Modem (Modulation/Demodulation) Definition

Modem (Modulation_Demodulation) Definition

We are all familiar with the basic idea of what a modem does. It’s that handy little device that gets you to the internet. From a 56K modem (our condolences if you are using one) to a cable modem- they can go just about as fast as you need them to. But what remains obscure to many is how they allow the bridge to the internet to be built.

How a Modem Works


The term modem is actually conceived from the two processes it performs: modulation and demodulation. Modulation is the process of turning a digital signal (sent from the sending computer) into an analog signal (so that it can be transmitted as electrical pulses). On the flipside we have demodulation, which takes an analog signal and turns it back into a digital signal that can be read by the receiving computer.

modulation demodulation

Early modems were classified as point-to-point connections. When a dialup connection was setup between two computers, that connection was only shared between them. That means that the transmission medium (the phone line) didn’t have to be shared by other resources- only the two computers communicating.
But as your may well know, this type of dialup connection isn’t very desirable. Connections made through a phone line are much slower than other counterparts such as Ethernet or fiber optic cable. But since the original modems used phone lines, they became vastly popular. After all- if you have a global telephone line system, why not take advantage of that and use it for internet access?
As far as Cisco exams go, just remember how modulation and demodulation works. Cisco doesn’t include a lot of material or exam questions on modems, so there isn’t much of a need to go into further detail.

Photo Credit: THE Holy Hand Grenade! Flickr via Compfight cc


  1. Nitin Bhosale November 11, 2008
  2. MMF March 31, 2009
  3. @nT December 7, 2010
  4. Joseph March 8, 2012

Leave a Reply