TYVM ispano.Charter is a cable company. So yes, they use DOCSIS. All you have to do is see if they use DOCSIS3 in your area, and if so it would be better for you and the network to grab a DOCSIS3 capable modem. The 6120 for example. It'll cost you ~$100 but it's usually better than what they'd lease you, unless they lease you one of those. Either way you'd be saving money after about 2 years. But with a leased modem, any issue with the modem and they just swap it for you.