Modems are what you use to connect to the internet or WAN (Wide Area Network).
Routers are just to rout traffic between computers.
When you sign up for an internet connection, they usually supply you a combined modem router device in order to simplify deployment.
However there are many cases you would want an independent modem and router, because you want greater control over how you route packets and how you connect to the WAN. So it is possible to purchase modems and routers independently.
Different Types of Modems:
- Dial Up Modems
- DSL Modems (ADSL, SDSL, VDSL)
- Cable Modems
- Powerline Modems
- Fibre Modems
- Wireless Modems (LTE, WiMAX, HSPA+, HSDPA, UMTS, EDGE, GPRS)
- Satellite Modems
This is a common architecture of modems:
LAN - Ethernet Cable - Ethernet Connector <-> Modem Connector - Modem Cable - WAN
Basically most modems use a specific kind of connector and cable to connect to the WAN, while providing a standardised ethernet connector to LAN (which is then plugged into your router). Each kind of modem can have different WAN connectors and WAN cables.
Here's a list:
- Telephone Connectors: https://en.wikipedia.org/wiki/Telephone_plug
- Telephone Cables: https://en.wikipedia.org/wiki/Twisted_pair
- Coaxial Cables: https://en.wikipedia.org/wiki/Coaxial_cable
- Coaxial Connectors: https://en.wikipedia.org/wiki/RF_connector
- Fibre Cables: https://en.wikipedia.org/wiki/Optical_fiber_cable
- Fibre Connectors: https://en.wikipedia.org/wiki/Optical_fiber_connector
- Ethernet Cables: https://en.wikipedia.org/wiki/Ethernet_physical_layer
- Ethernet Connectors: https://en.wikipedia.org/wiki/Registered_jack
DSL and Dial Up modems both tend to use telephone connectors and cables, while Cable modems tend to use Coaxial cables and connectors.
Here are some common connectors and cables you'll see around the house:
- For ethernet connections, you should see CAT5 cables and RJ45 connectors.
- For telephone connections, you should see phone cords and RJ11 connectors
- For cable connections, you should see RJ-6 cables.
Modems can be internal (PCI/PCI-E), external, or USB based (like those ISP dongles).
Did you know your mobile phone is a wireless modem as well? And with some software installed it can easily act as a router.
If you get a PCI modem installed onto your computer, you should be able to use your normal desktop or laptop as the actual modem. But this is not energy efficient, which is why use use small embedded devices to act as our modem.
Once you have chosen your type of modem, you can then connect the modem to a switch or omit the switch and connect directly to a router.
You can use your ISP supplied router, but it must be able to accept a connection from the independent modem. Some combined modem routers cannot do this. Generally there should be WAN ethernet port on the router.
Or if you need more control or more power, connect the modem directly to your general purpose PC, and run a router OS, or just use the OS supplied routing software. Linux plus some open source utilities can be a very capable router.
There are dedicated Linux based routing operating systems like DD-WRT and VyOS.