I install my new Motorola sb6121 cable modem . it take about 15 minute for Comcast to get it correctly set up . most of it be at they end , I think . however I ignore they instruction to turn off my computer and connect the modem directly to my computer . instead , I keep the modem connect to the router . I eventually do a reset on the router and reboot the computer . not sure if that be totally necessary , but everything be fine after that - though it might have be fine , anyway . I have do a speedtest -lrb- actually two of they on two different site -rrb- before I switch from the Comcast supply rca dcm425c modem . one show about 10 mb down and 1.3 mb up . the other show about 4 mb down and 1 mb up . I believe the 1st one . with the new modem the 1st site show 15 mb down and the same 1.3 mb up . I notice that the download light be blue -lrb- mean a bond connection -rrb- while the upload light be green mean a standard connection . I ask Comcast about this and they say they do not promise multiple channel on upload . accord to Comcast the level of service I be pay for should give 15 mb down and 2 mb up . the modem itself be very simplistic - no button . just three connection on the back and 5 light on the front . since I go through a router there be always activity and the link light just flash on and off at a fixed rate -lrb- not in time with activity light on the router -rrb- . since I have have it less than a day , I can not comment on reliability or speed change -lrb- if any -rrb- over time . but so far I like the improve download speed . it be really noticeable while watch hd video in real time .