Hi Frank, re: << ...the slide shows a slice of bandwidth associated with the DOCSIS area that is clearly labeled 5 to 42 MHz, and the remaing regions from 50 to 750 MHz going to the upper part, i.e., the digital set top box which includes the DAVIC area. >>
Right, but that's only the UPSTREAM DOCSIS path, with range as required by the DOCSIS spec; the downstream path isn't broken down by channel into service category or DOCSIS vs. DAVIC. It's hard to guess exactly what they're doing because there are several things that aren't shown, and because DOCSIS support is optional. The 2 PHY's (DOCSIS/DAVIC) aren't compatible, so channel breakdown with both DOCSIS and DAVIC is hard to just guess, as is exactly what "tool" (as they're called in the DAVIC spec) they're specifying. The words don't match the picture, as you originally indicated.
The DAVIC upstream for the bi-directional PHY on coax part of the spec is 8-26.5 MHz (which isn't shown). Downstream, DAVIC requires support to 1GHz. Few US cable plants support > 750MHz. For DAVIC there are a couple possible downstream implementations (which can coexist): 70-130 MHZ QPSK and 54-1000 MHz QAM.
My guess would be this model was driven by Time Warner and Scientific Atlanta (which was instrumental in defining DAVIC requirements) as a way to make it look like they embrace DOCSIS (half-heartedly, obviously). With this model, it would seem that a given plant could only support (for 2-way data) either DOCSIS or DAVIC OOB (but the slide shows otherwise). I can't think of a good reason why an MSO would support both upstreams, so DOCSIS is removed from consideration since it is data only, and they suceed in looking like they endorse DOCSIS when in fact it doesn't make economic sense given the rest of the model.
gotta run,
dh |
