How I doubled my Internet Speed

Recently I got an email from Comcast that they have doubled my internet speed, but in order to access it, I had to get a new cable modem that supported docsis 3.0. It sounded a bit too good to be true, but I thought I would give it a try since I had been using the same cable modem for over 7 years. Before buying a new modem, I decided to test my speed at speedtest.net and it came out to be 20Mbps.

Then I searched on gooogle to see if my old modem, the Motorola sb5100 supports Docsis 3.0 and sure enough Comcast was right, it did not.

Then, I looked at the Comcast approved device list to find a cable modem that supported the new speed tier.




I decided to stick with motorola again and chose their sb6121 model, which supports both docsis 3.0 and IPv6. Motorola got recently acquired by Google, and I don't know if they would be providing support for cable modems anymore, but I figured that if the sb6121 is as good as my old sb5100, I won't need support anyway.


Here is the Motorola SB6121 which I bought.



In order to activate the new modem, you have to call Comcast or chat with them online. They will ask you for the MAC address of the cable modem, which is on one of the white stickers at the bottom of the modem. After you give them the mac, you can then remove the old modem and connect the new one. After a couple of minutes, the modem will be initialized and you will be on your way.


The first list is for power and should obviously be on.
The second light is for incoming connection from the computer and this should be on when your computer is on. If you have connected your modem to a router, then it will be on when the router is on.
The third light is for the network connection to Comcast's network and this should be on as well as long as you have connected your modem with the coaxial cable.
The fourth light is on when you have internet connection. If it blinks, then the modem is not fully initialized and is searching for an internet Connection.
The fifth light looks scary because it is red, but this one shows activity -- i.e. it will blink constantly as long as you have one device connected to the internet, even if it is just the router.

The only thing to test then is the new speed. I tested my speed again on http://www.speedtest.net and saw it jump from 20Mbps to 50Mbps with the Comcast Blast Speed tier.