Comcast give I a Motorola 5120 the bandwidth be fluctuate horribly on speedtest.net also the modem max out at 30Mbps mega bit per second mbp be mega byte per second the difference be weather the b be lower case or b upper case . a byte be consider 8-bit . in some system there be error correction and other overhead route information of up to they say 15 % of you bandwidth . not to much testing and I have hit a high of 38 mbp download the bandwidth be nonfluctuating\/stable . the same of ~ 6mbp for upload . the follow be help with self install and self activation on Comcast you mileage may vary on cable company . Extra Paragraph\/note not on modem : after all of this be do if you want a suggestion on block different type of web site -lrb- 30 million people use it . -rrb- use free opendns.com simple or complex , 40 different category and certain add and spoof its free unless you want long term tracking of site successfully block or where the kid have try to access . corporate be not free . this next step be to set up so you can `` self activate '' on Comcast when you have switch , hub , router , wireless . pull the power cord on you modem and with preferably the same cable connect directly to a power off computer or laptop and then plug back the power back in you modem . Make sure the cable modem have initialize itself then turn on the computer test and make sure a refresh web page come up -lrb- in case you do not shut down you computer -rrb- . the next step be that you be go to give back you old cat-5 cable and test you new pre-test cat-6 cable . unplug modem , shut down computer . now plug in you new cat-6 cable which on mine be pre-test , and plug it in to the modem and computer . plug the power back in to the modem after the modem initialize turn on the computer verify that the cable work and you pull up a refreshed page not a current page -lrb- in case you do not shut down you computer . -rrb- if if say that there be `` no connection available '' , sometimes you have to see-see the connection back and forth which I have to do at the laptop connector . finally if you want do you last speedtest.com look for , first , the unevenness of the graph the peak and valley what you want be a nice stable plato  , second be write down the peak download speed in Mbps and third the upload speed peak in Mbps . now to swap the modem . First you want the modem to run when the cable company test it so pull the power first . then the pre-test cat-6 cable . now the cable tv rj-59u or rj-58u you might need pliers to start to loosen the connection but the rest should be hold with finger and spin . now the semus tough part that center wire of the cable will not want to go into that new gold plate connector so make sure the wire be in the center , its align , and push , that be the hard part -- finish screw in , plug in the pre-test cat-6 cable to the modem and this time I would really recommend shut down the computer because even I do because it go to take ~ 5 minute for the modem to initialize . mental note : I notice the box vent on one side and a very little from the front so I put the side with all the vent up . but I have air cleaner to clean it or you could get a hepa filter . Temp be nominal but I have it on a cement floor . now turn on you computer . go to Start , All Programs , Accessories , command Prompt . type : ipconfig\/release type : ipconfig\/renew now open internet Explorer in the address bar type activate.comcast.com \/ you will need you account number and account telephone . next call 1-800-xfinity 934-6489 go to tech support tell they you get you own modem , you install it and self activate it . and you need to give they you mac address its a Motorola Surf Board sb6121 I be in a sandstone building and go outside and use the cell phone do not take to long then they send I in to test and see if a web page would come up and it do and my cell connection hold and I say thanks to eternity the representative and that be all . this new modem have hit 8mbp higher at the highest and the bandwidth have a nice nonfluctuating platoe  . in Google Chrome I can re-open a dozen of closed web page and the load time seem reduce the reason I do not say for sure be that my 4 thread processor be not run at its normal burried 100 % so the program might not be fight for cpu time . Bruce Light color be Amber for on , blue upload , blue download , amber connect to computer , flash blue for the fastest connection .