On 10/14/2013 9:28 PM, Catherine Gramze wrote:
On Mon, 14 Oct 2013 21:12:32 -0400 Jerry Stuckle <jstuckle@attglobal.net> wrote:Maybe where you are, but not in the world scheme of things. A router is a specific box. A (A)DSL modem may also contain a firewall, etc. But most (A)DSL modems, cable modems, etc., only have one Ethernet port. So people install routers in addition to the one which may or may not be in the (A)DSL modem. Modems and routers are two entirely different things, with completely different uses. One box may contain both - but that does not mean all modems are routers (or vice versa).Hear, hear, Jerry! This is how I have always heard them referred to when I worked as a network admin. A router is a router, and a "cable modem" may or may not (usually not!) have any routing capability. It is really a bridge connecting two networks, as I mentioned previously. It doesn't do any modulating or demodulating. It simply allows the packets to go from one network to the other.
No, a cable modem does both MOdulation and DEModulation - which is why it is called a MODEM.
On the internet, input/output on one side of the modem is digital, through an RJ-45 to category cable.
But you can only have one digital signal on a wire. On the other side of the modem is 75 ohm coax cable. You *could* run the digital signal on this cable for a few hundred feet (some systems claim up to around 1500 feet), but this signal would not be compatible with the other signals (standard and hi-def TV and possibly music channels). As a side note, multiple hi-def TV signals, even though they are all digital, would not be able to share the same cable as digital signals, either.
Therefore, all these signals (including your internet) are modulated onto analog RF signals. Each signal has its own band, or range of RF frequencies it uses (a signal is not a single frequency). And coming the other way, the signal from the cable must be demodulated to convert it back to digital.
The cable company has another cable modem on the other end of the line to convert the signals between analog and digital, also.
So, you can see, a cable modem truly is a modem. Jerry