I have grow to be a fan of Linksys \/ Cisco product s for a while . I keep get call from Comcast state that my current purchase cable modem be no longer support , and they would be happy to send I a new one free of charge , but of course , add the $ 7 per month rental charge . I work out of my home and have notice my VOIP call , and download be not as fast as they should have be after I analyze my current system . I go ahead and purchase this product due to it be a Cisco product , and it be certify by Comcast . after receive the product , I run with the modem for almost a month and speed down and up be fantastic . my voip call be clearer , and streaming and video call be much smoother . however , I notice that the modem would randomly drop the signal , and re-synch up again . the modem be in a open area , so I new it be not a heat issue , nor do the unit ever become hot . I call Cisco support , who direct I to Comcast support , as they claim it be a firmware issue that Comcast would manage . I check online , and in the Comcast forum , I find other who also have the same issue . the current firmware release from January 2012 be the issue , and the only solution be for Comcast to roll-back the firmware to a August 2011 release . after almost 10 contact -lrb- phone or chat support -rrb- with Comcast to report the issue and direct they to they own forum , the firmware be never roll back , and the issue do not go away . I have to inevitably send the product back to and replace with a surfboard sb6121 . it be a alright modem so far , but upload speed not so good as upload be only bond to one channel . I 'll report back if something go wrong with this new modem .