[opendtv] Re: The End of TV as We Know It
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 13 Dec 2004 09:30:22 -0500
At 8:45 PM -0800 12/12/04, Kon Wilms wrote:
>On Sun, 2004-12-12 at 18:02 -0500, Manfredi, Albert E wrote:
>> We've been over these tradeoffs many times, and the
>> upshot of it is that unicast cannot save on bandwidth
>> unless the number of viewers on the network is lower
>> than the number of TV channels available to choose
>> from.
>
>Well unfortunately the writer of the article doesn't know what he is
>talking about and he really *does* mean multicast. Or he is talking
>about some new IPTV system that is doing something that everyone else is
>not (doubtful).
>
>Unicast adds nothing except more pipe bandwidth and headend server load.
>You can still track user operations just as easily as fully-fledged
>unicast sessions by doing delayed unicast reportback and initial
>requests for decryption keys et al to 'join' a session. Switching is now
>intelligent enough to prune sessions even if only one person is watching
>the broadcast. And you bet your bottom dollar all the channels coming as
>IP contribution feeds are being multicast as the broadcast channels they
>are.
>
>Handing out packets with continuous handshaking is so passe. :-)
>
>Cheers
>Kon
The author knew exactly what he was taking about, but he did not
describe it precisely. In essence, there are two segments of the IP
network that are used to get packets into the home. The first link is
between the head-end and the neighborhood router. IF ANYONE in the
neighborhood wants a specific channel, then the neighborhood router
joins the IP multicast for that channel which is available from the
router at the head end. IF NOBODY in the neighborhood is watching a
specific channel, then it IS NOT carried on the link from the
head-end to the neighborhood. This frees up bandwidth on both
segments of the network as described above.
At the neighborhood level, if multiple homes want the same channel,
then the IP multicast packets are routed to multiple homes.
You can think of this as a "filter" which only passes packets that
are needed in the neighborhood from the head-end. This is not that
different from the way the Internet works, however, it is much more
manageable in a local, private, branching -ree network environment.
The telcos will be even better equippend to deal with this, as they
can connect your home directly to the correct channels right in the
central office, if they so desire, or they can mimic what the cable
guys are doing, by putting routers out in the neighborhoods. And both
can also put servers into the neighborhoods to deal with on-demand
packets that a re heavily used.
Regards
Craig
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