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What is a modem?

From the text, a modem is what separates phone or tv signals from internet signals. This leads raises a few questions:

  1. Does the modem have a IP address?

  2. Does it deframe and reframe datagram units?

12 comments
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The MoDem stands for Modulator Demodulator. As stated in another post, it modulates and demodulates signal 'types.' For sake of simplicity just think of it as your computer speaks digitally, the modem converts that to 'telephone languge'. The data flows down the network (or internet) hits another modem that 'de'modulates that converts it back to data your computer can understand. Thing is... on CCNA, I wouldn't expect a question about a modem.

oh my god i'm old.

[deleted]
3 points · 3 months ago

Oh my God man. I thought this question was a joke or something. I realize I too am old.

Original Poster1 point · 3 months ago

Why are modems no longer a thing? Personally, I have fiber optic and all the business I have been to use fiber optic as well lol.

1 point · 3 months ago · edited 3 months ago

They are absolutely still a thing, although I'd imagine fiber doesn't need them as it communicates in light signals alone. Feel free to correct me, though, I'm talking out of my ass here.

Edit: I stand corrected, as I expected to be. My fellow networking nerds have kept me honest.

Fiber does use a modem, the ONT or MC.

3 points · 3 months ago · edited 3 months ago
  1. Modems don't have to have an ip address, but they usually do. My motorolla surfboard ip address is 192.168.100.1. Accessing it via web browser allows me to see its current status, modulation type, frequencies, logs, etc.

  2. It depends entirely on the what medium your data is being sent across and specifically what protocol it is using. So for cable modems, the layer 2 protocol is called DOCSIS. I think pretty much every cable company is using version 3.x.

So when your home router sends its data out to the cable modem, the layer 2 protocol is ethernet (i believe) and when your modem receives this frame, it adds its own docsis frame around the ethernet frame. A frame within a frame. This gets modulated into an RF signal and sent out via coaxial cable to the cable company's equipment where the reverse process occurs. The docsis frame is stripped off and the ethernet frame can be read by the cable company's router.

Thats the basic gist of it.

a MoDem Modulates and Demodulates analog to digital signaling.

Modulator Demodulator

and here I thought it was Mormon Democrats ... TIL

You're over-thinking...the definition of a modem is irrelevant to any modern CIsco certification.

In the simplest way possible, I'd say the a modem converts one type of signal into a different type of signal.

Which text and what page?

Original Poster1 point · 3 months ago

Dont remember, exactly It was in my notes, something about dsl and cable using modems. Then it dawned on me that most of the text I have seen never really gave any information about it besides the separating phone and tv.

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