I be a bit skeptical about the whole doc si 2.0 vs 3.0 thing . but I be sick and tired of my old bottlenecked network speed , and I decide to upgrade my modem , cable , and switch to gigabit configuration . at first I try to get Comcast to send I this modem . after four attempt , I be tell that they would charge $ 7 a month to use it ! forget that ! buy this one and hook it up yesterday . before with the old Motorola sb5101 , I be get about 2.6 mb download speed and 1.2 mb upload speed at the modem and about 1.6 mb download speed behind my 10\/100 t base standard switch . now ? while Comcast say we be pay for 12-16mb , with this new modem I be clock 24-26mb at the modem and behind the new gigabit switch . this be also with cat 5e and cat 6 cable all the way around . wow ! what a difference ! this modem be take advantage of the bond pair downstream , as the download lead stay blue . if you have a large network and you be use switch , make sure to upgrade they also to gigabit configuration . behind the only remain standard switch , my bandwidth increase only come to about 6.5 mb . behind the gigabit switch , it be a steady 24-26mb . have some issue get everything set up . the modem keep power cycling and downloading , and I could not connect . I decide to let it do its thing for about 30-45 minute . finally , it stay on and connect , and I hook my laptop up direcly to the modem and I be able to access Comcast 's activation page and within minute I be up and run , need nothing more than my account and phone number . we also have a gigabit Vonage router . that take a little more work to connect . ultimately , after several reset and reboot , the Vonage tech have I simply disconnect the coaxial cable from the modem for 30 seconds and reconnect it . not sure what that do , but it work . after that , vonage phone be up and run and network be good to go . very happy so far . update 8\/15\/2012 : after about 5 day , the Vonage router start bottleneck the bandwidth and I be only get 8-10 mb behind it while still get 25mb connect directly to the sb6121 . so I buy the Linksys e3200 gigabit router and use the Vonage vd22 device and that take care of it , back to full speed all the way around .