[opendtv] Re: The End of TV as We Know It
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 13 Dec 2004 12:24:41 -0500
Craig Birkmaier wrote:
> 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.
All you have done here is to describe IP multicast,
therby agreeing that the author didn't know what he was
talking about when he said:
"Instead of broadcasting every channel continuously,
service providers plan to transmit them only to subscribers
who request them. In effect, every channel will be streamed
on demand.."
> At the neighborhood level, if multiple homes want the
> same channel, then the IP multicast packets are routed to
> multiple homes.
Actually, this happens at every level. Even within the core
network, between routers. This is IP multicast.
But as I already said, what you achieve with this approach
is *not* VOD, as he stated, but rather something like NVOD.
You join a pre-existing stream, you don't start from the
top. To get real VOD, you need unicast sessions between
subscribers and servers. This would be an expensive
proposition. It either requires lots of distributed servers
or it requires fewer but faster servers, and lots of
network bandwidth.
> 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.
The telcos have the same problem as the cable companies.
The fact that each home gets a unique link to the CO does
not change the fact that the core network can only handle
a certain number of individual streams, to maintain
quality. If telcos were to do this with ATM vs IP, in
theory they might get more channels for a given network
bandwidth. But to do this correctly, subscribers would
have to be allowed to do proper ATM signaling, which
telcos have been unwilling to allow in the past.
In practice, even a telco using ATM would want to use
multicast to distribute TV programming, which means that
the end user will still see NVOD service rather than true
VOD. You can do multicast over ATM, although the really
clever technique once described in UNI 4.0 has since been
deleted.
Bert
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