Motorola SB6120 SURFboard DOCSIS 3.0 Cable Modem Review

© 2011 Brice Center (updated 5/18/2011)

Update 5/18/11:

Back in March/April 2011, Comcast changed the configuration parameters for this modem, which throttled this modem back in line with the speeds of the plan I'm paying for.  This reduced my download speed, but actually increased my upload.  Now I only get 23 Mbps download instead of 58 Mbps, but my upload went up from 2.7 Mbps to 3.5 Mbps.

At first glance, it might seem like I wasted my money on the DOCSIS 3.0 speed capability, but actually I didn't.  Three reasons:

  1. Distant servers twice as fast: I noticed that my speeds to distant servers are also much higher than my old DOCSIS 2.0 modem.  I live on the East Coast, and I used to get ~4 Mbps to servers in California with my old DOCSIS 2.0 modem, but now I get ~8 Mbps with this modem. 
  2. Better Speed Consistency: I noticed that my speeds to nearby servers are always 23 Mbps on this modem, whereas on my old 2.0 modem they would vary by +/- 10 Mbps.
  3. Future Proof: The Comcast tech that came to my house recently said that the old DOCSIS 1.0 modems are being completely phased out this year, and that eventually DOCSIS 2.0 will be obsoleted, too.  DOCSIS 3.0 should be around for much longer, even after 4.0 comes out.

Below is my original article:

The Best Modem I've Ever Owned - SB6120

Wow, Wow!, WOW!  This cable modem just blew me away. ► 

58.2 Mbps download speed, and 2.7 Mbps upload speed, at 8:30pm EST when everyone else in the neighborhood is on the internet, too. 

Again, WOW!

It is the:
Motorola SB6120 SURFboard DOCSIS 3.0 eXtreme Broadband Cable Modem.

Here's screenshot proof of my test results from Boston area to Washington, DC:
(Note: the time stamp shows PST)  Click here to see my tutorial and review of Speed Tests.

Compared to the Rental - There is no comparison.

Just minutes before switching to the SB6120 , I still had my old Comcast rental modem hooked up, and with the rental I got 17.34Mbps download and 2.01 Mbps upload to the same destination of Washington DC..  What a difference, especially on the download.

I've been a Comcast Cable Internet customer for about 10 years, and in that time I've had several cable modems.  Most were Comcast rental units, but I've also owned two modems myself.  This SB6120 is my second, and absolutely the fastest I've ever had.

(Just a note: since I started writing this article a couple hours ago, my speed to Wash. DC is now 44 Mbps download, but that is because it is now 11:30p EST / 8:30p PST, so the California folks are now at home online, and everyone from LA to NYC is on the internet's prime time, and speeds go down with heavy traffic.  Still impressive results for prime time, though).

Faster than a Speeding SB5101

The first cable modem I ever purchased and owned for myself was the Motorola SB5101.  I bought it from Amazon on May 3rd, 2008, and it blew me away when I first got it, too.  Again, the rental was around 16.6 Mbps download, while the SB5101 ended up typically got 19 to 28 Mbps download (both got around 1.7 Mbps upload).  Now, my new SB6120 blows the SB5101 away at OVER DOUBLE the speed!

The Death of my SB5101

You might ask why I was coming from a rental again this time.  Well, after 2.5 years of very solid, dependable service, my SB5101 finally started intermittently failing to connect.  It would act fine one day, and then another it either wouldn't connect, or it would work terribly slowly, which I diagnosed myself through a quick speed test.  I power cycled on a few occasions, which sometimes worked.  I also called Comcast a couple times hoping it was their issue, but they reported no network issues, so it had to be my modem.  Eventually it failed more than it worked.

Don't get me wrong, though, I loved my SB5101 for the 2.5 years that it worked without a hitch.  Also, it certainly paid for itself during that time: I paid $55 and it lasted me for 18 months.  A $5/month rental modem would have cost me $90 for 18 months, and it would have been much slower.

The Rise and Rapid Fall of the Rental

Since my SB5101 had failed, and I had no time to research new modems just then, I ran out to the local Comcast service center, and picked up a rental.  It was much slower, but it worked...well, sort of.  I've had the rental it for about 3 months, and every couple of weeks, I would notice that my upload speeds would drop to nearly nothing.  With a quick speed test I confirmed that my download was fine, but my upload speed was down at 0.3 Mbps, when it is usually 2.0 Mbps.  Yikes!.  A quick power cycle would clear up that problem temporarily. 

Finally, I buckled down and researched and purchased the SB6120.

Why is the SB6120 So Fast?

Answer: DOCSIS 3.0.  It's the latest cable network speed technology.  There is also the older, slower DOCSIS 2.0, which is what the SB5101 used.

DOCSIS 3.0 Service is Required to Reach Full Speed

Before you buy an SB6120 aware that you need to talk to your Internet Service Provider (ISP) to ensure that they offer DOCSIS 3.0 service in your area, the DOCSIS 3.0 capability and extra cost of the SB6120 may not benefit you.  If you don't have 3.0, but do have DOCSIS 2.0, you could consider saving 30 bucks and getting an SB5101, instead, although I've read reviews stating that the SB6120 was still faster than an SB5101 even on a DOCSIS 2.0-only system. 

If you're on a non-3.0 network, decide how critical the $30 price difference vs. the possibility of marginal extra speed.  They're both good modems.  However, if you're on a DOCSIS 3.0 network, you really ought to get the SB6120.  It really is that much better.  As stated above, my SB5101 got roughly 19-28 Mbps, and my SB6120 is getting in the 40-58 Mbps range.  It is literally twice as fast.

Why is Upload Speed So Slow?

Simple.  Because ISP's limit your upload speed.  It helps keep network congestion down, and most home users really only download anyway.  Only occasionally do typical users upload, and it's usually smaller files.  The ISP makes you pay more for more upload speed, usually in Business Class plans. 

Burn-in time

OK, I'm not actually sure if this is actually due to burn-in of electronic components, or simply the time required for the modem to update itself with latest firmware, but when I first got my old SB5101 two years ago, the speeds actually weren't much better than my rental modem right after I hooked it up.  Only 18.3 Mbps vs. 16.6 Mbps on the rental.  However, after a couple days, the speeds went up dramatically from the ~18 Mbps to ~25 Mbps.

I have not seen this same issue with my brand new SB6120.  The speed test screen shot I show above was taken literally 5 minutes after activating the modem.  Hmm...I wonder if it will get faster over time...probably not.  I'll let you know.

Hook Up and Initialization - How to Get Your New Modem Working

Well, hook up is simple.  Just plug in power and take the network and coax cables from your current modem, and plug them into the SB6120.  But that won't get it working.  You also have to call your ISP to have them initialize it on the network.  You will need the following info from your new modem:
  • Brand and Model Number
  • Serial Number
  • MAC ID
All of that info can be found either on the box the modem came in, or the sticker(s) on the side of the unit.

It only took about 10-15 minutes for me to call Comcast, give them the info from my SB6120, and have them complete the initialization.  Then, BAM, I was at 58 Mbps!

Speed Test - Where To, How To, What to Know

Please click here to go to my quick tutorial and review of speed test sites.