I purchase this modem because it seem to be well-reviewed and compatible with Comcast . it seem like a preferable alternative to pay $ 7\/month to rent a modem from Comcast . unfortunately , it do not work . upon reboot , it would take 10-15 minute to establish a link with Comcast . my Comcast subscription include 15mbp service , but this modem be only allow download at about 80kbp , if it be work at all . I purchase a sb6120 , and it connect in 1 minute and be average 16-18mbp for download . from what I understand from read around about this modem , the sb6121 be far less tolerant of signal issue -lrb- noise , weak signal -rrb- than older one . maybe the wiring in my apartment be not ideal . either way , the sb6121 do not work for I .