Friday, October 26, 2012

Comcast and DOCSIS 3.0 - Worth the upgrade?

By Tony Lee.

There doesn't seem to be a whole lot of useful information about Comcast's DOCSIS v3.0 upgrade available on the web, so I figured I would post my findings. About a month back I received a letter from Comcast saying that they have upgraded their “Blast Internet service” in my area and that their records showed that I was still on a DOCSIS 2.0 modem. They were advising me to purchase a DOCSIS 3.0 modem and I wondered if it would even be worth the upgrade. This article will explain the results.

Suggested Upgrade

Armed with this letter’s vague claim to upgrade, I went to the Internet to look for others who received the same letter, but I found nothing. I even went to Comcast’s website to find empirical evidence - that was met with more unsubstantiated claims of increased speeds and the benefits of DOCSIS 3.0. You will find wording such as:

Upgrade your speed
DOCSIS 3.0 is the next generation of DOCSIS (Data Over Cable Services Interface Specification), an international telecommunications standard that lets cable television operators add high-speed and telephony data to their current cable TV systems.

With DOCSIS 3.0, you’ll experience significantly faster speeds, so you can make the most of your online experience. DOCSIS 3.0 also opens the door to new Internet technologies.

Upgrade your equipment
To take advantage of DOCSIS 3.0, you need a DOCSIS 3.0 modem. DOCSIS 2.0 modems will still work with our speed tiers (except for Blast and Extreme 50), but you won’t experience the blistering fast speeds now available. We also recommend upgrading to an 802.11n wireless router; 802.11g routers only support up to 20 Mbps. If you lease your modem, router, or gateway device from us, we’ll upgrade it at no extra charge.

If you already have a DOCSIS 3.0 modem, you may need to power cycle it to take advantage of our new, faster speeds.

-- Source:

So what is an inquisitive nerd to do? -- Why, contact the expert technicians course! I asked multiple employees questions such as the following:

  • What sort of speed difference will I see?
  • Why does a DOCSIS 3.0 modem increase my speed?
  • Are you channel bonding? (explained later)
  • Do you support the SB6180 modem? (explained later)

However, to my frustration, no one could answer these questions. To understand the answer, you should understand a little bit about the difference in technology.

DOCSIS 1.0/2.0 vs. 3.0

The major difference between DOCSIS 1.X/2.0 vs. 3.0 that concerns the average person is the fact that DOCSIS 3.0 supports channel bonding. Channel bonding means combining multiple downstream and upstream channels to support greater speeds. The maximum usable downstream throughput on a single channel is 38 Mbit/s (EuroDOCSIS is 50Mbit/s). Since a DOCSIS 2.0 modem only supports a single channel up and down, 38 Mbit/s is the theoretical downstream max. Thus, if the cable provider rolls out a 50 Mbit/s service (such as Comcast’s Blast 50), you will most likely not see the entire speed increase.

So the big question is… Is Comcast channel bonding? Unfortunately, no one on the help chat or first level phone support could answer the question. It was not until I called upon an inside person did I get the answer I was seeking. The answer is YES! (In my area) Now, off to buy a modem… but which one?

Modem Choices

Personally, I am a huge fan of Motorola Cable modems because they just seem to work. I go all the way back to the DOCSIS 1.0 Motorola SB4100 (remember the hideous grey thing that came in a box with the gnarly surfer on it?) It just worked.

Then to my current DOCSIS 2.0 Motorola SB5120. So familiar to many of us—you probably own one or owned one at some point. It just worked too.

So, what model do we buy now? After doing a ton of research, I narrowed it down to two models:

  • Motorola SB6121
  • Motorola SB6180

Motorola SB6121

Amazon's description sounds great:

“It harnesses the power of DOCSIS 3.0 technology to bond up to four downstream channels and four upstream channels--providing you advanced multimedia services with data rates of more than 100 Mbps in each direction. That makes gaming, shopping, downloading, working, high-quality voice and video conferencing, and peer-to-peer networking applications far more realistic, faster, and efficient than ever before.”

Motorola SB6180

This one sounds even better!

“The SB6180 is the ideal competitive solution for the high-end residential user, the small home office owner, as well as for the medium-to-large business enterprise. Utilizing the power of DOCSIS® 3.0, the SB6180 enables channel bonding of up to 8 downstream channels and 4 upstream channels, which allows an operator to offer their customers advanced multimedia services with data rates of well over 300 Mbps in DOCSIS mode and 400 Mbps in EuroDOCSIS mode for downstream and 120 Mbps upstream.”

So, if you didn’t see the bolded difference, the SB6180 is a “future proofing” device that was originally marketed for small home office and business use. Ironically, you can also find it cheaper than the SB6121 on Amazon.

Here is a helpful chart from Wikipedia to understand the real numbers difference between 8 and 4 channel bonding:

So which one did I buy? - The SLOWER one of course :)

But why? - Comcast has a “Device Compatibility and Capability” page that lists the modems that work with their network. Unfortunately, the SB6180 is not listed anywhere on their site. Additionally, after asking no less than three Comcast techs, all of them said that the SB6180 would NOT work on their network—thus I did not take the chance. Although, the inner nerd in me is mad that I didn’t try it.

Modem Indicators

If you are not one for reading the documentation that accompanies purchases, shame on you—I don’t always read them either. However, the documentation with the SB6121 was very clear and useful. So useful, I scanned it into the computer for you. What you should notice is that if the downstream or upstream light turns blue, your cable provider is channel bonding. If either light is green, that channel is a single channel.

Having read this, I mumbled to myself… Those lights better be blue!

And they were! Whew! (Sorry to those who are blue/green color blind, you will have to take my word for it that upstream and downstream are blue)

Let’s see what those blue lights buy us…

Before upgrade tests

I made sure to test the bandwidth before and after the cable modem swap. To test the bandwidth, I used the ever-popular site: I had a respectable 28.60 Mbps down and 7.37 Mbps up prior to the modem upgrade.

After upgrade tests

Now for the moment I had anxiously been waiting for… the new modem test! At first I was getting the same speeds... Uhh What?? Then I reset the modem a couple of times and then finally--MOAR POWA!

That is a 24.38 Mbps increase in download speed and a 3.54 Mbps increase in upload speed. Not too bad for a modem upgrade that was less than $100.

Final thoughts

Overall, I am happy with the modem upgrade as it does provide a significant speed increase. I am also happy with Comcast for the free speed increase and letting me know that my cable modem should be upgraded. However, I am disappointed in the lack of support or at the very least the technical knowledge pertaining to the SB6180 (supporting the 8 channel bonded downstream instead of 4). Additionally, I feel that companies could provide graphics or case studies such as the one provided here illustrating why people should upgrade their modems and the potential difference they could see.

Hopefully this article has helped someone else make the decision to upgrade their modem. If anyone has the SB6180 working on Comcast’s network, I would be interested to know. Maybe if enough people have this modem working on their network, they will update their compatibility page.


  1. Funny that I would run across your article Tony, I about to do the same.

    Thanks for the research.

  2. Weird, I just got a letter saying the exact same from Comcast, except that they're sending me my "upgrade" for free. I have no idea what they're sending. It better not be junk.

    1. They are most likely sending you an upgrade for "free" because you are leasing the current modem from them. However, you do have the option to buy the modem and save the monthly fee by returning theirs and using your own. I don't know how much they are charging you for the lease, but it is typically $5-10 a month. Imagine that you are paying $7.50 a month. In one year you will have paid them $90. The SB6121 mentioned above sells on Amazon for $80. You will pay for the modem within one year of owning it and save money month after--just something to think about. Please let us know what they end up giving you. If it is the 6180, I will be both jealous and irritated. Ha!

  3. Glad we could be of assistance sir. I was pretty frustrated at the limited information that I found on-line. Additionally, I would have been pretty mad had I spent the money and not seen a return--or even worse slower speeds for some reason. Ha!

  4. I have an sb6180 I had to buy it from my previous internet provider. The funny thing is after I did some research I found it only worked on their network. After moving to another state where Comcast was available, I got their service. The tech came out hooked everything up then told me my modem wouldn't work. After some bsing he said it would suck to have just bought this modem and not have it work. He called the tech center and after a while they said they couldn't do anything. He then called the main guys in India. After about ten mins the lady said we were good. I don't know what the lady did but she got the network to recognize the sb6180.

    1. Ha! For some reason, I am not surprised. The first tech was most likely going by the book when looking at the model number. The lady probably just entered the MAC address into their system and it worked. Glad to hear that it is working for you though. :)

  5. I bought the SB6141 (spend the extra 5 bucks) and returning the leased one to Comcast stock. Payback in 10 months.... Everything is moving much-much faster.

    In fact it was one of the easiest installs with a cable company I have had.


    1. Indeed. I have also seen their self install portal which you can pretty much do everything yourself--including enter the MAC address of the new modem. Very convenient when it works properly. I just hate it when they say you have to install their Comcast bloatware on your computer to get the install to work properly. It rebrands your browser and sets your homepage to their xfinity page. Ugh...

  6. I am a triple play customer and operating on ARRIS Modem. Do you think the new up modem upgrade will really help.

    1. We would need more information to help you out. For example, there are ARRIS DOCSIS 3.0 cable modems, so if you went from a channel bonded modem to another channel bonded modem, you may not see a difference. Also if your triple play service does not exceed the DOCSIS 2.0 speeds, you won't see a difference. Bottom line is we need more information.
      1) What model modem do you have?
      2) What triple play service do you have (speed of Internet)?


  7. Thanks for sharing the details.

  8. I just went to Target I got a price match for the 6121 at $60. I like your review

    1. Nice! Glad it worked out for you. I was in a major retailer the other day and a lady was buying a router. I asked her if she owned the modem as well and she told me she was leasing it. I showed her the quick math and convinced her that she would save money by buying the modem too. She was very happy.

  9. just wasted 3o mins with Comcast trying to get more info since receiving my letter. So thrilled to come across your post now. Thank you very much!

    1. Ha! Sorry to hear that. I have wasted hours (maybe days) of my life on the phone with them. Anything I can do to help others avoid it must be some good karma. ;)

      Thanks for the feedback.

  10. Great post. Wish I had seen it before buying the 6180 and support telling me it wouldn't work. I see someone above got it to work so I'm going to call one more time and see if there is someone who can help me.

    1. Sorry for the late reply, but did you get it working? (crosses fingers)

  11. Great post! one question: Do I need to call them to activate the new modem? or just plug it and use it?

    1. It depends... I know that is a crappy answer... :(

      They need to register your MAC address somehow. If you are able to plug the new modem in and get to the self-service portal, you can enter it there. If for some reason you cannot get to it, you need to call them and read them the MAC address on the bottom of the new modem. Hope it goes smoothly for you.

  12. Got an Arris tg862g/ct. The speeds are the same if I use the Arris instead of my old router (it doubles as modem/router)...

    SHAME!!! If I hook up my old router to the tg862g/ct, I now get 40mbps down, 33% faster. LOL

    1. Ohhh geezz. What model is the old router?

      So you are saying: Arris (modem only) -> Old Router -> Comcast

      is faster than: Arris (modem/router) -> Comcast

    2. As I'm also satisfied with my modem and have no need for Docsis3, I have to ask why I can't keep it in use. Why doesn't Comcast continue its support? It's not a technology that can not work any longer on their network.
      Is there a technical reason why a Docsis1 modem isn't going to be allowed? I don't think so.

  13. I've been skeptical ever since I started getting these letters from Comcast. I have an old Docsis 1.0 Linksys and never had a problem with it. My gut feeling is that Comcast will be able to reduce my current speed with a Docsis 3 modem and force me to pay more money to get my current speed back.

    1. You are even more paranoid and skeptical than I am... lol. That takes years of practice. ha! Good stuff though. Maybe I should hold on to the old technology as I progress. ;)

  14. Yes, Comcast is being disingenuous and the people on the frontline at tech support, either have been told nothing or have been told to spin the story that the upgrade is required to preserve their excellent service. I have Performance speed and am currently using a old Linksys Etherfast cable modem. Using I'm getting 23MB download speed which is totally adequate for my needs. After getting the letter from Comcast that I would lose my Internet connection on October 30, 2013 if I didn't upgrade to a new modem (preferable rent one of theirs I'm certain), I would lose my ability to access the internet.

    I bought a Motorola Surfboard 6121, called Comcast and registered it. Guess what? No increase in download speed.

    So the real question is what is Comcast up to? I'd hoped my now we would have access to a Comcast alternative, unfortunately NO.

    1. Interesting.. depending on your level of service with Comcast, you may have had to reset the modem a couple of times. This was the case with mine before I saw the increase in speed. See above: "Now for the moment I had anxiously been waiting for… the new modem test! At first I was getting the same speeds... Uhh What?? Then I reset the modem a couple of times and then finally--MOAR POWA!"

      Good luck!

    2. I got the letter, but was skeptical from the start. Think back about what that letter said. They specifically told me I would be unable to access the internet, period. I put that info to the test, and I'm still using a piece of junk linksys 2.0 modem that I bought for $5 at Goodwill and it STILL works as good as always. And why would someone want to have increased speed with Comcast when they constantly complain about the stuff I download? Is anyone that crazy about downloading gigantic non-copyrighted files? Don't hate me because I didn't spend a dime. :)

  15. I got one of these letter today - I live in Eugene, OR. I'm going to ignore it for awhile, because at the moment my needs are met.

    My guess is that someone in upper management crunched some numbers and discovered that for whatever reason, sending out these letters would increase their profits. So they do it, because that's what corporations do these days, right? Perhaps investing in a modem will make customers less likely to jump if something else comes along? Or maybe they figure we will throw up our hands and rent the new modem?
    Comcast is an embarrassment to capitalism. The CEO (the founder's son) pays himself $30 million per year but can't afford to educate the employees about their own products. I've spent hours on the phone with people who could as well be selling tupperware - they really have no idea what Comcast is selling. This reflects, by my guess, how Comcast treats them.

    I hope that in the very near future technology will somehow allow that consumers themselves will organize into somesort of giant union and negotiate directly with the rent-seekers. For something as crucial and useful to everybody as internet, it would nice to have a CEO who is concerned with something besides his bonus.

  16. Has anyone gone past the date Comcast says internet will be unavailable??..If so, what were the results??...My cut-off date is mid November...They have been bugging me for at least a year about upgrading the modem...

    1. can you come back to this page and tell us if the letter was all hype or not ? Comcast says I need a new modem. But my modem is on the compatibility list on their website.

  17. My annoyance was that I had purchased a DOCSIS 3.0 modem over a year ago, upon original suggestion from Comcast, 'cause I didn't want to lease a modem from them. After the year, they insisted that I use their "new" modem/router and remove mine, supposedly to make it easier for them to bundle my phone and internet services that I agreed to use in my renewal.

    However, I saw no such performance increases over what I had with my original modem (a ZOOM cable modem model 5341J), and now I had to pay for the leasing of their modem/router/phone device, which added some complexity and overhead to my SOHO network.

    So, in the end, I'm now paying to lease a modem I didn't want, and have a modem that I already paid for (which worked great) that I can't use anymore!! If Comcast wasn't the only internet provider in my area, I'd switch.

  18. Does the •Motorola SB6121 work with Comcast's Triple Play service?

  19. Something interesting to think about is that Docsis 1.x and 2.0 can only use a single channel, so as more people are on Docsis 3.0 with channel bonding bandwidth availability on that single channel can cause performance to suffer at times, where as channel bonding will allow to offset traffic across multiple channels. It is kind of like the difference between a two lane highway and an interstate. On the two lane highway sure I can drive 75 but only if someone isn't in my way. On the interstate I can change lanes and not have to slow down (most of the time).

  20. The last comment from Anonymous (march 23) explains one reason why comcast is pushing this out. Another is that some of the new modems that they send out have 2 wifi antennas, one for you the other is an xfinity access point for all your neighbors and whoever drives by. That could reduce your speed.