When I originally wrote this guide, I wrote it for two distinct groups of people: those that only wanted a Local Area Network (LAN) - generally for use in a small office - and those that were just getting a broadband connection in their home that they wanted to share. My approach then (and now) was that most of a Broadband Connection Sharing (BCS) network is exactly the same as a LAN plus a couple new components. The new components are those directly involved with connecting your home to your ISP - namely the cable or DSL modem and the network router (if you don't already have one and even if you, the ISP insists on using theirs). Some ISPs are also using a single device this serves both as the cable or DSL modem and as the combination firewall & router. (Unfortunately, a number of those only offer a single LAN port, so you would need an Ethernet switch to connect more than one computer to the network.) A wireless access point (WAP) may or may not also be present. We will also ignore whether the incoming high-speed connection is a coaxial cable (used for high-speed cable), a telephone wire (used for DSL) or something else in most of the discussions here. We've already discussed routers to some degree in the discussion of the LAN, but in this section, we address the equipment and configuration needed above what is needed for just the LAN.
In the LAN examples, a simple Ethernet switch can be used to connect all the devices on your network together (or rather, connect the Ethernet cables from those devices). However, in the BCS type of network, the router is often also the switch. Therefore, when planning your network, you run your cables to wherever your cable/DSL modem and router is. (Conversely, you can place the router wherever it's convenient to run the cables to. Just make sure there is a power outlet nearby.) The cable/DSL router is usually placed near the cable/DSL modem. However, you don't have to locate your cable/DSL router next to your cable/DSL modem if that isn't a good place to concentrate the cables to. (This point is moot is you only have a single device that functions as the modem and router.) Example 2 in the section on Planning Your Physical Network Layout goes into this possibility. You can also still use a switch in addition to the router if you prefer or if you need more Ethernet ports for your internal network than are supplied by the router. Example 3 (second floor) shows an example of this setup.
The picture below should look similar to the picture titled "Typical Local Area Network Setup Using Only a Switch" found in the section The Network Hub/Switch. As has been said before, a LAN is a subset of the BCS network. The additional connections and equipment are illustrated by the red lines in the picture below. The notional router being used here is similar to a switch, but with an additional WAN (wide area network or Internet) port. The WAN port is connected with an Ethernet cable to the DSL or Cable modem that connects to your Internet service provider's high-speed connection (e.g., coax cable or telephone line). In the next several sections, we discuss the modem and routers and what additional capability they bring to the table.
If you have cable or DSL Internet service, your high-speed modem connection enters your house as a signal either on a coaxial cable (cable Internet service) or a pair of regular telephone wires (DSL Internet service). Some device is needed to convert the incoming line to standard Ethernet protocol signaling on a standard Ethernet port. That is the job of the DSL or cable modem. Often, the DSL or Cable modem you use is supplied by your Internet Service Provider (ISP), so you may not have any choice about what you get. If that modem dies, you may have some flexibility in what you can buy as a replacement, however. I know that my local cable provider gives you the choice of buying or renting the modem from them or buying the modem yourself (from a list of recommended modems). DSL providers usually sell a specific modem to be used with their service.
Sometimes though, not having a choice isn't all bad. Often, DSL providers run promotions to give away or rebate the cost of the modem. I personally believe they make little or no money on sales of the modem itself. I researched my DSL modem on the Internet and consistently found it priced more than what my DSL provider sold it too me for. On top of that, my provider gave me a rebate toward the full purchase price. I believe that ISPs want the equipment they send out to be as uniform (i.e., as few different types) as possible. That makes it easier for the ISP's technical and customer service representatives to do their jobs.
Installation of your modem will either be done by your ISP or they will ship you a package with the modem and anything else you need to install the modem yourself. The latter option is termed a "self-install" package or kit. At one time, cable and DSL modems were almost always installed by the ISP, but both DSL and cable companies have started using self-install kits more predominately. I take that as a good sign as it means the ISPs feel that the technology has reached a point where untrained professionals (i.e., you) can be expected to install the modem with a good chance of success.