Max Cable Internet Speed = Service Plan + Distance + Modem

This articles highlights an important feature of cable modems that can maximize or curb your Internet download and upload speeds.  To wit: Modem channels, provider speed, and provisioned rate.

To busy to read? 
OK. If you (or your cable company) think your modem is limiting your speed, get DOCSIS 16/4 modem that handles up to 600+ Mbps downstream.  You won't need to change for 5 or more years.

Have some time?
Read this article for insights into how cable modems work, the speeds available to you and how a cable modems channel configuration affects how much speed you can get.

Internet Speed = Speed tier, "provisioned" rate, distance to node, and modem channels!
In case you didn't notice, there is a customer-beneficial speed war between the handful of remaining Internet mega-carriers like Comcast, AT&T, Time Warner, etc.  Since we, here, are involved in product design, development, testing, evaluation, writing, graphics, photography, and industry research, we were only marginally content with our Comcast speed tier of 25 Mbps which, in truth, actually provided us 30+ Mbps.  I recall (not-so-fondly) how, long, long ago, in a board room not so far away, I had to fight, tooth and nail, for my systems design firm to provision a full "T1" line (a whopping 1.44 Mbps) from BBN to service our 3,000 desktops with Internet access.  How time, or should I say speeds, have changed.  The 30+ Mbps speeds many are now serving their home with was equal to 20 of those expensive T1 lines.

When 150 = 188.5 = 177

But, that was then and this is now - where 1+ Gbps services are coming available, albeit a bit costly for the individual but affordable for some SOHO and larger firms.  So, we visited our Comcast portal, as we frequently do for our product and services research.  On our last visit, we were surprised that we could now have the 150 bps service for only $13 more.  So we enabled it.  Within a minute, Ookla's Speedtest.net, the very popular Internet speed test site, was showing 130 Mbps down with 12 Mbps up (130/12) as compared to our previous 30/10.  Although that's not 150/12, it was a full 5 times faster down than our previous service and were happy to keep the service.

That event was also a convenient excuse for us to investigate the current menu of cable Internet speed tiers, advertised versus "provisioned" speeds, the channel architecture of cable systems, and the subsequent requirements of modern cable modems to support the speeds that are available.  The goal being to see if there was anything we could do to get the full 150 Mbps of our subscribed tier.

Some of you may have heard of a cable modem standard called "DOCSIS".  The current version is 3.0 with 3.1 released not long before this article.  The DOCSIS standard provides a standardized set of features and specifications that cable Internet providers can use to control their customer speed tiers, diagnose end-to-end connectivity and throughput problems, dump error logs, remotely reset modems, control the utilization of the modem's down and up channels, and much more.

A key part of the standard is the that it treats networking cable transmissions as standardized "channels" that are basically the same as the TV channels you can get over your cable line.  Each channel has a predefined, therefore limited, bandwidth which, in turn, limits the amount of data bits it can handle per second.  To achieve speeds up to 130 Mbps, the combined bandwidth of 4 channels is required. Even though the theoretical maximum is more like 170 Mbps for 4 channels, the overhead, distribution system signal issues, and other factors limit what your modem can actually achieve.

The table below is from a compendium of resources and shows the relationships of channels to total downstream and upstream data rates for both North American and European standards.  The sources suggest that the upstream rates are the same for either standard. The key column for North American readers is the "DOCSIS" Standard / Data Only" column.  It shows the speed you can achieve with different DOCSIS 3.0 modem channels configurations.

With such an architecture, the fundamental bandwidth/speed capabilities of cable modems are usually designated by how many "channels" they support for downloads and uploads.  E.g., a 4/4 modem has 4 channels in each direction.  A 16/4 has 16 down and 4 up.  The DOCSIS standard allots channel configurations such as 4/4, 16/4, 24/4, and 32/4.  Our previous DOCSIS 3.0 Motorola Surfboard SB6120 modem was a 4/4.  Therein lies the reason we were not seeing anything close to the provisioned rate of 188.5 Mbps which is revealed in the chart later in this article.

Note the chart above states that 4-channels down should provide up to 152 Mbps yet our SB6120 4x4 DOCSIS 3.0 modem only achieved 130 Mbps.  If the faster MB7420 16/4 modem we tried after the SB6120 also exhibited such an unknown loss, we'd attribute the losses to the cable system.  But that was not the case.  The MB7420 achieved 176-180 Mbps - close to the theoretical maximum (the provisioned rate of 188.5 Mbps). 

Keep in mind, unless you plug your modem into the chassis of a router inside the cable company's distribution center, it is impossible to enjoy the full provisioned rate on your PC.

So, all this testing clearly concluded that the combination of our SB6120 4x4 modem and Comcast Internet service could not reach the advertised 150 Mbps rate, let alone the 188.5 provisioned rate even though a 4x4 modem should reach 152 Mbps downstream.  With this research on DOCSIS and modem channels, we started shopping for a cable modem with more download channels.  That is when we came across the Motorola MB7420 16/4 cable modem that was certified for use with Comcast and some others.  Having 4 times more download channels (16 versus 4) seems to account for the modem's advertised top download speed of 686 Mbps.

So, a quick order on Amazon and the MB7420 was at our garage door 2 days later.  With hopeful anticipation, we installed it, activated it via the Comcast web page that a new modem triggers and were momentarily panicked when Speedtest.net reported a shocking low 20 Mbps downstream rate.  Our previous experience with such issues brought our heart rate back in check.  It looked like the common problem where the activation process and/or our customer record did not provide the correct codes to enable our modem for our 150 Mbps service tier.

Customer Support?

We made a quick call to Comcast internet support and suffered through the usual mind numbing VRU questions.  After shouting representative 10 times, we managed to get a human, albeit a first level support agent.  She patiently listened to my greatly detailed report on our problem, explaining that there appeared to be a problem with the configuration of our service at the head end and it looked like the classic problem of a wrong equipment code or customer service level being used.  I went on to say that we were getting 130 Mbps with our previous 4x4 modem and our newer, faster 16/4 MB7420 was giving us 20 Mbps.  Silence.  Then "Are you saying you have a connection problem?"

Ah, that old customer support feeling in the pit of my stomach!  In my very best, most sensitive and caring voice, I asked, "I mean no offense but did you understand what I just explained?"  Silence.  Then I heard a low and reluctant "No."  So, I reiterated the problem with a more concise and easier to digest version and asked again, "Did that help explain things better for you?" Silence.  Then <click> ... she hung up on me.

Reciting my mediation mantra, I called back.  This time I got a nice fellow named "Alvin" to whom I gave the full version.  He asked if I tried the usual things.  I said yes.  He was quick to understand I know a little about networking and agreed that my diagnosis was probably correct.  He went to check the head end config and, sure enough, the activation process had returned the wrong configuration code.  After a brief 20 seconds, he said it should be correct now.  We ran Comcast's version of Ookla's speed test (speedtest.comcast.net) and, voila, we were getting 176-178 Mbps.  With the provisioned rate for our 150 Mbps tier being about 188.5 Mbps, that's 94% of the maximum.

I thanked Alvin for his good service and asked to speak to the supervisor who was happy to take my kudos for Alvin and my note that the previous agent needed more training.  Further, that no agent should allow lack of knowledge to disrupt their customer relations, let alone hang up on them, but rather they should politely redirect the call to someone more experienced.  She then said that we should reboot every week or so, hinting that Comcast may soon upgrade their tier speeds.

Although we were happy with our speed, we did a few reboots over the next week or three.  Nothing changed.  We then got an update from Comcast (in Oct 2016) that speed tiers had just been increased and should reboot our cable modem.  Since we reboot recently, we immediately ran Speedtest.net and were very pleased to see speeds around 240 Mbps.  Uploads remained at 12 Mbps.

How to Choose a Modem:

When reviewing your own needs, take note of what the provisioned speed is, not just the advertised speed.  That is because you can usually get 90-95% of the provisioned rate with a modem that can pass it all through to you.  After all, why not get as many Mbps as you can get for the fee you are paying for your service tier.  As per my favorite adage, "any money you could save but don't is same as taking that much out of your purse and tossing it on the road," the same applies to Mbps you could have if you choose the right equipment.

So, to achieve your maximum speed, you should probably look for a modem that can handle the provisioned rate of the highest speed tier you might use in the next 3-5 years.  We were at 30 Mbps (actual).  So, we figured a 20 times increase in throughput should suffice for us in that time frame.  So, 20 x 30 Mbps = 600 Mbps.

We also insist on a well-reviewed product, a respected manufacturer, doesn't need manual intervention, and one that doesn't generate much heat since it runs 24/7 and might be running when the office is closed for a few days.  The Motorola MB7420 met those criteria.  As previously noted, after an upgrade from the 25 Mbps tier to the 150, we only saw 130 Mbps with the Motorola SB6120 4x4 modem.  As soon as we installed the Motorola MB7420 16x4, we were consistently getting 176-179 Mbps, and now, after their subsequent tier speed increase, 240 Mbps.

Speaking of advertised versus "provisioned" rates, the website DLS Reports ran a chart of Comcast's advertised and actual "provisioned" rates for their different speed tiers.  See the chart below.  As you can see below they provision roughly 25% faster than advertised.  With a proper modem, good cable lines, and proximity to the nearest Comcast node, you should get 90-95% of the provision rate.
NB. The following chart is now out of date due to recent increases of Comcast speed tiers.  E.g., the 150 Blast tier is now 200+ as of Oct-2016.  Other tiers may have similar upwards adjustments.

Advertised Speeds
Provisioned Rates
Economy Plus:
3 M / 768 K
3.75 M /.960 K
Internet 5 (West/Central):
5 M / 1 M
6.25 M / 1.25 M
Performance Starter:
6 M / 1 M
7.5 M / 1.25 M
Internet Essentials / Perform Starter 10
10 M / 2 M
12.5 M / 2.5 M
25 M / 5 M
31.25 M / 6.25 M
Performance [50]:
50 M / 5 M
62.5 M / 6.25 M
Performance Pro (NE/West):
75 M / 5 M
93.75 M / 6.25 M
Performance Pro [100] (California):
100 M / 5 M
125 M / 6.25 M
Blast [75] (Central):
75 M / 10 M
93.75 M / 12.5 M
Blast [105] (West):
105 M / 10 M
131.25 M / 12.5 M
Blast [150] (NE) / Blast Pro:
150 M / 10 M
187.5 M / 12.5 M
Blast Pro [200] (California):
200 M / 10 M
250 M / 12.5 M
Extreme 150 ( GF NE, CA & Huston):
150 M / 20 M
187.5 M / 25 M
Extreme 250 (Central/West):
250 M / 25 M
312.5 M / 31.25 M
Extreme 300:
300 M / 25 M
375 M / 31.25 M
Extreme 505 GF:
505 M / 100 M
555.5 M / 110 M  FTTH
1 G / 35 M
1.25 G / 43.75 M  DocSis 3.1
Gigabit Pro:
2 / 2 G
2.2 / 2.2 G  FTTH
Legend:  K=Kbps; M=Mbps; G=Gbps; GF = Grandfathered;  FTTH = Fiber To The Home

Another important point to consider is that having a modem that cannot support the provisioned rate, you will be effectively paying more for a lesser speed.  And then there's the competition in speeds.  As a rep at Comcast told me that they will be raising their 150 Mbps speed tiers by another 25 Mbps, that is, 175 Mbps (which they did).  That then means a provisioned rate of about 200 Mbps.  That further means you want a modem that can support more than that, perhaps, 300 Mbps.

But, wait, there's more.  What if you end up needing a faster Internet connection in the next few years for your work, to watch 1080p or 4K movies, to download videos or transfer gigabyte files.  You need to plan ahead so double that last estimate of 300 to 600 Mbps.  Hey, look a that.  The Motorola MB7420 just happens to support 686 Mbps. That's a 1 time cost of about $80 on sale which pays for itself in roughly 10 months as compared to the monthly rental fee that Comcast and others charge you month after month for life!   It also future proofs you to get a higher capacity modem in case the cable provider decides to use all the channels.  Sixteen down channels should work well for the next couple of years unless you are just a speed freak who gets high watching the meter peg at 1+ Gbps.

That last point raised yet another cold reality.   How can one use a 1+ Gbps data stream when the cables and adapters in the modern home operate at less than 1 Gbps.   They answer is, they can't.  Any spec is always theoretical and never possible in real life.  Gigabit Ethernet runs much slower than that.  Something like 600-800 Mbps.  So, tame the lust for speed and buy only what can be realistically supported from the cable system head end to your PC and over all the legs of the trip in between.  In 5-10 years, it will surely be a different story.

So, again, the 686 Mbps (0.67 Gbps) is a perfect maximum to carry you until the next stage of networking is upon us.  That will most like be in 5-10 years in some form of optical fiber with 100-1,000 Gbps.  Until then,  686 Mbps will do just fine.

We didn't want to mention the MB7420 too much here since we have a separate review of that modem in the works.  When it's published, we'll provide a link here or you can just find it in the list of articles in this venue.

Happy Streaming.

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