Buying the right box
Before you hit the streets to start shopping for a modem, check your ISP's terms regarding the use of customer-owned modems and see if it supplies a list of recommended or approved models. Many ISPs (like Comcast, Time Warner, Cox, and AT&T) even offer this information on their websites. Some give just a simple list, while others recommend specific models for the different speed packages they offer.
If you have a cable Internet connection, the biggest spec to compare when shopping for a modem is the version of DOCSIS standard it supports. Some cable ISPs currently support DOCSIS 2.0, and are (or will be) upgrading their infrastructure to DOCSIS 3.0 to provide faster speeds and better performance, especially if you subscribe to their higher-speed packages. You can call your ISP to see which DOCSIS version it supports. Even if your ISP is still on 2.0, you probably want to prepare for the future and upgrade to a modem that supports DOCSIS 3.0, like the Motorola SURFboard SB6141 or the Zoom 5341.
If you have a DSL Internet connection, note that there are different types and versions of DSL, and you need to buy a modem that's compatible. Check with your ISP to figure out its specific type, but residential connections typically use ADSL, ADSL2, or ADSL2+ (in order from oldest to newest), and business connections could also use SDSL or VDSL. Consider investing in a modem that also supports a newer type of DSL, so you'll be prepared if your ISP upgrades its system.
When shopping for a modem you might find modem/router combinations, commonly referred to as gateways, like the Motorola SURFboard Cable Gateway SBG6580 or the Actiontec DSL Modem Router GT784WN. These include the modem function to connect to the ISP and a wireless router function, so you can share the connection among multiple computers and devices wirelessly or by plugging them into the ethernet ports.
If your ISP has supplied you with a gateway instead of a simple modem and you intend to use your Internet access for more than one device, you should either buy another gateway or buy a separate modem and wireless router. Gateways are very convenient since there's only one device to set up, but if you want the best wireless router features and performance you should consider purchasing them separately. If you buy your own router, I recommend consulting our guide to enhancing it with open-source firmware if you want to get the best performance possible.
Installing your new modem
Installing or replacing your modem is usually a fairly straightforward process. You can follow the instructions that come with the new modem, but frankly you can probably figure out what to do just by looking at your existing modem and swapping it for the new one.
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