I finally take a look at my monthly Comcast bill and be surprise to see that I be pay $ 7\/month for rent my cable modem . I take a look and see that there be a variety of modem that I could purchase and come out ahead within a year . the sb6121 be one of they , and appear to be on the higher end of the `` future proofing '' curve with Comcast . switching to the new modem do take I about 1 hour as I need to call up Comcast Tech support and give they the MAC address of the new modem . but , everything do appear to work properly and I have be problem free for a few month .