Comcast offers a variety of modems from Arris, Netgear, Motorola, Cisco and SMCNetworks. Which modem Comcast provides to a given customer depends mostly on availability and the speed of the customer's service. Comcast has also approved a number of compatible modems that are for retail only.
Comcast leases its modems for a monthly fee. The fee depends on the type and value of the modem. Purchasing a modem from a retail source allows customers to avoid the monthly cost, as well as to choose which modem they wish to install. A list of compatible modems is available on Comcast's website, along with detailed information about each one. Customers who purchase retail modems must register them with Comcast in order for the modems to work on the company's network. ZoomTelephonics is one of several companies that makes retail-only models compatible with Comcast's network.
The main difference between available modem models is the speed of service that the modem can handle. Older modems rated at DOCSIS 2.0 are generally used for slower connections, while newer and retail models are usually rated at DOCSIS 3.0 and can handle Comcast's highest-tier speeds as of August 2015. For those customers who choose to lease modems, the company offers modem upgrades in conjunction with network service upgrades.