cable internet- how do they throttle?

the same cable internet provider - is able to give speeds at varying degrees? how do they do it? do they have electronic filter that they control?

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JohnBusiness Consultant (Owner)Commented:
The cable ISP can control characteristics in the user's modem and the local feed distribution box so that the user gets only the speed and the total amount of usage they pay for. I do not know what filter they apply (I am sure they secure their technology), but 4 users with 4 different plans all on the same basic feed can get different speeds and usage. I do not hear of users being able to thwart these limits.
Since the cable company is providing you with service, they can control how quickly they release data to you. Sometimes, throttling is a by-product of the limitations of the technology. For example, the theoretical maximum of 802.11b is 54 Mbps.

In this case, the ISP simply withholds data at a certain rate (or from certain sites or certain types).
JohnBusiness Consultant (Owner)Commented:
Where I am, the same physical modem can deliver higher or lower speeds, depending on what you pay for.
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Its very complex.
Data is sent in the form of packets (small chunks of data)
The volume of packets can be controlled.

You can understand this more by reading about:
Broadband remote access server
Link from

Also read:
Digital subscriber line access multiplexer
Link from
JohnBusiness Consultant (Owner)Commented:
There are small distribution boxes in my neighbourhood - each one services 6 or 8 residences. Then there is a large box at the entry to my subdivision. That box, inside, has a connector board with indicators and the technician can tell what is going on with my modem from that box.  I was looking at this setup a couple of years ago when construction crews tore up the main cable feed.

So I am quite sure that the cable companies have the equipment and software to control what speeds we get and it is not a function solely of the cable modem in my house.
Hi John.
Thanks for removing the blind links posted by the person posting after me.
But you have made reference to them as being the " The comment above was a blind link and deleted."
As you have deleted the persons complete post, your term"The comment above" may appear to some readers, as to refer to my comment, which may discredit my contribution to this question?
Can you please clarify that I was not the person who posted blind links in this question, and that you deleted "person xxx comments" , thanks in advance.
JohnBusiness Consultant (Owner)Commented:
Your post is still there so people should be able to figure out I was referring to a deleted post. I need to figure out a better way to refer to something not there. Project for me for 2015.
As the mechanism of limiting the internet speed is similar but not identical for different Internet Service Providers (ISP), consisting in a combination of hardware and software technology, therefore there is certain diversity, the easy way to understand it is using an analogy.
Imagine the internet network similar with a pipe network in which the water flows instead of data.
The volume per hour of water that you receive at your tap inside the house depends by pipe network from distributor to your house, let’s say diameter of pipe, how big is the pipe, then by the possibility of the water provider, how much water volume, pressure, flow can provide and by the main tap used by the distributor when the water leave the distribution. And imagine there is a pipe directly from your distribution to your house.
The water valve used at the distributor side is the equivalent of the hardware used by ISP.
Imagine that valve not a simple one, but something automatic, an electrical valve controlled by a computer, a digital controller which receive as input the information about the flow of the water along the pipes and at user side using all kind of sensors for flow, volume pressure. In this way the distributor knows/is in charge of the water in the pipe network from distribution point down to the end user.  That automation part, the loop of closing and opening the valve automatically is the equivalent of the software side at the ISP.
We can imagine a similar example with electricity instead of water.
Imagine that you have on the table, at small scale, a DC power supply as equivalent of the ISP, the 2 wires as for + and – as equivalent for internet cable network and a load, some LEDs for example as equivalent for internet end user. There are DC power supplies with constant current output. These power supplies can provide the same output current in a given range of output voltage of the power supplies. The intensity of the LEDs brightens may be seen as the speed of the internet/data on the cable. By dimming the constant current power supplies we get different brightness for LEDs. In the same way the speed of internet may be reduced.
A classical old method of limiting the internet speed for 1 end user is to connect it at the same channel of distribution together with other users, and then of course the maximum speed allocated for one user cannot be higher than the speed for all together. But today the mechanism is individual and personalized. It is also implemented at the Internet used in smartphones.
Simply just imagine that the ISP is closing the “tap/valve” for your line only.
And as I am not allowed to provide links, please just search Google for the term "Quality of Service" at which industry refers when they limit the internet speed.

@John Hurst
How did I manage it this time? Is it better?
Merry Christmas!
Call your cable internet provider to ask if your connection uses DOCSIS 3.
Such a modem has downloads as fast as 150 to 160mbps. Which is several times faster than a DOCSIS 2.
If the network where you live is not up to date then you may not need to upgrade to a DOCSIS 3 modem.
Your modem may have the capability of faster speeds but it depends on which plan you have subscribed too. To access faster speeds you may need a new modem.

The real old ones are DOCSIS 1 and our local cable company does not use those any more. We are thankful for that. Our neighbor has the slowest cable modem internet speed and thus they don't need to latest, highest standard modem which is a DOCSIS 3.
We have a plan which is the second fastest speeds they offer and our modem is capable of handling it. We upgraded the modem when we upgraded to the higher speed plan.

For your interest only here is a speed tester:

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