How Does a Cable Modem Work?

How Does A Cable Modem Work?

Did you just move and find out that your only choice of internet in the area is cable internet? Don’t feel so bummed just yet. Like any other kind of modem, cable modems can still connect to the internet and if you connect it to a router, it could connect devices to Wi-Fi.

And just like any other kind of modem (like DSL, or dial-up), cable modems can be designed to work as a half modem, then a half bridge, router, tuner, ethernet hub, encryption or decryption device, and so much more. 

What makes the cable modem special is that it could receive and translate data using the same jack and cables you use to watch television. This is why In most cases, your cable company gives you the cable modem as part of your subscription. If the box or modem isn’t included with the plan you paid for, you can always purchase the hardware separately.   

So how does a cable modem work? 

A cable modem is a hardware device that uses a coax cable to “communicate” with your internet service provider (ISP) and connect to the internet. 

Just like dial-up and DSL modems, cable modems all “modulate” and “demodulate” signals. Meaning, these devices send and receive data in two ways – downstream and upstream. 

  • In the downstream direction, data is modulated and placed on a 6MHz TV carrier between 42 and 750 MHz. On this method, data could go through different modulation methods, but it is common for cable internet to use QAM64 (with up to 36Mbps) and QPSK (with up to 10Mbps) signals. 
  • The reverse path (or upstream direction) transmits signals somewhere from 5 to 40 MHz, which is noisier than the downstream path because this is where your home appliances, HAM radio, and similar devices pass through. Cable companies solve this by using QPSK modulation technique, which reduces noise but is slower than QAM.

In layman’s terms:

  • The main cable is set up at the center of town, where signals would be carried down to feeder cables going into different, smaller neighborhoods. 
  • When you subscribe to cable internet, the cable provider will run a cable from one of the feeders directly into your home, which will then be attached to the TV box or directly to your TV. 
  • Your cable modem uses coax cables and receives data (such as emails, web pages, and other data) from the main cable to the feeder cable and now at your home.
  • The modem translates the data into something your router can understand 
  • Your router then distributes wireless signals to your devices. 

Pros and Cons of Cable Modems

Like DSL and dial-up modems that came before it, cable modems have their advantages and disadvantages. 


  • Cable internet is active 24/7 and does not require a landline for you to connect to the internet. 
  • The speed and performance of cable modem internet don’t depend on how near or far the cable provider is located. 
  • Cable internet does not drop out connections like dial-up. 
  • Cable modems provide faster internet connections than dial-up and perform similarly to DSL and sometimes satellite connection. 
  • Cable modems provide good speeds for gaming, streaming and uploading/downloading files


  • Cable internet isn’t available in all areas
  • Cable modem connections can be more expensive for businesses
  • Your cable connection could be affected by the number of people using the same cable in your area. 

You see, cable internet can be the fastest connection you’ve ever experienced, especially if you’re one of the first users to connect to a particular cable channel and you’re able to use an entire bandwidth of the channel freely. But this can change quickly if others in the area connect to the same channel. 

In the past, the reason cable internet suffered from bouts of slow speed was due to traffic. But now this can be solved once the cable company adds a new channel where other users could connect to. 

How fast is cable internet?

Cable internet isn’t the fastest internet currently available today (that would be Fiber-optic internet), which unfortunately isn’t available everywhere yet. 

However, cable internet isn’t all that bad. You can find the download speed of cable networks from 10 to 500 megabits per second (with upload speeds ranging from 5 to 50 Mbps). This upload and download speed is able to accommodate most households and small businesses. 

On average, cable internet offers speeds ranging from 20 to 100 Mbps. In some areas, cable providers could offer more. For example, Xfinity has a 1,000 Mbps plan, but only in select bigger cities. Do note that even higher plans can sometimes slow down during “peak use” times and this is normal with how cable modems work. 

Is a cable modem connection right for you? To know the connection speed you need, talk to your cable company or use a tool to measure the bandwidth or speed requirements of your household or business. 

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About the Author: Barry Lachey

Barry Lachey is a Professional Editor at Zobuz. Previously He has also worked for Moxly Sports and Network Resources "Joe Joe." he is a graduate of the Kings College at the University of Thames Valley London. You can reach Barry via email or by phone.


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