OK, I know that a modem stands for modulator/demodulator and that it turns an analog signal into a digital signal and vice versa.
Now, with my cable modem I am assuming that the cable company is sending a digital signal to my computer so the box isn’t doing any modulating or demodualting. So why then do we still call it a modem?
To the layperson, a cable modem seems to do exactly the same thing as a traditional modem. Why risk confusing them by introducing a new name?
A cable modem is not a modem is the strict sense. As mentioned in the OP modem stands for modulate/demodulate. None of that happens in a cable modem. More appropriately your cablem modem is actually a router.
That’s exactly what I thought it would be, a router, but then why not call it a cable router? I guess ultrafilter is right. Sometimes I forget that the majority of people don’t have even my limited knowledge of computers. Thanks guys.
I wouldn’t think it is a router, more along the lines of a NIC since the “cable modem service” is a giant network and your cable modem hooks you into that. Hell, every cable modem has a MAC address which should point you in that direction.
I disagree, a cable modem is aptly named. It modulates a digital signal from a 10 base-T ethernet or USB connection to an analog signal that can be transmitted on a specified band in the TV cable and vice-versa. Mine doesn’t have a router otherwise I wouldn’t have had to buy an additional router to reset the repeater count and isolate my additional IP addresses from the cable company.
Networking hasn’t been my specialty for some time but the cable modems that are commonplace now aren’t a whole lot different from the ones we used in the early nineties in Biosphere 2. We actually had two complete redundant CATV systems with two way transmission. A block of channels was transmitted outbound from the head end to the taps and a block transmitted the other way to the head end. This allowed the crew to plug in cameras modulated on the inbound channels and watch them on the outbound. The only serious problem was when someone plugged a device into the wrong system. Mark Van Thillo was notorious for plugging a TV modulator into the data network and hosing all the data connetions.
I’ll be damned…Padeye is correct (I’m not suggesting he’s usually wrong…just surprised he’s right in this case).
A Cable Modem is indeed a modem. I figured it was digital all the way through but apparently the signal is transmitted the same as the TV signals on the cable…in analog. Hence it modulates and demodulates the signal.
SOURCE: How a Cable Modem Works
What of those of us who have digital cable?
You know…looking at the link I provided I’m still not so sure that a Cable Modem is a modem. In the link it shows one box doing both TV and computer and assumes the signal is analog.
As ultrafilter mentioned there is digital cable to consider. I know in my area cable modems only became available at teh same time that digital cable (for TV) became available. I know the two boxes running the TV and the computer seem like completely different things (different look, different manufacturer, different connections, etc.). One would think they are better off keeping the signal digital all the way through.
Then again I’m no electrical/cable engineer so I give up.
From looking at Whack-a-Mole’s link, it does look to me like a cable modem is close enough to a standard modem that you can call it a modem and not be too far off.
But like I said earlier, the name was probably chosen because from a black box standpoint, modems and cable modems do the same thing: they connect you to the internet.
I’m sure a Doper EE can elaborate but digital TV data still needs to be modulated with a carrier to be transmitted over an RF cable. I’m sure the digital channels are modulated as a block rather than modulating each in its own bandwidth. In any case they have to shair available total bandwidth with the analog channels. At that level your digital cable box is a demodulator that pulls the specific data stream for the channel you want then remodulates it as baseband analog video and audio signals for your TV.
Padeye is pretty much right on.
It does mod/demod. Most cable modems would best be considered as a 10base to coaxial ethernet adapter. But, it does the adapting by modulating the digital data onto an RF carrier.
I’m quite surprised to learn that the cable modem signal on the coax network is actually analog. Interesting! (to a geek like me)
Ok then what about a DSL modem?
Whether it is an analog or digital signal, a device would still be needed to convert from carrier signal (Cable/dsl) to ethernet. It is still modulating and demodulating from one type of signal to another so therefore it is still a modem.