set up a new Comcast account , I have go through two attempt with Motorola modem . the first be the sb6020 , which be DOA -- would not even power up . send it back and decide to try the sb6121 , to see if they newer model perhaps have better quality control . I think I be go to have success -- the light come on -- but no luck . the first strike against this modem come when I call Comcast to try to do a `` self-install '' to save the service charge of the technician come out . in we new place , I know the previous tenant have use Comcast , so I be sure the house be already wire correctly . Comcast be unable to do a self-install over the phone for this modem , so a technician be send out . the Comcast technician , a nine-year veteran installer , spend over a hour fight with the sb6121 , try to get it to initialize . we wire it in directly , remove all splitter , etc. . . and it still refuse to recognize . keep cycling and drop service . I spend another hour on the phone with Motorola tech support , who be unable to help . finally , as a last resort , the Comcast technican plug in a similar Docsis 3.0 modem from he truck . the connection be up and work in seconds , with a stable signal and no drop service . of course , I be now fight with Comcast over the $ 99 service charge for the technician . all tell , this modem have cost I 3-4 hour of my life and $ 99 already ... and this be my second return of a Motorola modem to Amazon in less than 10 day . and I still need a modem . with the dubious quality of the current generation of Motorola modem , they have lose I as a customer for the forseeable future . if the next model be better , I 'll revisit the issue but for now , the aggravation and expense just be not worth it .