6 router, eg. Asus GT-AX11000, you get up to 10 "low-performance", consumer-lever Wi-Fi 5 routers, eg. Cudy WR2100. The Asus does not have significantly more range than a Cudy — which would most times be wasted anyhow, because usually the limiting factor is, you guessed it, client range — but it can handle more clients at the same time, thus it can support your typical household easily. So, if you know that you only need to cover a compact bubble with a, say, 10-12m radius and few walls, you will probably be fine with a good, single Wi-Fi router, such as the Belkin RT3200. If you notice that it does not work out, add more routers or AP to your network where your network falters. This has a cost disadvantage but allows you to build your network piece by piece.
If you know that you have to cover a larger area, do some math beforehand. Assume that each router/AP can service a 10m radius bubble. That's what I did and I came up with the result that I need four Cudys (a 160€ expense). As it turned out, I only needed three.
[1] Duckware discusses Wi-Fi range
The base assumption of this article is that you have a need to run two or more routers. The guide will distinguish three use cases:
1) a wired network with wired access points.
2) a wireless network with wireless access points (aka mesh).
3) a mix of wired and wireless access points.
The guide will go into all three use cases in the given sequence.