In your second paragraph I believe you meant “between 54 and 1 GHz”. But aside from that, a DOCSIS CMTS transmits digital data (1′s and 0′s) by first wrapping it into Ethernet Frames and then into and MPEG-TS Layer 2 188-byte long stream (you can google those terms for details). The MPEG stream is fed into a Quadrature Amplitude Modulator (QAM) device that converts the MPEG stream into either 64- or 256-QAM following the ITU J.86 Annex B standard (Annex A for Europe). This modulation is still considered to be in a digital format, but has a 6 MHz bandwidth centered around 0 MHz (baseband) or 8 MHz bandwidth for Annex A – Europe. But we really need to up-convert it to between 54 MHz to 1GHz as you know (actually, the new DOCSIS 3.0 specification defines the downstream to now be 108 MHz to 1 GHz). The upconversion uses a device called a mixer. The mixer takes a local oscillator (LO) and multiplies the baseband 64- or 256-QAM digital channel up to the desired frequency within the RF spectrum (54 MHz to 1 GHz). It will still be 6 MHz wide. And that is a very basic explanation of how a CMTS transmits digital data. The whole process of QAM and upconversion is actually a little more complex, but takes place all in one box so you never see the gory details. You just tell the CMTS or edge QAM what frequency you want it to transmit on.

I hope that helps.

-Brady

then

The CMTS sends data to the cable modems by transmitting a 6 MHz wide band of information

If available frequency is between 54 and 1k, how does CMTS transmits data at 6 MHZ.

Please let me understand.

thanks