I have be use a Motorola sb5120 successfully for a couple of year . recently I have be receive letter from Comcast indicate I may not be receive the best performance unless I upgrade to a DOCSIS 3.0 cable modem . I let it slide for a couple month but after the second or third reminder I figure I better look into replace the device . since I balk at pay Comcast anything more than necessary I know I do not want to rent one from they . so I research various model and with the knowledge the old Motorola never let I down I decide on the sb6121 . it receive good review online and the price be right at Amazon . I receive teh product when promise and quickly install it . I do have to call Comcast support to provision it . basically that be only to give they teh hardware or MAC address of teh new modem so they could configure my account . less than five minute later -lrb- and a pitch for they VOIP service -rrb- I be up and run . first question I have be do it improve my speed . could be a placebo effect but I would say yes . various `` speed test '' site indicate better speed both download and upload . for the price I be happy . hopefully long term test will confirm my previous experience with the brand and it will remain stable and reliable .