Firsthand experience with the Motorola SURFboard SB6141 DOCIS 3.0 Cable Modem

Posted by Paul Braren on Oct 7 2013 in
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    In the last few weeks, I've had intermittent internet issues, where the speed would drop to about 1Mbps down and 0.1Mbps up for a few minutes at a time. Checking into my cable modem's log files, I could tell Cox (US cable provider) what times I was affected, as we tried to get closer to a solution. Part of this process involved several truck rolls and replacing the cabling to the pole, so I got to spend some quality time with my local Cox installation contractor. In less than a week, I've gone through one somewhat obsolete modem, and another modem that died about 30 hours I first plugged it in. So I can now share that I've finally settled on a new Motorola SB6141 modem, and this article will discuss the many reasons why. I'll also add updates to this article over time, should this modem surprise me.


    I plan to continue to use to do 100 tests of my speed, every 5 minutes, for about 2 hours at a time. This will help see if my neighborhood's ongoing intermittent issues have gone away, and if my Cox Ultimate upgrade goes well, expected October 09 2013. Meanwhile, I'm getting the double the Cox Premier 50Mbps/10Mbps up speed upstream that I'm paying for, and slightly less latency than SB6120, when using a laptop directly attached to the cablemodem. Nice!


    Black and white OEM and retail models on Amazon, and on Newegg here and here. I went with the white retail model seen at right, for $3 extra dollars over the OEM brown box option. So I have no experience or comments on the possibly used cable carrier units found for a little less on eBay here.

    Why did I choose an 8 channel modem? Here's one reason:

    This modem can utilize up to 8 channels of downstream for a theoretical max speed of 343 Mbps whereas the Motorola SB6121 and other earlier/cheaper DOCSIS 3 modems can only utilize 4 channels maxing your download speeds out at 172 Mbps. Just something to think about if you plan on using this modem for a few years as speeds offered will inevitably increase.

    Why the SB6141? My SB6120 has served me well since 2011, with stable firmware, described here. But I'm preparing for the Cox Ultimate tier of service coming this week, which requires 8 channel capability. The highest spec model that handles 8 channels is the Motorola SB6141, where the product page mentions it has the same firmware as my trusty SB6210:

    Easily add the SB6141 to a deployed family of SB6120s and SB6121s, all three models utilize the same firmware image. This reduces qualification time for an Operator and eliminates configuration management headaches.

    Why buy, instead of rent? There's financial benefits to buying versus renting, as The Wirecutter explains:

    Should you decide to buy a modem as a Time Warner customer, it’ll take 23 months to recoup the cost of buying a modem like the SB6141, and at the other two carriers it only takes 13 months—not to mention you can always sell the modem if you ever decide to for a few bucks.

    Why not a hybrid cable modem/wireless router, aka, gateway? Well, it can be hard or impossible to get into their router to control things like port forwarding, and really leaves you with no service of any kind if the device dies, requiring a call to your cable company. Sure would also make workarounds to handle temporary cable outages tougher to implement, see also TinkerTry's How to seamlessly replace a cable modem with cellular during outages. Finally, the gateway could very well be located poorly for WiFi, with cable service often entering the household near the point of entry in a basement. Easiest to run just CAT6 to your upstairs for WiFi, rather than coaxial cable just so your combined gateway device can be located higher. Note that with cable company provided gateway devices, you likely won't be seeing the latest features such as 802.11ac any time soon.

    Why Motorola brand? I had a look at the Cisco DPC3010,which won't show log files. It also died (power supply failure) after only 30 hours of operation. A single data point, not a big deal, I'll RMA it. These things happen. But since I had to get a new one, I decided I prefer being able to view my cable modem log myself, via local IP address. This gets me a lot of tech details, including system up time, signal strengths (seen below), logs (seen below), and firmware level (seen below).




    The LEDs are very bright at night, and I would not recommend this device be located in any kind of sleeping area. Even if you use some black electrical tape over the LEDs, light scatters from the well ventilated body of the unit as well, seen pictured at right.

    Additional information.

     Last Updated Sep 18 2013

    DOCSIS 3.0 modems are capable of channel bonding, which enables multiple downstream and upstream channels to be used together at the same time by a single user. The more channels a device can bond, the higher the speeds it can achieve. There are two types of DOCSIS 3.0 modems:

    • 8 x 4 channels (8 downstream and 4 upstream): This is the newest generation modem and is recommended for all CHSI customers, regardless of the package that you select, and is strongly recommended for all Ultimate package customers to support future speed increases.
    • 4 x 4 channels (4 downstream and 4 upstream): While this modem will work with Premier and Premier Plus (where available) packages today, the 8 x 4 will be compatible with future speed increases, while the 4 x 4 may not.

     Last Updated Sep 19 2013

    Cox nicely lays out all the stuff you need to know about the SB6141, excerpt below:

    Manufacturer Resources

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    Oct 07 2013

    2 Repair trucks spotted nearby, at 2:15pm ETD Oct 07 2013.

    Measured watt use with Kill A Watt EZ, uses 7 watts at idle, and 8 watts under load. SB6141 continues to run only very slightly warm to the touch, even after hours of heavy load. The ambient temperature around the unit is 71 degrees Fahrenheit / 22 degrees Celsius.

    I have also learned that 9 homes in my Cox node of 750 homes are currently reporting issues, here in Wethersfield Connecticut, Zip Code 06109. Sure sounds like I finally might be getting somewhere, with this multi-week intermittent huge slowdowns (and spontaneous cable modem reboots, even with 2 different modems).

    Oct 09 2013

    The appointment I had with an installer today was very fruitful. He finally determined that my intermittent issue where every hour or so I'm getting this message in my cable modem logs:

    No Ranging Response received - T3 time-out;

    followed by a 2-5 minute extreme speed slowdown. This was something he could see at my telephone pole, affecting my neighbor's modem as well, with 500 such events in his logs daily. Cox agrees that again, a maintenance crew visit to the area is needed, expected tomorrow.

    So I'm assuming that problem should be squared away soon, likely just in time to truly enjoy the pretty remarkable speeds I'm now getting, now that they've changed my provisioning to Ultimate's 150Mbps down and 25Mbps up. This is quite the relief, after being told by Cox last week that I could get the Ultimate level of internet speed at my address, then being told I couldn't, then being told I could again. Today, with a Windows 8.1 laptop directly attached to the 6141, I'm now getting performance that is so very much faster than I've ever experienced in my home. Oh so very much faster, and a bit less latency too. These are representative samplings seen below. I took many readings around the time of each result below, with results only varying about +/- 5% on all 3 measurements. I'll need some weeks of monitoring and usage under my belt, and perhaps a new router, to be confident I'll be really enjoying these speeds on a regular basis. Meanwhile, a quick review of my preliminary results below looks promising. All these tests were with wired (CAT6) connections.

    Speed Test Timeline.

    Sep 29 2013 Premier Cox Service, Motorola SB6121 Cable Modem & Cisco/Linksys E4200 router

    These are the speeds I've had for about a year, which were actually a bit slower than 2011 for the upstream.


    Oct 01 2013 Premier Cox Service, Motorola SB6121 Cable Modem & Cisco/Linksys E4200 router

    This is the day Cox boosted our speeds, roughly doubling both directions, around 9am.


    Oct 04 2013 Premier Cox Service, Motorola SB6141 Cable Modem, no router

    This is the new 8 channel SB6141 modem, last week, Here's last week, when Cox doubled our neighborhood's speed, at no additional charge, on October first. This is something that we've been waiting a long time for, especially since the Cox Rhode Island market has enjoyed these faster speeds for many months before us:


    Oct 09 2013 Ultimate Cox Service, Motorola SB6141 Cable Modem & Cisco/Linksys E4200 router

    Interesting that I'm seeing quite a bottleneck when testing through my Cisco/Linksys E4200 router, even with QOS turned off. How do I know? Well, read onward, to see the ultimate, Ultimate speed test, bypassing the router.


    Oct 09 2013 Ultimate Cox Service, Motorola SB6141 Cable Modem, no router

    Drum roll moment. Today, on the Ultimate level of service that I'm paying about $17 more per month for, when directly attached to cable modem, I'm getting ~165 Mbps downstream, and 35 Mbps upstream, with a ping of 20 ms. Woo hoo! Got very similar speeds when bypassing the router, even during at 5:46pm local time  today. Not bad, especially when you consider the Ultimate plan is for 150 Mbps down and 25 Mbps up. Also good to know that there's room to grow further, up to closer to the theoretical 343 Mbps max this modem can handle. Given no FiOS or other fiber scheduled to arrive in my area anytime soon, this speed certainly makes the wait a lot more bearable. But with increasing use of video conferencing and high usage of VPN for my day job, I certainly hope those Cox bandwidth use warnings don't translate into even bigger monthly bills down the road.


    Nice how the timing is working out. It would also seem it's a good thing I already have 2 routers on the way to test tomorrow, to see if they can keep up with my new cable modem speeds. Read more at:


    Oct 10 2013 Ultimate Cox Service, Motorola SB6141 Cable Modem, no router

    Fastest download score yet noted tonight, as I prepared to fully test the new Netgear R7000.


    Oct 11 2013 Ultimate Cox Service, Motorola SB6141 Cable Modem, no router

    Even faster score, wow.


    Oct 12 2013 Update

    Problems with reliability, and speed again. Two more cable guys visited my home again this AM, and down the street, another maintenance crew again today. Yet still, sporadic outages, here's an example from my cable modem log:

    Jan 01 1970 00:00:15 6-Notice N/A Cable Modem Reboot due to T4 timeout ;CM-MAC=b8:16:19:f9:7e:1b;CMTS-MAC=00:1f:ca:20:27:9d;CM-QOS=1.1;CM-VER=3.0;

    These intermittent issues are now dragging into another week, making testing the 2 802.11ac routers I have rather difficult. A lot of time spent calling Cox service. They are trying.


    Oct 23 2013 Update

    Well, Twitter works! I tweeted out to Cox here (in the discussions section below), and got a reply within minutes, and a call from a supervisor that evening, with follow-up ever since. Finally, I also actually have a credit on my bill for weeks of intermittent service. This is in contrast to the numerous bill reduction promises made by previous Cox folks that weren't actually delivered.

    Since Oct 20 2013, I seem to have no T3 and T4 errors. But, I still saw a Cox contractor truck just yesterday, in the same area (as the photo above) up my street. Also, I am now experience erratic performance measurements, and am rarely obtaining anything above 100 Mbps downstream. My ping times have also gone up to 35 to 40 ms. So this saga is not yet over. Spent another 5-10 minutes on the phone with Cox folks to keep them updated. At least now I don't have to slog my way through L1 and L2 support personnel calls, having to explain my whole situation over and over again.

    Oct 23 2013 Update Part 2

    Cox sent a truck to my house, no appointment, just rang bell. Happily shows the guy to my basement "lab" with 3 routers and my modem all laid out, ready for us to test together. His new laptop with Windows XP SP3 was getting 188 downstream, using Cox speed test. Interesting.

    When my older ThinkPad T61 is directly attached to cable modem, I'm getting slower speeds, despite its gigabit ethernet and fresh Windows 8.1 load. How much slower? Rarely breaks 100Mbps downstream. Also interesting. Especially considering I had no issue obtaining higher speeds last week, same laptop, same OS.

    Last night, had also tried my ThinkPad W520 with Windows 8.1 directly attached to cable modem, same problem, less than 100Mbps downloads.

    I still have much more investigating to do here.

    Oct 25 2013 Update

    Stability seems to be better. Motorola SB6182 the installer left behind for free doesn't work any better, or worse, than my SB6141, although it is a little bit more miserly (7 watts instead of 8 watts, while in use). Honestly, I'm still struggling to find the magic pill here. I finally have reliability, with those pesky T3 and T4 errors pretty much gone now. But I don't have any systems in my home that get anything beyond 100Mbps speeds, day or night.  Yet the installer's XP laptop gets >180 Mbps, every time. Still trying to fathom what was different. We tried identical cables and eliminated all variables, with his speed tests to the same server always blowing my speed tests away. Very strange. And none of the TCP/IP tuning stuff here made any difference, so I rolled back to the stock Windows 8.1 build.

    Nov 06 2013 Update

    Nevermind, it's back, the T3 and T4 timeout errors, worse than ever actually, many 2-3 minute outages per day, whether on SB6182 or SB6141. Same issues. Another call to L1 on Nov 5th, escalated to L2, who said he can't dispatch maintenance, can only schedule another truck roll to my house. Cox technician to my house Nov 6th, who couldn't offer help, other than calling for maintenance crews. Rinse, repeat. Like 5 times now. Argh!


    Nov 08 2013 Update

    Maybe this is one of those it gets worse before it gets better things. Remember, it's not the modem, I tried other modems, same internet outages/T3 error issues.


    Dec 19 2013 Update

    Things are better, with only one or two blips a week now. This situation can finally probably be considered over. Cox did work hard to get this right, with many neighborhood maintenance crews spotted, and good follow-up over email. So glad this is finally squared away. Be on the lookout for a future post that talks about what you can and can't do with such a fat pipe!

    Jul 12 2014 Update


    See also this Google+ post, where I say the following:

    Another great podcast Jim/Renny/John! Sure had me laughing too, always a good thing! Jim, you mentioned on the podcast that Cox Communications is doing their free double speed rollout in Nebraska, cool! FYI, Cox rolled out 2x speeds at no cost to my area of Connecticut last October. It wasn't smooth, likely because I went to their top speed tier, so really pushing the envelope as early adopter of 8 channel service, the first week it became available. 6x-8x speed boost for me, once I got it all working.

    Full story here:

    If you already have a DOCIS 3.0 cable modem with 8 channels from <2 years ago, you'll probably be just fine though. But just in case you don't (such as the very common but older 4 channel Motorola SB6121), you may want to step-up to an 8 channel model, especially if your testing shows you're not getting what the package you're paying for promises. The 8 channel cable modem model I've tested is the Motorola (Arris) SB6141, it's been stable for many months total use now, widely available at Amazon and Best Buy too for around $99.

    For my area, I've also found that the only speed test tool that actually works as you get past around 80Mbps down (not sure what package you're on) is Cox's own test site:
    (requires Cox customer login)

    All the others give a little lower measurements, particularly on the upstream:

    Have fun, and will be fun to see what results you get. Not sure John and Renny will be as thrilled to hear back. That said, honestly, these kind of speeds you and I are now lucky to have available are currently really only noticeable for big downloads (VMware appliance downloads, MSDN ISOs, etc.), and only if using the various download managers that use things like Akamai local caching, and even then, usually only when multiple downloads are happening concurrently, as I show here:

    In other words, for day-to-day browsing, things don't likely change noticeably, as the typical web server out there is a limiting factor. The vast majority of stuff I do is the same is the same as when I had ~25Mbps downstream connection. Things like Skype and Google Plus still only generally use a tiny fraction of your pipe, up and down.

    Latency measurements are likely even more important for a podcaster/Skype guy like you.

    Just some of my thoughts/opinions.

    Thanks guys again, for a great listen!

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    Jul 25 2014 Update

    Over the last 2 weeks or so, I've had 3-4 incidents of suddenly slowed upstream internet. Strange, because downstream is still between 150Mbps and 180Mbps, but only the upstream drops from the usual 25-45Mbps range all the way down to 5Mbps.  The problem won't clear until I've power cycled the SB6141 cable modem, or rebooted it through the browser UI.

    Contacted Cox, got to L2 support, they don't have any new firmware to see the issue from their end, so we agreed that as a test, I'd try out Motorola (Arris) SB6182 I already had on hand. I'll see how it goes, and if the speed stays the same. No idea if it's wiring, SB6141 hardware/software, or other cause, way too early to know much of anything for sure. Just passing along what I do know, so far.

    FYI, the SB6183 came out earlier this year, with Cox and Comcast supporting it. Here's the SB6182 manual to compare to the SB6183 manual and SB6183 datasheet. Same small form factor, but fully Arris branded this time around, even the web UI, and with 16 channel capability. Having 16 channels wouldn't be likely to mean much of anything to me for years yet, given Cox just rolled out DOCIS 3.0 150 MBps Ultimate service in my area in 3Q2013.

    Doesn't really matter, neither the SB6182 or SB6183 seem to be readily available anywhere for reasonable prices, so my recommendation for most folks is still likely the SB6141.

    See also

    SB6182? New modem? and SB6183, 16x4 modems are here!

    MOTOROLA ARRIS SB6141 SURFBOARD 6141 MODEM CONNECTION DROPPING FIX (mine is stable/not dropping, this is just an FYI)

    [AZ] SB6182 Firmware/Software General Thoughts

    SB6182: Troubleshoot Internet Connection (Arris Consumer Care, with signal strengths to look for)

    DOCSIS Speeds for Motorola Cable Modems and Gateways (Arris Consumer Care)