KingDaveRa
12-06-2010, 14:25
This could go in the Internet or TV forum.
Now I'm taking TV and Broadband, it got me thinking about the maximum capability of that bit of coax coming into my house.
I've read bits and bobs about DOCSIS (http://en.wikipedia.org/wiki/DOCSIS) and how much is possible through it. As I understand it, the cable must have a maximum bandwidth in terms of signal (i.e. the highest and lowest possible signal rate). This would then limit the number of DOCSIS channels available to then use for TV, VoD or Broadband. But what IS the limit?
Watching TV I can tell VM are squeezing the bandwidth as there's definitely more macroblocking and artefacting on SD and HD channels than there is on Sky, but nowhere near as much as on Freeview (for most channels).
Freeview MUXes are around 25Mb/s iirc. A quick 'back of the fag packet' calculation I reckon on Freeview's bandwidth the TV channels are using about 500Mb/s, and that doesn't take into account the HD channels - I'd reckon they'd take it up to 800Mb/s or more. Add in all the other stuff (VOD and the general rubbish the Box wants to do in the background) plus the broadband, and you must be into a Gigabit of bandwidth over that bit of coax - which is quite astounding if that's right.
With that in mind, they must be reaching the limits of the cable, in terms of the frequency limits of the wire. Which if true, raises the question of what next? Or does that bit of wire work similar to a LNB arrangement on a satellite dish, in that some device further up the wire, probably on the end of the fibre portion, is switching frequencies dynamically onto the wire from higher frequencies elsewhere, or on a different backhaul system? However, I don't think that is the case.
The point I'm making is that the growth in HD channels must be putting a massive strain on the capabilities of the network, and squeezing the image quality seems to be the tradeoff.
Now I'm taking TV and Broadband, it got me thinking about the maximum capability of that bit of coax coming into my house.
I've read bits and bobs about DOCSIS (http://en.wikipedia.org/wiki/DOCSIS) and how much is possible through it. As I understand it, the cable must have a maximum bandwidth in terms of signal (i.e. the highest and lowest possible signal rate). This would then limit the number of DOCSIS channels available to then use for TV, VoD or Broadband. But what IS the limit?
Watching TV I can tell VM are squeezing the bandwidth as there's definitely more macroblocking and artefacting on SD and HD channels than there is on Sky, but nowhere near as much as on Freeview (for most channels).
Freeview MUXes are around 25Mb/s iirc. A quick 'back of the fag packet' calculation I reckon on Freeview's bandwidth the TV channels are using about 500Mb/s, and that doesn't take into account the HD channels - I'd reckon they'd take it up to 800Mb/s or more. Add in all the other stuff (VOD and the general rubbish the Box wants to do in the background) plus the broadband, and you must be into a Gigabit of bandwidth over that bit of coax - which is quite astounding if that's right.
With that in mind, they must be reaching the limits of the cable, in terms of the frequency limits of the wire. Which if true, raises the question of what next? Or does that bit of wire work similar to a LNB arrangement on a satellite dish, in that some device further up the wire, probably on the end of the fibre portion, is switching frequencies dynamically onto the wire from higher frequencies elsewhere, or on a different backhaul system? However, I don't think that is the case.
The point I'm making is that the growth in HD channels must be putting a massive strain on the capabilities of the network, and squeezing the image quality seems to be the tradeoff.