If I buy the Time Capsule or the Airport Extreme will there be a need for the Time Warner modem?  Aren’t both of those modem/router combinations also?  Thanks
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yes.  You would still need a modem.  The modem from TW.  The modem's job is to convert the internet in from the coaxial cable coming into the house to ethernet.   The router's job is to distribute it around the house once it's been converted from coaxial to ethernet.  Airport extreme or time capsules are routers only.  Not modems.