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Given the different speeds of dialup, and different architectures, plus the different types of DSL (IDSL/ADSL/SDSL), types of cable internet, sattelite, T1 framing, etc etc...plus the options included with modems (routers/switches/gateways/firewalls), I would say four.
You missed ISDN. I've heard that DSL modems should be/can be classified as bridges rather than modems. In fact, my DSL modem at home is operating in Bridge mode. So is it a modem or a Bridge?
It's proably a bridge/router rather than a modem. The functionality of the various hardware starts to blur. Bridges/modems/routers/switches/hubs/access points/firewalls/ all start to blurr very easily.
First of all, there is actually one type of modem that you will easily find on the market. Most are the 56bps modems that are used in a dialup connection. Modem is short for MOdulate/DEModulate. What a modem does is take the analog signal that is sent over phone lines and convert it to a digital signal a computer can read and vice versa. It MOdualtes the signal into analog before sending it out and DEModulates received signals.
Since people were used to thinking of the device that connects them to the Internet as a modem, the name stuck to what are essentially specialized routers that are used for broadband connections. There is no conversion of signal since broadband is already digital transmissions.
When I think of modems I'm reminded of a funny story. A number of years ago (before PCs), when I was an admin for a 401K plan, we worked with our recordkeeper to provide me a way to enter transactions directly, rather then send them paper forms to be keyed in. We got a second phone line in my office with an acoustic coupler (for the youngster's out there an acoustic coupler is a modem with cups to accept the phone handset). Anyway, we tried to connect the the record keeper's system, but couldn't. Until I realized that the handset on the phone they had given me was a newer one with squared off edges. So we dug up an old style phone with circles on the handset. That worked fine. We were trying to literally stick a square peg in a roound hole
Actually the name is still valid...cable modems, while they use digital, still have to modulae signal to certain frequencies. They communicate differently, but the device still has to demodulate what's sent to it from an analog signal (most commonly for cable modems it's some form of QAM modulation), and then modulate whatever they send back (QAM or PSK modulation).
I see what you are saying Chris but the "modem" term may originally refer only to converting analog/digital signals which is not the case with DSL/cable "modems".
You missed ISDN. I've heard that DSL modems should be/can be classified as bridges rather than modems. In fact, my DSL modem at home is operating in Bridge mode. So is it a modem or a Bridge?
It's proably a bridge/router rather than a modem. The functionality of the various hardware starts to blur. Bridges/modems/routers/switches/hubs/access points/firewalls/ all start to blurr very easily.
Basically it's a bridge modem. Dialup modems operate in bridge mode too... The difference is that in Bridge mode, it's connecting whatever's plugged into it to the ISP's network (like a regular bridge) instead of being in Gateway modem, where it connects to the ISP's network itself, and then can be used as a gateway to GET to the ISPs network. We actually have a few dialup gateways here at the office sitting on a shelf. They're funny. Some of them are even dual phone line, so you can shotgun your way to the intarwebs. Unfortunately, I think they're somthing like 14.4k each, so you'd be using up two phone linkes and still be surfing at the amazing speed of a snail.
We've also got a bunch of network cards with BNC connector ports on them...man, if only I'd been old enough to do this back then.
I see what you are saying Chris but the "modem" term may originally refer only to converting analog/digital signals which is not the case with DSL/cable "modems".
All the cable systems I've ever worked on still have analog signal. Still, you have to modulate and demodulate the signal with a MODEM unless your ISPs 'last mile' consists entirely of the same network media (I'll say ethernet) that you're running to your devices. Otherwise, data has to be recieved by the modem, demodulated, converted to ethernet, and anything sent back the oppisite way. I still don't see how being a digital signal means you wouldn't have to modulate anything...
Digital cable has to modulate too... Analog TV has a 6mhz wide band with the picture and sound information, and color at the end of the band. Digital uses the same size band but compresses between 4 and 10 stations (called an epoch) into the band, then modulates combinations of 1's and 0's to different amplitudes, depending on the type of modulation.
With analog, the TV just displays whatever it recieves. It's like the difference between WAV and MP3, if MP3 were lossless.
I'm kinda a purist on this and its always kind of bugged me that they continued to use the term modem. Like we consumers are too dumb to understand the difference.
Linear Mode
