I use it to replace a lease comcast motorolum 5121 . the 5121 be give I 10mbps down\/0 .10 mbp up . after switch to the sb6121 , I now get 20 mbp down and 6 mbp up , which be the speed tier I be pay for + I do not have to pay comcast modem lease fee anymore . the speed measurement be do multiple time use speedtest.net . the installation be easy , have to get on the phone with a comcast tech to get the new modem enable , after that the modem work fine . UPDATE Sep 14 , 2012 . it be be a year since I have be use this . it be still go strong and work fine . I have add a manual timer to it so that the modem be reboot every weekend .