ewh@druky.UUCP (HarkinsEW) (10/17/84)
re: CATV or broadband lans. When talking about a channel thereof, be aware that your basic building block is 6 Mhz, the same as an ordinary TV channel. What you do to further subdivide that channel is up to you, or Sytek or 3M or whoever. That gives you a theoretical data rate of 12 Mb per channel, with somewhere between 50 and 120 channels on a coax cable, depending on the age and quality of the cable (ie: attenuation). There are different layouts of those channels, subsplit, midsplit and highsplit, which basically just move the "dividing line" between upstream frequencies and downstream frequencies up or down to balance (or unbalance) the number of up vs. downstream channels. The crudest of the layouts is based on actual broadcast TV (and radio, FM, police, etc) frequency allocations; that's why you could hook up your ordinary TV to the older cable systems directly. There were some gaps and some historical anomalies in the allocation that essentially wasted some bandwidth. That's why most cable systems now have those magic boxes that decipher the channel you want and modulate the info onto channel 3 (usually) before stuffing it onto your TV. Once those channels are reorganized into a contiguous scheme, you can see how 3M can claim to support 10k terminals on a single cable, plus video... ernie harkins