say a local PBS station has an HD channel plus 2 subchannels that total 19.4mbps. Their carriage agreement may require TW to carry all three channels which are passed thru as is fed to them. That total 19.4 would be muxed (or combined) with another local network's 19.4 to create a 38.8mbps 256 QAM channel.
in addition to that "exact duplication" PBS OTA feed, TW is required to carry an SD simulcast or downconvert of the main channel. SD simulcast is typically 3.5mbps and usually muxed with 9 or so other locals (CBS, NBC,Fox, etc) to create a separate 38.8 256 QAM channel.
eventually those SD simulcasts will no longer be required and the bandwith can be reclaimed for other use like more HD,VOD, SDV, DOCSIS.
Bottom line is a local station will not get more than 19.4 mbps (or 3MHz if you will) plus 1 SD simulcast (or 0.6MHz) on a cable system. In some systems that figure is 9.6MHz (HD plus subchannels @ 3MHz, SD simulcast @ 0.6MHz, and analog simulcast @ 6MHz). But as most of us know, most systems are agressively doing away with analog alltogether.
Edited by nyctveng - 3/2/13 at 9:28pm
Originally Posted by davehancock
Please clarify the last statement. 19.4mbps is the max. Your statement implies (19.4+3.5= 22.9mbps). If a station has one 3.5 mbps SD sub, then the main would only be capable of 15.9, if they have two SD subs, then the main would be left with 12.4 mbps. At one time, our local PBS had THREE SD subs - leaving 9 bps. Some of the stations here feed TW with fiber (lots of fiber in this town), so there is no need to limit the quality of the main feed to cable. TW puts the SD subs on entirely different (SD dedicated) QAMs, so if the station feeds 19.4mbps, that's what TW passes on.