out of nowhere , I be have excruciatingly slow internet speed on Comcast . the Comcast tech advise that my Motorola sb 4100 be at the `` end of life '' and that I should upgrade . skeptical , I purchase this modem which be a DOCSIS 3.0 -lrb- and backwards compatible -rrb- modem . it work . I go from a 2mbp download speed to over 17mbp . what a difference . there be one installation glitch that you need to be aware of . when you hook up the modem -lrb- connect the coax cable , connect the ethernet cable , and plug it in , that be it -rrb- , and then try to get online , it will direct you to a Comcast self-activation screen -lrb- no other site be available -rrb- . after enter my account number and phone number and hit the `` next '' button , I get a blank screen , and nothing happen . so I call Comcast and they say that usually happen if you be do a upgrade ; it mostly work only for a new service connection . however , it be a simple matter to give the tech you MAC address and the serial number . after about 5 minute , while he stay on the line , it come alive , no problem . BUT , here be the thing : the serial number they need be the customer serial number . this be only find on the bottom of the Motorola box the modem come in . this be different from the `` s\/n '' serial number that be on the label that be on the instruction sheet and on the bottom of the modem itself . the customer s\/n have letter in it ; the regular S\/N have only number in it and be too long . my first Comcast tech do not know that and it take a day to sort it out . other than that , it work well with my iMac and Apple Airport Extreme Base wireless router . enjoy